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Influence of injection timing on the exhaust emissions of a dual-fuel CI engine
ARTICLE IN PRESS
Renewable Energy 33 (2008) 1314–1323 www.elsevier.com/locate/renene
Influence of injection timing on the exhaust emissions of a dual-fuel CI engine Cenk Sayina, Kadir Uslub, Mustafa Canakcic,d, a
Department of Mechanical Education, Marmara University, 34722 Istanbul, Turkey Department of Automotive Education, Fatih Vocational High School, 54100 Sakarya, Turkey c Department of Mechanical Education, Kocaeli University, 41380 Kocaeli, Turkey d Alternative Fuels R&D Center, Kocaeli University, 41040 Kocaeli, Turkey
b
Received 3 October 2006; accepted 9 July 2007 Available online 4 September 2007
Abstract Environmental concerns and limited amount of petroleum fuels have caused interests in the development of alternative fuels for internal combustion (IC) engines. As an alternative, biodegradable, and renewable fuel, ethanol is receiving increasing attention. Therefore, in this study, influence of injection timing on the exhaust emission of a single cylinder, four stroke, direct injection, naturally aspirated diesel engine has been experimentally investigated using ethanol blended diesel fuel from 0% to 15% with an increment of 5%. The engine has an original injection timing 271 CA BTDC. The tests were performed at five different injection timings (211, 241, 271, 301, and 331 CA BTDC) by changing the thickness of advance shim. The experimental test results showed that NOx and CO2 emissions increased as CO and HC emissions decreased with increasing amount of ethanol in the fuel mixture. When compared to the results of original injection timing, at the retarded injection timings (211 and 241 CA BTDC), NOx and CO2 emissions increased, and unburned HC and CO emissions decreased for all test conditions. On the other hand, with the advanced injection timings (301 and 331 CA BTDC), HC and CO emissions diminished, and NOx and CO2 emissions boosted for all test conditions. r 2007 Elsevier Ltd. All rights reserved. Keywords: Diesel engine; Ethanol; Emissions; Injection timing; Alternative fuel
1. Introduction Most of the internal combustion (IC) engines use petroleum fuels which are limited and expected to be exhausted in about 40 years. Limited energy sources leads to the warning of potential lack of energy in the future. Approximately 1/3 of the petroleum fuels are consumed in the IC engines which have lesser power than 185 kW and Abbreviations: ATDC, after top dead center; BTDC, before top dead center; CA, crank angle; CI, compression ignition; CO, carbon monoxide; CO2, carbon dioxide; HC, hydrocarbon; LHV, lower heating value; NOx, nitrogen oxides; ppm, particulate per million; rpm, revolution per minute; TDC, top dead center Corresponding author. Department of Mechanical Education, Kocaeli University, 41380 Kocaeli, Turkey. Tel.:+90 262 3032285; fax: +90 262 3032203. E-mail addresses: [email protected], [email protected] (M. Canakci). 0960-1481/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2007.07.007
exhaust gases emitted from these engines are one of the main reasons of the environmental pollution. In the last years, many studies on the IC engines aiming to reduce exhaust emissions have been carried out by changing operating parameters such as valve timing, injection timing, and atomization rate. At the same time, depletion of fossil fuels and environmental considerations has led to investigations on the renewable fuels such as ethanol, hydrogen, and biodiesel [1,2]. Since 19th century, ethanol has been used as a fuel for compression ignition (CI) engines. Ethanol can be fermented and distilled from biomasses. Therefore, it can be considered as a renewable fuel. As a fuel for CI engines, ethanol has some advantages over diesel fuel, such as the reductions of soot, carbon monoxide (CO) and unburned hydrocarbon (HC) emissions. Although having these advantages, due to limitation in technology, economic and regional considerations, ethanol still cannot be used
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extensively. However, ethanol blended diesel fuels can be practically used in CI engines [3,4]. Ethanol (C2H5OH) is a pure substance. However, diesel fuel is composed of C3–C25 HCs, and has wider transitional properties. Ethanol contains an oxygen atom so that it can be viewed as a partially oxidized HC. Ethanol is completely miscible with water. This may cause the blended fuel to contain water, and further results in the corrosion problems on the mechanical components, particularly for components made from aluminum, brass, and copper. To diminish this problem on the fuel delivery system, such materials stated above should be avoided. Ethanol can react with most rubber and create jam in the fuel pipe. Therefore, it is advised to use fluorocarbon rubber as a replacement for rubber. The auto-ignition temperature of ethanol is higher than that of diesel fuel, which makes it safer for transportation and storage. On the other hand, ethanol has a much lower flash point than that of diesel fuel, a disadvantage with respect to safety [5,6]. Sustaining a clean environment has become an important issue in an industrialized society. Air pollution caused by IC engines is one of the important environmental problems to be tackled. Since using ethanol blended diesel fuel can ease off the air pollution and depletion of petroleum fuels simultaneously, many researchers have devoted to studying the influence of these alternative fuels on the exhaust emissions of IC engines. Weidman and Menrad [7], for instance, studied the effect of 30% (vol.) ethanol blended diesel fuel on emissions of an engine, and found that ethanol could reduce CO, unburned HC, and soot emission to some degree. Can [4] studied the exhaust emissions of a turbocharged, indirect diesel engine having different fuel injection pressures (100, 150, 200, and 250 bar) when adding ethanol (10%, 15%, and 20% as vol.) to diesel fuel. The experimental results showed that ethanol addition reduces CO, soot and sulfur dioxide (SO2) emissions, although it caused increasing in nitrogen oxides (NOx) emissions. Likos and Callaha investigated the exhaust emissions of a direct injection CI engine when using 10%, 20%, and 30% ethanol blended diesel fuels [8]. According to their experimental results, they determined decreasing CO and HC emissions and increasing NOx emissions with rising ethanol amount in the fuel mixture. Moreover, minimum exhaust emissions were obtained in 10% ethanol–diesel blend. For a diesel engine, fuel injection timing is a major parameter that affects the combustion and exhaust emissions. The state of air into which the fuel injected changes as the injection timing is varied, and thus ignition delay will vary. If injection starts earlier, the initial air temperature and pressure are lower, so the ignition delay will increase. If injection starts later (when piston is closer to the TDC) the temperature and pressure are initially slightly higher, a decrease in ignition delay proceeds. Hence, injection timing variation has a strong effect on the exhaust emissions, especially on the NOx emissions,
