Blends of karanja and jatropha biodiesels for diesel engine applications

Abstract

Over a number of years, the work of exploring different biodiesels as an alternative to diesel fuel has been carried out worldwide. Not much focus on the use of combination of different biodiesels and their behaviour in diesel engines has been reported. This work is an attempt in this direction, which reports on the use of combination of biodiesels derived from jatropha and karanja oils. Jatropha oil methyl ester (JOME) and honge oil methyl ester (HOME) represent the respective biodiesels derived from these non-edible oils. Experiments were conducted on a four-stroke, single-cylinder diesel engine using these biodiesel combinations in order to check their feasibility as alternative fuels to diesel. Initially, experiments were conducted on each biodiesel and their blends with diesel and engine parameters were optimised in terms of injection pressure and injection timing. Advancing the injection timing improved the overall performance of the engine fuelled with JOME while retarding the injection timing favoured the HOME. Both biodiesels performed better with an injector opening pressure of 230 bar. Finally, experiments were conducted with the combination of both biodiesels with different blend ratios. It was observed that increasing the JOME content in the biodiesels blend improved the performance with reduced emissions of smoke, hydrocarbons and carbon monoxide emissions. However NO _x emission increased.

Keywords:

• biodiesel
• jatropha
• karanja
• ethanol
• combination of biodiesels
• injection timing

1. Introduction

The environment is greatly polluted by emissions such as carbon monoxide (CO), CO₂, NO _x , SO _x , unburnt or partially burnt hydrocarbons (HC) and particulate from transport vehicles. The chief contributors to urban air pollution and major source of greenhouse gases are fossil fuels, and they are considered to be the major cause of global warming. India imports petroleum products at an annual cost of approximately $50 billion in foreign exchange. In view of this high demand/cost of fossil fuels associated with higher emissions, it is necessary to find a suitable alternative to diesel oil. Replacing just 5% of petroleum fuel by biofuel could enable India to save $2.5 billion per year in foreign exchange. Exhaustive literature work on the use of vegetable oils and their blends in diesel engine applications has been published by various researchers. Various non-edible oils, such as jatropha, honge, honne, rubber seed, mahua, hazelnut kernel, waste cooking and cotton seed oils, are investigated for their suitability to diesel engine fuels (Altin et al. 2001, Pramanik 2003, Ramadhas et al. 2005, Agarwal and Rajamanoharan 2009, Yage et al. 2009, Banapurmath et al. 2010, Belagur and Chitimini 2010, Buyukkaya 2010, Chao et al. 2010, Chitimini 2010, Gumus 2010, Gumus and Kasifoglu 2010, Jiafeng et al. 2010, Ryu 2010). The literature survey mainly suggests that work on the use of the combination of different biodiesels and their behaviour in diesel engines has not been explored in detail. The combination of the two biodiesels was used in this study as not much work has been reported in the literature.

Effect of injection pressures, injection timings and exhaust gas recirculation (EGR) on the performance of different vegetable oils in compression ignition (CI) engines has been reported by many investigators (Hountalas et al. 2001, Bari et al. 2004, Tao et al. 2005, Gajendra Babu 2007, Roy 2009). Changes in injection timings change the position of the piston and cylinder pressure and temperature at the injection. Retarded injection timings showed significant reduction in diesel NO _x and biodiesel NO _x (Hountalas et al. 2001; Tao et al. 2005). Cylinder pressures and temperatures gradually decrease when injection timings are retarded (Roy 2009). Advanced injection timing by 4° before top dead centre (BTDC) with waste cooking oil in direct injection diesel engine resulted in better efficiency with reduced CO and higher NO emissions (Bari et al. 2004). Retarding the injection timing by 4° BTDC with honge biodiesel has resulted in better efficiency with reduced HC, CO and smoke emissions (Banapurmath et al. 2009). Many researchers have also performed tests on CI engine with different vegetable oils at different injection pressures (Bakar et al. 2008, Puhan et al. 2009). Better performance, higher peak cylinder pressure and temperature were observed at an increased injection pressure (Bakar et al. 2008, Banapurmath and Tewari 2009, Roy 2009). Performance tests on CI engine with vegetable oils at different compression ratios have also been reported in the literature. Better performance, higher peak cylinder pressure and temperature were observed at an increased compression ratio (Laguitton et al. 2007, Rehman and Ghadge 2008).

