biodiesel on dual fuel mode HCCI engine for different engine load conditions

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Full Length Article

Experimental investigation of ethanol/diesel and ethanol/biodiesel on dual fuel mode HCCI engine for different engine load conditions ⁎

Ganesh R. Gawale , G. Naga Srinivasulu Department of Mechanical Engineering, National Institute of Technology, Warangal 506004, Telangana, India

A R T I C LE I N FO

A B S T R A C T

Keywords: Dual fuel HCCI engine Premixed ratio Alternative fuels Combustion characteristics Fuel jets Optimization

Homogeneous charge compression ignition (HCCI) engine has fuel flexibility and potential to reduce NOX and soot emissions. The aim of this work is to investigate the effect of different mass flow rates of ethanol on dual fuel mode HCCI engine working under different load conditions. Ethanol (primary fuel) was supplied through the carburetor at the time of suction and diesel /biodiesel blend (secondary fuel) was injected to start the combustion at the end of the compression. Mass flow rate of ethanol varied by the use of different fuel jets (Jet 40, Jet 60, Jet 70, Jet 80, and Jet 90) in the carburetor. The results showed that with an increase in the mass flow rate of ethanol, ignition delay (ID) increases, combustion duration (CD), in-cylinder pressure and temperature are reduced; which leads to reduce NOX emission and smoke opacity of ethanol/diesel (E + D) and ethanol/biodiesel (E + B20) dual-fuel mode HCCI engine compared to neat diesel engine. However, HC and CO emissions are highly increased for dual fuel mode HCCI engines compared to neat diesel engine. Instead of diesel, biodiesel (B20) triggers the combustion and reduces ID (by 4 deg. crank angle (CA)) for 100% load with the use of jet 90 in the carburetor. Finally, it is concluded that Jet 40 and Jet 60 are suitable for 20% load and 40% load of engine respectively and also Jet 70 is suitable for 60%, 80% and 100% load conditions in order to optimize higher thermal efficiency, low NOX emissions and low smoke opacity.

1. Introduction Over the past few decades, vehicle population has been increasing due to urbanization and industrialization. The entire globe is experiencing a serious problem of reduction in petroleum-based oil resources. Vehicles are emitting hazardous gases into the environment in large quantities which causes severe health problems to human beings and also greatly contaminates the environment. Because of these problems, the government has been recommending stringent norms over vehicle emissions. Further, increasing cost of fossil fuel and fast depletion of such fuels are forcing to find alternative fuels with low emissions. Based on the latest data available, the researcher used alcohol-based fuels, and biodiesel fuels in the diesel engine [1,2]. Most of the heavy vehicles operate on diesel engine and, which is advantageous compared to spark ignition (SI) engine, in terms of fuel consumption, maintenance, durability, fuel cost, etc. [3]. However, diesel engine emits more nitrogen oxide (NOX) and soot emission. For the reduction of NOX and soot emissions, Sindhu et al. [4] studied the effects of variation of fuel injection timing, exhaust gas recirculation (EGR) and split injection. From the study, it was observed that split injections are better at controlling NOX emission compared to EGR and retardation of injection timing. The ⁎

influence of diesel/butanol blend on NOX and smoke emission was carried out by Wang et al. [5]. Authors came to the conclusion that with the use of diesel/butanol blend, the ignition delay (ID) increases retard combustion phasing and increases premixed combustion ratio. This blend also reduced smoke opacity without any variations in NOX emissions; however, fuel economy was reduced. A fixed quantity of hydrogen induction with biodiesel was initiated by Rahman et al. [6] to reduce hydrocarbon (HC), carbon monoxide (CO), and smoke emissions and to simultaneously increase the thermal efficiency (ηT) of the engine. Further induction of 10% EGR reduces NOX emission at low load but at high load, it shows an adverse effect on brake specific fuel consumption (bsfc), ηT, carbon dioxide (CO2), CO, HC, and smoke opacity. Recently Algayyim et al. [7] had successfully proved that biodiesel is one of the best options to replace conventional fuels without modifying the engine design. In-built oxygen in the biodiesel blends advantages to reduce the CO and HC. Furthermore, the properties of biodiesel and diesel are similar; biodiesel is easily permissible to blend with diesel [8]. Experimental evaluation of the influence of higher blend biodiesel/diesel on the performance of variable compression ratio (VCR) engine was executed by Warkhade et al. [9]. They came to the

Corresponding author. E-mail address: [email protected] (G.R. Gawale).

https://doi.org/10.1016/j.fuel.2019.116725 Received 14 October 2019; Received in revised form 14 November 2019; Accepted 21 November 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.

Please cite this article as: Ganesh R. Gawale and G. Naga Srinivasulu, Fuel, https://doi.org/10.1016/j.fuel.2019.116725

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Nomenclature

IMEP Jet 40 Jet 60 Jet 70 Jet 80 Jet 90 LTC MFB NOX PFLP PM PRR PRPR SI SOC TDC

Abbreviations aTDC bTDC B20 CA CD CI CO CO2 CR E + B20 E+D EGR HC HCCI HSU HRR ID

After top dead center Before top dead center 20% neem biodiesel and 80% diesel by volume Crank Angle Combustion duration Compression-Ignition Carbon monoxide Carbon dioxide Compression ratio Ethanol and biodiesel (B20) dual-fuel mode HCCI engine Ethanol and diesel dual fuel mode HCCI engine Exhaust gas recirculation Hydrocarbon Homogeneous charged compression ignition Hartridge smoke unit Heat release rate Ignition delay

Indicated means effective pressure Fuel jet with 0.4 mm diameter Fuel jet with 0.6 mm diameter Fuel jet with 0.7 mm diameter Fuel jet with 0.8 mm diameter Fuel jet with 0.9 mm diameter Low-temperature combustion Mass fraction burn Nitrogen oxide (ppm) Peak fuel line pressure Particle matter Pressure rise rate Peak rate of pressure rise. Spark ignition Start of combustion Top dead center

Symbol ηT

Thermal efficiency

cetane number properties. It can sustain a high compression ratio (CR), thereby giving more power and fuel economy. Due to high latent heat of vaporization, combustion temperature assists to decrease NOX, HC, CO emissions [2,12]. However, as alcohol has low cetane number, using it in the compression ignition (CI) engine is very tough without using ignition assistant. Generally, alcohol-based fuels are used in the HCCI engine. HCCI engine is a low-temperature combustion (LTC) engine. HCCI engine has the features of both SI and CI engines [13,14]. It is advantageous for low NOX and soot emissions, it can sustain high CR and more importantly, it has fuel flexibility. However HCCI engine has some challenges such as narrow operating range, inability to function under high load condition, high-pressure rise rate (PRR) and heat release rate (HRR) at full load conditions [13,15,16]. Dual-injection technique was used by Das et al. [17] to run the

conclusion that up to 30% biodiesel blending can be used without affecting the performance characteristics of the engine. However, a higher blend proportion increases exhaust emission like HC, CO2, CO, NOX, Soot. Thus, researchers intended to find additives for reduction of emission with biodiesel as a fuel. Katam et al. [10] experimentally studied the use of Mixed culture Microalgae in coconut, with Karanja biodiesel as an antioxidant. The results show low NOX emission and high ηT compared to a diesel engine. Above all literature related to biodiesel, biodiesel blend with additives, blending with alcohol, split injection, EGR usage, and beyond this, some alcohol-based fuels like methanol, ethanol, butanol, propanol, etc. can be used in the diesel engine [11]. Alcohol fuels are suitable for SI engine because of the high octane number and low