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because of the changing of the maximum temperature in the engine cylinder [9,10]. Several studies have showed that the injection timing affects the level of exhaust emissions of CI engines. Parlak et al. [11] studied the influence of injection timing on the NOx emissions and brake specific fuel consumption (BSFC) of a low heat rejection (LHR) indirect injection diesel engine using diesel fuel. The tests were conducted with variable loads at engine speeds of 1000, 1400, 1800, and 2000 rpm and the static injection timing of 38o, 36o, 34o and 32o crank angle (CA). After the load tests were conducted for original diesel engine, same tests order was adopted for LHR engine. When the LHR engine was operated with the injection timing of 38o CA before top dead center (BTDC), which is the optimum value of the original engine, it showed that NOx emission increased by about 15%. However, when the injection timing retarded to 34o CA in the LHR case, a decrease in the exhaust emissions of about 40% and about 6% compared to that of the original case was observed. Nwafor [12] examined the effect of advanced injection timing on the exhaust emissions of natural gas used as a primary fuel in dual-fuel CI engine. The test engine has an original injection timing of 301 CA BTDC. The injection was advanced by 3.51 (i.e. 33.51 CA BTDC). The results indicated that dual fuel combustion produces larger percentage of HC emissions than those of pure diesel fuel. Significant reductions in CO and CO2 emissions were obtained when running the engine with the advanced injection timing. As mentioned above, it can be realized that ethanol blended diesel fuel can effectively reduce the pollutant emissions. However, the influence of injection timing on the exhaust emissions has not been clearly studied when using ethanol blended diesel fuels in the CI engines. Therefore, in this study, both effects of injection timing and ethanol blended diesel fuel on the exhaust emissions were experimentally investigated on a single cylinder CI engine. 2. Experimental apparatus and procedure The experiments were conducted on a single cylinder, four stroke, direct injection, naturally aspirated, four stroke CI engine. Details of the engine specification are Table 1 Technical specifications of the test engine [13] Engine type
Super Star 7710
Cylinder number Cylinder bore stroke Total cylinder volume Original injection timing Compression ratio Maximum torque Maximum power
1 98 100 mm 770 cc 271 CA BTDC 17:1 39.8 Nm at 1650 rpm 7.4 kW at 1900 rpm
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The engine has an original injection timing of 271 CA BTDC. Thickness of advance shim, located in the connection place between engine and fuel pump is 0.25 mm and adding one shim advances the injection timing by 31 CA. Experiments were carried out at five different injection timing (211, 241, 271, 301, and 331 CA BTDC) values with decreasing or increasing advance shim. All test runs were conducted on the test bench. In each run, engine speed and load were recorded. The combination of all tests included engine setting at two constant loads (15 and 30 Nm) and five different engine speeds (1000–1800 rpm) with 200 rpm intervals for each injection timing. The values of engine oil temperature, mass flow rate of air, engine speed, torque, exhaust temperature, and pollutants such as CO, CO2, unburned HC, and NOx were recorded during the experiments. Each test was repeated three times. The values given in this study are the average of these three results. Before each experiment, the engine was regulated according to the catalogue values. All data were collected after the engine stabilized. The photo of the experimental apparatus is shown in Fig. 2.
shown in Table 1. The engine was coupled to a hydraulic dynamometer to control engine speed and load. Engine oil temperature, coolant temperature, exhaust temperature, and inlet air temperature were measured using K type thermocouples. The exhaust emissions (CO, unburned HC, NOx, and CO2) were measured using two different gas analyzers (Opus 40 and Kane-May Quintox). Pressure in the intake manifold was determined by inclined manometer. To prepare ethanol blended fuel mixture, two fuels (euro-diesel and ethanol) were used. Euro-diesel was obtained from TUPRAS Petroleum Corporation. Ethanol, with a purity of 99%, was purchased from a commercial supplier. The fuel properties are shown in Table 2. The euro-diesel was blended with ethanol to get 4 different fuel blends ranging 0–15% with an increment of 5%. The fuel blends were prepared just before starting the experiment to ensure that the fuel mixture is homogenous. A mixer was also mounted inside the fuel tank in order to prevent phase separation. The experimental setup is shown in Fig. 1.
Table 2 Properties of the fuels used in the tests [14]
Formula Molecular weight Boiling temperature ( 1C) Density (kg/m3, at 20 1C) Flash point ( 1C) Autoignition temperature ( 1C) Lower heating value (kJ/kg) Cetane number Vapor pressure (kPa, at 38 1C) Stoichiometric air–fuel ratio Latent heat of vaporization (kJ/kg)
3. Results and discussion
Ethanol
Euro diesel
C2H5OH 46.07 78.3 811.5 13 425 27 415 17 8.96 921.1
C12H26—C14H30 170–198 190–280 820–845 52 300–340 43 504 0.34 14.7 620
Ethanol blended diesel fuel can reduce the pollutant emissions. However, to reach the emission reduction, it may require some modification on the engine. The injection timing has a significant effect on the exhaust emissions in a CI engines. Therefore, the effects of injection timing and ethanol blended diesel fuel on the engine emissions were experimentally investigated on a single cylinder CI engine. The experimental conditions were selected as follows: five engine speeds (1000, 1200, 1400, 1600, and 1800 rpm), two constant loads (15 and 10 Nm) and five injection timings (211, 241, 271 ORG, 301, and 331 CA BTDC) were used.
Air tank
Orifice
Inclined manometer
Mixer
Fuel Tank
Heat exchanger Dijital scales
T
T
Exhaust gas analyser NO
Exhaust gas analyser HC, CO CO
Exhaust probe
Exhaust line
Test engine
Dynamometer T
Fig. 1. The experimental setup.
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The fuels were E0, E5, E10, and E15, indicating the content of ethanol in different volume ratios (e.g., E5 contains 5% ethanol and 95% diesel fuel in volume). 3.1. Carbon monoxide (CO) emissions CO emission is toxic and must be controlled. It is an intermediate product in the combustion of a HC fuel, so its emission results from incomplete combustion. Emission of CO is therefore greatly dependent on the air–fuel ratio relative to the stoichiometric proportions. Rich combustion invariably produces CO, and emissions increase nearly linearly with the deviation from the stoichiometry [9]. CO emissions results are presented in Figs. 3 and 4 for different engine speeds and injection timings, respectively.
Fig. 2. The experimental apparatus used in the tests.
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The results show that when the ethanol ratio in the mixture increased, the CO concentrations in the exhaust decreased. This is a result of improving combustion process since oxygen content in the ethanol causes better combustion. As the engine speed increased, the values of CO decreased. Increase in speed could probably augment volumetric efficiency, boosting turbulence in combustion chamber, hence ensuring better combustion [15]. Minimum CO found was 0.06% with the E15, 0.11% with the E10, 0.38% with the E5, and 0.42% with the E0 at maximum speed (1800 rpm) and 30 Nm load at ORG injection timing. CO emission reduced steadily when the engine load increased in the engine. When the engine load increases at constant speed, combustion temperatures boost. Therefore CO emissions start to decrease [16]. The results obtained in this study confirmed this statement. At 1600 rpm constant speed and ORG injection timing, while CO emission was measured to be 0.11% with E10 at 30 Nm load, it was 0.18% at 15 Nm. Fig. 4 shows the CO emission results for different ethanol blended diesel fuels and injection timings at two constant loads and 1800 rpm. When the injection timing advanced, the level of CO emission decreased. Advancing the injection timing by 31 (from 271 to 301 CA BTDC) caused the emission reduction by 15.5% for E15 at 30 Nm load and 1800 rpm. Fig. 5 shows the effect on combustion temperature of the of with injection timing. The advanced injection timing produced a higher cylinder temperature which caused an increase in the chemical reaction speed of combustion region. Also, the advanced injection timing increased the oxidation process between carbon and oxygen molecules. These cause reduction of the CO emissions [17]. However, retarding the injection timing by 61 (from 271 to 211 CA BTDC) caused 59.1% increase in
0.8 E0, 15 Nm E5, 15 Nm
0.7
E10, 15 Nm E15, 15 Nm
0.6
E0, 30 Nm E5, 30 Nm
CO (%)
0.5
E10, 30 Nm E15, 30 Nm
0.4 0.3 0.2 0.1 0.0 800
1000
1200
1400 1600 Engine speed (rpm)
1800
2000
Fig. 3. CO emission results at different engine speeds and loads (ORG injection timing).
