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diesel blends
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Effect of exhaust gas recirculation (EGR) on performance and emissions of a constant speed DI diesel engine fueled with pentanol/diesel blends
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B. Rajesh kumar a,⇑, S. Saravanan b,1
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a b
IC Engines Division, Department of Mechanical Engineering, Jeppiaar Institute of Technology, Chennai, TN, India Department of Mechanical Engineering, Sri Venkateswara College of Engineering, Chennai, TN, India
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h i g h l i g h t s Higher blends of pentanol–diesel blends up to 45% can be used in a diesel engine without any modifications.
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Simultaneous reduction of smoke and NOx emissions is realized with the combination of appropriate EGR rates and pentanol–diesel blends.
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Engine performance suffers lightly with EGR introduction.
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Smoke emissions can be kept under control up to medium EGR rates beyond which it increases.
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a r t i c l e 2 4 1 3 22 23 24 25 26 27 28 29 30 31 32 33
i n f o
Article history: Received 21 May 2015 Received in revised form 23 July 2015 Accepted 28 July 2015 Available online xxxx Keywords: Pentanol–diesel blends Diesel engine EGR Performance Emission
a b s t r a c t In this work, the effects of blending n-pentanol, a second generation biofuel with diesel on the performance and emission characteristics of a diesel engine under exhaust gas recirculation (EGR) conditions are investigated. Tests were performed on a single-cylinder, constant-speed, un-modified, direct-injection diesel engine using four n-pentanol/diesel blends: 10%, 20%, 30% and 45% (by volume). The possibility of using a high pentanol/diesel blend (45%) was also explored with an objective to maximize the renewable fraction in the fuel. Three EGR rates (10%, 20% and 30%) were utilized with an intention to reduce the high nitrogen oxides (NOx) that were prevalent at high engine loads using these blends. Test results showed that increasing EGR rates brought down NOx emissions by up to 41% at medium load and 33.7% at high load. Smoke opacity hardly increased up to 20% EGR rate and beyond that it increased for all blends. It was found that simultaneous reduction of NOx and smoke emissions can be achieved using the combination of pentanol/diesel blends and a medium EGR rate (20–30%) with a small drop in performance. Increase in hydrocarbons (HC) and carbon-monoxide (CO) emissions were experienced with all blends when compared to diesel fuel under EGR conditions. It was concluded that 45% pentanol/diesel blends can be used in diesel engines without any modifications and without causing any visible damage to the engine parts subject to long-term durability tests. Ó 2015 Published by Elsevier Ltd.
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1. Introduction
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Despite high fuel conversion efficiency and high power output, diesel engines remain as sources of greenhouse-gas emissions that degrade environment and produces carcinogenic substances that deteriorate human health [1]. Public concerns about global warming and energy security have increased the attention of researchers on biologically-derived fuels that are capable of complementing petroleum-derived fuel resources [2]. Modifying fuel
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⇑ Corresponding author. Tel.: +91 4427269072. E-mail addresses: [email protected] (B. Rajesh kumar), idhayapriyan@ yahoo.co.in (S. Saravanan). 1 Tel.: +91 4427152000; fax: +91 4427162462.
characteristics has become a focus of interest to meet the stringent emission legislations because they require very few or no changes to the existing engine infrastructure [3]. The use of alcohol–diesel blends can address both the concerns of energy crisis and environmental degradation because alcohols can be produced in bio-refineries from renewable sources and they can bring down emissions due to their oxygenated nature. However there are some difficulties in using alcohols in compression-ignition engines owing to their low cetane number, high latent heat of vaporization and longer ignition delay [4]. Further the less calorific value, poor miscibility and instability during blending, poor lubricating properties challenge their use in diesel engines [5]. Several techniques like alcohol fumigation, dual-injection, alcohol–diesel blends and alcohol–diesel emulsions
http://dx.doi.org/10.1016/j.fuel.2015.07.089 0016-2361/Ó 2015 Published by Elsevier Ltd.
Please cite this article in press as: Rajesh kumar B, Saravanan S. Effect of exhaust gas recirculation (EGR) on performance and emissions of a constant speed DI diesel engine fueled with pentanol/diesel blends. Fuel (2015), http://dx.doi.org/10.1016/j.fuel.2015.07.089
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Table 1 Fuel properties of diesel, ethanol,a n-butanola and n-pentanol.a
a
76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127
Properties
Diesel
Ethanol
n-Butanol
n-Pentanol
Chemical formula Cetane number Low heating value (MJ/kg) Latent heat of vaporization (kJ/kg) Kinematic viscosity at 40 °C (mm2/s) Oxygen (% by wt) Density (kg/m3) Flash point (°C) Self-ignition temperature (°C)
C12H26–C14H30 52 43.356 256 3.522 0 850 53 254
C2H5OH 11 26.83 918.42 1.13 34.73 789.4 14 363
C4H9OH 17 32.01 585.40 2.22 21.59 809.7 35 345
C5H11OH 20 32.16 308.05 2.89 18.15 814.8 49 300
Data have been taken from Refs. [14,15].
have been used to overcome these shortcomings of alcohols as a diesel engine fuel [6]. The use of higher alcohols in diesel engines has gained interest in the recent years with the focus especially on butanol and its isomers [3–9]. Their results showed that butanol–diesel blends have significantly reduced soot and CO emissions with slight impact in performance. It has been established that butanol can be blended up to 30% with diesel and can be used without any modifications in a diesel engine and without any apparent damage to the engine parts [5]. Chen et al. [8] have showed that the combination of high n-butanol/diesel blend with medium EGR rate of 40% can achieve ultra-low NOx and soot emissions simultaneously. In this context, n-butanol is researched for its use in low temperature combustion (LTC) which is a promising strategy that adopts high EGR rates to simultaneously suppress smoke and NOx formation by extending the ignition delay (for effective pre-mixing) and reducing the overall combustion temperature respectively [10–15]. Butanol/diesel blends can help realize LTC; (a) by offering resistance to auto-ignition (due to its low cetane number), (b) by providing adequate ignition delay period for mixing and (c) by vaporizing faster that can increase the mixing rate [15]. Recently another higher alcohol, n-pentanol has gathered the attention of researchers for use in diesel engines because of its advantages over butanol. Pentanol is a 5-carbon straight-chain alcohol that has greater potential as a blending component with diesel fuel owing to its higher energy density, higher cetane number, better blend stability and less hygroscopic nature when compared to other widely-studied lower alcohols like ethanol, methanol and even butanol. The latent heat of vaporization, density and viscosity of pentanol is also close to diesel fuel compared to other alcohols. A comparison of properties of some important alcohols is shown in Table 1. Pentanol is an excellent renewable alternative. It can be produced from biological pathways like natural microbial fermentation of engineered micro-organisms [16] and biosynthesis from glucose [17]. Pentanol being an alcohol with longer carbon chains also consumes lesser energy during its production when compared to other lower alcohols [5]. Very few studies related to pentanol usage in diesel engines have been conducted so far [5,18–21]. Campos-Fernandez et al. [18] studied the performance of a DI diesel engine fueled with 10%, 15%, 20% and 25% pentanol–diesel blends and reported slight power loss, slight increase in fuel consumption and better brake thermal efficiency. The study concluded that 25% pentanol/diesel blends can be used in diesel engines without any modifications. However their study did not include information on emissions. Li et al. [19] studied the combustion and emission characteristics of a diesel engine fueled with pentanol/diesel and pentanol/biodiesel/diesel blends. Their results indicated that simultaneous reduction in soot and NOx emissions occurred at only low-middle loads while NOx emissions increased at high loads when compared to diesel fuel operation. Wei et al. [20] examined the effect of using 10%, 20% and 30% pentanol/diesel blends in a DI
diesel engine and their results showed that brake specific fuel consumption (BSFC) increased with increase in n-pentanol in diesel while the brake thermal efficiency was unaffected. They reported reductions in particulate emissions at all loads, but they found that NOx emissions increased to maximum of 8% at high engine loads. Li et al. [21] investigated the combustion and emission characteristics of a single cylinder DI diesel engine fueled with neat pentanol under pilot-main and single-injection strategies and have concluded that simultaneous reduction of NOx and soot can be achieved without EGR with neat pentanol operation. From the few available literature on pentanol/diesel blends, it could be inferred that higher blends beyond 30% have not been investigated. Further it is also essential to reduce the high NOx emissions that are prevalent during high engine loads when using pentanol/diesel blends [19,20]. EGR technology is highly effective in reducing the flame temperature and oxygen concentration of the working fluid inside the combustion chamber [22]. Hence in the present study, the effect of EGR on performance and emission characteristics of four pentanol/diesel blends (10%, 20%, 30% and 45% by vol.) under three EGR rates of 10%, 20% and 30% was investigated. The results are then compared with baseline diesel operation.
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2. Materials and methods
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2.1. Test fuel
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For this study, n-pentanol which is certified to a purity of 98% (analytical grade) was procured from AVRA synthesis. Diesel fuel which is the reference fuel for this study was purchased from Indian oil corporation, Chennai. Four pentanol fuel blends were prepared by mixing them with diesel at blending ratios of 10/90 (PEN10), 20/80 (PEN20), 30/70 (PEN30) and 45/55 (PEN45) by volume basis. The properties of all test fuels were measured following ASTM test methods and are shown in Table 2. Solubility of n-pentanol with diesel was tested and no phase separation was found after 48 h. During experimentation, all the blends were stirred well using a mixer to ensure homogeneity just before fueling.
