Effects of EGR, swirl augmentation techniques on combustion of biodiesel/ethanol and their blends in a diesel engine

Abstract

The diminishing resources and continuously increasing cost of petroleum in association with their alarming pollution levels from diesel engines have caused an interest in finding alternative fuels to diesel which are renewable and sustainable. Emission control and engine efficiency are two most important parameters in current engine design. The impending introduction of emission standards such as Euro IV and Euro V is forcing the research towards developing new technologies for combating engine emissions. The classification of Euro IV and V norms is applicable to heavy-duty engines in Europe, where as Euro 5 is applicable to light-duty engines. This paper presents the effects of exhaust gas recirculation (EGR), swirl augmentation techniques and ethanol addition on the combustion of Honge oil methyl ester (HOME) and its blends with ethanol in a diesel engine. From the experimental work conducted, it is found that the combustion of HOME plus up to 15% ethanol blend in a diesel engine operated with optimised parameters of injection timing 23° Before Top Dead Centre and compression ratio 17.5 results in acceptable combustion emissions and improved brake thermal efficiency (BTE). The addition of ethanol increased BTE with reduced hydrocarbons (HCs), CO and smoke emissions. However, NO _x emissions increased dramatically. Use of appropriate EGR reduces NO _x to acceptable levels. The implementation of swirl augmentation techniques further resulted in increased BTE and considerable reduction in tail pipe emissions such as smoke, HCs, CO and NO _x . The effect of swirl by providing grooves on the piston was taken into consideration to find the overall biodiesel engine performance, which gives scope for further studies.

Keywords:

• Honge oil
• Honge oil methyl ester
• diesel engine
• combustion
• swirl
• ethanol

1. Introduction

The demand for petroleum fuel will rise steeply with every passing decade and is expected to reach nearly 250 million metric tonnes by the year 2024 (Barnwal and Sharma 2005, Agarwal 2006, Yage et al. 2009). A large amount of energy is needed to sustain industrial growth and agricultural production. The diminishing and continuously increasing cost of petroleum resources associated with their alarming pollution levels from diesel engines has created an interest in finding a suitable alternative and renewable fuel to diesel. The use of such alternative fuels in diesel engines will ensure energy security of many developing countries such as India and will simultaneously address environmental concerns. India imports 83% of its total crude oil requirement. Biodiesel is one of the best substitutes for petroleum fuels because it is environmentally benign, sustainable and economically suitable for agricultural countries (Raheman and Phadatare 2004). Biodiesel derived from Honge non-edible oil is found to be particularly suitable as it is locally and abundantly available (Banapurmath et al. 2008, 2009, Murugesan et al. 2009).

Ethanol is a renewable energy source and can be made from many raw materials such as sugar cane, molasses, waste biomass materials, corn and sugar beets by using already improved and demonstrated technologies (Xingcai et al. 2004, Banapurmath and Tewari 2010, Lei et al. 2011). By increasing ethanol in biodiesel–ethanol blends, cold flow characteristics of the blends will improve with decreased specific gravity and viscosity. Adding ethanol to Honge oil methyl ester (HOME) improves the efficiency of dual fuel engines as it lowers the viscosity of the blends and further increases the mixture volatility (Banapurmath and Tewari 2010). Biodiesel and ethanol are therefore more popular contenders as alternative fuels to diesel.