Fig. 1. Schematic diagram of Ethanol/diesel dual fuel HCCI engine. Where, F1 = Fuel Line (Diesel), F2 = Fuel Line (Ethanol), F3 = Air-fuel mixture Line, F4 = Cooling water, N = Engine speed in rpm, W = Eddy current dynamometer, PT = Pressure transducer, DAS = Data acquisition system, T1 = Inlet cooling water temperature, T2 = Outlet cooling water temperature, T3 = Exhaust gas temperature, Cb = Carburetor, Ga = Five gas analyzer, Sm = Smoke meter, Eg = Exhaust gas flow. 2

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An experimental study on port-injected Ricardo hydra test engine was carried out by Uyumaz [19] to investigate the impact of pure nheptane, blends of n-heptane and n-butanol (B20, B30, B40), and blend of n-heptane and isopropanol (P20, P30, P40) fuels. The author concluded that n-heptane and B20 blend were responsible for knocking and that other than these two fuels (n-heptane and B20) other fuels reduced NOX emissions drastically. Fuel blending is the most popular method to control HCCI combustion; apart from this, injection of two different fuels at two different locations (port and in-cylinder) can also control HCCI combustion. Examples of such methods are given below. Experiments with methanol and diesel dual fuel HCCI engine was carried out by Jia, and Denbratt [20] to examine the effect of methanol in three different locations. Here methanol fuel was injected at three different timings; port injection was injected at −3500 aTDC, direct injection (DI_E) at −3580 aTDC and direct injection at the compression stroke at (DI_L) −1000 aTDC. The results show that DI_L combustion strategy gave poorer performance than port injection and DI_E injection. The authors came to the conclusion that DI_E strategy showed very low NOX and soot emission compared to the remaining two strategies. Further experiments and numerical analyses were done by Lalwani et al. [21]; they used gasoline for port injection and diesel for direct injection. They concluded that HCCI mode possibly would not persist after 40% of engine load, hence after 40% engine load, the engine shifted on diesel mode. In HCCI mode, NOX, CO2 and ηT improved by 80%, 30% and 15% correspondingly. However, HC and CO emissions severely increased at part load conditions compared to a conventional diesel engine. Dou et al. [22] performed experiments to examine the impact of methanol contribution, EGR, intake temperature, injection timing on soot emission in diesel/methanol dual-fuel engine. Methanol was supplied into the intake manifold and diesel was injected in the combustion chamber. The experiment was conducted for constant speed (1660 rpm) and at 50% of engine load. The results indicate that increase of methanol percentage and retardation of diesel injection timing were responsible for the drop off soot and PM emissions, compared to early injection of diesel. Researchers used reactivity controlled compression ignition (RCCI) technique for overcoming the HCCI engine challenges which are similar to the dual-fuel mode HCCI engine. Examples of RCCI combustion are given below. Wang et al. [23] conducted an experiment to determine the influence of several parameters (intake pressure, EGR rate, gasoline

Table 1 Engine specification. Engine characteristics

Specifications

Engine Manufacture/Model Cylinder/ Stroke Bore Diameter × Stroke length Compression ratio Rated output kW(HP) Rated speed (rpm) Connecting rod length (mm) Type of injection Injection pressure (bar) No of holes per nozzle Fuel injection Timing Displacement (cc) Cooling system Dynamometer type Dynamometer load range Dynamometer arm length

Kirloskar oil diesel engine/ AV1 1/ Four Stoke Engine 87.5 × 110 (mm × mm) 17.5:1 3.5(5) 1500 234 Direct injection 210 3 23° bTDC 661.45 Water cooling Eddy current 0–50 kg 185 mm

diesel engine on HCCI mode in order to reduce NOX and smoke emissions. In this experiment, a pilot injection was made at the time of suction stroke and main injection at the end of compression near the top dead center (TDC). Experimentation was performed for constant speed and 0–67% engine load conditions. In this study premixed ratio was used from 0% to 80% and the effect of 15% and 30% EGR rate studied for 80% premixed ratio. It was found that increasing the mass of pilot fuel advances the start of combustion (SOC), PRR, and HRR. Further using 80% premixed ratio and 30% EGR reduces NOX by 76% and smoke opacity by 40%. From the study it was concluded that if premixed ratio rises from 0 to 80%, 17.8% peak pressure increases with 1.5 deg advancement; for the same peak pressure, reduced by 4.5% and 12.7% for 15% and 30% EGR respectively. Turkcan et al. [18] interrogated the influence of ethanol and methanol blend on combustion and emissions of gasoline direct injection HCCI engine. In this study, gasoline, E10, E20, M10, and M20 blend fuels were used; the first injection timing was fixed at 1200 after top dead Centre (aTDC) and second injection timing was varying from 300 to 15°CA before top dead center (bTDC). During the experiment, 80% of the total amount of fuel was injected at 1200 aTDC and the rest of the fuel was injected on second injection timing. It was concluded that the retard of second injection timing delayed the SOC, reduced cylinder pressure and HRR. Further, second injection timing did not affect HC and CO emissions compared to NOX and soot emissions.

Fig. 2. (a) Experimental setup for dual fuel mode HCCI engine, (b) Location of carburetor at inlet manifold. 1-Diesel injector, 2-ethanol injection (carburetor), 3Diesel fuel tank, 4-Ethanol fuel tank, 5-Computer interface, 6-Indus five gas analyzer, 7-NETEL smoke meter. 3

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Fig. 3. Carburetor different fuel jet numbers. Table 2 Various jets number and its varying mass flow rate.

Table 4 Smoke meter specification (NPM-SM-111B).

Fuel Jet number

Ethanol mass flow rate (kg/hr)

Parameters

Resolution

Accuracy

Range

Jet Jet Jet Jet Jet

0.340 0.480 0.697 0.798 0.948

HSU K

0.1% 0.01

– ± 0.1 m−1

0–99.9 0- ∞

40 60 70 80 90

Table 5 Physical & chemical properties of gasoline, diesel, and ethanol [1,14].

proportion, diesel injection timing, etc.) on RCCI engine. Here gasoline was supplied at the time of suction and diesel was injected after compression of a homogeneous mixture. It was observed that gasoline/ diesel RCCI engine was suitable for moderate to high load conditions with very low NOX, soot emissions, and improved ηT; however, for low load conditions, single-shot fuel injection was better. Further, high EGR rate, increasing gasoline fraction, and early injection timing was favorable for RCCI combustion at high load condition; conversely, very high EGR rate or more advanced fuel injection caused uncontrolled combustion. A similar kind of experimental work was carried out by Park, and Yoon [24] on RCCI engine. Authors used gasoline and biogas for port injection and diesel for direct injection. Here, port injection fuel ratio was varied between 0.2 and 0.8 and direct injection diesel was injected at 400 bTDC. It was found that increasing the mass of port injected fuel caused more ID, while the period of ID was more for biogas-diesel dual fuel mode compared to gasoline-diesel dual fuel mode combustion. In addition, NOX and soot emission reduced highly; however, HC and CO increased for dual fuel mode. From the literature, it is clearly understood that HCCI engine (use of alcohol-based fuels with biodiesel) is a better option to reduce the NOX and soot emissions up to zero levels as well as to increase the fuel economy. To overcome HCCI engine challenges, many researchers used dual fuel HCCI or RCCI engine for part-load or specific load conditions. Few researchers have studied varying load conditions. In this work, varying load conditions are investigated by supplying different mass flow rates of ethanol with the help of carburetor which is connected to the inlet manifold. The objectives of the present work are (1) to reduce NOX and smoke opacity by using dual fuel mode HCCI combustion methods. (2) To