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0.8 E0, 15 Nm E5, 15 Nm
0.7
E10, 15 Nm E15, 15 Nm
0.6
E0, 30 Nm E5, 30 Nm
CO (%)
0.5
E10, 30 Nm E15, 30 Nm
0.4 0.3 0.2 0.1 0.0 18
21
24 27 30 Injection timing (CA). BTDC
33
36
Fig. 4. CO emission results at different injection timings and loads (1800 rpm).
320 310 E0, 30 Nm Exhaust gas temperature (°C)
300
E5, 30 Nm E10, 30 Nm E15, 30 Nm
290 280 270 260 250 240 18
21
24
27
30
33
36
Injection timing (CA), (BTDC) Fig. 5. Exhaust gas temperatures at different injection timings (1800 rpm).
the CO emission at the same test condition mentioned above. 3.2. Unburned hydrocarbon (HC) emissions Unburned HC emissions consist of fuel that is incompletely burned. The term HC means organic compounds in the gaseous state; solid HCs are part of the particulate matter. Typically, unburned HCs are a serious problem at light loads in CI engines. At light loads the fuel is less apt
to impinge on surfaces; but, because of poor fuel distribution, large amounts of excess air and low exhaust temperature, lean fuel–air mixture regions may survive to escape into the exhaust [18–20]. The influence of different blends on unburned HC emission can be clearly seen in Fig. 6. As the ethanol content increases, unburned HC emission decreased for all engine speeds. Unburned HC concentrations diminished moderately with increasing speed and load that was in the same trend with CO. The experimental results indicated
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180 E0, 15 Nm
170
E5, 15 Nm
160
E10, 15 Nm
150
E15, 15 Nm E0, 30 Nm
140 HC (ppm)
E5, 30 Nm 130
E10, 30 Nm
120
E15, 30 Nm
110 100 90 80 70 60 800
1000
1200
1400 1600 Engine speed (rpm)
1800
2000
Fig. 6. HC emission results at different engine speeds and loads (ORG injection timing).
that the minimum unburned HC emissions were found as 96, 86, 80, and 64 ppm for E0, E5, E10, and E15, respectively, at 30 Nm load and 1600 rpm, which were obtained around the speed of maximum torque of the engine. When ethanol is added to the diesel fuel, it can provide more oxygen for the combustion process and leads to improved combustion. In addition, ethanol molecules are polar, which cannot be absorbed easily by non-polar molecule lubrication oil layer; and therefore ethanol can lower the possibility of production of HC emissions [21,22]. Fig. 7 shows the variations of the unburned HC with different ethanol blended diesel fuels at different injection timings for the 1800 rpm and two constant loads (15 and 30 Nm). It can be seen that advancing the injection timing reduces unburned HC emissions. Advancing the injection timing from 271 to 331 CA BTDC caused the emission of unburned HC to decrease by 18.8% for E15 at 30 Nm load. Advancing the injection timing causes earlier start of combustion relative to the TDC. Because of this, the cylinder charge, being compressed as the piston moves to the TDC, had relatively higher temperatures, as shown in Fig. 5. Increasing the temperature decreased the flame quenching layer thickness and thus lowered the unburned HC emissions [21,23]. However, for the same test condition, when the injection timing was retarded by 6o (from 271 to 211 CA BTDC), the unburned HC increased by 51.2%. 3.3. Nitrogen oxides (NOx) emissions The most troublesome emissions from CI engines are NOx. The oxides of nitrogen in the exhaust emissions contain nitric oxide (NO) and nitrogen dioxide (NO2). The
formation of NOx is highly dependent on in-cylinder temperatures, the oxygen concentration, and residence time for the reaction to take place [3,24,25]. The changes in the NOx emissions at different engine speeds are shown in Fig. 8. NOx concentration generally increased with increasing engine speed and load. However, after the speed of the maximum torque of the engine, they started to decrease. The experimental results indicated that NOx values of E15 were higher than those of others, which will be explained later. Maximum NOx was observed at 486 ppm with E15 and 395, 417, and 455 ppm with E0, E5, and E10, respectively, at maximum loads (30 Nm) and 1600 rpm, which are obtained around the maximum torque speed of the engine. Fig. 9 indicates the variations of NOx emissions for different ethanol blended diesel fuels under different injection timings at 1800 rpm and two constant loads (15 and 30 Nm). When the injection timing is retarded, a decrease in the NOx emissions for all the fuel mixtures was observed. When the injection timing was retarded by 6o CA BTDC in comparison to ORG, NOx emissions decreased by 37.3% for E5 at 30 Nm load. Retarding the injection timing decreases the peak cylinder pressure because more fuel burns after TDC. Lower peak cylinder pressures results in lower peak temperatures, as observed in Fig. 5. As a consequence, the NOx concentration starts to diminish [26]. Ethanol contains 34% oxygen and its cetane number is lower than that of diesel fuel, which increases the peak temperature in the cylinder. On the other hand, the lower heating value (LHV) of ethanol is nearly 1.7 times lower than that of diesel fuel and latent heat of vaporization of ethanol is about 1.5 times greater than that of diesel fuel,
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190 180
E0, 15 Nm
170
E5, 15 Nm E10, 15 Nm
160
E15, 15 Nm
HC (ppm)
150
E0, 30 Nm
140
E5, 30 Nm
130
E10, 30 Nm
120
E15, 30 Nm
110 100 90 80 70 60 50 18
21
24
27
30
33
36
Injection timing (CA), BTDC Fig. 7. HC emission results at different injection timings and loads (1800 rpm).
500 E0, 15 Nm E5, 15 Nm
450
E10, 15 Nm E15, 15 Nm
400
E0, 30 Nm
NOX (ppm)
E5, 30 Nm E10, 30 Nm
350
E15, 30 Nm 300
250
200
150 800
1000
1200
1400
1600
1800
2000
Engine speed (rpm) Fig. 8. NOx emission results at different engine speeds and loads (ORG injection timing).
which decreases the peak temperature in the cylinder [9,27]. As shown in Fig. 10, the exhaust temperature increased with increasing ethanol ratio in the fuel mixture. It is clear from the figure that the cetane number and oxygen content are more effective than LHV and latent heat of vaporization with regard to increasing peak temperature in the cylinder. Therefore, the concentration of NOx emission increased as the ethanol content increased in the blended fuel for both of the engine loads.