Swirl augmentation techniques result in better combustion with increased brake thermal efficiency (BTE) and reduced emissions. In addition, swirl augmentation leads to decreased carbon deposits, fuel consumption, exhaust gas temperature and tendency to knock (Parker and Walker 1972, Timotey 1985, Van Gerpen et al. 1985, Heywood 1988, Rao et al. 1993, Kang and Reitz 1999, Benajes et al. 2004, Bonatesta et al. 2007). Swirling is created by providing grooves on the bowl-shaped cavity on the piston and manifold designs (Prasad et al. 2011). The effect of initial swirl can be the solution for overcoming the power loss in a dual fuel engine and prevention of knock. Reduced NO _x is observed as a result of increased heat loss to the wall and reduced temperature with introduction of swirl. Swirl also influences the ignition delay by exchanging the portion between physical and chemical ignition delay. In order to achieve different swirl intensities inside the cylinder, two design parameters were changed: the cylinder head (CH) and the inlet valve masking. This intensification of the swirl is done by cutting grooves and adding bridges on the CH. Two different configurations of the CH were considered for this study: one includes two grooves and one bridge, and the other three grooves and two bridges. The inlet valve masking with angle of mask 50°, 70° and 90° was provided on the inlet valve for this study.

Different methods of NO _x reduction have been used and reported in the literature, which include retarded injection timing, lowered intake temperature, water injection emulsified in the fuel, exhaust gas recirculation (EGR) and lowered compression ratio (Gros 1991, Pierpont et al. 1995, Ladommatos et al. 1998, Yoshimoto and Tamoki 2001, Abd Alla 2002, Tomazic and Pfeifer 2002, Agarwal et al. 2004, 2006, Srinivasan et al. 2006, Peng et al. 2008). These methods reduce NO _x emissions but increase particulate emissions at higher engine loads. Hence, there is a trade-off between NO _x and smoke emissions. Therefore, it is essential to use particulate trap to reduce the amount of unburnt particulates in EGR. The objective of this work involves studying the effects of EGR, swirl augmentation techniques and ethanol addition to biodiesel in the modified diesel engine. Comparison of performance, emission and combustion characteristics of the biodiesel-fueled engine with EGR, swirl augmentation techniques and ethanol addition effects is presented.

2. Characterisation of fuels used

Honge oil being a non-edible oil with viscosity nearly 16 times more than diesel was suitably converted into its methyl ester using the transesterification process.

2.1 Transesterification of Honge oil and fuel properties

The set-up for transesterification process is shown in Figure 1 with the upper layer showing HOME and the lower layer showing glycerol. Figure 1 also shows the water washing of HOME and the subsequent moisture removal from ester using silica gel crystals. Initially, parameters such as temperature, molar ratio and catalytic concentration affecting the transesterification of Honge oil were optimised. The transesterification set-up consists of a 2-l capacity, round-bottomed flask provided with three necks, which was placed in a water container for heating the oil. A high-speed motor with a magnetic stirrer was used for vigorous mixing of the oil. In the transesterification process, triglycerides of Honge oil react with methyl alcohol in the presence of a catalyst (NOH/KOH) to produce a fatty acid ester and glycerol. In this process, 1000 g Honge oil, 230 g methanol (MERC brand) and 8 g sodium hydroxide pellets were placed in a round-bottomed flask. The contents were heated to 70°C and stirred vigorously for 1 h to promote ester formation. The mixture was next transferred to a separating funnel and allowed to settle under gravity overnight. The upper layer in the separating funnel consists of home methyl ester whereas the lower layer consists of glycerol that was removed. The separated ester was mixed with 250 g hot water and allowed to settle under gravity for 24 h. Water washing separates residual fatty acids and catalyst, and were removed by using a separating funnel. Finally, silica gel crystals were added to remove the moisture from the ester (Banapurmath et al. 2008).

Figure 1 Transesterification set-up showing different stages of biodiesel production.

The properties of Honge oil and its biodiesel (HOME) are provided in Table 1.

Table 1 Property of diesel, Honge and HOME, and blends of HOME with ethanol.

Property	Diesel	Honge oil	HOME	Ethanol	BE 5	BE 7.7	BE 15
Density (kg/m^3)	840	930	890	780	880	870	862
Kinematic viscosity (cSt) @ 40°C	3.5	56	5.6	1.2	5.0	4.8	4.4
Flash point °C	56	187	163	13–14	152	146	140
Calorific value (kJ/kg)	43,000	35,800	36,100	26,820	35,958	35,896	35,834
Lower heating value
Cetane number	45–55	40	45	8	–	–	–
Carbon residue (%)	0.1	0.66	–	–	–	–	–
Oxygen content (wt%)	–	10	–	35	–	–	–
Note: BE, biodiesel ethanol.