Characteristics

Unit

Gasoline

Diesel

Ethanol

Chemical Formula Molecular Weight Composition by weight: Carbon Hydrogen Oxygen Specific gravity Boiling point Latent heat of vaporization Lower calorific value Stoichiometric air/fuel ratio Flash point Self-ignition temperature Research octane number Motor octane number Cetane number

– g/mol %

C4 to C12 100–105

C8 to C25 190–211.7

C2H5OH 46.06

85–88 12–15 – 0.69–0.79 30–215 290–420 43.8 14.7 −43 247–280 85–88 12–15 –

84–87 13–16 – 0.81–0.89 188–360 233 43.5 15 > 55 210 – – 40–55

52.2 13.0 34.8 0.785 78.4 921 27 9.0 13 363–442 108 92 8

– °C kJ/kg MJ/kg – °C °C – – –

Table 6 Properties of Neem biodiesel. Fuel Property 2

Kinematic viscosity (mm /sec) at 40 °C Clorific value (MJ/kg) Density (kg/m3) Cetane number

B100

B20

4.63 38.72 881 53.5

3.79 43.22 839 –

maximize the use of alcohol-based fuel (ethanol) in the HCCI engine at various engine load conditions by using different fuel jets. (3) To find out the technical feasibility of biodiesel blend instead of diesel through the direct injector in HCCI engine. (4) To optimize the mass flow rate of ethanol for each and every load in order to obtain the highest thermal

Table 3 INDUS (PEA 205N) Five gas analyzer specifications. Exhaust gases

CO

CO2

HC

O2

NOX

Range of gases Resolution of gases Accuracy of gases

0 – 15% vol. 0.01% Vol. ± 0.02% Vol.

0 – 20% vol. 0.01% Vol. ± 0.3% Vol.

0–30000 ppm ≤2.0:1ppm vol. < 2000 ppm vol.: ± 4ppm vol.

0 – 25% 0.01% vol. ± 0.02% vol.

0–5000 ppm 1 ppm vol. ± 5 ppm vol.

4

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60

In-cylinder Pressure (bar)

Jet 60

E+D 100% Diesel 100% E+D 80% Diesel 80% E+D 60% Diesel 60% E+D 40 % Diesel 40% E+D 20% Diesel 20%

70

50 40 30

70 60 50 40 30 20 -5

0

5

10

15

20

25

20 10 0 -100

-50

0 50 Crank Angle (deg)

100

150

Fig. 4. Comparing diesel and dual-fuel mode HCCI engine in-cylinder pressure vs. crank angle under different load conditions, for jet 60.

load on the engine, orifice meter for measurement of air-fuel ratio, and fuel burette for measurement of fuel consumptions. All this data was captured by “ICEnginesoft” software on a computer for combustion analysis. To analyze the combustion characteristics of dual-fuel HCCI engine, 50 consecutive combustion cycles for each operation were considered. INDUS five gas analyzer (PEA 205N) was used to measure the exhaust gases such as CO, HC, CO2, O2, and NOX. NETEL smoke meter model no. NPM-SM-111B was used to measure smoke opacity. The specification of five gas analyzer and smoke meter were shown in Table 3 and Table 4 respectively. Table 5 shows the detailed properties of the test fuels (diesel, gasoline, and ethanol) used in the experiment. Table 6 shows the properties of a biodiesel blend (B20) and pure biodiesel (B100).

efficiency, lowest smoke opacity and lowest NOX emissions. 2. Experimental setup and methodology The schematic diagram for dual fuel HCCI mode engine is shown in Fig. 1. A single-cylinder, constant speed (1500 RPM), 3.5 kW rated power, naturally aspirated VCR diesel engine was used for this study. The detailed specifications of the engine are shown in Table 1. The CR of the engine was fixed at 17.5 for all experimental tests. The single-cylinder engine converted into dual fuel HCCI mode engine by using carburetor at inlet pipe as shown in Fig. 2(a) and Fig. 2(b). From the carburetor, ethanol (primary fuel) was supplied and through the fuel injector diesel/biodiesel blend (secondary fuel) was injected. The injection pressure of the diesel/biodiesel blend was 210 bar. The intake system of the existing engine was modified for a dual fuel mode HCCI engine. For the preparation of a homogeneous mixture of ethanol with intake air, open throttle carburetor (bullet-500 carburetor) was used (rated flow range 0–22 g/sec). To change the mass flow rate of ethanol, 5 different diameter fuel jet numbers (40, 60, 70, 80, and 90) were used, which is shown in Fig. 3, and the fixed mass flow rate of each jet number is shown in Table 2. The diameter of fuel jet in mm is equal to the fuel jet number divided by 100. For all the selected jets, experimental tests were conducted to examine the engine combustion and emissions performance. Eddy current dynamometer (50 kg) was used for loading the engine. Ethanol was supplied into the carburetor at the time of suction stroke and diesel was injected at 23° bTDC. The experiment was conducted at an interval of 20% engine load. Sensor RTD, PT100 and type K Thermocouple were used to record the temperature of exhaust gases, inlet and outlet water temperature with ± 0.1 °C accuracy. The engine water cooling temperature was maintained between 55 and 60 °C for all load conditions; by adjusting suitable water flow rates with a Rotameter. The in-cylinder pressure and fuel line pressure were recorded by 2 different piezoelectric sensors (0–5000 PSI). In-cylinder pressure was useful to calculate the heat release rate (HRR), cumulative heat release rate (CHRR), indicated means effective pressure (IMEP), etc. Crank angle sensor was used to record the speed, injection timing and generate the timing pulse according to cam and crankshaft position with resolution 1 deg, speed 5500 RPM with TDC pulse. The total engine setup was computer interface with digital panels for measuring the temperatures, combustion pressure, fuel line pressure, engine load indicator, load control knob to vary the

3. Result and discussion Several experiments were carried out on the dual-fuel HCCI mode engine with ethanol and diesel/biodiesel. Ethanol was used in the carburetor at the time of suction stroke and diesel/biodiesel blend was used to initiate the ignition in the homogenous charge of ethanol at the end of the compression stroke. Three sets of readings were taken throughout the experiment in order to minimize the error and final average value was considered for evaluation. Experiment was done for varying load conditions with different mass flow rate of ethanol fuel. The carburetor was used with different fuel jet numbers (jet 40, jet 60, jet 70, jet 80, and jet 90) to change the mass flow rate of ethanol. For a particular load, various fuel jet numbers are mentioned below.

• Jet 40 and jet 60 were used for 20% engine load. • Jet 40, jet 60 and jet 70 were used for 40% engine load. • Jet 40, jet 60, jet 70 and jet 80 were used for 60% engine load. • For 80% and 100% engine load jet 40, jet 60, jet 70, jet 80, and jet 90 were used.