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2.2. Test engine and facilities
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Tests were performed in a naturally-aspirated, air-cooled, constant-speed (1500 rpm), single-cylinder, direct-injection diesel engine. Specifications of the engine are given in Table 3. The schematic diagram of the experimental setup is presented in Fig. 1. A swinging field electrical dynamometer was used to apply the load on the engine. This electrical dynamometer consisted of a 5-kVA AC alternator (220 V, 1500 rpm) mounted on bearings and on a rigid frame for swinging field type loading. The output power was obtained by measuring the reaction torque by a strain gauge type load cell. The pressure inside the combustion chamber was measured using an AVL GH12D miniature pressure transducer
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Test method
Diesel
PEN10
PEN20
PEN30
PEN45
T10 (°C) T50 (°C) T90 (°C) Calculated cetane index Low heating value (MJ/kg) Kinematic viscosity at 40 °C (mm2/s) Density (kg/m3) Oxygen content (%wt)
ASTM D86
227 270 335 52 43.356 3.522 850 0
137 265 329 47.7 42.321 3.443 847 1.75
137 254 324 46.5 41.745 3.389 843 3.53
137 239 318 44.1 40.233 3.321 838 5.25
137 229 315 42.8 38.987 3.227 832 7.88
ASTM ASTM ASTM ASTM –
D4737 D240 D445 D4052
Table 3 Engine specifications.
b
175 176 177 178 179
Make and model
Kirloskar, TAFI make
Number of cylinders Bore Stroke Swept volume Clearance volume Compression ratio Rated output Rated speed Injection system Injection pressure Fuel injection timing Fuel injection duration Valve timing Intake valve opening Intake valve closing Exhaust valve opening Exhaust valve closing
One 87.5 mm 110 mm 661cm3 36.87cm3 17.5:1 4.7 kW at 1500 rpm 1500 rpm Direct injection 20–21 MPa 23° CAb bTDC 20–30° CA BTDC 4.5° CA bTDC 35.5° CA aBDC 35.5° CA bBDC 4.5° CA aTDC
CA – Crank angle.
connected to an AVL3066A02 Piezo Charge Amplifier. The crank angle and the position of top dead center (TDC) were measured using an AVL364 Angle Encoder. The charge amplifier and the encoder were connected to an AVL 615 Indimeter A/D card, which converts analog input to digital output. Al/Cr K-type thermocouple
was used to measure the exhaust gas temperature, which is taken as an indication of the temperature in the combustion chamber. AVL 615 Indimeter software was used to analyze the output data from the A/D card. This generates a pressure-crank angle diagram that indicates the variation of pressure and heat release rate at every crank angle and also indicates the crank angles at which the combustion starts and at which the percentage (10%, 50% and 90%) of heat released during the combustion. Measurements of all these parameters were carried out for 100 cycles and an average value of these cycles was recorded as a measured parameter at that load. Hence the combustion parameters such as cylinder pressure, heat release rate, ignition delay, peak pressure and crank angles were obtained with an accuracy of 0.01. The fuel consumption rate was measured using an electronic weighing scale of sensitivity 0.1 g and a digital stop watch of resolution 0.01s. Gaseous emissions including NOx, CO and HC emissions were measured using MRU Delta 1600L exhaust gas analyzer and smoke opacity was measured using AVL 439 opaci-meter. Table 4 shows the range and accuracy of the instruments used in this study.
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2.3. EGR setup
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In the current study, an external cooled EGR system was used. Cooled EGR reduces the intake charge temperature and lowers the peak in-cylinder temperatures which in-turn inhibits NOx formation. Cooling also increases the density of EGR which allows a
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Fig. 1. Schematic of the experimental setup.
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Table 4 Range and accuracy of instruments used. Instrument Gas analyzer
Opacimeter K-type thermocouple Speed measuring unit Pressure pickup Crank angle encoder Burette Digital stop watch
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Measured quantity
Range
Accuracy
Smoke opacity Temperature Engine speed Cylinder pressure Crank angle Fuel quantity Time
0–100% 0–1000 °C 0–9999 rpm 0–250 bar 0–360° 0–1000 cc –
±2% ±1 °C ±5 rpm ±0.1 bar ±1° ±0.1 cc ±0.6 s
As per Eq. (2), the maximum possible error in the calculation of BTE and BSFC was determined to be 0.33%. Similarly, the errors associated with the measurements of temperature, cylinder pressure and crank angle was determined to be 0.5%, 1.35% and 2% respectively.
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2.5. Test procedure
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All the tests were conducted under steady state conditions. No modifications were made to the test engine. The temperature of the lubricating oil was maintained between 85 and 90 °C. Experiments were carried out at constant ambient temperature to improve the reliability of the recordings. The engine was first run with diesel fuel which forms the reference fuel for this study and the baseline data was recorded. The engine always ran for 15 min at each load condition to allow for stabilization before the readings were recorded. Each test was repeated three times to ensure repeatability. The engine was always allowed to run for some time before changing the blends in-order for it to consume the fuel that remained in the fuel system during the previous trial.
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3. Results and discussion
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Engine tests were carried out at five different load conditions that are 0%, 25%, 50%, 75% and 100% of the rated load which correspond to the break mean effective pressures (bmep) of 0, 1.3, 2.6, 4 and 5.3 bar respectively. In each of the section that follows, the performance and emission characteristics of the engine fueled with n-pentanol/diesel blends without EGR is discussed at first and then followed by the discussions on the effect of increasing EGR rates. This is done together for the sake of brevity.
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3.1. Engine performance
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3.1.1. Brake thermal efficiency Fig. 2(a) shows the effect of n-pentanol/diesel blends on brake thermal efficiency as a function of engine load with no EGR applied. It can be seen that BTE increases with engine load but decreases slightly from 75% to 100% loads. This slight drop could be due to the low excess air ratio at high engine loads that worsened combustion [20]. It can be seen that pentanol blends have lesser BTE than diesel. Increasing pentanol fraction in the blend caused a drop in BTE due to the less energy content of pentanol when compared to diesel fuel. A maximum drop of 7.2% from baseline diesel performance was realized with PEN45 blend at high engine loads. The effect of increasing EGR rates on n-pentanol/diesel blends at high engine load (bmep = 5.3 bar) was presented in Fig. 2(b). It can be see that BTE decreases very slightly for all pentanol/diesel blends at increasing EGR rates. Increase in EGR impedes the normal combustion process and reduces the burning rate. The higher CO and HC emissions due to increased EGR rates also accounts for combustion losses and decreased performance of higher blends of pentanol with diesel.
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3.1.2. Brake specific fuel consumption Fig. 3(a) shows the effect of n-pentanol/diesel blends on BSFC as a function of engine load without EGR. It can be seen BSFC increases with increase in pentanol quantity in the blend as more
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greater proportion of EGR to be used. Thus a fraction of exhaust gas is sent to the EGR cooler before it is diverted into the intake manifold for mixing with the incoming air. EGR cooler is a heat exchanger in which cooling water is maintained at a constant temperature to absorb heat from the incoming exhaust gas. It has to be noted that temperature of the exhaust gas re-circulated is kept cooler than the engine exhaust and warmer than the intake air charge. In this experiment, the exhaust gas is cooled down to 35 °C. EGR rate is controlled by an EGR valve. An orifice is used to measure the flow rate of the exhaust gas. Sufficient mixing of incoming air and re-circulated exhaust gas is ensured inside the mixing chamber before it gets inducted into the combustion chamber. EGR quantity was determined as a percentage using the following relation,
CO2intake 100 EGR% ¼ ðCO2 Þexhaust
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The errors associated with various measurements and calculations of parameters are computed in this section. The maximum possible error in calculations was estimated by using the method proposed by Moffat [24]. Errors were estimated from minimum values of the output and accuracy of the instrument. If an estimated quantity S, depends on independent variables like ðx1 ; x2 ; x3 xn Þ, then the error in the value of S is calculated by using Eq. (1).
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( 2 2 2 )12 @x1 @x2 @xn þ þ þ x1 x2 xn
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@S ¼ S
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where,
249 250
@x1 x1
254
@BTE ¼ BFCE
2.4. Error analysis
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253
±1 ppm ±1 ppm ±0.01 %
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223
252
0–4000 ppm 0–20,000 ppm 0–20%
235
222
2 2 2 !12 @Torque @rpm @time þ þ Torque rpm time
251
NOx HC CO
where ðCO2 Þintake represents the concentration of CO2 in the inlet manifold, ðCO2 Þexhaust represents the concentration of CO2 in the exhaust manifold. The concentration of CO2 in the inlet is affected by the opening/closing of EGR valve and the concentration of CO2 in the exhaust gas. The concentration of CO2 in the exhaust gas depends on the burning of the fuel. Since the fuel consumption of the engine is independent of the EGR ratio, this method provides a practical measure of required EGR at stable rates during steady state engine operation. The quantity of CO2 in the inlet and exhaust was measured by the MRU gas analyzer. The flow rate of the exhaust gas re-circulated was adjusted by using the EGR valve until the quantity of CO2 in the intake reaches the desired value (10%, 20% and 30%). Similar method was used by Bhaskar et al. [23] to determine the EGR rates in a similar engine.
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Since brake thermal efficiency (BTE) is calculated from fuel consumption, errors associated with it can be represented by Eq. (2) as follows,
ð1Þ
2 , @x , etc. are the errors in the independent variables. x2
@x1 is the accuracy of the measuring instrument and x1 is the minimum value of the output measured during the experiment.
ð2Þ
Please cite this article in press as: Rajesh kumar B, Saravanan S. Effect of exhaust gas recirculation (EGR) on performance and emissions of a constant speed DI diesel engine fueled with pentanol/diesel blends. Fuel (2015), http://dx.doi.org/10.1016/j.fuel.2015.07.089
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Fig. 2. Brake thermal efficiency (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
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amount of blends are required to produce the same amount of power by the engine due to the less energy content of pentanol when compared to diesel fuel. The effect of increasing EGR rates on BSFC for n-pentanol/diesel blends at high engine load is presented in Fig. 3(b). BSFC generally increases for all pentanol/diesel blends at increasing EGR rates with the consumption being more for PEN45 blends. This is because of the reduction in in-cylinder temperature due to the application of EGR leading to incomplete combustion. 3.1.3. Exhaust temperature Fig. 4(a) shows the variation of exhaust temperature as a function of engine load under no EGR. It can be seen that exhaust temperature decreases with increasing pentanol content in the blend. Low energy content of pentanol causes less combustion temperature and PEN45 having the lowest energy content among all the blends produces lowest exhaust temperatures at all engine loads. The higher latent heat of vaporization of pentanol/diesel blends also reduces the exhaust temperature. The effect of increasing EGR percentages on exhaust temperature for all pentanol/diesel blends at high engine loads are shown in Fig. 4(b). It can be seen that the exhaust temperature slightly decreases with increase in EGR rates for all blends as a result of reduction in peak combustion temperature brought about by the increase of EGR conditions. The higher latent of vaporization of
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Fig. 3. Brake specific fuel consumption (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
pentanol/diesel also provides a cooling effect during combustion and hence a decrease in exhaust temperatures.