In the present investigation, honge oil methyl ester (HOME), jatropha oil methyl ester (JOME) and their blends have been used in the diesel engine, and the effects of injection pressures and injection timings on the engine performance have been presented.

2. Characteristics of Karanja and Jatropha biodiesels and their blends

In the present study, the karanja and jatropha vegetable oils were subsequently converted into their respective biodiesels, i.e. HOME (KB100) and JOME (JB100). The detailed transesterification procedure used in the study is presented in Section 2.1. These biodiesels were then blended with diesel at different proportions such as KB20, KB40, KB80 and JB20, JB40, JB80. Here, KB20 represents karanja biodiesel with 20% karanja and 80% diesel on volume basis, while JB20 represents jatropha biodiesel with 20% jatropha and 80% diesel on volume basis, respectively. Finally, both biodiesels were blended in different proportions namely KJB20, KJB40, KJB60 and KJB80. Here KJB20 represents karanja and jatropha biodiesels with 20% karanja and 80% jatropha on volume basis. The physical and chemical properties of the above fuel combinations are listed in Tables 1-4, respectively.

Table 1 Fuel properties of diesel, HOME and JOME.

Sl. No.	Property	Diesel	HOME	JOME
1	Density (kg/m^3)	840	890	870
2	Specific gravity	0.840	0.890	0.870
3	Kinematic viscosity (cSt) at 40°C	3.5	5.5	5.6
4	Flashpoint (°C)	56	170	170
5	Calorific value (kJ/kg)	43,000	36,100	38,450

Table 2 Fuel properties of HOME blends with diesel.

Properties	Diesel	Honge	KB20	KB40	KB80	B100
Chemical formula	C13H24	–	–	–	–	–
Density (kg/m^3)	840	927	835	856	869	890
Calorific value (kJ/kg)	43,000	35,800	42,123	41,296	37,476	36,010
Viscosity (cSt)	2–5	56	4.12	4.46	5.42	5.6
Flashpoint (°C)	56	187	104	108	120	163
Cetane number	45–55	40	–	–	–	45
Carbon residue (%)	0.1	0.66	–	–	–	–

Table 3 Fuel properties of JOME biodiesel with blends.

Properties	Diesel	Jatropha	JB20	JBB40	JBB80	B100
Chemical formula	C13H24	–	–	–	–	–
Density (kg/m^3)	840	920	830	850	865	870
Calorific value (kJ/kg)	43,000	38,450	42,153	41,300	38,126	39,628
Viscosity (cSt)	2–5	56	4.0	4.34	5.00	5.2
Flashpoint (°C)	56	187	104	108	120	170
Cetane number	45–55	51	–	–	–	45
Carbon residue (%)	0.1	0.66	–	–	–	–

Table 4 Composition of honge and jatropha oils.

Sl. No.	Composition	Fatty acid contribution of honge oil	Fatty acid contribution of jatropha oil	Chemical name	No. of bonds	Structure	Saturated /unsaturated	Chemical formula	Mol. weight
1	Palmitic	10.5	16.0	Hexadecanoic	–	16:0	Saturated	C16H32O2	256
2	Stearic	5.56	6.0–7.0	Octadecanoic	–	18:0	Saturated	C18H36O2	284
3	Oleic	49.39	42.0–43.5	Cis-9 octadecanoic	Single	18:1	Unsaturated	C18H34O2	282
4	Linoleic	20.37	33.0–34.4	Cis-9, cis-12 octadecanoic	Double	18:2	Unsaturated	C18H32O2	280
5	Linolenic	3.66	>0.80	Cis-9, cis-12, cis-15 octadecanoic	Triple	18:3	Unsaturated	C18H30O2	278
6	Arachidic	1.36	0.20	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
Source: Banapurmath et al. (2009, 2010), Singh et al. (2008), Yaliwal et al. (2010).

2.1 Transesterification of honge and jatropha oils

Honge and jatropha oils were transesterified as their viscosity is more than diesel. The factors affecting the transesterification process are temperature, reaction time, molar ratio and catalyst concentration. These were optimised for both the fuels during transesterification process. In the transesterification process, refined vegetable oil (honge or jatropha oil), methanol, sodium hydroxide (NaOH) and distilled water were used. The process was performed in a reactor as shown in Figure 1. This reactor was immersed in a constant temperature water bath. Both the water bath and reactor were equipped with thermometers to measure the temperature. The reactor has a magnetic stirrer and is used to achieve necessary agitation of the oil mixture. A constant speed of 300 rpm was maintained throughout the experiment. Initially, the reactor was filled with 1 l of vegetable oil (honge or jatropha oil) and heated to 65°C to remove the moisture. A catalytic solution of NaOH (1% by weight of oil) dissolved in the methanol (molar ratio of alcohol/oil is 1:5) was then added to the reactor. The mixture was then stirred and heated simultaneously to facilitate reaction for 60 min. Finally, the glycerol was separated from the upper layer of biodiesel by gravity. The catalyst and unreacted methanol were removed by warm water washing to obtain biodiesel of respective oils as shown in Figure 1.