The engine performance results have been presented in the form of combustion characteristics, performance characteristics and emissions characteristics. 3.1. In-cylinder pressure for neat diesel and ethanol/diesel (E + D) dualfuel mode HCCI engine Fig. 4 presents in-cylinder pressure with respect to crank angle (CA) 5

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Jet 40 Jet 60 Jet 70 Jet 80 Jet 90 Diesel

In-cylinder Pressure (bar)

60 50

Load 100% 70 60 50

40

40

30

30

20

20 -10

0

10

20

30

10 0

Load 80%

Jet 40 Jet 60 Jet 70 Jet 80 Jet 90 Diesel

60 In-cylinder Pressure (bar)

70

50 40

60

50

40

30

30

20 -10

20

20

30

40

10

-100

-50

0

50

100

150

-150

-100

Crank Angle (deg)

-50

40

60 60

50

50

In-cylinder Pressure (bar)

50

50

100

150

(b)

Load 60%

Jet 40 Jet 60 Jet 70 Jet 80 Diesel

60

0

Crank Angle (deg)

(a)

In-cylinder Pressure (bar)

10

0 -150

40 30

30 20 -10

20

0

10

20

30

40

10 0

Load 40%

Jet 40 Jet 60 Jet 70 Diesel

60

50

40

40

30

30

20

20

-10

0

10

20

30

40

10 0

-150

-100

-50

0

50

100

150

-150 -100

-50

0

50

100

150

Crank Angle (deg)

Crank Angle (deg)

(c)

(d)

Load 20%

50 Jet 40 Jet 60 Diesel

40 In-cylinder Pressure (bar)

0

50

40

30 30

20

20 -10

0

10

20

30

10 0 -150

-100

-50

0

50

100

150

Crank Angle (deg)

(e) Fig. 5. The variation of in-cylinder pressure for different fuel jets of dual fuel mode HCCI combustion at different engine loads (a) 100% (b) 80% (c) 60% (d) 40% (e) 20%.

6

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Load 100% Jet 40 Jet 60 Jet 70 Jet 80 Jet 90 Diesel

Heat Release Rate (J/deg)

50 40 30

60

5

50 40 30 20

20

10 -10

0

10

20

30

10

Load 100%

Jet 40 Jet 60 Jet 70 Jet 80 Jet 90 Diesel

6 Pressure rise rate (bar/deg)

60

4 3

6 5 4 3 2 1 0 -1 -15

2

-10

-5

0

5

10

15

1 0 -1

0

-2

-10 -100

-50 0 50 Crank Angle (deg)

100

150

-100

-75

-50

-25 0 25 Crank Angle (deg)

(a)

50

75

100

(b)

Fig. 6. Variation of (a) heat release rate and (b) pressure rise rate for different fuel jets under 100% load conditions.

30

Load 100%

ID

MFB 50%

25 7.5

Ignition delay (0CA)

MFB 50% burned (0CA aTDC)

10.0

5.0

2.5

20 15 10 5

0.0 CI

Jet 40

Jet 60

Jet 70

Jet 80

0

Jet 90

Diesel

Fig. 7. MFB 50 for different fuel jet under 100% rated engine load.

Jet 40

Jet 60

Jet 70

Jet 80

Jet 90

Fig. 8. Varying Ignition delay (ID) for different fuel jet under 100% rated engine load.

for 20% to 100% rated power of engine using fuel jet 60. It was observed that for both neat diesel and dual-fuel mode HCCI engines, incylinder pressure was increasing with increasing load on the engine. Increasing load on engine demanding more fuel, and burning more fuel releases more energy which results to increase in-cylinder pressure. In the dual-fuel mode, SOC is delayed compared to neat diesel engine. The results indicated that Ethanol/Diesel (E + D) dual-fuel mode HCCI incylinder pressure curves are shifting forward compare to neat diesel engine. It indicates that ethanol contribution resists SOC and it helps to low temperature combustion (LTC).

with increasing mass flow rate of ethanol, combustion got delayed in the dual fuel mode HCCI engine compared to neat diesel engine. It increases ID (shown in Fig. 8.) and ignition timing is retarded due to high auto-ignition temperature and high octane number of ethanol. Increasing mass flow rate of ethanol retards the combustion phase (ethanol is low reactive fuel so it retards the combustion) and more part of combustion is completed in the expansion stroke so that it leads to lower in-cylinder pressure. This helps to run the engine at LTC mode which reduces NOX emissions. Similar results have been noticed in the case of gasoline/methanol port injected fuel with diesel as a direct injection fuel [25,26]. It is noticed that in-cylinder pressure for jet 70, jet 80, and jet 90 is lower than neat diesel engine. However, jet 40 and jet 60 in-cylinder pressures are found equal to a neat diesel engine. The maximum incylinder pressure values for jet 40, jet 60, jet 70, jet 80, and jet 90 are 62.05 bar, 62.79 bar, 61.98 bar, 58.42 bar, and 55.07 bar respectively, but, neat diesel engine in-cylinder pressure is 61.16 bar. Similarly, peak pressure crank angle for jet 40, jet 60, and jet 70 are 100 aTDC, for jet

3.2. Effect of a different mass flow rate of ethanol on ethanol/diesel (E + D) dual-fuel mode HCCI engine 3.2.1. Effect on In-cylinder pressure Fig. 5 indicates in-cylinder pressures of the engine for different mass flow rate of ethanol by the use of different fuel jets in the carburetor. Fig. 5(a) shows in-cylinder pressure for 100% rated load on the engine. The in-cylinder pressure curve is shifted towards TDC. It means that 7

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35 Load 100%

CD

Diesel Jet 40 Jet 60 Jet 70 Jet 80 Jet 90

30

20

Smoke Opacity (%)

Combustion Duration (0CA)

25

15

10

25 20 15 10 5

5

0 20

0 Diesel

Jet 40

Jet 60

Jet 70

Jet 80

Jet 90

Mass fraction burn (%)

90 80 60

Jet 40 Jet 60 Jet 70 Jet 80 Jet 90 Diesel

40

50 20

40 30

0 -5

0

5

10

15

20 10 0 -30

-20

-10

0 10 20 Crank Angle (deg)

30

40

Fig. 10. Mass burn fraction with a crank angle for various jet under 100% engine load.