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3.1.4. Ignition delay In this study, ignition delay is calculated as the difference between fuel injection timing and the timing at which 5% mass fraction of fuel is burnt. Fig. 5(a) shows the variation of ignition delay for all pentanol/diesel blends with reference to diesel for the entire load spectrum of the engine with no EGR. It can be seen that ignition delay gets longer with increasing pentanol content in the fuel. The increase is obviously due to the decrease in cetane number of diesel brought about by the addition of pentanol. Fig. 5(b) shows the effect of increasing EGR rates on ignition delay of pentanol/diesel blends at high engine load. One of the important effects of EGR is prolongation of ignition delay [8] and hence increase in EGR rates increased the ignition delay for all blends.
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3.2. Engine emissions
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3.2.1. NOx emissions Fig. 6 shows the effect of blends on NOx emissions at various load conditions without EGR. NOx emissions generally increased with engine load for all blends similar to diesel fuel. It can be inferred that, at low/medium load conditions, NOx emissions decreased for all blends with the decrease being higher with higher percentages of pentanol in the blend when compared to diesel fuel. This may be due to low calorific value and high latent heat of
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Fig. 4. Exhaust temperature (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
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vaporization of pentanol that reduces in-cylinder temperatures leading to less thermal NOx formation. At high engine loads, it can be seen that NOx emissions are high compared to diesel fuel as reported earlier with pentanol/diesel blends [19,20]. This behavior may be a result of dominating influence of the oxygen content and lower cetane number of pentanol blends over the cooling effect caused by the high latent heat of vaporization of pentanol. Addition of pentanol to diesel decreases the cetane number of the blend which leads to a longer ignition delay. Hence more fuel blend gets injected into the cylinder during this period and when this high quantity of fuel gets combusted during the premixed combustion phase, it results in elevated gas temperatures favoring NOx emissions [20]. Further the increased fuel intake during high load conditions increases the in-cylinder temperatures and favor NOx formation. The effects of various EGR percentages on NOx emissions for all pentanol/diesel blends at medium and high loads are shown in Fig. 7(a) and (b) respectively. Two loads are discussed due to the difference in behavior of NOx between low/medium and high loads. Increasing EGR rates decreases the flame temperature and oxygen concentration leading to lower NOx emissions. As seen earlier, NOx emissions are generally lower for pentanol/diesel blends at medium loads when compared to diesel and with the introduction of EGR, further reductions were realized for all EGR rates tested. From Fig. 7(a), it can be inferred that at medium loads, PEN45 blends showed a maximum reduction of up to 41% in NOx emissions by 30% EGR while for neat diesel fuel, the reduction is 26.8% for the same levels of EGR.
Fig. 5. Ignition delay (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
Fig. 6. NOx emissions vs engine load without EGR.
Generally at high loads and high EGR rates, the concentration of inert gases present in EGR is more and these gases absorb the energy released by combustion and reduce the peak temperatures inside the combustion chamber. From Fig. 7(b), it can be deduced that at higher loads, NOx emissions were reduced by 33.7% with 30% EGR for PEN45 blend while a reduction of 35% is realized with diesel fuel under similar conditions. The difference in percentage reductions between PEN45 at medium (41%) and high loads (33.7%) shows that NOx emissions are less sensitive to EGR at high loads than at medium loads.
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less with all n-pentanol/diesel blends compared to diesel fuel. This can be explained on the basis of similar observations reported with n-butanol/diesel blends. The oxygen atoms bonded to the hydroxyl group of n-pentanol reduces soot formation inhibiting smoke pre-cursors [7]. The oxygen content of pentanol contributes to improved combustion resulting in the reduction of smoke [25]. Smoke is reduced by up to 77.8% using 45PEN compared to baseline diesel operation under no EGR conditions. The effects of various EGR percentages on smoke opacity for all pentanol/diesel blends at medium and high loads are shown in Fig. 9(a) and (b) respectively. It is obvious that at any given EGR rate and at both loads, smoke emissions remained low for all pentanol/diesel blends when compared to diesel fuel. This can be due to dominant influence of increased oxygen fraction and lower overall equivalence ratio as a result of adding pentanol to diesel over the effects of EGR. Similar scenario was also reported with n-butanol/diesel blends under high EGR rates [8,26]. It can be clearly seen from Fig. 9(b) that smoke emissions hardly increase up to 20% EGR rate and beyond which the smoke emissions has increased for all blends. Increasing EGR rates decrease the oxygen concentration and increase the local equivalence ratio causing incomplete combustion and promote soot formation. As a result of high EGR, cylinder temperature also gets reduced and smoke formation is promoted [26,27]. Studies have shown that soot emissions increases rapidly with EGR increment, once the EGR rate exceeds a specific value [9,28,29]. A soot-bump exists in a specific EGR range where the soot emissions are sensitive to variation in EGR rates making combustion control difficult [10]. Similar
Fig. 7. NOx emissions vs EGR rate at (a) medium load (bmep = 2.6 bar), (b) high load (bmep = 5.3 bar).
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In summary, NOx emissions were reduced by 57% and 30% for PEN45 blend at 30% EGR rate for medium and high loads respectively compared to diesel fuel operation without EGR. 3.2.2. Smoke opacity Fig. 8 compares the variations of smoke opacity for all pentanol/diesel blends at different load conditions without EGR. It can be observed that smoke opacity increases with increase in engine load and is significantly high at high engine loads. This is due to the burning of more fuel to produce higher power output at high engine loads [20]. It can be seen that smoke emissions is
Fig. 8. Smoke opacity vs engine load without EGR.
Fig. 9. Smoke opacity vs EGR rate at (a) medium load (bmep = 2.6 bar), (b) high load (bmep = 5.3 bar).
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observations were also made with different blends of n-butanol Isomers with diesel, where a soot-bump occurred at around 30% EGR rate [9]. In a specific case with 20% n-butanol/diesel blends, it was found that the soot reduction caused by the prolonged ignition delay (due to lower cetane number) and oxygen content cannot compensate for the higher soot formation rate in a certain EGR region between 45% and 56%. As a result, soot increased rapidly in that region [29]. In case of pentanol/diesel blends, the soot-bump might be starting at a region between 20% and 30% EGR rates as seen in Fig. 9(b). An attempt was made to run the engine with
Fig. 10. Variations of smoke and NOx emissions with EGR rates for 45PEN at high load (bmep = 5.3 bar).
Fig. 11. HC emissions (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
higher EGR rates than considered in the present study but it was found that smoke emissions increased rapidly and controlling combustion became difficult. From Figs. 7 and 9, it can be seen that simultaneous reductions in smoke and NOx emissions could be achieved by an addition of pentanol up to 45% with diesel and with an application EGR rates between 20% and 30% at high loads when compared to baseline diesel operation without EGR. Fig. 10 shows the trade-off between NOx emissions and smoke opacity for 45% pentanol/diesel blends at high load conditions under various EGR rates. The trade-off can be better represented by normalizing the values of smoke and NOx emissions to dimensionless numbers, since their units were different. It can be seen clearly that the trade-off relation between smoke and NOx re-appears between 20% and 30% EGR rates for 45PEN blend.
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3.2.3. HC emissions The variation of HC emissions of the engine with pentanol/diesel fuel blends with reference to pure diesel fuel is shown in Fig. 11(a). HC emission increases with increasing pentanol content in the blends at all engine loads. This increase is attributed to the lower cetane number of pentanol/diesel blends. Low cetane number causes longer ignition delay. This deteriorates the self-ignition characteristics of the blends and promotes quenching effect in the leaner mixture zone of the cylinder which in-turn increases HC emissions [4]. The effect of various EGR percentages on HC emissions for all pentanol/diesel blends at high loads is shown in Fig. 11(b). HC emission increases with increasing EGR rates, with the emissions being higher with higher blends of pentanol. Increase in EGR rates
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Fig. 12. (a) CO emissions (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
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causes lower flame temperatures which results in the formation of larger flame quenching zones where combustion cannot happen easily [30]. HC emission increases from 23 ppm to 35 ppm as a result of 30% EGR rate for 45PEN blend.
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3.2.4. CO emissions The variation of CO emissions for pentanol/diesel fuel blends with reference to pure diesel fuel is shown in Fig. 12(a). CO emissions generally increase at low loads and decrease favorably with increasing engine loads due to high in-cylinder temperatures. Similar increase was reported in literature involving higher alcohol/diesel blends [4,20]. It can also be seen that CO emissions increases with increasing pentanol content in the blend. The high latent heat of vaporization of pentanol blends decreases the in-cylinder temperature and causes a cooling effect that promotes the formation of CO. Introduction of EGR prevents CO oxidation due to lower oxygen concentration and as a result, CO emission increases slightly with increasing EGR rates as seen in Fig. 12(b). CO emission of PEN45 is more than other blends.
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4. Conclusions
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The effect of using pentanol/diesel blends up to 45% in proportion on the performance and emission characteristics of pentanol/diesel blends were investigated and compared with baseline diesel fuel in a DI diesel engine. The effect of increasing EGR rates up to 30% was also investigated. EGR was intended to reduce the high NOx emissions that are prevalent during high engine loads with n-pentanol addition to diesel fuel. The following conclusions were drawn from the experimental study.