Figure 1 Transesterification set-up.

3. Experimental set-up

Experiments were conducted on a four-stroke, single-cylinder, water-cooled diesel engine. Table 5 shows the specifications of the engine used. Figure 2 shows the schematic diagram of the engine set-up. The experiments were conducted at constant engine speed of 1500 rev/min. Initially, experiments were conducted to study the effect of injection timing and injection pressure on the performance of diesel engine fuelled with HOME and JOME. Experiments were also conducted to study the effect of blends of HOME and JOME with diesel on the diesel engine performance. Finally, blends of HOME and JOME were considered to study the influence of the different biodiesels when used in engine. Tables 6 and 7 show the specification of exhaust gas analyser and smoke meter, respectively.

Table 5 Specification of CI engine.

Sl. No.	Parameters	Specification
1	Machine supplier	Apex Innovations Pvt Ltd. Sangli
2	Type	TV1 (Kirloskar make)
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	5.2 kW (7 hp) at 1500 rpm
10	Cylinder diameter (bore)	0.0875 m
11	Stroke length	0.11 m
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
19	Flow	Water must flow through dynamometer during the use
20	Dynamometer arm length	0.180 m
21	Fuel measuring unit – range	0–50 ml

Figure 2 Schematic diagram of the engine set-up.

Table 6 Specification of exhaust gas analyser.

Type	DELTA 1600S
Object of measurement	CO, CO2 and HC
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% V
	O2 = 0.1% 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 × 210 × 50 mm

Table 7 Specifications of smoke meter.

Type	Hartridge smoke meter-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 at 15 amp
Size	100 × 210 × 50 mm

4. Results and discussions

4.1 Effect of injection timing on the performance of diesel engine fuelled with HOME and JOME operations

This section presents the effect of injection timing on the performance and emission characteristics of single-cylinder diesel engine fuelled with HOME and JOME.Experiments were conducted at a constant engine speed of 1500 rev/min, and the compression ratio of the engine was maintained at 17.5 for all the tested fuels. Diesel fuel was injected at a constant fuel injection pressure of 205 bar while the biodiesels were injected at a pressure of 230 bar. The main reason for injecting the biodiesel at higher injection pressure is due to their higher viscosity (nearly two times) compared to diesel fuel. The static injection timings were varied to include 19°, 23° and 27° BTDC.

4.1.1 Effect of injection timing on the brake thermal efficiency

Figure 3 shows the effect of injection timing on the brake thermal efficiency (BTE) of the engine fuelled with diesel, HOME and JOME. It is observed that the highest BTE for diesel was found to be 30.90% at 23° BTDC. However, the values of BTE using HOME and JOME are found be lower than that of the diesel fuel. The lower values of BTE for biodiesel fuels are due to their lower calorific value compared to diesel fuel, resulting in higher brake specific fuel consumption for the same power developed by the engine. The BTE with HOME operation increases with retarding injection timing while BTE for JOME increases with advancing injection timing. Biodiesels derived from different vegetable oils behave differently when used in diesel engines. The maximum BTE obtained using HOME is 29.5% at 19° BTDC and minimum 27.96% at 27° BTDC. Similarly, the maximum BTE obtained using JOME is 29.31% at 27° BTDC and minimum being 26.6% at 19° BTDC. Retarded injection timing of 19° BTDC is found to be better for HOME operation, while for JOME operation advanced injection timing of 27° BTDC is found to be optimum.

Figure 3 Effect of injection timing on the BTE of diesel, JB100 and KB100.