1800

Diesel Jet 40 Jet 60 Jet 70 Jet 80 Jet 90

1600 1400 NOX (ppm)

1200

3.2.2. Effect on heat release rate and pressure rise rate Fig. 6 illustrates the effect of increasing the jet number on HRR and PRR of E + D dual-fuel mode combustion for 100% rated load. It is noticed that with the increase of ethanol mass flow rate, retards the peak HRR and peak PRR crank angle. This is due to delay in SOC (shown in Fig. 10); which results in LTC in dual fuel mode HCCI engine compared to the neat diesel engine. Therefore low HRR and PRR are observed. Further, it is noticed that E + D dual fuel mode HCCI engine running very smoothly without knocking. In this test, PRR is less than the 6 bar/0 CA for all loads. The majority of researchers define the knocking criteria of the engine in PRR value, which should be less than 10–20 bar/CA [21,27,28]. Fig. 7 shows 50% mass-burn fraction (MFB50) duration from the start of injection of diesel. The results show that with an increase in jet MFB50, duration is increased, because of delay in the start of ignition due to inherent octane number and high auto-ignition properties of ethanol. Polat has recorded similar results for ethanol HCCI engine

1000 800 600 400 200 0 20

40

60

80

100

80 is 130 aTDC, for jet 90 is 150 aTDC, whereas for diesel is 90 aTDC. Fig. 5(b) shows the in-cylinder pressure for 80% engine load. Jet 40, jet 60, jet 70, jet 80 and jet 90 were used for 80% engine load. Similar nature of in-cylinder pressure was found for 80% engine load, peak incylinder pressures for jet 40, jet 60, jet 70, jet 80, and jet 90 are 58.25 bar, 58.82 bar, 55.42 bar, 47.85 bar, and 42.3 bar respectively; however, diesel peak in-cylinder pressure is 58.45 bar. Peak pressure crank angle for jet 40, jet 60, are 100 aTDC, for jet 70 it is 120 aTDC, for jet 80 it is 170 aTDC and for jet 90 it is 200 aTDC, whereas for diesel engine it was 90 aTDC. Fig. 5(c) shows the in-cylinder pressure for 60% engine load. For 60% engine load jet 40, jet 60, jet 70, and jet 80 were used. In this load condition, in-cylinder pressures are reduced and the combustion phase retarded was similar to engine load 80 and 100%. Peak in-cylinder pressure and CA for jet 40 is 54.13 bar at 100 aTDC, for jet 60 it is 52.71 bar at 120 aTDC, for jet 70 it is 46.04 bar at 160 aTDC and for jet 80 it is 43.67 bar at 180 aTDC. Fig. 5(d) shows the in-cylinder pressure with a CA for 40% engine load. For 40% engine load, jet 40, jet 60, and jet 70 were used. Peak incylinder pressure and CA for jet 40 is 47.12 bar at 120 aTDC, for jet 60 it is 45.49 bar at 140 aTDC and for jet 70 it is 36.21 bar at 180 aTDC, however, diesel engine in-cylinder pressure is 50.46 bar at 90 aTDC. Fig. 5(e) shows the in-cylinder pressure for 20% engine load. Peak in-cylinder pressures with a CA for jet 40, jet 60 are 40.77 bar at 130 aTDC, 37.29 bar at 150 aTDC respectively; however, for diesel, it was 47.26 bar at 90 aTDC.

Load 100%

60

80

Fig. 12. Variation of smoke opacity for varying load condition.

100

70

60 Load (%)

Fig. 9. Varying combustion duration (CD) for different fuel jet numbers under 100% rated engine load.

110

40

100

Load (%) Fig. 11. Variation of NOX emissions for varying load conditions. 8

Fuel xxx (xxxx) xxxx

G.R. Gawale and G. Naga Srinivasulu

0.35

Diesel Jet 40 Jet 60 Jet 70 Jet 80 Jet 90

300 250 HC (ppm)

0.30 CO (% vol.)

350

Diesel Jet 40 Jet 60 Jet 70 Jet 80 Jet 90

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Load (%)

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80

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Load (%)

(a)

(b)

Fig. 13. Variation of CO and HC emissions for varying load conditions.

Diesel Jet 40 Jet 60 Jet 70 Jet 80 Jet 90

Thermal Efficiency (%)

35 30 25

1.0

Diesel Jet 40 Jet 60 Jet 70 Jet 80 Jet 90

0.8

bsfc (kg/kw.hr)

40

20 15 10

0.6

0.4

0.2

5 0.0

0 20

40

60

80

20

100

40

60

80

100

Load (%)

Load (%) Fig. 14. The effect of different fuel jets on the thermal efficiency of E + D dual fuel mode HCCI engine.

Fig. 15. The effect of different fuel jet number on bsfc of dual-fuel engine.

load. The results show that CD is reduced with the increase of mass flow rate of ethanol. Homogeneous fuel has longer ID due to maximum amount of fuel burns in the rapid combustion phase aTDC in a lowtemperature environment; very less fuel is burnt in diffusion combustion, therefore, it reduces CD. Similar results have been found for alcohol-based fuel with diesel RCCI engine [32]. Fig. 10 shows the mass fraction burn for different jet dual fuel HCCI engine and neat diesel engine under 100% engine load condition. It is observed that the mass fraction burn curve is shifting towards TDC with an increase in ethanol mass contribution. It is observed from these results that SOC is delayed with an increase in ethanol energy contribution in HCCI engine.

[29]. The CA interval between the injections of fuel to SOC is called an ignition delay (ID). However, in this study, ID is in degree crank angle interval between the peak rate of pressure rise (PRPR) and peak fuel line pressure (PFLP) [30]. The combustion duration (CD) is the interval of degree CA between SOC to end of combustion. In this study, CD is defined as the degree of CA interval of MFB10 to MFB90 [19,31]. MFB10 defines 10% mass fraction burn and MFB90 defines 90% mass fraction burn, MFB 50 defines degree CA of 50% mass fraction burn. In general, the end of combustion is tough to find because of loss of heat in the combustion chamber and incomplete combustion due to crevices. So MFB10 to MFB90 is used to define CD. Fig. 8 shows the ID with an increase in jet number for 100% rated load of the engine. The ID is increased with increase in ethanol mass flow rate because ethanol has high self-ignition temperature, octane number and higher latent heat of vaporization compared to neat diesel; so it absorbs more energy from the compressed air and it increases the ignition timing and delays SOC. Fig. 9 shows the CD period for different fuel jets under 100% engine

3.2.3. Effect on exhaust emissions and engine performance Fig. 11 represents NOX emission with varying loads of the engine. It is observed that NOX emissions are reduced with an increase in the mass flow rate of ethanol (increase in jet number) for all load conditions compared to a neat diesel engine. Dual fuel mode HCCI engine is working on the lean homogeneous mixture because of which combustion occurs at low temperature and for NOX emissions, temperature of 9

Fuel xxx (xxxx) xxxx

G.R. Gawale and G. Naga Srinivasulu

E+D E+B20 Diesel

60

60

Jet 90 70 60 50

50

40 30

40

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10 -10

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Mass Fraction Burn (%)

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(a)

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-25 0 25 50 Crank Angle (deg)

75

100

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-10

0

10

20

30

40

Crank Angle (deg)

(c)

(d)

Fig. 16. Comparison of combustion characteristics of Ethanol/Diesel and Ethanol/B20 dual fuel mode HCCI engine (a) In-cylinder pressure, (b) Heat Release rate, (c) Pressure rise rate, (d) Mass fraction burn rate.

