Effect of Parameters Behavior of Simarouba Methyl Ester Operated Diesel Engine

: Being an energy source of another origin, the compression ignition

. Influence of injection pressure and nozzle geometry on engine performance using different biodiesels.

Type of Biodiesel and
Blends Ratios Engine Parameters Engine Type Output Ref.
Simarouba oil, B5, B10 B15, and B20 220 bar, 23 • bTDC with three-hole injector Kirloskar, single-cylinder, 3.5 kW, 1500 rpm naturally aspirated engine CO 2 was lesser than diesel. BTE was higher for all blends [33] Pumpkin seed oil methyl ester, B25 Observed increase in BSFC, HRR, CO, HC, and smoke with a reduction in BTE and NO x [40] Roselle oil, B20, B40 and B100 IP: 180, 200, 220, 240, and 260 bars Legion Brothers, single cylinder, 3.7 kW, 1500 rpm BTE was higher for RB20 at 180 bar, BSFE also lesser for RB 20 blends. EGT and smoke was higher for the optimized fuel [41] Waste cooking oil biodiesel, B20 IP 170 bar to 220 bar, engine speed at 1000 rpm to 3000 rpm Kirloskar TV1, DI, CI, 5.2 kW, 1500 rpm UHC and smoke opacity decreased while NO x and CO 2 increased with the increasing IP [42] Honge oil methyl ester IP 210, 220, 230 and 240 bars, IT 19,23 and 27 • bTDC combustion chamber slots 5.5, 6.5 and 7.5 mm. NG 3,4,5 holes TV1 (Kirlosker make), 200 to 225 bar, 5 HP @1500 rpm The highest performance was achieved at 230 bar [43] Simarouba oil methyl ester and producer gas CC HCC and RCC, NG 0.4 mm hole size, IP 230 bar Kirloskar make, TV1 type, 3.7 KW, 1500 rpm 4.3% higher BTE, 18% reduction in smoke, 11.6% lesser HC, 14.28% reduced CO, 3.9% increased NO x level with reduced ignition delay [44] Simarouba oil methyl ester, B100 CC-TRCC, LSCC, DSCC, LDSCC, NG-6 holes with 0.2 and 0.25 mm Kirloskar make, TV1 type, 5.2 KW, 1500 rpm 6 holes with 0.2 mm hole diameter for LDSCC resulted in increased performance than other NG and CC [45] From the literature, the fuel injection pressure nozzle geometry viz.; the number of holes and diameter of holes has a higher impact on biodiesel-operated diesel engines [46]. This may be attributed to higher viscosity, reduced vaporization, lower heating, and spray characteristics of biodiesel fuels [47][48][49]. As the injection pressure increases, the area of spray increases for biodiesels. In addition, due to biodiesel's higher injection pressure, the injected fuel breaks more massive droplet sizes into a finely atomized form [50]. This gives improved engine performance compared to the baseline operation. Hence an injection pressure for 100% SuOME is not optimized for use in a diesel engine. Emissions of CO 2 are based on load and engine operating conditions. Hence, the CO 2 emissions of biodieseloperated engine are higher than diesel modes of operation due to their low gross calorific value. On the other hand, based on the study carried by Argonne National Laboratory, use of biodiesel causes less environmental concern as the study on B100 revealed that the life cycle of greenhouse gas emission of biodiesel is 74% lesser than conventional diesel.
Similarly, as the number of injector holes increases, they tend to supply more fuel into the combustion chamber, improving combustion. However, due to the increased quantity of fuel, SFC reduces. Hence previous work showed there is a significant effect of injector hole size for different biodiesel. However, less work has been observed on a combination of injection pressure and the effect of injector hole diameters on engine performance using SuOME as fuel. Hence, studying the combined effects of injection pressure and injector hole size is crucial to obtain higher efficiency and reduced emissions. Hence, the current study aims to improve the overall performance of SuOME fueled diesel engines by optimizing both fuel injection pressure and injector geometry.

Materials and Methods
In the following section, details about Simarouba biodiesel's preparation, properties of prepared biodiesel, experimental setup, specifications of the setup used for experimentation, different fuel injectors used, and modifications on the engine are explained.