2.2 Use of ethanol in diesel engines

Ethanol has a much lower flash point than diesel and requires greater precautions while preparing its blends with biodiesels (Hansen et al. 1989). Anhydrous ethanol is highly hygroscopic and is practically impossible to stay as such in diesel under a wide range of conditions. At lower temperatures, the miscibility is limited. Additives or emulsifiers, co-solvent or iso-propane must be used to ensure its solubility in diesel fuel. Anhydrous ethanol (200 proof) does not require an emulsifying agent and lower proof ethanol requires an emulsifying agent to form the opaque macro-emulsion. This could separate into its two phases if allowed to stagnate for a long period (Noguchi et al. 1996, Corkwell et al. 2003, Jeuland et al. 2004, Park et al. 2008, Zhu et al. 2011). In view of engine durability, blends up to 15% (by vol.) ethanol in diesel/biodiesel fuel can be considered relatively safe for diesel engine applications. Adding ethanol to diesel fuel can reduce its lubricity and create potential wear problems in fuel pumps (Banapurmath and Tewari 2010).

In this study, HOME was further blended with ethanol in different proportions of 7.7% and 15%, and the resulting blend properties are shown in Table 2. A stirrer was mounted inside the fuel tank to prevent phase separation, and the mixture was supplied instantaneously to the engine. Figure 4 shows the mechanical stirrer used to mix the biodiesel–ethanol blend mixtures. At and beyond 20% ethanol blend in biodiesel, the results were not encouraging, since a clear separation was observed between the biodiesel and the ethanol layers. At present, only 7.7% ethanol blend has been successfully adopted in the state road transport sector. However, use of higher ethanol blend ratio needs further investigation.

Table 2 Composition of Honge oil (Shirsath et al. 2012).

Sl no.	Composition	Fatty acid contribution of Honge oil	Chemical name	No. of bonds	Structure	Saturated /unsaturated	Chemical formula	Mol. weight
1	Palmitic	10.5	Hexadecanoic	–	16:0	Saturated	C16H32O2	256
2	Stearic	5.56	Octadecanoic	–	18:0	Saturated	C18H36O2	284
3	Oleic	49.39	Cis-9-octadecanoic	Single	18:1	Unsaturated	C18H34O2	282
4	Linoleic	20.37	Cis-9,cis-12-octadecanoic	Double	18:2	Unsaturated	C18H32O2	280
5	Linolenic	3.66	Cis-9,cis-12,cis-15-octadecanoic	Triple	18:3	Unsaturated	C18H30O2	278
6	Arachidic	1.36	Etcosanoic	–	20:0	Saturated	C20H40O2	312
7	Lignoceric	1.53	Tetracosanoic	–	24:0	Unsaturated	C24H48O2	368
8	Behenic	5.82	Docosanoic	–	22:0	Unsaturated	C22H44O2	340

Figure 2 Fuel tank with mechanical stirrer and its position in the set-up.