mixture, hence the smoke opacity of E + D dual-fuel mode HCCI engine is reduced compared to neat diesel engine. The results show that smoke opacity reduced almost 90% for jet 90 at 100% load. It is observed that more ethanol mass contribution at the time of suction gave less smoke compared to a neat diesel engine. For 100% load, smoke opacity reduced from 32% to 3.89% for E + D dual-fuel mode HCCI engine. Fig. 13 displays CO and HC emission with varying loads for different jet numbers. The results show that CO and HC emissions increase with increase in jet number at any particular load compared to a neat diesel engine. CO and HC emissions occur due to LTC, incomplete combustion, and the combustion near the misfire. In Fig. 13 jet 40 results show that HC and CO emissions are very high for low load condition and it reduces with increase in load conditions. It indicates that for any particular load in E + D dual fuel HCCI mode engine if the contribution of ethanol fuel is more compared to diesel fuel, combustion is done near misfire at low temperature and impingement on the wall of the cylinder, it promotes the formation of HC and CO emissions. Fig. 14 shows the thermal efficiency (ηT) with varying loads for

the combustion chamber is the main affecting factor. Further, ethanol has high latent heat of vaporization, and it helps to absorb the heat from combustion chamber and reduces the combustion chamber temperature. Fig. 5 displays the low peak in-cylinder pressure and Fig. 6(b) displays low PRR with increase in jet number means that the dual fuel mode HCCI engine working on LTC mode and it helps to reduce NOX emissions. In the present study Jet 60 reduces NOX emission from 320 ppm to 42 ppm for 20% engine load. And jet 90 reduces NOX emission from 1614 ppm to 585 ppm for 100% load conditions. Up to 70% of NOX emissions are reduced by E + D dual-fuel mode HCCI engine compared to a neat diesel engine for all load conditions. Fig. 12 shows the smoke opacity in percentage with varying loads for different jets. The results display that the smoke opacity is reduced with an increase in jet numbers. Smoke opacity depends on inhomogeneity of air–fuel mixture in the combustion chamber. In this study, ethanol is supplied with air at the time of suction stroke and plenty time is available for ethanol to mix with air. Ethanol is the most volatile fuel and it easily mixes with air and forms a homogenous 10

Fuel xxx (xxxx) xxxx

G.R. Gawale and G. Naga Srinivasulu

(E + B20) dual-fuel mode HCCI engine. Biodiesel blend (20% neem oil + 80% diesel) is done on a volume basis. Fig. 16 shows the comparison of ethanol with diesel/biodiesel combustion performance (a) In-cylinder pressure, (b) Heat Release rate, (c) Pressure rise rate, (d) Mass fraction burn rate for 100% rated load by use of jet 90. Fig. 16(a) displays the variation of in-cylinder pressure for ethanol and diesel/biodiesel HCCI mode engine at 100% engine load with use of jet 90. The results show that the in-cylinder pressure of E + B20 is more compared to E + D dual fuel mode HCCI engine. Because biodiesel contains inherent oxygen, which triggers combustion compared to neat diesel in dual fuel mode HCCI engine, it forces early start of combustion, reduces the ID (shown in Fig. 17), increases the combustion temperature and in-cylinder pressure of engine. Fig. 16(b) and Fig. 16(c) shows the variation of HRR and PRR for E + D, E + B20 dual fuel mode HCCI engine, and neat diesel engine. The results indicate that instead of diesel, biodiesel blend (B20) increases HRR and PRR for dual fuel mode HCCI engine. Fig. 16(d) shows the mass fraction burn for E + D, E + B20 dual fuel mode HCCI engine, and neat diesel engine. The results are noted that E + D dual fuel mode HCCI engine has more ID and it retards the SOC, however inherent oxygen present in the biodiesel reduces the ID (as shown in Fig. 17) and forces combustion to start early for E + B20 dual fuel mode HCCI engine. Fig. 18(a) and Fig. 18(b) shows the comparison of CO and HC emissions for 80% and 100% engine load conditions. CO and HC emissions are reduced for E + B20 compared to E + D dual-fuel mode HCCI engine; conversely, it is higher than neat diesel engine. CO and HC emissions are reduced for B20 because B20 contains extra oxygen, it helps to convert CO into CO2 and HC into H2O. Fig. 18(c) shows NOX emission of dual-fuel mode HCCI engine for 80% and 100% rated load. It is noted that NOX emission is decreased for both dual fuel mode HCCI engine (E + D and E + B20) compared to the neat diesel engine. NOX is increased for E + B20 dual fuel mode HCCI engine because integral additional oxygen in the B20 combines with nitrogen to generate more NOX emission. Further, high in-cylinder pressure increases the combustion chamber temperature which increases NOX emission. Fig. 18(d) shows smoke opacity for different fuel engines under 80% and 100% load. It is noticed that smoke opacity is slightly increased for E + B20 compared to E + D dual fuel mode HCCI engine; still, it is low compared to a neat diesel engine. Smoke opacity is increased because biodiesel fuel is more viscous and has less heating value compared to diesel; hence to fulfill the requirement of load condition, more fuel is required; it produces fuel-rich region and increases smoke opacity. Fig. 19 shows ηT versus engine load for dual fuel mode HCCI engine and diesel engine. The results show that E + B20 dual fuel mode HCCI engine had more ηT compared to E + D dual fuel mode HCCI engine and neat diesel engine. It is concluded from the results that B20 helps to reduce HC and CO emissions; however, it slightly increases smoke opacity and NOX emissions. Further, it is noted that the use of B20 instead of diesel in dual fuel mode HCCI engine is an advantage in terms of fuel economy.

Fig. 17. Variation of ignition delay for dual fuel mode HCCI engine by use of jet 90.

different fuel jets. ηT of dual-fuel engine defined as the ratio of work done to heat energy supplied by both fuels.

Thermal efficiency,ηT (%) =

BP × 3600 × 100 [(mE CVE) + (mDCVD)]

(1)

where, BP is brake power of engine in kW, mE and mD are the mass of ethanol and diesel fuel in kg/hr respectively. Similarly, CVE and CVD are a lower calorific value of ethanol and diesel/B20 fuel in kJ/kg respectively. It is observed that ηT for 60%, 80%, and 100% engine load are more than that for neat diesel engine. Jet 40 and jet 60 show the highest ηT for 60%, 80%, and 100% engine load. The mass flow rate of ethanol for jet 40 and jet 60 is low and ID is also low. The peak in-cylinder pressure is nearly equal to neat diesel engine but due to homogeneous mixture of ethanol, total fuel properly utilized to obtain the required power hence ηT increases for 60%, 80%, and 100% engine load. However, NOX and smoke opacity emissions are very poor for jet 40 and jet 60. Jet 90 shows less fuel economy compared to neat diesel engine because jet 90 ID is highest and peak pressure is also reduced due to late combustion so that more fuel is utilized to achieve the required power of the engine. Fig. 15 shows the comparison of bsfc under different load conditions. The results show that bsfc for dual fuel mode HCCI engine is high as compared to neat diesel engine because bsfc of dual fuel HCCI mode engine depends upon the mass of both fuel consumption. It is defined as,

bsfc(kg/kWh) =

(mE) + (mD) BP

(2)

The calorific value of ethanol is 27 MJ/kg and diesel is 43.5 MJ/kg and BP is the constant parameter. Therefore to fulfill, the requirement of power, ethanol fuel consumption is more compared to neat diesel and it directly depends upon the bsfc of engine.