3.4. Carbon dioxide (CO2) emissions CO2 occurs naturally in the atmosphere and is a normal product of combustion. Ideally, combustion of a HC fuel should produce only CO2 and water (H2O). Fig. 11 describes the effect of using ethanol blended diesel fuels on CO2 emission. As seen in the Figs. 3 and 4, when the ethanol amount increased in the fuel mixture, the CO and unburned HC concentration in the exhaust decreased. The
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500 E0, 15 Nm E5, 15 Nm
450
E10, 15 Nm E15, 15 Nm
400
E0, 30 Nm E5, 30 Nm
NOX (ppm)
350
E10, 30 Nm E15, 30 Nm
300 250 200 150 100 18
21
24
27
30
33
36
Injection timing (CA), BTDC Fig. 9. NOx emission results at different injection timings and loads (1800 rpm).
300
Exhaust gas temperature (°C)
290 280
E0, 30 Nm
270
E5, 30 Nm E10, 30 Nm
260
E15, 30 Nm
250 240 230 220 210 200 190 800
1000
1200
1400 1600 Engine speed (rpm)
1800
2000
Fig. 10. Exhaust gas temperatures at different engine speeds (ORG injection timing).
CO2 concentrations have an opposite behavior when compared with the CO concentrations, and this is due to the improving of the combustion process as a result of the oxygen content in the ethanol. Maximum CO2 observed was 9%, 8.6%, 6.6%, and 6.4% at E15, E10, E5, and E0, respectively, for 30 Nm engine load and 1600 rpm. As shown in Table 1, producing the maximum torque from the test engine is at 1650 rpm. Therefore, the combustion and volumetric efficiencies improve around this speed. And
thus, at the speed of the maximum torque of the test engine, CO2 emissions reach the maximum level. In this study, CO2 emissions increased with an increase of the advancing of injection timing, as shown in Fig. 12, for all the fuel mixtures. When the injection timing was advanced from 271 to 331 CA BTDC, the level of CO2 emission boosted by 30.2% for E0 at 30 Nm constant load and 1800 rpm. As shown in Fig. 5, the advanced injection timing created a higher cylinder temperature and this
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9 E0, 15 Nm E5, 15 Nm
8
E10, 15 Nm E15, 15 Nm
7
CO2 (%)
E0, 30 Nm E5, 30 Nm
6
E10, 30 Nm E15, 30 Nm 5
4
3
2 800
1 000
1200
1400 Engine speed (rpm)
1600
1800
2000
Fig. 11. CO2 emission results at different engine speeds and loads (ORG injection timing).
10 E0, 15 Nm E5, 15 Nm 9
E10, 15 Nm E15, 15 Nm E0, 30 Nm
CO2 (%)
8
E5, 30 Nm E10, 30 Nm E15, 30 Nm
7
6
5
4 18
21
24
27
30
33
36
Injection timing (CA), BTDC Fig. 12. CO2 emission results at different injection timings and loads (1800 rpm).
augmented the chemical reaction speed. And thus an increase in the CO2 emissions occurs. 4. Conclusions In this study, the influence of injection timing on the exhaust emissions of a diesel engine has been experimentally investigated using ethanol blended diesel fuel. The results indicated that NOx emissions slightly increased; CO
and unburned HC emissions decreased dramatically by ethanol addition; and CO2 emissions increased because of the improved combustion. By using ethanol blended diesel fuels, CO and unburned HC emissions reduced 10–70% and 10–45%, while CO2 and NOx emissions increased 10–50% and 5–15%, respectively, depending on the engine running conditions. Increasing the amount of ethanol in the fuel mixture produced higher peak temperature in the cylinder. This effect increased NOx emissions.
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In terms of injection timing, the test results demonstrated that, on advancing the injection timing, CO and unburned HC emissions decreased while NOx and CO2 emissions increased. When the injection timing was advanced, CO emission decreased due to improved reaction between fuel and oxygen. This caused an increase in the CO2 emissions. Advancing the injection timing caused an earlier start of combustion relative to the TDC. Because of this, the cylinder charge, being compressed as the piston moves to the TDC, had relatively higher temperatures and thus, lowered the unburned HC emissions and increased NOx emissions. Advancing the injection timing by 61 CA BTDC (33o CA BTDC) at 30 Nm load and 1800 rpm gave the best results for the unburned HC and CO emissions. At these conditions, CO and unburned HC emissions were found as 0.06% and 60 ppm, respectively, for E15. On the other hand, retarding the injection timing by 61 CA BTDC (211CA BTDC) at 15 Nm load and 1800 rpm presented the minimum results of NOx and CO2 emissions. At these working conditions, NOx and CO2 emissions were found as 100 ppm and 4.15%, respectively. Acknowledgments This study was supported by Faculty of Technical Education in Sakarya University. The authors would like to thank the individuals at the engine test laboratory who were involved in making this work possible. References [1] Durgun O, Ayvaz Y. The use of diesel fuel–gasoline blends in diesel engines. In: Proceedings of the first international energy and environment symposium, Trabzon, Turkey, July 29–31, 1996. p. 9105–20. [2] Yu¨ksel F, Yu¨ksel B. The use of ethanol–gasoline blends as a fuel in a SI engine. Renew Energy 2004;29:1181–91. [3] Ajav EA, Singh B, Bhattacharya TK. Performance of a stationary diesel engine using vaporized ethanol as supplementary fuel. Biomass Bioenergy 1998;15(6):493–502. [4] Can O. Effects of ethanol–diesel fuel blends on engine performance and exhaust emissions of a diesel engine. MSc thesis, Gazi University, 2003 [in Turkish]. [5] Fuery RL, Perry KL. Composition and reactivity of fuel vapor emissions from gasoline–oxygenate blends. SAE paper 912429. [6] Nageli DW, Lacey PI, Alger M. Surface corrosion in ethanol fuel pumps. SAE paper 971648.