3. Experimental set-up

The experimental investigations were carried out on a single cylinder four-stroke Compression Ignition (CI) engine test rig operated on biodiesel and blends of biodiesel and ethanol. The effects of EGR and swirl augmentation techniques on the performance of the engine fueled with the above fuel combinations were studied. Figures 2 and 3 show the arrangement of fuel blending and overall view of the test rig modified to operate on biodiesel–ethanol blended fuels. The specifications of the engine are given in Table 3. The engine was always operated at a rated speed of 1500 rpm. A piezoelectric pressure transducer was mounted on the CH surface to measure the cylinder pressure for combustion study. The engine tests were conducted with HOME–ethanol blends at different load conditions. The injection timing was kept fixed at 23° Before Top Dead Centre (BTDC), and the compression ratio was maintained at 17.5. Masking was provided on the inlet valve with angle of mask varying from 50°, 70° and 90°, respectively, as shown in Figure 4. In addition to the inlet valve masking, the CHs were also suitably provided with different grooves and bridges to study the effect of swirl augmentation techniques on engine performance. In one CH denoted as CH1, one bridge and two grooves were provided, whereas in another denoted as CH2 two bridges and three grooves were provided accordingly as shown in Figure 5. Tables 4 and 5 show the specifications of exhaust gas analyser and the smoke meter used for the emission measurements with measurement accuracies and uncertainties reported. The emissions of hydrocarbons (HCs) and NO _x are measured in ppm whereas those of CO and CO₂ were measured in percentage. The smoke is measured in Hartridge Smoke Units (HSU).

Figure 3 Schematic diagram of experimental set-up.

Table 3 Specification of the engine.

Sl no.	Parameters	Specification
1	Machine supplier	Apex Innovations Pvt Ltd
2	Type	TV1 (Kirlosker made)
3	Software used	Engine soft
4	Nozzle opening pressure	200–225 bar
5	Governor type	Mechanical centrifugal type
6	No. of cylinders	Single cylinder
7	No. of strokes	Four stroke
8	Fuel	H. S. diesel
9	Rated power	3.7 kW (5 HP) @1500 rpm
10	Cylinder diameter (bore)	87.5 mm
11	Stroke length	110 mm
12	Compression ratio	17.5:1
Air measurement manometer
13	Made	MX 201
14	Type	U-Type
15	Range	100–0–100 mm
Eddy current dynamometer
16	Model	AG–10
17	Type	Eddy current
18	Maximum	7.5 kW at 1500–3000 rpm

Figure 4 Angle of mask provided on the inlet valve.

Figure 5 Modified CHs with different number of grooves and bridges.

Table 4 Specifications of exhaust gas analyser.

Type	DELTA 1600S
Object of measurement	Carbon monoxide (CO), carbon dioxide (CO2) and hydrocarbons (HCs)
Range of measurement	HC = 0–20,000 ppm as C3H8 (propane)
	CO = 0–10%
	CO2 = 0–16%
	O2 = 0–21%
	NO x  = 0–5000 ppm (as nitric oxide)
Accuracy	HC = ± 30 ppm HC
	CO = ± 0.2% CO
	CO2 = ± 1% CO2
	O2 = ± 0.2% O2
	NO x  = ± 10 ppm NO
Resolution	HC = 1 ppm
	CO = 0.01% vol.
	CO2 = 0.1% vol.
	O2 = 0.01% vol
	NO x  = 1 ppm
Warm-up time	10 min (self-controlled) at 20°C
Speed of response time	Within 15 s for 90% response
Sampling	Directly sampled from tail pipe
Power source	100–240 V AC/50 Hz
Weight	800 g
Size	100 mm × 210 mm × 50 mm

Table 5 Specifications of smoke meter.

Type	Hartridge Smokemeter-4
Object of measurement	Smoke
Measuring range opacity	0–100%
Accuracy	± 2% relative
Resolution	0.1%
Smoke length	0.43 m
Ambient temperature range	− 5°C to +45°C
Warm-up time	10 min (self-controlled, at 20°C)
Speed of response time	Within 15 s for 90% response
Sampling	Directly sampled from tail pipe
Power supply	100–240 V AC/50 Hz
	10–16 V DC @15 amps
Size	100 mm × 210 mm × 50 mm.

EGR arrangement was suitably designed and fabricated and was provided to the engine. The EGR rate was accurately calculated using the following equation:

4. Results and discussion

The results and discussion section is explained under three headings. In the first two cases, diesel engine operation with HOME and ethanol is considered with and without the induction of EGR. In the last case, use of swirl augmentation techniques on the performance of the engine with HOME operation is considered.