4.1.2 Effect of injection timing on the HC emission

Figure 4 shows the effect of injection timing on the HC emissions of the engine fuelled with diesel, HOME and JOME. The HC emissions in the diesel engines are mainly caused due to lean mixture during delay period and undermixing of fuel leaving fuel injector nozzle at lower velocity. From this figure, it is observed that the HC emissions are more for JOME and HOME fuels as compared to that of diesel. The maximum value of HC emission obtained for JOME is 120 ppm at 19° BTDC and the minimum value of 100 ppm at 27° BTDC. Similarly for HOME operation, the maximum value of HC obtained is 73 ppm at 27° BTDC and the minimum value of 69 ppm at 19° BTDC. Hence for HOME and JOME operation, injection timing of 19° BTDC and 27° BTDC is found to be optimum.

Figure 4 Effect of injection timing on the HC emission for diesel, JB100 and KB100.

4.1.3 Effect of injection timing on the CO emission

Figure 5 shows the effect of injection timing on the CO emissions of the engine fuelled with diesel, HOME and JOME. CO is a toxic by-product and is a clear indication of incomplete combustion of premixed mixture. From the figure, it is observed that the CO emissions are more for JOME and HOME fuels as compared to that of diesel fuel. The maximum value of CO emission for JOME is 0.268% at 19° BTDC while it is 0.24% which is lower at 27° BTDC. Similarly, the maximum value of CO emission obtained for HOME is 0.182% at 27° BTDC and a minimum of 0.13% at 19° BTDC. CO emission decreases with advancing injection timing for HOME, whereas it decreases with retarded injection timing for JOME.

Figure 5 Effect of injection timing on the CO emission for diesel, JB100 and KB100.

4.1.4 Effect of injection timing on the NO _x emission

Figure 6 shows the effect of injection timing on the NO _x emission of the engine fuelled with diesel, HOME and JOME. Normally, retarded injection results in substantial reduction in NO _x emission. When the injection timing is retarded, the combustion process gets retarded. The NO _x concentration levels are lower when peak temperature is lower. From the figure, it is observed that the NO _x emissions are lower for JOME and HOME operation as compared to that of diesel fuel. This is because premixed combustion associated with diesel fuel is more compared with biodiesel operation. It is observed that the NO _x emission for HOME increases further with advancing injection timings, whereas the trend of NO _x for JOME has no much deviations with advancing injection timings. The maximum NO _x emission obtained for JOME is 610 ppm at 19° BTDC while it is minimum of 600 ppm at 27° BTDC. Similarly, the maximum NO _x emission for HOME is 1720 ppm at 27° BTDC and is minimum, i.e. 1080 ppm at 19° BTDC.

Figure 6 Effect of injection timing on the NO _x emission for diesel, JB100 and KB100.

4.1.5 Combustion analysis with effect of injection timing on HOME/JOME and their blends with diesel

In this section as a part of combustion analysis, pressure–crank angle variation and heat release rate variation have been presented for JOME at different injection timings.

Figure 7 shows the cylinder gas pressure plotted for three injection timings of 19, 23 and 27° BTDC. The cylinder pressure shows a slight decrease in peak pressure value with the retarding of fuel injection timings. Moreover, it can be seen that crank angle corresponding to the peak cylinder pressure become retarded at low cylinder pressure. The slow combustion rate of JOME is considered to be the main reason for low cylinder pressure.

Figure 7 In-cylinder pressure versus crank angle for different injection timings for 100% load.

Figure 7 shows heat release rate with different fuel injection timings. Similar to the behaviour of cylinder pressure versus injection timings, heat release rate decreases with retarding of injection timing. The injection timings retarded yielded lower efficiencies. The most retarded injection timings resulted in combustion delayed into the expansion stroke. The phasing of the rate of heat release curves away from top dead centre (TDC) combined with combustion occurring at low temperatures resulted in a loss in fuel conversion efficiency. The most advanced injection timings with their very long ignition delay period result in more fuel prepared for burning at the start of combustion compared to retarded injection timings. Simultaneous ignition of a large proportion of HOME fuel leads to fast combustion and a short burning time, as shown in Figure 8.

Figure 8 Rate of heat release versus crank angle for different injection timings for 100% load.

4.2 Effect of HOME/JOME and their blends with diesel

Experiments were conducted on HOME and JOME and their blends with diesel to study the effect of biodiesel to blend ratio on the diesel engine performance. Experiments were conducted at a constant engine speed of 1500 rev/min, and the compression ratio of the engine was maintained at 17.5 with varying loads for all fuels tested. Trials were conducted on JOME/HOME and their blends with diesel. The blends prepared with HOME are represented as KB20, KB40 and KB80. Similarly, the blends prepared with JOME were JB20, JB40 and JB80. The injection timing for all the tests was maintained constant at 23° BTDC.