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1. It is possible to operate a DI diesel engine with up to 45% pentanol/diesel blends with and without EGR. The operation required no modifications to be made to the engine and no visible damage to the engine parts was observed. However, to recommend it as a regular fuel, long-term durability tests are required. 2. Ignition delay gets longer for all pentanol/diesel blends at all EGR rates tested. 3. BTE decreases for all pentanol/diesel blends at increasing EGR rates with the loss being more for PEN45 blends. A maximum drop of 7.2% from baseline diesel performance was realized with PEN45 blend at high engine loads. BSFC also decreased for pentanol/diesel blends with increase in EGR rates. 4. NOx emissions were reduced by 57% and 30% for PEN45 blend at 30% EGR rate for medium and high loads respectively compared to diesel fuel operation. 5. Smoke opacity decreased for all pentanol/diesel blends with the reduction being higher with higher proportion of pentanol. Smoke opacity hardly increased due to the dominance of oxygenated conditions for all pentanol/diesel blends up to 20% EGR and beyond that, smoke opacity has increased for all blends. Further research is required using the combination of n-pentanol blends and high EGR rates to achieve low temperature combustion in diesel engines. 6. The combination of medium EGR rates and blends up to 45% pentanol content can simultaneously reduce smoke and NOx emissions with a little drop in engine performance. 7. HC and CO emissions increased with increasing EGR rates for all pentanol/diesel blends. In summary, n-pentanol is an excellent next generation fuel that can find potential use in diesel engines and has the capability to offer both energy security and environmental safety.
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References
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[1] Benbrahim-Tallaa L, Baan RA, Grosse Y, Lauby-Secretan B, El Ghissassi F, Bouvard V, et al. Carcinogenicity of diesel-engine and gasoline-engine exhausts and some nitroarenes. Lancet Oncol 2012;13(7):663–4. http://dx.doi.org/ 10.1016/s1470-2045(12)70280-2. [2] Tseng H-C. Production of pentanol in metabolically engineered Escherichia Coli. Massachusetts: Massachusetts Institute of Technology; 2011. [3] Rakopoulos DC, Rakopoulos CD, Giakoumis EG, Dimaratos AM, Kyritsis DC. Effects of butanol–diesel fuel blends on the performance and emissions of a high-speed DI diesel engine. Energy Convers Manage 2010;51(10):1989–97. http://dx.doi.org/10.1016/j.enconman.2010.02.032. [4] Karabektas M, Hosoz M. Performance and emission characteristics of a diesel engine using isobutanol–diesel fuel blends. Renew Energy 2009;34(6):1554–9. http://dx.doi.org/10.1016/j.renene.2008.11.003. [5] Campos-Fernández J, Arnal JM, Gómez J, Dorado MP. A comparison of performance of higher alcohols/diesel fuel blends in a diesel engine. Appl Energy 2012;95:267–75. http://dx.doi.org/10.1016/j.apenergy.2012.02.051. [6] Ozsezen AN, Turkcan A, Sayin C, Canakci M. Comparison of performance and combustion parameters in a heavy-duty diesel engine fueled with iso-butanol/ diesel fuel blends. Energy Explor Exploit 2011;29(5):525–41. http://dx.doi.org/ 10.1260/0144-5987.29.5.525. [7] Siwale L, Kristóf L, Adam T, Bereczky A, Mbarawa M, Penninger A, et al. Combustion and emission characteristics of n-butanol/diesel fuel blend in a turbo-charged compression ignition engine. Fuel 2013;107:409–18. http:// dx.doi.org/10.1016/j.fuel.2012.11.083. [8] Chen Z, Wu Z, Liu J, Lee C. Combustion and emissions characteristics of high nbutanol/diesel ratio blend in a heavy-duty diesel engine and EGR impact. Energy Convers Manage 2014;78:787–95. http://dx.doi.org/10.1016/ j.enconman.2013.11.037. [9] Zheng Z, Li C, Liu H, Zhang Y, Zhong X, Yao M. Experimental study on diesel conventional and low temperature combustion by fueling four isomers of butanol. Fuel 2015;141:109–19. http://dx.doi.org/10.1016/j.fuel.2014.10.053. [10] Zhang Q, Yao M, Zheng Z, Liu H, Xu J. Experimental study of n-butanol addition on performance and emissions with diesel low temperature combustion. Energy 2012;47(1):515–21. http://dx.doi.org/10.1016/j.energy.2012.09.020. [11] Valentino G, Corcione FE, Iannuzzi SE, Serra S. Experimental study on performance and emissions of a high speed diesel engine fuelled with nbutanol diesel blends under premixed low temperature combustion. Fuel 2012;92(1):295–307. http://dx.doi.org/10.1016/j.fuel.2011.07.035. [12] Liu H, Bi X, Huo M, Lee CF, Yao M. Soot emissions of various oxygenated biofuels in conventional diesel combustion and low-temperature combustion conditions. Energy Fuels 2012;26(3):1900–11. http://dx.doi.org/10.1021/ ef201720d. [13] Liu H, Huo M, Liu Y, Wang X, Wang H, Yao M, et al. Time-resolved spray, flame, soot quantitative measurement fueling n-butanol and soybean biodiesel in a constant volume chamber under various ambient temperatures. Fuel 2014;133:317–25. http://dx.doi.org/10.1016/j.fuel.2014.05.038. [14] Zheng Z, Yue L, Liu H, Zhu Y, Zhong X, Yao M. Effect of two-stage injection on combustion and emissions under high EGR rate on a diesel engine by fueling blends of diesel/gasoline, diesel/n-butanol, diesel/gasoline/n-butanol and pure diesel. Energy Convers Manage 2015;90:1–11. http://dx.doi.org/10.1016/ j.enconman.2014.11.011. [15] Tornatore C, Marchitto L, Mazzei A, Valentine G, Corcione FE, Merola SS. Effect of butanol blend on in-cylinder combustion process. Part 2: Compression ignition engine. J KONES Powertrain Transp 2011;18(2):473–83. [16] Cann AF, Liao JC. Pentanol isomer synthesis in engineered microorganisms. Appl Microbiol Biotechnol 2009;85(4):893–9. http://dx.doi.org/10.1007/ s00253-009-2262-7. [17] Zhang K, Sawaya MR, Eisenberg DS, Liao JC. Expanding metabolism for biosynthesis of nonnatural alcohols. Proc Natl Acad Sci 2008;105(52):20653–8. http://dx.doi.org/10.1073/pnas.0807157106. [18] Campos-Fernandez J, Arnal JM, Gomez J, Lacalle N, Dorado MP. Performance tests of a diesel engine fueled with pentanol/diesel fuel blends. Fuel 2013;107:866–72. http://dx.doi.org/10.1016/j.fuel.2013.01.066. [19] Li L, Wang J, Wang Z, Xiao J. Combustion and emission characteristics of diesel engine fueled with diesel/biodiesel/pentanol fuel blends. Fuel 2015. http:// dx.doi.org/10.1016/j.fuel.2015.04.048. [20] Wei L, Cheung CS, Huang Z. Effect of n-pentanol addition on the combustion, performance and emission characteristics of a direct-injection diesel engine. Energy 2014;70:172–80. http://dx.doi.org/10.1016/j.energy.2014.03.106. [21] Li L, Wang J, Wang Z, Liu H. Combustion and emissions of compression ignition in a direct injection diesel engine fueled with pentanol. Energy 2015;80:575–81. http://dx.doi.org/10.1016/j.energy.2014.12.013. [22] Pandian M, Sivapirakasam SP, Udayakumar M. Investigations on emission characteristics of the pongamia biodiesel–diesel blend fuelled twin cylinder compression ignition direct injection engine using exhaust gas recirculation methodology and dimethyl carbonate as additive. J Renew Sustain Energy 2010;2(4):043110. http://dx.doi.org/10.1063/1.3480016. [23] Bhaskar K, Nagarajan G, Sampath S. Optimization of FOME (fish oil methyl esters) blend and EGR (exhaust gas recirculation) for simultaneous control of NOx and particulate matter emissions in diesel engines. Energy 2013;62:224–34. http://dx.doi.org/10.1016/j.energy.2013.09.056. [24] Moffat RJ. Using uncertainty analysis in the planning of an experiment. J Fluids Eng 1985;107(2):173–8. http://dx.doi.org/10.1115/1.3242452.
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[25] Tsolakis A, Megaritis A, Wyszynski M, Theinnoi K. Engine performance and emissions of a diesel engine operating on diesel-RME (rapeseed methyl ester) blends with EGR (exhaust gas recirculation). Energy 2007;32(11):2072–80. http://dx.doi.org/10.1016/j.energy.2007.05.016. [26] Gu X, Li G, Jiang X, Huang Z, Lee CF. Experimental study on the performance of and emissions from a low-speed light-duty diesel engine fueled with nbutanol–diesel and isobutanol–diesel blends. Proc Instit Mech Eng Part D: J Automob Eng 2013;227(2):261–71. http://dx.doi.org/10.4271/2012-28-0011. [27] Zhu R, Wang X, Miao H, Yang X, Huang Z. Effect of dimethoxy-methane and exhaust gas recirculation on combustion and emission characteristics of a direct injection diesel engine. Fuel 2011;90(5):1731–7. http://dx.doi.org/ 10.1016/j.fuel.2011.01.035.
[28] Alriksson M, Rente T, Denbratt I. Low soot, Low NOx in a heavy duty diesel engine using high levels of EGR; 2005. http://dx.doi.org/10.4271/2005-013836. [29] Liu H, Li S, Zheng Z, Xu J, Yao M. Effects of n-butanol, 2-butanol, and methyl octynoate addition to diesel fuel on combustion and emissions over a wide range of exhaust gas recirculation (EGR) rates. Appl Energy 2013;112:246–56. http://dx.doi.org/10.1016/j.apenergy.2013.06.023. [30] Heywood JB. Internal combustion engine fundamentals. New York (USA): McGraw-Hill; 1988.
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Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel 5 6
4
Effect of exhaust gas recirculation (EGR) on performance and emissions of a constant speed DI diesel engine fueled with pentanol/diesel blends
7
B. Rajesh kumar a,⇑, S. Saravanan b,1
3
8 9
a b
IC Engines Division, Department of Mechanical Engineering, Jeppiaar Institute of Technology, Chennai, TN, India Department of Mechanical Engineering, Sri Venkateswara College of Engineering, Chennai, TN, India
10 11 1 3 14 15
h i g h l i g h t s Higher blends of pentanol–diesel blends up to 45% can be used in a diesel engine without any modifications.