4.1 Performance and emission tests on biodiesel and ethanol blends without EGR: performance parameters

Variation in BTE with power output for HOME and HOME–ethanol blends is presented in Figure 6. For all the loads tested, HOME and its blends with ethanol showed inferior performance compared to diesel. The reason for poor biodiesel performance is mainly attributed to its lower calorific value, volatility and Cetane number associated with its higher viscosity. Ethanol has a lower Cetane number as well as boiling point and higher oxygen content than HOME (Table 1). For the same injection pressure and injection timings, the BTE improved with ethanol–HOME blended fuels with increasing ethanol content in blends. The reason could be that the quality of the spray improved with blended fuels due to lower boiling point of ethanol than of HOME itself. The combustion is more complete in the fuel-rich zone due to the oxygen present in ethanol-blended fuels. This results in enhanced combustion efficiency and decreased heat losses in the cylinder due to lower flame temperature of ethanol-blended fuels compared to HOME. Fifteen percent ethanol–HOME blend resulted in improved performance.

Figure 6 Brake thermal efficiencies for different fuel combinations.

4.1.1 Emission parameters

Variation in smoke opacity with power output for HOME and HOME–ethanol blends is shown in Figure 7. Smoke opacity is an indicator of dry soot emissions. Adding oxygenates to HOME has a remarkable effect on the reduction in smoke emissions, especially at high loads. Smoke opacity decreased with increased ethanol content in the blended fuels. Presence of bonded oxygen reduces the probability of soot nuclei formation in locally rich zones. The enrichment of oxygen content in the fuel due to the addition of oxygenates by HOME and ethanol resulted in more complete combustion. Fifteen percent ethanol–HOME blend resulted in lower smoke emissions.

Figure 7 Smoke emissions for different fuel combinations.

Unburned HC emissions consist of incompletely burnt fuels that represent a serious problem at light loads in diesel engines. Figure 8 shows the variation in HC emission with power output for HOME and HOME–ethanol blends. HC emissions were reduced with HOME–ethanol blends because of their improved combustion. Ethanol added to the HOME provides more oxygen for the combustion process and leads to improved combustion. In addition, ethanol molecules are polar, which cannot be absorbed easily by the non-polar molecule lubrication oil layer, and therefore, ethanol can lower the possibility of production of HC emissions. HC emission is lower for 15% ethanol–HOME blend.

Figure 8 HC emissions for different fuel combinations.

Emissions of CO are greatly dependent on the air–fuel ratio relative to stoichiometric proportions. Rich combustion invariably produces CO emissions and increases linearly with the deviation from the stoichiometry. Figure 9 shows variation in CO emission with power output for HOME and HOME–ethanol blends. For ethanol–HOME blends, the CO emission reduced due to oxygen content in ethanol. CO emission was lower for ethanol 15% blend.

Figure 9 CO emissions for different fuel combinations.

Figure 10 shows variation in NO _x emission with power output for HOME and HOME–ethanol blends. The NO _x emission behaviour for all the fuels was found to be similar at lower load with a slight increase in its magnitude at higher load. This is because at lower load, the adiabatic flame temperature of stoichiometric air–ethanol flame is slightly lower. However, the lower Cetane number of ethanol leads to an increase in the ignition delay and the greater rates of pressure rise resulting in higher peak pressure and combustion temperatures. Ethanol blending in biodiesel has little influence on NO _x emission (Ren et al. 2008, Shudo et al. 2009). The exhaust gas temperature increases with increasing ethanol ratio in the fuel mixture. This high peak temperature increases NO _x emissions. Hence, as ethanol concentration increases, NO _x emissions also increase. Also ethanol and ester being the oxygenated fuel combinations result in higher NO _x emissions due to more complete combustion than the ester considered alone. At lower loads, the BTE reduces with relatively lower combustion temperatures inside the engine cylinder when compared with higher load operation. The incomplete combustion leading to reduced premixed combustion could also be the reason for this behaviour.