3.4. Identifying the suitable jet number in carburetor for different engine load conditions

3.3. Effect of biodiesel blend (B20) injection instead of diesel in dual fuel mode HCCI engine

In the experiment for 20% engine load condition the jets used in the carburetor were jet 40 and jet 60, for 40% engine load condition, jet 40, jet 60, and jet 70, for 60% engine load condition, jet 40, jet 60, jet 70, and jet 80 and, for 80% and 100% engine load condition, jet 40, jet 60, jet 70, jet 80, and jet 90. From the above combustion and emission performance analysis for E + D dual-fuel mode HCCI engine, it is observed that few jets showed promise in terms of reducing NOX and smoke opacity, while some were good for fuel economy under varying load conditions. Hence, as per

From this experiment, the effect of biodiesel blend (B20) injection instead of diesel in dual fuel mode HCCI engine on combustion, emissions and performance characteristics of the engine was investigated. Experiments conducted for 80% and 100% engine load, to supply ethanol fuel in the carburetor, jet 90 was used. In this experiment, instead of diesel neem biodiesel blend (B20) was injected at the end of the compression stroke to start the combustion in the ethanol/Biodiesel 11

Fuel xxx (xxxx) xxxx

G.R. Gawale and G. Naga Srinivasulu

Diesel

0.30

E+D

Diesel

E+B20

E+D

E+B20

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CO (% vol)

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25 20 15 10

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0 80

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(c)

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Fig. 18. Comparison of exhaust emissions for dual fuel mode HCCI engine (a) CO (%vol) (b) HC (ppm) (c) NOX (ppm) (d) smoke opacity (%).

(HB) formula is used to normalize it,

equal weightage for reduction of NOX emissions, reduction of smoke opacity and high thermal efficiency, fuel jet numbers were optimized for a particular load. The maximum percentage of ethanol fuel was used at each engine load condition. The engine performance results have been presented in the form of combustion characteristics, performance characteristics and emissions characteristics. The main aim of dual-fuel mode HCCI engine is to use alcohol-based fuel, reduce hazardous exhaust gases such as NOX, smoke opacity, and increase the ηT of the engine compared to a neat diesel engine. The relative optimum equation is derived on the basis of lowest NOX, lowest smoke opacity, and highest ηT for different load conditions. In this study, responses are NOX, smoke opacity, and ηT. The input factors are different fuel jets and engine load. The range of each response is different and the units are different too because of which actual results are impacted. Hence the original experimental data should be normalized to avoid such differences. There are two kinds of normalization with respect to the necessity of responses like smaller the better, the higher the better, etc. Brake ηT is aimed to be as high as possible, so the higher the better

xj (t) =

yj (t) − minyj (t) maxyj (t ) − minyj (t)

(3)

NOX emissions and smoke opacity are preferred to be as low as possible, so the lower the better (LB) formula is used to normalize it,

xj (t) =

maxyj (t) − yj (t) maxyj (t ) − minyj (t)

(4)

where, xj(t) is the normalized value, min yj(t) is the smallest value of yj(t) for t-th response, and the max yj(t) is the largest value of yj(t) for tth response. Whole values of ηT, NOX emissions, and smoke opacity are normalized and converted in between 0 and 1. The objective is to accomplish it by choosing different jets for different loads for achieving optimum response. The input parameters (jet 40, jet 60, jet 70, jet 80, and jet 90) are utilized to get the optimum fuel jet for a particular load by considering low NOX, low smoke opacity, and high ηT. The final 12

Fuel xxx (xxxx) xxxx

G.R. Gawale and G. Naga Srinivasulu

Diesel

E+D

for highest ηT, lowest NOX emissions and lowest smoke opacity jet 40 is suitable for 20% engine load, jet 60 is suitable for 40% engine load and jet 70 is suitable for 60%, 80%, and 100% engine load. The main advantage of the developed optimize function is that a designer can define the weights as per the emission norms and fuel economy standards requirement.

E+B20

Thermal Efficiency (%)

33 32 31

3.5. Optimization of premixed ratio for varying load conditions 30

The premixed ratio is defined as the ratio of heat energy contributed by port injected fuel to heat energy contributed by both port injection fuel plus direct injection fuels. Here port injected fuel is nothing but carbureted fuel that is ethanol and direct injection fuel is diesel/biodiesel(B20).

29 28 27

Pmx (%) = 80

85

90

95

100

Load (%)

optimized responses are assigned by weighting factors to thermal efficiency, NOX, and smoke opacity. Weighting factors are extremely valuable for the required design of engine. Weightage factor depends upon the engine designer requirement, it can be considered in number of cases. In the current study, only one case consider and almost equal priority gave to all responses [33]. In this study 34%, 33%, and 33% weightage were considered for ηT, NOX emissions, and smoke opacity respectively. The main goal is to increase the fuel economy and reduce smoke opacity and NOX emissions. Hence there is no weightage to HC and CO emissions. HC and CO emissions can be easily reduced by aftertreatment methods compared to the smoke opacity and NOX emissions. These responses are achieved without affecting the brake power. The optimum response equation with assumed weightage factor is designed, as follows: (5)

here, Y(t) is the optimum value for optimum responses. Fig. 20 represents the best fuel jets for different load conditions. It is observed that by considering the weightage of 34% for ηT, 33% for NOX emissions, and 33% for smoke opacity, all jets in dual fuel mode HCCI engines are better than a neat diesel engine. The authors concluded that Diesel

Jet40

Jet60

Jet 70

Jet 80

0.2

Y value

0.0

-0.2

-0.4

-0.6

-0.8 20

40

(6)

where, mE and mD are the mass of ethanol and diesel/B20 fuel in kg/hr respectively. Similarly, CVE and CVD are lower calorific value of ethanol and diesel/B20 fuel in kJ/kg respectively. Table 2 shows different mass flow rates of ethanol for different jets. In the experiment, ethanol mass is constant and load is controlled by diesel fuel. Fig. 21 shows the variation of premixed ratio for E + D dual fuel mode HCCI engine for varying load conditions. The result shows that the premixed ratio of any particular jet reduces with an increase in load condition which means that with an increase in load on the engine, diesel contribution increases. Further, experiments were conducted with varying jets to know the maximum permissible use of ethanol for different load conditions. A maximum premixed ratio can be acceptable by engine at 80% engine load, that is 75.94%; however for 100% load maximum premixed ratio is 68%. Fig. 22 shows the premixed ratio for 80% and 100% load by the use of jet 90. The results show that premixed ratio for E + B20 dual fuel mode HCCI engine is more compared to E + D dual fuel mode HCCI engine for 100% load conditions. For E + B20 dual fuel mode HCCI engine, the maximum premixed ratio is 76% and 71.71% for 80% and 100% load conditions; however, for E + D dual fuel mode HCCI engine, it is 75.94% and 68% respectively. Accordingly, the optimized fuel jets with optimizing premixed ratio are shown in Table 7 for E + D dual fuel mode HCCI engine. Table 7 shows the varying load with different premixed ratios; the maximum contribution of ethanol is at 60% engine load, however, for

Fig. 19. Comparison of thermal efficiency (ηT) for dual fuel mode HCCI engine.

Y(t) = 0.34 ηT + 0.33 NOX + 0.33 Smoke Opacity

(mE CVE) × 100 [(mE CVE) + (mDCVD)]

60

80

100

Load (%) Fig. 20. An optimum value (Y value) of different jets for varying load conditions. 13

Jet 90

Fuel xxx (xxxx) xxxx

G.R. Gawale and G. Naga Srinivasulu

Jet 40

Jet 60

Jet 70

Jet 80

Jet 90

80

Premixed Ratio (%)

70 60 50 40 30 20 10 0 20

40

60

80

100

Load (%) Fig. 21. Variation of the premixed ratio of different jets for varying load conditions.