16
Simultaneous reduction of smoke and NOx emissions is realized with the combination of appropriate EGR rates and pentanol–diesel blends.
17
Engine performance suffers lightly with EGR introduction.
18
Smoke emissions can be kept under control up to medium EGR rates beyond which it increases.
19
a r t i c l e 2 4 1 3 22 23 24 25 26 27 28 29 30 31 32 33
i n f o
Article history: Received 21 May 2015 Received in revised form 23 July 2015 Accepted 28 July 2015 Available online xxxx Keywords: Pentanol–diesel blends Diesel engine EGR Performance Emission
a b s t r a c t In this work, the effects of blending n-pentanol, a second generation biofuel with diesel on the performance and emission characteristics of a diesel engine under exhaust gas recirculation (EGR) conditions are investigated. Tests were performed on a single-cylinder, constant-speed, un-modified, direct-injection diesel engine using four n-pentanol/diesel blends: 10%, 20%, 30% and 45% (by volume). The possibility of using a high pentanol/diesel blend (45%) was also explored with an objective to maximize the renewable fraction in the fuel. Three EGR rates (10%, 20% and 30%) were utilized with an intention to reduce the high nitrogen oxides (NOx) that were prevalent at high engine loads using these blends. Test results showed that increasing EGR rates brought down NOx emissions by up to 41% at medium load and 33.7% at high load. Smoke opacity hardly increased up to 20% EGR rate and beyond that it increased for all blends. It was found that simultaneous reduction of NOx and smoke emissions can be achieved using the combination of pentanol/diesel blends and a medium EGR rate (20–30%) with a small drop in performance. Increase in hydrocarbons (HC) and carbon-monoxide (CO) emissions were experienced with all blends when compared to diesel fuel under EGR conditions. It was concluded that 45% pentanol/diesel blends can be used in diesel engines without any modifications and without causing any visible damage to the engine parts subject to long-term durability tests. Ó 2015 Published by Elsevier Ltd.
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53 54
1. Introduction
55
Despite high fuel conversion efficiency and high power output, diesel engines remain as sources of greenhouse-gas emissions that degrade environment and produces carcinogenic substances that deteriorate human health [1]. Public concerns about global warming and energy security have increased the attention of researchers on biologically-derived fuels that are capable of complementing petroleum-derived fuel resources [2]. Modifying fuel
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⇑ Corresponding author. Tel.: +91 4427269072. E-mail addresses: [email protected] (B. Rajesh kumar), idhayapriyan@ yahoo.co.in (S. Saravanan). 1 Tel.: +91 4427152000; fax: +91 4427162462.
characteristics has become a focus of interest to meet the stringent emission legislations because they require very few or no changes to the existing engine infrastructure [3]. The use of alcohol–diesel blends can address both the concerns of energy crisis and environmental degradation because alcohols can be produced in bio-refineries from renewable sources and they can bring down emissions due to their oxygenated nature. However there are some difficulties in using alcohols in compression-ignition engines owing to their low cetane number, high latent heat of vaporization and longer ignition delay [4]. Further the less calorific value, poor miscibility and instability during blending, poor lubricating properties challenge their use in diesel engines [5]. Several techniques like alcohol fumigation, dual-injection, alcohol–diesel blends and alcohol–diesel emulsions
http://dx.doi.org/10.1016/j.fuel.2015.07.089 0016-2361/Ó 2015 Published by Elsevier Ltd.
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Table 1 Fuel properties of diesel, ethanol,a n-butanola and n-pentanol.a
a
76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127
Properties
Diesel
Ethanol
n-Butanol
n-Pentanol
Chemical formula Cetane number Low heating value (MJ/kg) Latent heat of vaporization (kJ/kg) Kinematic viscosity at 40 °C (mm2/s) Oxygen (% by wt) Density (kg/m3) Flash point (°C) Self-ignition temperature (°C)
C12H26–C14H30 52 43.356 256 3.522 0 850 53 254
C2H5OH 11 26.83 918.42 1.13 34.73 789.4 14 363
C4H9OH 17 32.01 585.40 2.22 21.59 809.7 35 345
C5H11OH 20 32.16 308.05 2.89 18.15 814.8 49 300
Data have been taken from Refs. [14,15].
have been used to overcome these shortcomings of alcohols as a diesel engine fuel [6]. The use of higher alcohols in diesel engines has gained interest in the recent years with the focus especially on butanol and its isomers [3–9]. Their results showed that butanol–diesel blends have significantly reduced soot and CO emissions with slight impact in performance. It has been established that butanol can be blended up to 30% with diesel and can be used without any modifications in a diesel engine and without any apparent damage to the engine parts [5]. Chen et al. [8] have showed that the combination of high n-butanol/diesel blend with medium EGR rate of 40% can achieve ultra-low NOx and soot emissions simultaneously. In this context, n-butanol is researched for its use in low temperature combustion (LTC) which is a promising strategy that adopts high EGR rates to simultaneously suppress smoke and NOx formation by extending the ignition delay (for effective pre-mixing) and reducing the overall combustion temperature respectively [10–15]. Butanol/diesel blends can help realize LTC; (a) by offering resistance to auto-ignition (due to its low cetane number), (b) by providing adequate ignition delay period for mixing and (c) by vaporizing faster that can increase the mixing rate [15]. Recently another higher alcohol, n-pentanol has gathered the attention of researchers for use in diesel engines because of its advantages over butanol. Pentanol is a 5-carbon straight-chain alcohol that has greater potential as a blending component with diesel fuel owing to its higher energy density, higher cetane number, better blend stability and less hygroscopic nature when compared to other widely-studied lower alcohols like ethanol, methanol and even butanol. The latent heat of vaporization, density and viscosity of pentanol is also close to diesel fuel compared to other alcohols. A comparison of properties of some important alcohols is shown in Table 1. Pentanol is an excellent renewable alternative. It can be produced from biological pathways like natural microbial fermentation of engineered micro-organisms [16] and biosynthesis from glucose [17]. Pentanol being an alcohol with longer carbon chains also consumes lesser energy during its production when compared to other lower alcohols [5]. Very few studies related to pentanol usage in diesel engines have been conducted so far [5,18–21]. Campos-Fernandez et al. [18] studied the performance of a DI diesel engine fueled with 10%, 15%, 20% and 25% pentanol–diesel blends and reported slight power loss, slight increase in fuel consumption and better brake thermal efficiency. The study concluded that 25% pentanol/diesel blends can be used in diesel engines without any modifications. However their study did not include information on emissions. Li et al. [19] studied the combustion and emission characteristics of a diesel engine fueled with pentanol/diesel and pentanol/biodiesel/diesel blends. Their results indicated that simultaneous reduction in soot and NOx emissions occurred at only low-middle loads while NOx emissions increased at high loads when compared to diesel fuel operation. Wei et al. [20] examined the effect of using 10%, 20% and 30% pentanol/diesel blends in a DI
diesel engine and their results showed that brake specific fuel consumption (BSFC) increased with increase in n-pentanol in diesel while the brake thermal efficiency was unaffected. They reported reductions in particulate emissions at all loads, but they found that NOx emissions increased to maximum of 8% at high engine loads. Li et al. [21] investigated the combustion and emission characteristics of a single cylinder DI diesel engine fueled with neat pentanol under pilot-main and single-injection strategies and have concluded that simultaneous reduction of NOx and soot can be achieved without EGR with neat pentanol operation. From the few available literature on pentanol/diesel blends, it could be inferred that higher blends beyond 30% have not been investigated. Further it is also essential to reduce the high NOx emissions that are prevalent during high engine loads when using pentanol/diesel blends [19,20]. EGR technology is highly effective in reducing the flame temperature and oxygen concentration of the working fluid inside the combustion chamber [22]. Hence in the present study, the effect of EGR on performance and emission characteristics of four pentanol/diesel blends (10%, 20%, 30% and 45% by vol.) under three EGR rates of 10%, 20% and 30% was investigated. The results are then compared with baseline diesel operation.
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2. Materials and methods
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2.1. Test fuel
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For this study, n-pentanol which is certified to a purity of 98% (analytical grade) was procured from AVRA synthesis. Diesel fuel which is the reference fuel for this study was purchased from Indian oil corporation, Chennai. Four pentanol fuel blends were prepared by mixing them with diesel at blending ratios of 10/90 (PEN10), 20/80 (PEN20), 30/70 (PEN30) and 45/55 (PEN45) by volume basis. The properties of all test fuels were measured following ASTM test methods and are shown in Table 2. Solubility of n-pentanol with diesel was tested and no phase separation was found after 48 h. During experimentation, all the blends were stirred well using a mixer to ensure homogeneity just before fueling.