Figure 10 NO _x emissions for different fuel combinations.

4.2 Performance and emission tests on biodiesel and ethanol blends with EGR

4.2.1 Performance parameters

Figure 11 shows the effect of power on BTE levels for HOME and HOME–ethanol blends. It can be seen that, with 10% EGR induction, BTE reduced with an increase in power output. This is because deterioration in combustion occurs when 10% EGR is introduced and the gaseous fuel–air mixture becomes diluted with exhaust gas. The introduction of 10% EGR reduces the rates of auto ignition reactions, as indicated by an increase in the ignition delay period. The premixed combustion fraction increases and causes a delay in the whole diffusive combustion event with 10% EGR, because a larger amount of fuel is injected during the longer ignition delay period. Deterioration in the air–fuel mixture reduces the oxygen concentration leading to incomplete combustion. Although the presence of oxygen in vegetable oils compensates for oxygen deficiency, their lower calorific value and higher density leads to reduced BTE.

Figure 11 Effect of ethanol blending on BTE.

4.2.2 Emission parameters

The effect of brake power on smoke opacity for standard diesel operation and HOME and HOME–ethanol blends is shown in Figure 12. It was observed that smoke emission was higher for the HOME and HOME–ethanol blends than for standard diesel operation. This may be due to the presence of heavier molecular structure, higher viscosity and higher free fatty acids with HOME. Ethanol-blended HOME results in lower smoke emissions. The smoke opacity for HOME and HOME–ethanol blends was even higher with 10% EGR induction. This negative effect of EGR on smoke opacity could be due to the reduction in the engine air–fuel ratio.

Figure 12 Effect of ethanol blending on smoke opacity.

The effect of brake power on HC emission is shown in Figure 13, and it can be observed that HC emissions are comparatively higher for HOME and HOME–ethanol blends. With the 10% EGR induction, the combustion degradation lowers the temperature. The decreased air–fuel ratio associated with EGR induction and reduced combustion temperature results in incomplete fuel combustion. These factors may lead to the higher HC emissions.

Figure 13 Effect of ethanol blending on HC emission.

Figure 14 shows the effect of brake power on CO emissions. CO is comparatively low for standard engine operation with diesel. For HOME and HOME–ethanol blends, 10% EGR induction dilutes the combusting mixture. Therefore, insufficient oxygen is available for better combustion, and the lower combustion temperature prevailing in the engine cylinder leads to comparatively higher CO emissions.

Figure 14 Effect of ethanol blending on CO emission.

Figure 15 shows the effect of brake power on NO _x emissions. The lowest values were obtained with HOME and HOME–ethanol blends with 10% EGR induction. EGR appears to reduce the adiabatic flame temperature and, thereby, the combustion temperature and hence NO _x emissions were reduced. Therefore, NO _x concentration decreases as CI engine inlet airflow is diluted at a constant fuelling rate.

Figure 15 Effect of ethanol blending on NO _x emission.

4.3 Effect of swirl

Swirl effect on the performance of HOME-fueled diesel engine is discussed in this section. The values presented refer to full load engine operation at 3.7 kW. The study on the effect of swirl on the engine performance is divided into two main headings. The first presents the results obtained on the engine performance considering the effect of swirl introduced by the inlet valve masking alone and the second involves use of both inlet valve masking and grooves provided on the CHs.

4.3.1 Effect of swirl using inlet valve masking

4.3.1.1 Brake thermal efficiency

Figure 16 shows variation in BTE with angle of masking for HOME operation. As the angle of masking increases, the BTE increased considerably with HOME till 90°. The reason for this increase in BTE is due to better mixing of the fuel combinations inside the engine cylinder. For 120° angle of mask, there was no improvement noticed in engine performance as well in engine emissions due to drop in volumetric efficiency and incomplete combustion. Hence, the results obtained with 120° angle of masking are not reported in this study.