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[7] Wiedman K, Menrad H. Fleet test, performance and emissions of diesel engines using different alcohol–diesel fuel blends. SAE paper 810249. [8] Likos B, Callaha TL. Performance and emissions of ethanol and ethanol–diesel blends in direct-injected and pre-chamber diesel engines. SAE paper 821039. [9] Heywood JB. Internal combustion engines. USA: McGraw-Hill; 1984. [10] Borat O, Balcı M, Su¨rmen A. Internal combustion engines. Turkey: Gazi University Publishing; 2000 [in Turkish]. [11] Parlak A, Yas-ar H, Has-imog˘lu C, Kolip A. The effects of injection timing on NOx emissions of a low heat rejection indirect diesel injection engine. Appl Therm Eng 2005;25:3042–52. [12] Nwafor OMI. Knock characteristics of dual-fuel combustion in diesel engines using natural gas as primary fuel. Sadhana 2002;27(3): 375–82. [13] Super Star. Engine technical specification. Turkey: 2000 [in Turkish]. [14] TUPRAS. Product specification. Turkey: 2005 [in Turkish]. [15] Sayin C, Kilicaslan I, Canakci M, Ozsezen N. An experimental study of the effect of octane number higher than engine requirement on the engine performance and emissions. Appl Therm Eng 2005;25: 1315–24. [16] Abdel-Rahman AA. On the emissions from internal-combustion engines. Int J Energy Res 1998;22:483–513. [17] Uslu K. Influence on performance and emission on using diesel fuel and ethanol at the different injection timing in the diesel engine. MSc thesis, Marmara University, 2006 [in Turkish]. [18] Canakci M. Idealized engine emissions resulting from the combustion of isooctane supplemented with hydrogen. MSc thesis, Vanderbilt University, Tennessee, 1996. [19] Whitten GZ, Reyes S. Air quality and ethanol in gasoline. In: Proceedings of the ninth annual ethanol conference, policy and marketing, 2004. p. 16–8. [20] Borman GL, Ragland KW. Combustion engineering. New York, USA: McGraw-Hill; 1999. [21] Alla GH, Soliman HA, Badr OH, Rabbo MF. Effect of injection timing on the performance of diesel engine. Energy Convers Manage 2002;43:269–77. [22] Wu CW, Chen RH, Pu JY, Lin TH. The influence of air–fuel ratio on engine performance and pollutant emission of an SI engine using ethanol–gasoline blend. Atmos Environ 2004;40:7093–100. [23] Pukrakek WW. Engineering fundamentals of the internal combustion engine. USA: Simon and Schuster Company; 1997. [24] Andrea TD, Henshaw PF, Ting DS. The addition of hydrogen to gasoline-fuelled SI engine. Int J Hydrogen Energy 2004;29: 1541–52. [25] Challen B, Baranescu R. Diesel engine reference book. 2nd ed. England: Butterworth and Heinemann Publishing; 1999. [26] BOSCH. Automotive handbook. 5th ed. Germany; 2000. [27] Nwafor OMI, Rice G, Ogbonna AI. Effect of advanced injection timing on the performance of rapeseed oil in diesel engines. Renew Energy 2000;21:433–44.
Renewable Energy 33 (2008) 1314–1323 www.elsevier.com/locate/renene
Influence of injection timing on the exhaust emissions of a dual-fuel CI engine Cenk Sayina, Kadir Uslub, Mustafa Canakcic,d, a
Department of Mechanical Education, Marmara University, 34722 Istanbul, Turkey Department of Automotive Education, Fatih Vocational High School, 54100 Sakarya, Turkey c Department of Mechanical Education, Kocaeli University, 41380 Kocaeli, Turkey d Alternative Fuels R&D Center, Kocaeli University, 41040 Kocaeli, Turkey
b
Received 3 October 2006; accepted 9 July 2007 Available online 4 September 2007
Abstract Environmental concerns and limited amount of petroleum fuels have caused interests in the development of alternative fuels for internal combustion (IC) engines. As an alternative, biodegradable, and renewable fuel, ethanol is receiving increasing attention. Therefore, in this study, influence of injection timing on the exhaust emission of a single cylinder, four stroke, direct injection, naturally aspirated diesel engine has been experimentally investigated using ethanol blended diesel fuel from 0% to 15% with an increment of 5%. The engine has an original injection timing 271 CA BTDC. The tests were performed at five different injection timings (211, 241, 271, 301, and 331 CA BTDC) by changing the thickness of advance shim. The experimental test results showed that NOx and CO2 emissions increased as CO and HC emissions decreased with increasing amount of ethanol in the fuel mixture. When compared to the results of original injection timing, at the retarded injection timings (211 and 241 CA BTDC), NOx and CO2 emissions increased, and unburned HC and CO emissions decreased for all test conditions. On the other hand, with the advanced injection timings (301 and 331 CA BTDC), HC and CO emissions diminished, and NOx and CO2 emissions boosted for all test conditions. r 2007 Elsevier Ltd. All rights reserved. Keywords: Diesel engine; Ethanol; Emissions; Injection timing; Alternative fuel
1. Introduction Most of the internal combustion (IC) engines use petroleum fuels which are limited and expected to be exhausted in about 40 years. Limited energy sources leads to the warning of potential lack of energy in the future. Approximately 1/3 of the petroleum fuels are consumed in the IC engines which have lesser power than 185 kW and Abbreviations: ATDC, after top dead center; BTDC, before top dead center; CA, crank angle; CI, compression ignition; CO, carbon monoxide; CO2, carbon dioxide; HC, hydrocarbon; LHV, lower heating value; NOx, nitrogen oxides; ppm, particulate per million; rpm, revolution per minute; TDC, top dead center Corresponding author. Department of Mechanical Education, Kocaeli University, 41380 Kocaeli, Turkey. Tel.:+90 262 3032285; fax: +90 262 3032203. E-mail addresses: [email protected], [email protected] (M. Canakci). 0960-1481/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2007.07.007
exhaust gases emitted from these engines are one of the main reasons of the environmental pollution. In the last years, many studies on the IC engines aiming to reduce exhaust emissions have been carried out by changing operating parameters such as valve timing, injection timing, and atomization rate. At the same time, depletion of fossil fuels and environmental considerations has led to investigations on the renewable fuels such as ethanol, hydrogen, and biodiesel [1,2]. Since 19th century, ethanol has been used as a fuel for compression ignition (CI) engines. Ethanol can be fermented and distilled from biomasses. Therefore, it can be considered as a renewable fuel. As a fuel for CI engines, ethanol has some advantages over diesel fuel, such as the reductions of soot, carbon monoxide (CO) and unburned hydrocarbon (HC) emissions. Although having these advantages, due to limitation in technology, economic and regional considerations, ethanol still cannot be used
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extensively. However, ethanol blended diesel fuels can be practically used in CI engines [3,4]. Ethanol (C2H5OH) is a pure substance. However, diesel fuel is composed of C3–C25 HCs, and has wider transitional properties. Ethanol contains an oxygen atom so that it can be viewed as a partially oxidized HC. Ethanol is completely miscible with water. This may cause the blended fuel to contain water, and further results in the corrosion problems on the mechanical components, particularly for components made from aluminum, brass, and copper. To diminish this problem on the fuel delivery system, such materials stated above should be avoided. Ethanol can react with most rubber and create jam in the fuel pipe. Therefore, it is advised to use fluorocarbon rubber as a replacement for rubber. The auto-ignition temperature of ethanol is higher than that of diesel fuel, which makes it safer for transportation and storage. On the other hand, ethanol has a much lower flash point than that of diesel fuel, a disadvantage with respect to safety [5,6]. Sustaining a clean environment has become an important issue in an industrialized society. Air pollution caused by IC engines is one of the important environmental problems to be tackled. Since using ethanol blended diesel fuel can ease off the air pollution and depletion of petroleum fuels simultaneously, many researchers have devoted to studying the influence of these alternative fuels on the exhaust emissions of IC engines. Weidman and Menrad [7], for instance, studied the effect of 30% (vol.) ethanol blended diesel fuel on emissions of an engine, and found that ethanol could reduce