4.2.1 Effect of brake power on BTE

Figure 9 shows the effect of brake power on BTE for JOME/HOME and their blends with diesel. As compared to diesel, the efficiency decreases with increased blend ratio of biodiesel in the diesel. The possible reason could be the lower volatility, higher viscosity and density of the biodiesel blends that overcomes the excess oxygen percent (11%) present in the biodiesel. The higher fuel consumption of the blends for the same power output resulting in lower BTE is generally observed. The maximum BTE obtained using the B20 blend of JOME/HOME, i.e. JB20 and KB20 blends are 29.10 and 28.79%, respectively, whereas with the diesel it is 30%.

Figure 9 Effect of brake power on BTE for HOME/JOME blends.

4.2.2 Effect of brake power on smoke

Figure 10 shows that with an increase in power there is higher smoke emissions for the JOME/HOME blends as compared with diesel. The higher viscosity of the JOME/HOME blends could be the reason for this higher level of smoke compared to that of diesel. Higher viscosity of the fuel results in poor atomisation and poor spray pattern. From the figure, the higher smoke opacity is observed with JB80/KB80 and is 69 and 72 HSU, respectively, while the lower smoke emission is observed with JB20/KB20 (53.76 HSU) at full load. The smoke opacity for the diesel at full load is found near to be 47 HSU.

Figure 10 Effect of brake power on smoke for HOME/JOME blends.

4.2.3 Effect of brake power on HC emission

Figure 11 shows that with an increase in load there are higher HC emissions observed for the JOME/HOME blends as compared with diesel. Lower BTE associated with JOME/HOME biodiesel blends results in higher HC emissions compared with that of the diesel fuel. Also the higher viscosity of the blends results in poor spray characteristics and poor mixing and hence incomplete combustion. Higher value of the HC emission was obtained with JB80/KB80 blends and found to be 55 and 58 ppm, respectively. Lower HC emissions were obtained with JB20/KB20 blends and were found to be 41 and 34 ppm which is quite closer to that of 34 ppm obtained with diesel at full load.

Figure 11 Effect of brake power on HC emissions for HOME/JOME blends.

4.2.4 Effect of brake power on CO emission

Figure 12 shows that with an increase in engine load there are higher CO emissions observed for the JOME/HOME blends as compared with diesel. The higher values of CO emissions observed with biodiesel blends are mainly due to their lower BTE and the incomplete combustion prevailing inside the engine cylinder. Higher value of the CO emission were obtained with JB80/KB80 blends and found to be 0.124% and 0.13%, respectively. Lower CO emissions were obtained with JB20/KB20 blends and were found to be 0.082 and 0.083, which is quite closer to that of 0.08% obtained with diesel at full load.

Figure 12 Effect of brake power on CO emissions for HOME/JOME blends.

4.2.5 Effect of brake power on NO _x emission

Figure 13 shows the effect of brake power on NO _x emission for JOME and HOME biodiesel blends with diesel. NO _x for biodiesel blends was observed to be lower compared to diesel operation. This reduction is basically linked with the reduced premixed burning rate following the delay period. However, NO _x increases with an increase in biodiesel blends. The higher value of NO _x observed with JB20 and KB20 are 940 and 902 ppm, respectively, while minimum of 848 and 814 ppm were observed with JB80 and KB80, respectively. For diesel fuel, 1000 ppm at full load is observed.

Figure 13 Effect of brake power on NO _x emissions for HOME/JOME blends.

4.2.6 Combustion analysis

The cylinder pressure–crank angle history is obtained for 100 cycles for JOME and blends of HOME with diesel at 100% load, and the average pressure variation with crank angle is shown in Figure 14. It is observed that peak pressure increases as the load increases and combustion starts later in comparison to diesel fuel for JOME and blends of HOME and diesel.

Figure 14 In-cylinder pressure versus crank angle for different injection timings for 100% load.