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2.2. Test engine and facilities
163
Tests were performed in a naturally-aspirated, air-cooled, constant-speed (1500 rpm), single-cylinder, direct-injection diesel engine. Specifications of the engine are given in Table 3. The schematic diagram of the experimental setup is presented in Fig. 1. A swinging field electrical dynamometer was used to apply the load on the engine. This electrical dynamometer consisted of a 5-kVA AC alternator (220 V, 1500 rpm) mounted on bearings and on a rigid frame for swinging field type loading. The output power was obtained by measuring the reaction torque by a strain gauge type load cell. The pressure inside the combustion chamber was measured using an AVL GH12D miniature pressure transducer
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Test method
Diesel
PEN10
PEN20
PEN30
PEN45
T10 (°C) T50 (°C) T90 (°C) Calculated cetane index Low heating value (MJ/kg) Kinematic viscosity at 40 °C (mm2/s) Density (kg/m3) Oxygen content (%wt)
ASTM D86
227 270 335 52 43.356 3.522 850 0
137 265 329 47.7 42.321 3.443 847 1.75
137 254 324 46.5 41.745 3.389 843 3.53
137 239 318 44.1 40.233 3.321 838 5.25
137 229 315 42.8 38.987 3.227 832 7.88
ASTM ASTM ASTM ASTM –
D4737 D240 D445 D4052
Table 3 Engine specifications.
b
175 176 177 178 179
Make and model
Kirloskar, TAFI make
Number of cylinders Bore Stroke Swept volume Clearance volume Compression ratio Rated output Rated speed Injection system Injection pressure Fuel injection timing Fuel injection duration Valve timing Intake valve opening Intake valve closing Exhaust valve opening Exhaust valve closing
One 87.5 mm 110 mm 661cm3 36.87cm3 17.5:1 4.7 kW at 1500 rpm 1500 rpm Direct injection 20–21 MPa 23° CAb bTDC 20–30° CA BTDC 4.5° CA bTDC 35.5° CA aBDC 35.5° CA bBDC 4.5° CA aTDC
CA – Crank angle.
connected to an AVL3066A02 Piezo Charge Amplifier. The crank angle and the position of top dead center (TDC) were measured using an AVL364 Angle Encoder. The charge amplifier and the encoder were connected to an AVL 615 Indimeter A/D card, which converts analog input to digital output. Al/Cr K-type thermocouple
was used to measure the exhaust gas temperature, which is taken as an indication of the temperature in the combustion chamber. AVL 615 Indimeter software was used to analyze the output data from the A/D card. This generates a pressure-crank angle diagram that indicates the variation of pressure and heat release rate at every crank angle and also indicates the crank angles at which the combustion starts and at which the percentage (10%, 50% and 90%) of heat released during the combustion. Measurements of all these parameters were carried out for 100 cycles and an average value of these cycles was recorded as a measured parameter at that load. Hence the combustion parameters such as cylinder pressure, heat release rate, ignition delay, peak pressure and crank angles were obtained with an accuracy of 0.01. The fuel consumption rate was measured using an electronic weighing scale of sensitivity 0.1 g and a digital stop watch of resolution 0.01s. Gaseous emissions including NOx, CO and HC emissions were measured using MRU Delta 1600L exhaust gas analyzer and smoke opacity was measured using AVL 439 opaci-meter. Table 4 shows the range and accuracy of the instruments used in this study.
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2.3. EGR setup
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In the current study, an external cooled EGR system was used. Cooled EGR reduces the intake charge temperature and lowers the peak in-cylinder temperatures which in-turn inhibits NOx formation. Cooling also increases the density of EGR which allows a
200
Fig. 1. Schematic of the experimental setup.
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Table 4 Range and accuracy of instruments used. Instrument Gas analyzer
Opacimeter K-type thermocouple Speed measuring unit Pressure pickup Crank angle encoder Burette Digital stop watch
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Measured quantity
Range
Accuracy
Smoke opacity Temperature Engine speed Cylinder pressure Crank angle Fuel quantity Time
0–100% 0–1000 °C 0–9999 rpm 0–250 bar 0–360° 0–1000 cc –
±2% ±1 °C ±5 rpm ±0.1 bar ±1° ±0.1 cc ±0.6 s
As per Eq. (2), the maximum possible error in the calculation of BTE and BSFC was determined to be 0.33%. Similarly, the errors associated with the measurements of temperature, cylinder pressure and crank angle was determined to be 0.5%, 1.35% and 2% respectively.
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2.5. Test procedure
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All the tests were conducted under steady state conditions. No modifications were made to the test engine. The temperature of the lubricating oil was maintained between 85 and 90 °C. Experiments were carried out at constant ambient temperature to improve the reliability of the recordings. The engine was first run with diesel fuel which forms the reference fuel for this study and the baseline data was recorded. The engine always ran for 15 min at each load condition to allow for stabilization before the readings were recorded. Each test was repeated three times to ensure repeatability. The engine was always allowed to run for some time before changing the blends in-order for it to consume the fuel that remained in the fuel system during the previous trial.
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3. Results and discussion
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Engine tests were carried out at five different load conditions that are 0%, 25%, 50%, 75% and 100% of the rated load which correspond to the break mean effective pressures (bmep) of 0, 1.3, 2.6, 4 and 5.3 bar respectively. In each of the section that follows, the performance and emission characteristics of the engine fueled with n-pentanol/diesel blends without EGR is discussed at first and then followed by the discussions on the effect of increasing EGR rates. This is done together for the sake of brevity.
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3.1. Engine performance
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3.1.1. Brake thermal efficiency Fig. 2(a) shows the effect of n-pentanol/diesel blends on brake thermal efficiency as a function of engine load with no EGR applied. It can be seen that BTE increases with engine load but decreases slightly from 75% to 100% loads. This slight drop could be due to the low excess air ratio at high engine loads that worsened combustion [20]. It can be seen that pentanol blends have lesser BTE than diesel. Increasing pentanol fraction in the blend caused a drop in BTE due to the less energy content of pentanol when compared to diesel fuel. A maximum drop of 7.2% from baseline diesel performance was realized with PEN45 blend at high engine loads. The effect of increasing EGR rates on n-pentanol/diesel blends at high engine load (bmep = 5.3 bar) was presented in Fig. 2(b). It can be see that BTE decreases very slightly for all pentanol/diesel blends at increasing EGR rates. Increase in EGR impedes the normal combustion process and reduces the burning rate. The higher CO and HC emissions due to increased EGR rates also accounts for combustion losses and decreased performance of higher blends of pentanol with diesel.
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3.1.2. Brake specific fuel consumption Fig. 3(a) shows the effect of n-pentanol/diesel blends on BSFC as a function of engine load without EGR. It can be seen BSFC increases with increase in pentanol quantity in the blend as more
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greater proportion of EGR to be used. Thus a fraction of exhaust gas is sent to the EGR cooler before it is diverted into the intake manifold for mixing with the incoming air. EGR cooler is a heat exchanger in which cooling water is maintained at a constant temperature to absorb heat from the incoming exhaust gas. It has to be noted that temperature of the exhaust gas re-circulated is kept cooler than the engine exhaust and warmer than the intake air charge. In this experiment, the exhaust gas is cooled down to 35 °C. EGR rate is controlled by an EGR valve. An orifice is used to measure the flow rate of the exhaust gas. Sufficient mixing of incoming air and re-circulated exhaust gas is ensured inside the mixing chamber before it gets inducted into the combustion chamber. EGR quantity was determined as a percentage using the following relation,
CO2intake 100 EGR% ¼ ðCO2 Þexhaust
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The errors associated with various measurements and calculations of parameters are computed in this section. The maximum possible error in calculations was estimated by using the method proposed by Moffat [24]. Errors were estimated from minimum values of the output and accuracy of the instrument. If an estimated quantity S, depends on independent variables like ðx1 ; x2 ; x3 xn Þ, then the error in the value of S is calculated by using Eq. (1).
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( 2 2 2 )12 @x1 @x2 @xn þ þ þ x1 x2 xn
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@S ¼ S
248
where,
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@x1 x1
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@BTE ¼ BFCE
2.4. Error analysis
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253
±1 ppm ±1 ppm ±0.01 %
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223
252
0–4000 ppm 0–20,000 ppm 0–20%
235
222
2 2 2 !12 @Torque @rpm @time þ þ Torque rpm time
251
NOx HC CO
where ðCO2 Þintake represents the concentration of CO2 in the inlet manifold, ðCO2 Þexhaust represents the concentration of CO2 in the exhaust manifold. The concentration of CO2 in the inlet is affected by the opening/closing of EGR valve and the concentration of CO2 in the exhaust gas. The concentration of CO2 in the exhaust gas depends on the burning of the fuel. Since the fuel consumption of the engine is independent of the EGR ratio, this method provides a practical measure of required EGR at stable rates during steady state engine operation. The quantity of CO2 in the inlet and exhaust was measured by the MRU gas analyzer. The flow rate of the exhaust gas re-circulated was adjusted by using the EGR valve until the quantity of CO2 in the intake reaches the desired value (10%, 20% and 30%). Similar method was used by Bhaskar et al. [23] to determine the EGR rates in a similar engine.
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Since brake thermal efficiency (BTE) is calculated from fuel consumption, errors associated with it can be represented by Eq. (2) as follows,
ð1Þ
2 , @x , etc. are the errors in the independent variables. x2
@x1 is the accuracy of the measuring instrument and x1 is the minimum value of the output measured during the experiment.
ð2Þ
Please cite this article in press as: Rajesh kumar B, Saravanan S. Effect of exhaust gas recirculation (EGR) on performance and emissions of a constant speed DI diesel engine fueled with pentanol/diesel blends. Fuel (2015), http://dx.doi.org/10.1016/j.fuel.2015.07.089
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Fig. 2. Brake thermal efficiency (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
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amount of blends are required to produce the same amount of power by the engine due to the less energy content of pentanol when compared to diesel fuel. The effect of increasing EGR rates on BSFC for n-pentanol/diesel blends at high engine load is presented in Fig. 3(b). BSFC generally increases for all pentanol/diesel blends at increasing EGR rates with the consumption being more for PEN45 blends. This is because of the reduction in in-cylinder temperature due to the application of EGR leading to incomplete combustion. 3.1.3. Exhaust temperature Fig. 4(a) shows the variation of exhaust temperature as a function of engine load under no EGR. It can be seen that exhaust temperature decreases with increasing pentanol content in the blend. Low energy content of pentanol causes less combustion temperature and PEN45 having the lowest energy content among all the blends produces lowest exhaust temperatures at all engine loads. The higher latent heat of vaporization of pentanol/diesel blends also reduces the exhaust temperature. The effect of increasing EGR percentages on exhaust temperature for all pentanol/diesel blends at high engine loads are shown in Fig. 4(b). It can be seen that the exhaust temperature slightly decreases with increase in EGR rates for all blends as a result of reduction in peak combustion temperature brought about by the increase of EGR conditions. The higher latent of vaporization of
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Fig. 3. Brake specific fuel consumption (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
pentanol/diesel also provides a cooling effect during combustion and hence a decrease in exhaust temperatures.