CO, unburned HC, and soot emission to some degree. Can [4] studied the exhaust emissions of a turbocharged, indirect diesel engine having different fuel injection pressures (100, 150, 200, and 250 bar) when adding ethanol (10%, 15%, and 20% as vol.) to diesel fuel. The experimental results showed that ethanol addition reduces CO, soot and sulfur dioxide (SO2) emissions, although it caused increasing in nitrogen oxides (NOx) emissions. Likos and Callaha investigated the exhaust emissions of a direct injection CI engine when using 10%, 20%, and 30% ethanol blended diesel fuels [8]. According to their experimental results, they determined decreasing CO and HC emissions and increasing NOx emissions with rising ethanol amount in the fuel mixture. Moreover, minimum exhaust emissions were obtained in 10% ethanol–diesel blend. For a diesel engine, fuel injection timing is a major parameter that affects the combustion and exhaust emissions. The state of air into which the fuel injected changes as the injection timing is varied, and thus ignition delay will vary. If injection starts earlier, the initial air temperature and pressure are lower, so the ignition delay will increase. If injection starts later (when piston is closer to the TDC) the temperature and pressure are initially slightly higher, a decrease in ignition delay proceeds. Hence, injection timing variation has a strong effect on the exhaust emissions, especially on the NOx emissions,
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because of the changing of the maximum temperature in the engine cylinder [9,10]. Several studies have showed that the injection timing affects the level of exhaust emissions of CI engines. Parlak et al. [11] studied the influence of injection timing on the NOx emissions and brake specific fuel consumption (BSFC) of a low heat rejection (LHR) indirect injection diesel engine using diesel fuel. The tests were conducted with variable loads at engine speeds of 1000, 1400, 1800, and 2000 rpm and the static injection timing of 38o, 36o, 34o and 32o crank angle (CA). After the load tests were conducted for original diesel engine, same tests order was adopted for LHR engine. When the LHR engine was operated with the injection timing of 38o CA before top dead center (BTDC), which is the optimum value of the original engine, it showed that NOx emission increased by about 15%. However, when the injection timing retarded to 34o CA in the LHR case, a decrease in the exhaust emissions of about 40% and about 6% compared to that of the original case was observed. Nwafor [12] examined the effect of advanced injection timing on the exhaust emissions of natural gas used as a primary fuel in dual-fuel CI engine. The test engine has an original injection timing of 301 CA BTDC. The injection was advanced by 3.51 (i.e. 33.51 CA BTDC). The results indicated that dual fuel combustion produces larger percentage of HC emissions than those of pure diesel fuel. Significant reductions in CO and CO2 emissions were obtained when running the engine with the advanced injection timing. As mentioned above, it can be realized that ethanol blended diesel fuel can effectively reduce the pollutant emissions. However, the influence of injection timing on the exhaust emissions has not been clearly studied when using ethanol blended diesel fuels in the CI engines. Therefore, in this study, both effects of injection timing and ethanol blended diesel fuel on the exhaust emissions were experimentally investigated on a single cylinder CI engine. 2. Experimental apparatus and procedure The experiments were conducted on a single cylinder, four stroke, direct injection, naturally aspirated, four stroke CI engine. Details of the engine specification are Table 1 Technical specifications of the test engine [13] Engine type
Super Star 7710
Cylinder number Cylinder bore stroke Total cylinder volume Original injection timing Compression ratio Maximum torque Maximum power
1 98 100 mm 770 cc 271 CA BTDC 17:1 39.8 Nm at 1650 rpm 7.4 kW at 1900 rpm
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The engine has an original injection timing of 271 CA BTDC. Thickness of advance shim, located in the connection place between engine and fuel pump is 0.25 mm and adding one shim advances the injection timing by 31 CA. Experiments were carried out at five different injection timing (211, 241, 271, 301, and 331 CA BTDC) values with decreasing or increasing advance shim. All test runs were conducted on the test bench. In each run, engine speed and load were recorded. The combination of all tests included engine setting at two constant loads (15 and 30 Nm) and five different engine speeds (1000–1800 rpm) with 200 rpm intervals for each injection timing. The values of engine oil temperature, mass flow rate of air, engine speed, torque, exhaust temperature, and pollutants such as CO, CO2, unburned HC, and NOx were recorded during the experiments. Each test was repeated three times. The values given in this study are the average of these three results. Before each experiment, the engine was regulated according to the catalogue values. All data were collected after the engine stabilized. The photo of the experimental apparatus is shown in Fig. 2.
shown in Table 1. The engine was coupled to a hydraulic dynamometer to control engine speed and load. Engine oil temperature, coolant temperature, exhaust temperature, and inlet air temperature were measured using K type thermocouples. The exhaust emissions (CO, unburned HC, NOx, and CO2) were measured using two different gas analyzers (Opus 40 and Kane-May Quintox). Pressure in the intake manifold was determined by inclined manometer. To prepare ethanol blended fuel mixture, two fuels (euro-diesel and ethanol) were used. Euro-diesel was obtained from TUPRAS Petroleum Corporation. Ethanol, with a purity of 99%, was purchased from a commercial supplier. The fuel properties are shown in Table 2. The euro-diesel was blended with ethanol to get 4 different fuel blends ranging 0–15% with an increment of 5%. The fuel blends were prepared just before starting the experiment to ensure that the fuel mixture is homogenous. A mixer was also mounted inside the fuel tank in order to prevent phase separation. The experimental setup is shown in Fig. 1.
Table 2 Properties of the fuels used in the tests [14]
Formula Molecular weight Boiling temperature ( 1C) Density (kg/m3, at 20 1C) Flash point ( 1C) Autoignition temperature ( 1C) Lower heating value (kJ/kg) Cetane number Vapor pressure (kPa, at 38 1C) Stoichiometric air–fuel ratio Latent heat of vaporization (kJ/kg)
3. Results and discussion
Ethanol
Euro diesel
C2H5OH 46.07 78.3 811.5 13 425 27 415 17 8.96 921.1
C12H26—C14H30 170–198 190–280 820–845 52 300–340 43 504 0.34 14.7 620
Ethanol blended diesel fuel can reduce the pollutant emissions. However, to reach the emission reduction, it may require some modification on the engine. The injection timing has a significant effect on the exhaust emissions in a CI engines. Therefore, the effects of injection timing and ethanol blended diesel fuel on the engine emissions were experimentally investigated on a single cylinder CI engine. The experimental conditions were selected as follows: five engine speeds (1000, 1200, 1400, 1600, and 1800 rpm), two constant loads (15 and 10 Nm) and five injection timings (211, 241, 271 ORG, 301, and 331 CA BTDC) were used.
Air tank
Orifice
Inclined manometer
Mixer
Fuel Tank
Heat exchanger Dijital scales
T
T
Exhaust gas analyser NO
Exhaust gas analyser HC, CO CO
Exhaust probe
Exhaust line
Test engine
Dynamometer T
Fig. 1. The experimental setup.
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The fuels were E0, E5, E10, and E15, indicating the content of ethanol in different volume ratios (e.g., E5 contains 5% ethanol and 95% diesel fuel in volume). 3.1. Carbon monoxide (CO) emissions CO emission is toxic and must be controlled. It is an intermediate product in the combustion of a HC fuel, so its emission results from incomplete combustion. Emission of CO is therefore greatly dependent on the air–fuel ratio relative to the stoichiometric proportions. Rich combustion invariably produces CO, and emissions increase nearly linearly with the deviation from the stoichiometry [9]. CO emissions results are presented in Figs. 3 and 4 for different engine speeds and injection timings, respectively.
Fig. 2. The experimental apparatus used in the tests.