Figure 16 Variation in BTE with angle of mask for HOME.

4.3.1.2 Smoke emission

Figure 17 shows variation in smoke emission levels with angle of mask for HOME. As the angle of mask increases, the smoke emission levels decreases considerably with the HOME till 90° angle of mask. This could be due to swirl; it helps to achieve better mixing of air and HOME and results into better combustion. Therefore, swirl improves the combustion of fuel by considerably reducing smoke emissions.

Figure 17 Variation in smoke emission levels with angle of mask for HOME.

4.3.1.3 HC emission

Figure 18 shows variation in HC emissions with angle of mask for HOME. As the angle of mask increased, the HC emission levels decreased considerably with the HOME operation. From the figure, it follows that reduction in HC emissions was due to better combustion with higher heat release as it is affected by the swirl induced.

Figure 18 Variation in HC emissions with angle of mask for HOME.

4.3.1.4 NO _x emission

Figure 19 shows variation in NO _x emission levels with angle of mask for HOME. From the figure, it follows that as the angle of mask increases, the NO _x decreases considerably with the HOME operation. Increasing the initial swirl reduces the in-cylinder temperature which in turn reduces thermal NO _x .

Figure 19 Variation in HC emissions with angle of mask for HOME.

4.3.2 Effect of swirl using combination of inlet valve masking and CH grooves on the CH

From Figure 20 it is observed that BTE increases with swirl. A shorter combustion period is generally observed with swirl compared to normal engine without swirl effect. This may also be due to higher heat release during the early stage of combustion. BTE further increases with three groove 90° mask CH.

Figure 20 Effect of swirl on BTE.

4.3.2.1 Emissions

From Figure 21 it follows that swirl improves the combustion, reducing the smoke considerably. The smoke further decreases with CH2. From Figures 22 and 23 it follows that swirl improves the combustion process reducing HC and CO emissions considerably. The HC and CO further decrease with CH2. Compared to CH1, CH2 resulted in overall better performance with increased BTE and reduced emissions. From Figure 24 it follows that the effect of swirl increases NO _x when compared to normal engine (without swirl) with three grooves 90° mask CH.

Figure 21 Effect of swirl on smoke opacity.

Figure 22 Effect of swirl on HC.

Figure 23 Effect of swirl on CO.

Figure 24 Effect of swirl on NO _x .

Figure 25 shows the heat release rate with different swirl augmentations used. Swirl shows significant influence on the combustion process. As the swirl increases, the rate of heat release becomes faster, enhancing the fuel–air mixing process, which makes faster distribution of fuel accelerating plane propagation. Higher swirl reduces fuel penetration. The heat release rate increases with CH1 compared with CH2. The slow combustion rate is considered to be the main reason for low heat release rate inside CH1.

Figure 25 Rate of heat release versus crank angle for different swirl configurations at 100% load.

5. Conclusion

Exhaust emissions and combustion characteristics of a diesel engine operated with HOME were carefully examined to study the different effects of fuel modification, EGR and swirl on the engine performance. From this study, the following conclusions were made:

1.	Use of ethanol in diesel engines is still a critical issue. As the percentage of ethanol in biodiesel blend increases beyond 15%, a phase separation is observed.
2.	The performance of HOME–15% ethanol blends resulted in better performance. However, NOx emissions increased.
3.	The NOx emissions were significantly reduced by 28% with 10% EGR induction. The overall performance with 10% EGR was poor due to increased smoke, HC and CO emissions.
4.	It was observed that swirl arrangement provided in the combustion chamber further improved the overall performance of the engine fueled with HOME. Inlet valve masking along with grooves and bridges provided on the CH1 and CH2 could be the reason for the smoke and particulate emissions of the biodiesel fueled engine.