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3.1.4. Ignition delay In this study, ignition delay is calculated as the difference between fuel injection timing and the timing at which 5% mass fraction of fuel is burnt. Fig. 5(a) shows the variation of ignition delay for all pentanol/diesel blends with reference to diesel for the entire load spectrum of the engine with no EGR. It can be seen that ignition delay gets longer with increasing pentanol content in the fuel. The increase is obviously due to the decrease in cetane number of diesel brought about by the addition of pentanol. Fig. 5(b) shows the effect of increasing EGR rates on ignition delay of pentanol/diesel blends at high engine load. One of the important effects of EGR is prolongation of ignition delay [8] and hence increase in EGR rates increased the ignition delay for all blends.
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3.2. Engine emissions
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3.2.1. NOx emissions Fig. 6 shows the effect of blends on NOx emissions at various load conditions without EGR. NOx emissions generally increased with engine load for all blends similar to diesel fuel. It can be inferred that, at low/medium load conditions, NOx emissions decreased for all blends with the decrease being higher with higher percentages of pentanol in the blend when compared to diesel fuel. This may be due to low calorific value and high latent heat of
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Fig. 4. Exhaust temperature (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
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vaporization of pentanol that reduces in-cylinder temperatures leading to less thermal NOx formation. At high engine loads, it can be seen that NOx emissions are high compared to diesel fuel as reported earlier with pentanol/diesel blends [19,20]. This behavior may be a result of dominating influence of the oxygen content and lower cetane number of pentanol blends over the cooling effect caused by the high latent heat of vaporization of pentanol. Addition of pentanol to diesel decreases the cetane number of the blend which leads to a longer ignition delay. Hence more fuel blend gets injected into the cylinder during this period and when this high quantity of fuel gets combusted during the premixed combustion phase, it results in elevated gas temperatures favoring NOx emissions [20]. Further the increased fuel intake during high load conditions increases the in-cylinder temperatures and favor NOx formation. The effects of various EGR percentages on NOx emissions for all pentanol/diesel blends at medium and high loads are shown in Fig. 7(a) and (b) respectively. Two loads are discussed due to the difference in behavior of NOx between low/medium and high loads. Increasing EGR rates decreases the flame temperature and oxygen concentration leading to lower NOx emissions. As seen earlier, NOx emissions are generally lower for pentanol/diesel blends at medium loads when compared to diesel and with the introduction of EGR, further reductions were realized for all EGR rates tested. From Fig. 7(a), it can be inferred that at medium loads, PEN45 blends showed a maximum reduction of up to 41% in NOx emissions by 30% EGR while for neat diesel fuel, the reduction is 26.8% for the same levels of EGR.
Fig. 5. Ignition delay (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
Fig. 6. NOx emissions vs engine load without EGR.
Generally at high loads and high EGR rates, the concentration of inert gases present in EGR is more and these gases absorb the energy released by combustion and reduce the peak temperatures inside the combustion chamber. From Fig. 7(b), it can be deduced that at higher loads, NOx emissions were reduced by 33.7% with 30% EGR for PEN45 blend while a reduction of 35% is realized with diesel fuel under similar conditions. The difference in percentage reductions between PEN45 at medium (41%) and high loads (33.7%) shows that NOx emissions are less sensitive to EGR at high loads than at medium loads.
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less with all n-pentanol/diesel blends compared to diesel fuel. This can be explained on the basis of similar observations reported with n-butanol/diesel blends. The oxygen atoms bonded to the hydroxyl group of n-pentanol reduces soot formation inhibiting smoke pre-cursors [7]. The oxygen content of pentanol contributes to improved combustion resulting in the reduction of smoke [25]. Smoke is reduced by up to 77.8% using 45PEN compared to baseline diesel operation under no EGR conditions. The effects of various EGR percentages on smoke opacity for all pentanol/diesel blends at medium and high loads are shown in Fig. 9(a) and (b) respectively. It is obvious that at any given EGR rate and at both loads, smoke emissions remained low for all pentanol/diesel blends when compared to diesel fuel. This can be due to dominant influence of increased oxygen fraction and lower overall equivalence ratio as a result of adding pentanol to diesel over the effects of EGR. Similar scenario was also reported with n-butanol/diesel blends under high EGR rates [8,26]. It can be clearly seen from Fig. 9(b) that smoke emissions hardly increase up to 20% EGR rate and beyond which the smoke emissions has increased for all blends. Increasing EGR rates decrease the oxygen concentration and increase the local equivalence ratio causing incomplete combustion and promote soot formation. As a result of high EGR, cylinder temperature also gets reduced and smoke formation is promoted [26,27]. Studies have shown that soot emissions increases rapidly with EGR increment, once the EGR rate exceeds a specific value [9,28,29]. A soot-bump exists in a specific EGR range where the soot emissions are sensitive to variation in EGR rates making combustion control difficult [10]. Similar
Fig. 7. NOx emissions vs EGR rate at (a) medium load (bmep = 2.6 bar), (b) high load (bmep = 5.3 bar).
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In summary, NOx emissions were reduced by 57% and 30% for PEN45 blend at 30% EGR rate for medium and high loads respectively compared to diesel fuel operation without EGR. 3.2.2. Smoke opacity Fig. 8 compares the variations of smoke opacity for all pentanol/diesel blends at different load conditions without EGR. It can be observed that smoke opacity increases with increase in engine load and is significantly high at high engine loads. This is due to the burning of more fuel to produce higher power output at high engine loads [20]. It can be seen that smoke emissions is
Fig. 8. Smoke opacity vs engine load without EGR.
Fig. 9. Smoke opacity vs EGR rate at (a) medium load (bmep = 2.6 bar), (b) high load (bmep = 5.3 bar).
Please cite this article in press as: Rajesh kumar B, Saravanan S. Effect of exhaust gas recirculation (EGR) on performance and emissions of a constant speed DI diesel engine fueled with pentanol/diesel blends. Fuel (2015), http://dx.doi.org/10.1016/j.fuel.2015.07.089
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observations were also made with different blends of n-butanol Isomers with diesel, where a soot-bump occurred at around 30% EGR rate [9]. In a specific case with 20% n-butanol/diesel blends, it was found that the soot reduction caused by the prolonged ignition delay (due to lower cetane number) and oxygen content cannot compensate for the higher soot formation rate in a certain EGR region between 45% and 56%. As a result, soot increased rapidly in that region [29]. In case of pentanol/diesel blends, the soot-bump might be starting at a region between 20% and 30% EGR rates as seen in Fig. 9(b). An attempt was made to run the engine with
Fig. 10. Variations of smoke and NOx emissions with EGR rates for 45PEN at high load (bmep = 5.3 bar).
Fig. 11. HC emissions (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
higher EGR rates than considered in the present study but it was found that smoke emissions increased rapidly and controlling combustion became difficult. From Figs. 7 and 9, it can be seen that simultaneous reductions in smoke and NOx emissions could be achieved by an addition of pentanol up to 45% with diesel and with an application EGR rates between 20% and 30% at high loads when compared to baseline diesel operation without EGR. Fig. 10 shows the trade-off between NOx emissions and smoke opacity for 45% pentanol/diesel blends at high load conditions under various EGR rates. The trade-off can be better represented by normalizing the values of smoke and NOx emissions to dimensionless numbers, since their units were different. It can be seen clearly that the trade-off relation between smoke and NOx re-appears between 20% and 30% EGR rates for 45PEN blend.
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3.2.3. HC emissions The variation of HC emissions of the engine with pentanol/diesel fuel blends with reference to pure diesel fuel is shown in Fig. 11(a). HC emission increases with increasing pentanol content in the blends at all engine loads. This increase is attributed to the lower cetane number of pentanol/diesel blends. Low cetane number causes longer ignition delay. This deteriorates the self-ignition characteristics of the blends and promotes quenching effect in the leaner mixture zone of the cylinder which in-turn increases HC emissions [4]. The effect of various EGR percentages on HC emissions for all pentanol/diesel blends at high loads is shown in Fig. 11(b). HC emission increases with increasing EGR rates, with the emissions being higher with higher blends of pentanol. Increase in EGR rates
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Fig. 12. (a) CO emissions (a) variations with engine load without EGR, (b) variations with EGR rate at high load (bmep = 5.3 bar).
Please cite this article in press as: Rajesh kumar B, Saravanan S. Effect of exhaust gas recirculation (EGR) on performance and emissions of a constant speed DI diesel engine fueled with pentanol/diesel blends. Fuel (2015), http://dx.doi.org/10.1016/j.fuel.2015.07.089
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causes lower flame temperatures which results in the formation of larger flame quenching zones where combustion cannot happen easily [30]. HC emission increases from 23 ppm to 35 ppm as a result of 30% EGR rate for 45PEN blend.
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3.2.4. CO emissions The variation of CO emissions for pentanol/diesel fuel blends with reference to pure diesel fuel is shown in Fig. 12(a). CO emissions generally increase at low loads and decrease favorably with increasing engine loads due to high in-cylinder temperatures. Similar increase was reported in literature involving higher alcohol/diesel blends [4,20]. It can also be seen that CO emissions increases with increasing pentanol content in the blend. The high latent heat of vaporization of pentanol blends decreases the in-cylinder temperature and causes a cooling effect that promotes the formation of CO. Introduction of EGR prevents CO oxidation due to lower oxygen concentration and as a result, CO emission increases slightly with increasing EGR rates as seen in Fig. 12(b). CO emission of PEN45 is more than other blends.
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4. Conclusions
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The effect of using pentanol/diesel blends up to 45% in proportion on the performance and emission characteristics of pentanol/diesel blends were investigated and compared with baseline diesel fuel in a DI diesel engine. The effect of increasing EGR rates up to 30% was also investigated. EGR was intended to reduce the high NOx emissions that are prevalent during high engine loads with n-pentanol addition to diesel fuel. The following conclusions were drawn from the experimental study.