Figure 15 shows the variation of heat release rate with JOME and its blends with diesel. All the fuels experience rapid premixed burning followed by a diffusion combustion which is typical for naturally aspirated engines. After the ignition delay period, the premixed fuel–air mixture burns rapidly releasing heat at a very rapid rate, followed by diffusion combustion wherein the burning rate is controlled by the availability of combustible fuel–air mixture. The premixed burning phase associated with a high heat release rate is significant with diesel operation which is responsible for higher peak pressure and higher rates of pressure rise. This is the reason for the higher thermal efficiency of diesel. The diffusion-burning phase indicated under the second peak is greater for B20 followed by B100, B40 and B80 blends, respectively, when compared to diesel. It follows that when engine is fuelled with B20, the combustion starts earlier compared to other blends. Therefore, more burning occurs in the diffusion phase rather than in the premixed phase with these HOME blends with diesel. However, B20 shows improvement in heat release rate compared to other HOME blends with diesel.

Figure 15 Rate of heat release versus crank angle for different injection timings for 100% load.

4.3 Effect of blends of HOME and JOME on performance of CI engine

In the last leg of the experiments, blends of HOME and JOME were considered to study the influence of biodiesel combinations on the engine performance. These blends namely KJB20 (20% HOME+80% JOME), KJB40 (40% HOME+60% JOME), KJB60 (60% HOME+40% JOME) and KJB80 (80% HOME+20% JOME) were considered for the study.

4.3.1 Effect of brake power on BTE

Figure 16 shows the effect of brake power on the BTE with blends of JOME and HOME in different proportions. As the percentage of karanja in the mixture of biodiesels increases, the BTE decreases with an increase in load. This is because HOME has lower calorific value and higher viscosity compared to the JOME. Diesel shows a maximum BTE of 30%. This is because for the same power output, more amounts of biodiesel blends need to be injected compared to that of diesel. Maximum BTE of 21.18% is obtained with KJB20 while a minimum BTE of 19.26% with KJB80. KJB20 gives the better results as compared with the other biodiesel combinations.

Figure 16 Effect of brake power on BTE with blends of JOME and HOME.

4.3.2 Effect of brake power on HC and CO emissions

Figures 17 and 18 show the effect of brake power on HC and CO emissions using the combination of two biodiesels. Higher viscosity and density of HOME compared to JOME result in poor combustion, and hence lead to higher HC and CO emissions. As the percentage of the HOME is increased in the blends of biodiesels, the combustion worsens. The poor spray characteristics and poor air–fuel mixture are also responsible for incomplete combustion.

Figure 17 Effect of brake power on HC with blends of JOME and HOME.

Figure 18 Effect of brake power on CO with blends of JOME and HOME.

4.3.3 Effect of brake power on NO _x emission

Figure 19 shows the effect of brake power on NO _x emission using the combination of two biodiesels. Drastic increase in NO _x is observed with an increase in the percentage of JOME in the mixture of biodiesels. This reduction is basically associated with reduced premixed burning rate following the delay period (Figure 20).

Figure 19 Effect of brake power on NO _x with blends of JOME and HOME.

Figure 20 Rate of heat release versus crank angle for blends of JOME and HOME at 100% load.

4.3.4 Combustion analysis

Figure 20 shows heat release rate with different blends of JOME and HOME. From the figure, it follows that heat release rate decreases with increasing percentage of HOME in the blends of JOME and HOME. The KJB80 results in combustion delayed the expansion stroke followed by KJB60 and KJB40. The phasing of the rate of heat release curves away from TDC combined with combustion occurring at low temperatures resulted in a loss in fuel conversion efficiency. These blends with their very long ignition delay period result in more fuel prepared for burning at the start of combustion compared to KJB20 blend. Simultaneous ignition of a large proportion of JOME in the blends of JOME and HOME leads to fast combustion and a short burning time, as shown in Figure 20.

5. Conclusions

Exhaustive experimentation on the suitability of biodiesel utilisation to diesel engine applications was carried out. For this, two biodiesels derived from honge and jatropha non-edible oils were considered. From the study, it is concluded that each biodiesel behave differently when used in diesel engines in terms of injection timings. The performance with HOME was better at retarded injection timing of 19° BTDC while with JOME advancing, injection timing to 27° BTDC was found to be satisfactory. However, both biodiesels behaved similarly when used in diesel engine with engine parameters of compression ratio and injection pressure. For biodiesel and diesel blends operation, KB20 and JB20 resulted in overall smooth engine operation. For biodiesel blends of HOME and JOME engine operation, KJB20 performs better compared to other combination of biodiesel blends. Smoke, CO and HC emissions increased with increased percentage of HOME in HOME and JOME blends while the NO_x values decreases. Overall, it is observed that the KJB20 gives the better results than the other combination such as KJB40, KJB60 and KJB80.