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The results show that when the ethanol ratio in the mixture increased, the CO concentrations in the exhaust decreased. This is a result of improving combustion process since oxygen content in the ethanol causes better combustion. As the engine speed increased, the values of CO decreased. Increase in speed could probably augment volumetric efficiency, boosting turbulence in combustion chamber, hence ensuring better combustion [15]. Minimum CO found was 0.06% with the E15, 0.11% with the E10, 0.38% with the E5, and 0.42% with the E0 at maximum speed (1800 rpm) and 30 Nm load at ORG injection timing. CO emission reduced steadily when the engine load increased in the engine. When the engine load increases at constant speed, combustion temperatures boost. Therefore CO emissions start to decrease [16]. The results obtained in this study confirmed this statement. At 1600 rpm constant speed and ORG injection timing, while CO emission was measured to be 0.11% with E10 at 30 Nm load, it was 0.18% at 15 Nm. Fig. 4 shows the CO emission results for different ethanol blended diesel fuels and injection timings at two constant loads and 1800 rpm. When the injection timing advanced, the level of CO emission decreased. Advancing the injection timing by 31 (from 271 to 301 CA BTDC) caused the emission reduction by 15.5% for E15 at 30 Nm load and 1800 rpm. Fig. 5 shows the effect on combustion temperature of the of with injection timing. The advanced injection timing produced a higher cylinder temperature which caused an increase in the chemical reaction speed of combustion region. Also, the advanced injection timing increased the oxidation process between carbon and oxygen molecules. These cause reduction of the CO emissions [17]. However, retarding the injection timing by 61 (from 271 to 211 CA BTDC) caused 59.1% increase in
0.8 E0, 15 Nm E5, 15 Nm
0.7
E10, 15 Nm E15, 15 Nm
0.6
E0, 30 Nm E5, 30 Nm
CO (%)
0.5
E10, 30 Nm E15, 30 Nm
0.4 0.3 0.2 0.1 0.0 800
1000
1200
1400 1600 Engine speed (rpm)
1800
2000
Fig. 3. CO emission results at different engine speeds and loads (ORG injection timing).
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0.8 E0, 15 Nm E5, 15 Nm
0.7
E10, 15 Nm E15, 15 Nm
0.6
E0, 30 Nm E5, 30 Nm
CO (%)
0.5
E10, 30 Nm E15, 30 Nm
0.4 0.3 0.2 0.1 0.0 18
21
24 27 30 Injection timing (CA). BTDC
33
36
Fig. 4. CO emission results at different injection timings and loads (1800 rpm).
320 310 E0, 30 Nm Exhaust gas temperature (°C)
300
E5, 30 Nm E10, 30 Nm E15, 30 Nm
290 280 270 260 250 240 18
21
24
27
30
33
36
Injection timing (CA), (BTDC) Fig. 5. Exhaust gas temperatures at different injection timings (1800 rpm).
the CO emission at the same test condition mentioned above. 3.2. Unburned hydrocarbon (HC) emissions Unburned HC emissions consist of fuel that is incompletely burned. The term HC means organic compounds in the gaseous state; solid HCs are part of the particulate matter. Typically, unburned HCs are a serious problem at light loads in CI engines. At light loads the fuel is less apt
to impinge on surfaces; but, because of poor fuel distribution, large amounts of excess air and low exhaust temperature, lean fuel–air mixture regions may survive to escape into the exhaust [18–20]. The influence of different blends on unburned HC emission can be clearly seen in Fig. 6. As the ethanol content increases, unburned HC emission decreased for all engine speeds. Unburned HC concentrations diminished moderately with increasing speed and load that was in the same trend with CO. The experimental results indicated
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180 E0, 15 Nm
170
E5, 15 Nm
160
E10, 15 Nm
150
E15, 15 Nm E0, 30 Nm
140 HC (ppm)
E5, 30 Nm 130
E10, 30 Nm
120
E15, 30 Nm
110 100 90 80 70 60 800
1000
1200
1400 1600 Engine speed (rpm)
1800
2000
Fig. 6. HC emission results at different engine speeds and loads (ORG injection timing).
that the minimum unburned HC emissions were found as 96, 86, 80, and 64 ppm for E0, E5, E10, and E15, respectively, at 30 Nm load and 1600 rpm, which were obtained around the speed of maximum torque of the engine. When ethanol is added to the diesel fuel, it can provide more oxygen for the combustion process and leads to improved combustion. In addition, ethanol molecules are polar, which cannot be absorbed easily by non-polar molecule lubrication oil layer; and therefore ethanol can lower the possibility of production of HC emissions [21,22]. Fig. 7 shows the variations of the unburned HC with different ethanol blended diesel fuels at different injection timings for the 1800 rpm and two constant loads (15 and 30 Nm). It can be seen that advancing the injection timing reduces unburned HC emissions. Advancing the injection timing from 271 to 331 CA BTDC caused the emission of unburned HC to decrease by 18.8% for E15 at 30 Nm load. Advancing the injection timing causes earlier start of combustion relative to the TDC. Because of this, the cylinder charge, being compressed as the piston moves to the TDC, had relatively higher temperatures, as shown in Fig. 5. Increasing the temperature decreased the flame quenching layer thickness and thus lowered the unburned HC emissions [21,23]. However, for the same test condition, when the injection timing was retarded by 6o (from 271 to 211 CA BTDC), the unburned HC increased by 51.2%. 3.3. Nitrogen oxides (NOx) emissions The most troublesome emissions from CI engines are NOx. The oxides of nitrogen in the exhaust emissions contain nitric oxide (NO) and nitrogen dioxide (NO2). The
formation of NOx is highly dependent on in-cylinder temperatures, the oxygen concentration, and residence time for the reaction to take place [3,24,25]. The changes in the NOx emissions at different engine speeds are shown in Fig. 8. NOx concentration generally increased with increasing engine speed and load. However, after the speed of the maximum torque of the engine, they started to decrease. The experimental results indicated that NOx values of E15 were higher than those of others, which will be explained later. Maximum NOx was observed at 486 ppm with E15 and 395, 417, and 455 ppm with E0, E5, and E10, respectively, at maximum loads (30 Nm) and 1600 rpm, which are obtained around the maximum torque speed of the engine. Fig. 9 indicates the variations of NOx emissions for different ethanol blended diesel fuels under different injection timings at 1800 rpm and two constant loads (15 and 30 Nm). When the injection timing is retarded, a decrease in the NOx emissions for all the fuel mixtures was observed. When the injection timing was retarded by 6o CA BTDC in comparison to ORG, NOx emissions decreased by 37.3% for E5 at 30 Nm load. Retarding the injection timing decreases the peak cylinder pressure because more fuel burns after TDC. Lower peak cylinder pressures results in lower peak temperatures, as observed in Fig. 5. As a consequence, the NOx concentration starts to diminish [26]. Ethanol contains 34% oxygen and its cetane number is lower than that of diesel fuel, which increases the peak temperature in the cylinder. On the other hand, the lower heating value (LHV) of ethanol is nearly 1.7 times lower than that of diesel fuel and latent heat of vaporization of ethanol is about 1.5 times greater than that of diesel fuel,
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190 180
E0, 15 Nm
170
E5, 15 Nm E10, 15 Nm
160
E15, 15 Nm
HC (ppm)
150
E0, 30 Nm
140
E5, 30 Nm
130
E10, 30 Nm
120
E15, 30 Nm
110 100 90 80 70 60 50 18
21
24
27
30
33
36
Injection timing (CA), BTDC Fig. 7. HC emission results at different injection timings and loads (1800 rpm).