E+D

obtained leads to the following conclusions: The stationary diesel engine in the laboratory was able to operate on dual fuel HCCI mode at high load conditions by the use of ethanol and diesel/biodiesel fuels with reduction of NOX, smoke opacity, and increased thermal efficiency (ηT). Ethanol/diesel (E + D) dual-fuel mode HCCI engine results show that with an increase in a mass flow rate of ethanol, increases the ID as well as retards SOC. It shows that in-cylinder pressure reduces, and NOX and smoke opacity are reduced; conversely HC and CO emissions increase compared to neat diesel engine for all loads. At 100% load condition jet 90 reduces the NOX emissions and smoke opacity from 1646 ppm to 585 ppm and 32% to 3.89% respectively. Almost 65% of NOX and 88% of smoke opacity were reduced correspondingly; however, a penalty of 1.5% of ηT compared to neat diesel engine. In terms of ηT jet 40 gave the highest ηT for 60% and 80% engine loads; further jet 60 was best for 100% engine load compared to all other jets and neat diesel engine. However, for low load conditions, HCCI engine performance diminished in terms of fuel economy; however, NOX and smoke opacity were reduced compared to neat diesel engine. Further optimization of fuel jet numbers for varying load condition was done on the basis of highest ηT, lowest NOX emissions, and lowest smoke opacity by considering 34%, 33%, 33% weightage respectively. For 20% load, jet 40, for 40% load, jet 60 and for 60%, 80%, and 100% load, jet 70 were best for E + D dual-fuel mode HCCI engine. On the basis of optimization, jets for particular load results were summarized. For low load condition, NOX emissions reduced by 86%, 79%, and 81% for 20%, 40%, and 60% engine load respectively; however ηT also reduced by 2%, 3%, and 1% correspondingly. Similarly, smoke opacity reduced by 38%, 34%, and 63% for 20%, 40%, and 60% engine load respectively; however, HC and CO emissions increased to some extent. By optimization weightage factor, dual-fuel engine gave best performance in the terms of fuel economy for high engine load conditions. For load of 80% and 100%, ηT of E + D dualfuel mode HCCI engine increased by 3% and 1.5% respectively compared to neat diesel engine. The results show that maximum premixed ratio was used for 60% engine load and minimum premixed ratio was used for 20% engine load. From this it was concluded that on an average 56.5% of diesel can be replaced by ethanol with 70% NOX reduction and 61% smoke opacity reduction in dual fuel mode HCCI engine compared to neat diesel engine. Instead of diesel fuel, neem biodiesel blend (B20) was used as a direct injection fuel for 80% and 100% engine load condition by use of jet 90 in the carburetor. It was observed that E + B20 reduces ID and

E+B20

80

Premixed Ratio (%)

70 60 50 40 30 20 10 0 80

100 Load (%)

Fig. 22. Comparison of premixed ratio for ethanol/diesel and ethanol/biodiesel engine. Table 7 Varying load with a different premixed ratio. Load

Optimize Fuel Jet

Ethanol mass flow rate (kg/h)

Premixed ratio

20 40 60 80 100 Average

Jet Jet Jet Jet Jet

0.340 0.480 0.697 0.697 0.697

47.55335 56.12101 64.76087 60.71384 53.56378 56.54

40 60 70 70 70

20% engine load it is minimum for dual fuel mode HCCI engine.

4. Conclusion The experiments were carried out to assess the performance of ethanol/diesel dual fuel mode HCCI engine with a different mass flow rate of ethanol for varying load conditions. Also, experiment was carried out using a neem biodiesel blend (B20) instead of diesel with jet 90 in dual fuel mode HCCI engine for high load conditions. The results 14

Fuel xxx (xxxx) xxxx

G.R. Gawale and G. Naga Srinivasulu

forces early start to combustion compared to E + D dual-fuel mode HCCI engine. The results show that HC and CO emissions were reduced; however NOX and smoke opacity increased little compared to E + D dual-fuel mode HCCI engine. In terms of ηT, E + B20 gave good performance for 100% load. For this condition, 76% and 71.7% premixed ratio was used for 80% and 100% engine load respectively. From this study, it is concluded that dual fuel mode HCCI engine can replace the diesel fuel by ethanol as an alternative fuel with low NOX, low smoke opacity, and better fuel economy without penalty of brake power for higher load conditions.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgment The authors would like to thank TEQIP-II/CoE, NIT Warangal, for providing the Engine Testing facility and, TEQIP III, NIT Warangal as well as SPARC project (SPARC/2018-2019/P773/SL) (MHRD, India) for funding the procurement of consumables. References [1] Çelebi Y, Aydın H. An overview on the light alcohol fuels in diesel engines. Fuel 2019;236:890–911. https://doi.org/10.1016/j.fuel.2018.08.138. [2] Agarwal AK. Biofuels (alcohols and biodiesel) applications as fuels for internal combustion engines. Prog Energy Combust Sci 2007;33:233–71. https://doi.org/10. 1016/j.pecs.2006.08.003. [3] Heywood JB. Internal combustion engines fundamentals. New York (USA): McGraw-Hill; 1988. [4] Sindhu R, Rao GAP, Murthy KM. Effective reduction of NOx emissions from diesel engine using split injections. Alexandria Eng J 2018;57:1379–92. https://doi.org/ 10.1016/j.aej.2017.06.009. [5] Wang Q, Sun W, Guo L, Fan L, Cheng P, Zhang H, et al. Effects of EGR and combustion phasing on the combustion and emission characteristic of direct-injection CI engine fueled with n-butanol/diesel blends. Energy Proc 2019;160:364–71. https:// doi.org/10.1016/j.egypro.2019.02.169. [6] Rahman A, Ruhul AM, Aziz MA, Ahmed R. Experimental exploration of hydrogen enrichment in a dual fuel CI engine with exhaust gas recirculation. Int J Hydrogen Energy 2016:1–10. https://doi.org/10.1016/j.ijhydene.2016.11.109. [7] Algayyim SJM, Wandel AP, Yusaf T. Butanol – acetone mixture blended with cottonseed biodiesel: Spray characteristics evolution, combustion characteristics, engine performance and emission. Proc Combust Inst 2019;37:4729–39. https://doi. org/10.1016/j.proci.2018.08.035. [8] Manigandan S, Gunasekar P, Devipriya J, Nithya S. Emission and injection characteristics of corn biodiesel blends in diesel engine. Fuel 2019;235:723–35. https:// doi.org/10.1016/j.fuel.2018.08.071. [9] Warkhade GS, Babu AV. Experimental investigations on the feasibility of higher blends of biodiesel in variable compression ratio diesel engine. Int J Ambient Energy 2018:1–11. https://doi.org/10.1080/01430750.2018.1525574. [10] Babu KG, Babu AV, Warkhade GS. Experimental investigations of Direct Injection Compression Ignition (DI CI) engine by using Coconut, and Karanja biodiesel fuels with emulsions of Microalgae based Antioxidant. Int J Ambient Energy 2018:1–14. https://doi.org/10.1080/01430750.2018.1432505. [11] Yang R, Hariharan D, Zilg S, Lawler B, Mamalis S, Brook S. Efficiency and emissions characteristics of an HCCI engine fueled by primary reference fuels. SAE Int 2018. https://doi.org/10.4271/2018-01-1255. [12] Kim N, Cho S, Min K. A study on the combustion and emission characteristics of an SI engine under full load conditions with ethanol port injection and gasoline direct injection. Fuel 2015;158:725–32. https://doi.org/10.1016/j.fuel.2015.06.025.

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