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1. It is possible to operate a DI diesel engine with up to 45% pentanol/diesel blends with and without EGR. The operation required no modifications to be made to the engine and no visible damage to the engine parts was observed. However, to recommend it as a regular fuel, long-term durability tests are required. 2. Ignition delay gets longer for all pentanol/diesel blends at all EGR rates tested. 3. BTE decreases for all pentanol/diesel blends at increasing EGR rates with the loss being more for PEN45 blends. A maximum drop of 7.2% from baseline diesel performance was realized with PEN45 blend at high engine loads. BSFC also decreased for pentanol/diesel blends with increase in EGR rates. 4. NOx emissions were reduced by 57% and 30% for PEN45 blend at 30% EGR rate for medium and high loads respectively compared to diesel fuel operation. 5. Smoke opacity decreased for all pentanol/diesel blends with the reduction being higher with higher proportion of pentanol. Smoke opacity hardly increased due to the dominance of oxygenated conditions for all pentanol/diesel blends up to 20% EGR and beyond that, smoke opacity has increased for all blends. Further research is required using the combination of n-pentanol blends and high EGR rates to achieve low temperature combustion in diesel engines. 6. The combination of medium EGR rates and blends up to 45% pentanol content can simultaneously reduce smoke and NOx emissions with a little drop in engine performance. 7. HC and CO emissions increased with increasing EGR rates for all pentanol/diesel blends. In summary, n-pentanol is an excellent next generation fuel that can find potential use in diesel engines and has the capability to offer both energy security and environmental safety.
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References
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[1] Benbrahim-Tallaa L, Baan RA, Grosse Y, Lauby-Secretan B, El Ghissassi F, Bouvard V, et al. Carcinogenicity of diesel-engine and gasoline-engine exhausts and some nitroarenes. Lancet Oncol 2012;13(7):663–4. http://dx.doi.org/ 10.1016/s1470-2045(12)70280-2. [2] Tseng H-C. Production of pentanol in metabolically engineered Escherichia Coli. Massachusetts: Massachusetts Institute of Technology; 2011. [3] Rakopoulos DC, Rakopoulos CD, Giakoumis EG, Dimaratos AM, Kyritsis DC. Effects of butanol–diesel fuel blends on the performance and emissions of a high-speed DI diesel engine. Energy Convers Manage 2010;51(10):1989–97. http://dx.doi.org/10.1016/j.enconman.2010.02.032. [4] Karabektas M, Hosoz M. Performance and emission characteristics of a diesel engine using isobutanol–diesel fuel blends. Renew Energy 2009;34(6):1554–9. http://dx.doi.org/10.1016/j.renene.2008.11.003. [5] Campos-Fernández J, Arnal JM, Gómez J, Dorado MP. A comparison of performance of higher alcohols/diesel fuel blends in a diesel engine. Appl Energy 2012;95:267–75. http://dx.doi.org/10.1016/j.apenergy.2012.02.051. [6] Ozsezen AN, Turkcan A, Sayin C, Canakci M. Comparison of performance and combustion parameters in a heavy-duty diesel engine fueled with iso-butanol/ diesel fuel blends. Energy Explor Exploit 2011;29(5):525–41. http://dx.doi.org/ 10.1260/0144-5987.29.5.525. [7] Siwale L, Kristóf L, Adam T, Bereczky A, Mbarawa M, Penninger A, et al. Combustion and emission characteristics of n-butanol/diesel fuel blend in a turbo-charged compression ignition engine. Fuel 2013;107:409–18. http:// dx.doi.org/10.1016/j.fuel.2012.11.083. [8] Chen Z, Wu Z, Liu J, Lee C. Combustion and emissions characteristics of high nbutanol/diesel ratio blend in a heavy-duty diesel engine and EGR impact. Energy Convers Manage 2014;78:787–95. http://dx.doi.org/10.1016/ j.enconman.2013.11.037. [9] Zheng Z, Li C, Liu H, Zhang Y, Zhong X, Yao M. Experimental study on diesel conventional and low temperature combustion by fueling four isomers of butanol. Fuel 2015;141:109–19. http://dx.doi.org/10.1016/j.fuel.2014.10.053. [10] Zhang Q, Yao M, Zheng Z, Liu H, Xu J. Experimental study of n-butanol addition on performance and emissions with diesel low temperature combustion. Energy 2012;47(1):515–21. http://dx.doi.org/10.1016/j.energy.2012.09.020. [11] Valentino G, Corcione FE, Iannuzzi SE, Serra S. Experimental study on performance and emissions of a high speed diesel engine fuelled with nbutanol diesel blends under premixed low temperature combustion. Fuel 2012;92(1):295–307. http://dx.doi.org/10.1016/j.fuel.2011.07.035. [12] Liu H, Bi X, Huo M, Lee CF, Yao M. Soot emissions of various oxygenated biofuels in conventional diesel combustion and low-temperature combustion conditions. Energy Fuels 2012;26(3):1900–11. http://dx.doi.org/10.1021/ ef201720d. [13] Liu H, Huo M, Liu Y, Wang X, Wang H, Yao M, et al. Time-resolved spray, flame, soot quantitative measurement fueling n-butanol and soybean biodiesel in a constant volume chamber under various ambient temperatures. Fuel 2014;133:317–25. http://dx.doi.org/10.1016/j.fuel.2014.05.038. [14] Zheng Z, Yue L, Liu H, Zhu Y, Zhong X, Yao M. Effect of two-stage injection on combustion and emissions under high EGR rate on a diesel engine by fueling blends of diesel/gasoline, diesel/n-butanol, diesel/gasoline/n-butanol and pure diesel. Energy Convers Manage 2015;90:1–11. http://dx.doi.org/10.1016/ j.enconman.2014.11.011. [15] Tornatore C, Marchitto L, Mazzei A, Valentine G, Corcione FE, Merola SS. Effect of butanol blend on in-cylinder combustion process. Part 2: Compression ignition engine. J KONES Powertrain Transp 2011;18(2):473–83. [16] Cann AF, Liao JC. Pentanol isomer synthesis in engineered microorganisms. Appl Microbiol Biotechnol 2009;85(4):893–9. http://dx.doi.org/10.1007/ s00253-009-2262-7. [17] Zhang K, Sawaya MR, Eisenberg DS, Liao JC. Expanding metabolism for biosynthesis of nonnatural alcohols. Proc Natl Acad Sci 2008;105(52):20653–8. http://dx.doi.org/10.1073/pnas.0807157106. [18] Campos-Fernandez J, Arnal JM, Gomez J, Lacalle N, Dorado MP. Performance tests of a diesel engine fueled with pentanol/diesel fuel blends. Fuel 2013;107:866–72. http://dx.doi.org/10.1016/j.fuel.2013.01.066. [19] Li L, Wang J, Wang Z, Xiao J. Combustion and emission characteristics of diesel engine fueled with diesel/biodiesel/pentanol fuel blends. Fuel 2015. http:// dx.doi.org/10.1016/j.fuel.2015.04.048. [20] Wei L, Cheung CS, Huang Z. Effect of n-pentanol addition on the combustion, performance and emission characteristics of a direct-injection diesel engine. Energy 2014;70:172–80. http://dx.doi.org/10.1016/j.energy.2014.03.106. [21] Li L, Wang J, Wang Z, Liu H. Combustion and emissions of compression ignition in a direct injection diesel engine fueled with pentanol. Energy 2015;80:575–81. http://dx.doi.org/10.1016/j.energy.2014.12.013. [22] Pandian M, Sivapirakasam SP, Udayakumar M. Investigations on emission characteristics of the pongamia biodiesel–diesel blend fuelled twin cylinder compression ignition direct injection engine using exhaust gas recirculation methodology and dimethyl carbonate as additive. J Renew Sustain Energy 2010;2(4):043110. http://dx.doi.org/10.1063/1.3480016. [23] Bhaskar K, Nagarajan G, Sampath S. Optimization of FOME (fish oil methyl esters) blend and EGR (exhaust gas recirculation) for simultaneous control of NOx and particulate matter emissions in diesel engines. Energy 2013;62:224–34. http://dx.doi.org/10.1016/j.energy.2013.09.056. [24] Moffat RJ. Using uncertainty analysis in the planning of an experiment. J Fluids Eng 1985;107(2):173–8. http://dx.doi.org/10.1115/1.3242452.
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[25] Tsolakis A, Megaritis A, Wyszynski M, Theinnoi K. Engine performance and emissions of a diesel engine operating on diesel-RME (rapeseed methyl ester) blends with EGR (exhaust gas recirculation). Energy 2007;32(11):2072–80. http://dx.doi.org/10.1016/j.energy.2007.05.016. [26] Gu X, Li G, Jiang X, Huang Z, Lee CF. Experimental study on the performance of and emissions from a low-speed light-duty diesel engine fueled with nbutanol–diesel and isobutanol–diesel blends. Proc Instit Mech Eng Part D: J Automob Eng 2013;227(2):261–71. http://dx.doi.org/10.4271/2012-28-0011. [27] Zhu R, Wang X, Miao H, Yang X, Huang Z. Effect of dimethoxy-methane and exhaust gas recirculation on combustion and emission characteristics of a direct injection diesel engine. Fuel 2011;90(5):1731–7. http://dx.doi.org/ 10.1016/j.fuel.2011.01.035.
[28] Alriksson M, Rente T, Denbratt I. Low soot, Low NOx in a heavy duty diesel engine using high levels of EGR; 2005. http://dx.doi.org/10.4271/2005-013836. [29] Liu H, Li S, Zheng Z, Xu J, Yao M. Effects of n-butanol, 2-butanol, and methyl octynoate addition to diesel fuel on combustion and emissions over a wide range of exhaust gas recirculation (EGR) rates. Appl Energy 2013;112:246–56. http://dx.doi.org/10.1016/j.apenergy.2013.06.023. [30] Heywood JB. Internal combustion engine fundamentals. New York (USA): McGraw-Hill; 1988.
Please cite this article in press as: Rajesh kumar B, Saravanan S. Effect of exhaust gas recirculation (EGR) on performance and emissions of a constant speed DI diesel engine fueled with pentanol/diesel blends. Fuel (2015), http://dx.doi.org/10.1016/j.fuel.2015.07.089
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