500 E0, 15 Nm E5, 15 Nm
450
E10, 15 Nm E15, 15 Nm
400
E0, 30 Nm
NOX (ppm)
E5, 30 Nm E10, 30 Nm
350
E15, 30 Nm 300
250
200
150 800
1000
1200
1400
1600
1800
2000
Engine speed (rpm) Fig. 8. NOx emission results at different engine speeds and loads (ORG injection timing).
which decreases the peak temperature in the cylinder [9,27]. As shown in Fig. 10, the exhaust temperature increased with increasing ethanol ratio in the fuel mixture. It is clear from the figure that the cetane number and oxygen content are more effective than LHV and latent heat of vaporization with regard to increasing peak temperature in the cylinder. Therefore, the concentration of NOx emission increased as the ethanol content increased in the blended fuel for both of the engine loads.
3.4. Carbon dioxide (CO2) emissions CO2 occurs naturally in the atmosphere and is a normal product of combustion. Ideally, combustion of a HC fuel should produce only CO2 and water (H2O). Fig. 11 describes the effect of using ethanol blended diesel fuels on CO2 emission. As seen in the Figs. 3 and 4, when the ethanol amount increased in the fuel mixture, the CO and unburned HC concentration in the exhaust decreased. The
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500 E0, 15 Nm E5, 15 Nm
450
E10, 15 Nm E15, 15 Nm
400
E0, 30 Nm E5, 30 Nm
NOX (ppm)
350
E10, 30 Nm E15, 30 Nm
300 250 200 150 100 18
21
24
27
30
33
36
Injection timing (CA), BTDC Fig. 9. NOx emission results at different injection timings and loads (1800 rpm).
300
Exhaust gas temperature (°C)
290 280
E0, 30 Nm
270
E5, 30 Nm E10, 30 Nm
260
E15, 30 Nm
250 240 230 220 210 200 190 800
1000
1200
1400 1600 Engine speed (rpm)
1800
2000
Fig. 10. Exhaust gas temperatures at different engine speeds (ORG injection timing).
CO2 concentrations have an opposite behavior when compared with the CO concentrations, and this is due to the improving of the combustion process as a result of the oxygen content in the ethanol. Maximum CO2 observed was 9%, 8.6%, 6.6%, and 6.4% at E15, E10, E5, and E0, respectively, for 30 Nm engine load and 1600 rpm. As shown in Table 1, producing the maximum torque from the test engine is at 1650 rpm. Therefore, the combustion and volumetric efficiencies improve around this speed. And
thus, at the speed of the maximum torque of the test engine, CO2 emissions reach the maximum level. In this study, CO2 emissions increased with an increase of the advancing of injection timing, as shown in Fig. 12, for all the fuel mixtures. When the injection timing was advanced from 271 to 331 CA BTDC, the level of CO2 emission boosted by 30.2% for E0 at 30 Nm constant load and 1800 rpm. As shown in Fig. 5, the advanced injection timing created a higher cylinder temperature and this
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9 E0, 15 Nm E5, 15 Nm
8
E10, 15 Nm E15, 15 Nm
7
CO2 (%)
E0, 30 Nm E5, 30 Nm
6
E10, 30 Nm E15, 30 Nm 5
4
3
2 800
1 000
1200
1400 Engine speed (rpm)
1600
1800
2000
Fig. 11. CO2 emission results at different engine speeds and loads (ORG injection timing).
10 E0, 15 Nm E5, 15 Nm 9
E10, 15 Nm E15, 15 Nm E0, 30 Nm
CO2 (%)
8
E5, 30 Nm E10, 30 Nm E15, 30 Nm
7
6
5
4 18
21
24
27
30
33
36
Injection timing (CA), BTDC Fig. 12. CO2 emission results at different injection timings and loads (1800 rpm).
augmented the chemical reaction speed. And thus an increase in the CO2 emissions occurs. 4. Conclusions In this study, the influence of injection timing on the exhaust emissions of a diesel engine has been experimentally investigated using ethanol blended diesel fuel. The results indicated that NOx emissions slightly increased; CO
and unburned HC emissions decreased dramatically by ethanol addition; and CO2 emissions increased because of the improved combustion. By using ethanol blended diesel fuels, CO and unburned HC emissions reduced 10–70% and 10–45%, while CO2 and NOx emissions increased 10–50% and 5–15%, respectively, depending on the engine running conditions. Increasing the amount of ethanol in the fuel mixture produced higher peak temperature in the cylinder. This effect increased NOx emissions.
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In terms of injection timing, the test results demonstrated that, on advancing the injection timing, CO and unburned HC emissions decreased while NOx and CO2 emissions increased. When the injection timing was advanced, CO emission decreased due to improved reaction between fuel and oxygen. This caused an increase in the CO2 emissions. Advancing the injection timing caused an earlier start of combustion relative to the TDC. Because of this, the cylinder charge, being compressed as the piston moves to the TDC, had relatively higher temperatures and thus, lowered the unburned HC emissions and increased NOx emissions. Advancing the injection timing by 61 CA BTDC (33o CA BTDC) at 30 Nm load and 1800 rpm gave the best results for the unburned HC and CO emissions. At these conditions, CO and unburned HC emissions were found as 0.06% and 60 ppm, respectively, for E15. On the other hand, retarding the injection timing by 61 CA BTDC (211CA BTDC) at 15 Nm load and 1800 rpm presented the minimum results of NOx and CO2 emissions. At these working conditions, NOx and CO2 emissions were found as 100 ppm and 4.15%, respectively. Acknowledgments This study was supported by Faculty of Technical Education in Sakarya University. The authors would like to thank the individuals at the engine test laboratory who were involved in making this work possible. References [1] Durgun O, Ayvaz Y. The use of diesel fuel–gasoline blends in diesel engines. In: Proceedings of the first international energy and environment symposium, Trabzon, Turkey, July 29–31, 1996. p. 9105–20. [2] Yu¨ksel F, Yu¨ksel B. The use of ethanol–gasoline blends as a fuel in a SI engine. Renew Energy 2004;29:1181–91. [3] Ajav EA, Singh B, Bhattacharya TK. Performance of a stationary diesel engine using vaporized ethanol as supplementary fuel. Biomass Bioenergy 1998;15(6):493–502. [4] Can O. Effects of ethanol–diesel fuel blends on engine performance and exhaust emissions of a diesel engine. MSc thesis, Gazi University, 2003 [in Turkish]. [5] Fuery RL, Perry KL. Composition and reactivity of fuel vapor emissions from gasoline–oxygenate blends. SAE paper 912429. [6] Nageli DW, Lacey PI, Alger M. Surface corrosion in ethanol fuel pumps. SAE paper 971648.
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