Simarouba Oil Methyl Ester Production
The details about the experimental procedure used to prepare SuOME, its characterization, and the experimental test rig used for engine experimentation are shown in the following sections. The Simarouba oil methyl ester used in the study was produced at the University of Agricultural Sciences, Bangalore. SuOME was produced from Simarouba seed oil by the transesterification process. The various steps involved in converting Simarouba seeds to their biodiesel are shown in Figure 1. The transesterification setup consists of a 3-neck round-bottom flask of 2 L capacity and a high-speed magnetic stirrer for mixing all the oil. KOH as a catalyst, and methanol as alcohol is used in the production of SuOME.
life cycle of greenhouse gas emission of biodiesel is 74% lesser than conventional diesel.
Similarly, as the number of injector holes increases, they tend to supply more fuel into the combustion chamber, improving combustion. However, due to the increased quantity of fuel, SFC reduces. Hence previous work showed there is a significant effect of injector hole size for different biodiesel. However, less work has been observed on a combination of injection pressure and the effect of injector hole diameters on engine performance using SuOME as fuel. Hence, studying the combined effects of injection pressure and injector hole size is crucial to obtain higher efficiency and reduced emissions. Hence, the current study aims to improve the overall performance of SuOME fueled diesel engines by optimizing both fuel injection pressure and injector geometry.

Materials and Methods
In the following section, details about Simarouba biodiesel's preparation, properties of prepared biodiesel, experimental setup, specifications of the setup used for experimentation, different fuel injectors used, and modifications on the engine are explained.

Simarouba Oil Methyl Ester Production
The details about the experimental procedure used to prepare SuOME, its characterization, and the experimental test rig used for engine experimentation are shown in the following sections. The Simarouba oil methyl ester used in the study was produced at the University of Agricultural Sciences, Bangalore. SuOME was produced from Simarouba seed oil by the transesterification process. The various steps involved in converting Simarouba seeds to their biodiesel are shown in Figure 1. The transesterification setup consists of a 3-neck round-bottom flask of 2 L capacity and a highspeed magnetic stirrer for mixing all the oil. KOH as a catalyst, and methanol as alcohol is used in the production of SuOME. The reaction procedure involves 1000 gm of Simarouba oil, 230 gm of methanol, and 8 gm of potassium hydroxide pellets mixed vigorously by starrier by maintaining a temperature of 60 • C (±2 • C) for 60 min to produce SuOME. The mixture was then transferred to a conical funnel and allowed overnight to separate the ester and glycerol by gravity. Next, glycerol, salt, and methanol were removed from the conical flask, and the esters were mixed with 250 gm of hot water and allowed to settle for 2 h. This assisted in separating the residual FFA and catalyst [51][52][53][54]. To remove the moisture content from the SuOME, silica gel crystals were added, and the ester was heated at 110 • C for 2 h. The properties of SuOME and the percentage of different fatty acids have been determined at the Bangalore test house, Bangalore, and shown in Tables 2 and 3, respectively. All experiments were carried with 100% pure SuOME, and the results were compared with diesel results.

Experimental Procedure
The experimental test rig and the injector patterns used in the present study are depicted in Figure 2a,b, respectively. All the experiments were carried out on 4-stroke single-cylinder Kirloskar to make a direct injection water-cooled CI engine capacity of 5.2 kW at 1500 rpm. The manufacturer specified that the injection pressure is 205 bar with a 3-hole injector with a 0.3 mm diameter for diesel fuel. All the experiments were carried at 1500 rpm, which the governor provided with the engine achieved. On the head of the cylinder, a piezoelectric pressure transducer was attached by the manufacturer. Emissions from the engine were measured using a DELTA 1600S (5-gas analyzer) and HARTRIDGE Smoke meter-4 to measure smoke opacity. The technical specification of the engine, 5-gas analyzer, and smoke meters are shown in Table 4.  Type of sensor Piezoelectric 10 Type of gas analyzer DELTA 1600S 11 Gas HC, CO, CO2, O2 and NOX 12 Type of smoke meter HARTRIDGE SMOKEMETER- 4 13 Measuring range opacity 0-100% (a) Line diagram of experimental setup (reproduced with permission from the publisher)

Results
This section presents the outcomes of tests carried out at two different loads (4.16 and 5.2 kW) operating at 1500 rpm for four injection pressures (205, 220, 240, and 260 bar) and nozzle geometry (a three, four, five, and six-hole injector with 0.2, 0.25 and 0.3 mm) on the performance of an engine fueled with SuOME. All the readings recorded from the instruments with the total uncertainty of ±2.3% were calculated based on the square root method.

Effect of Fuel Injector Pressure
Baseline fuel injection pressure was 205 bar for diesel as prescribed by the engine supplier. However, to study the impact of injection pressure on SuOME mode of operation on engine performance, the injection pressure was varied from 205 to 260 bars. An optimum fuel injection pressure was fixed for SuOME for further studies based on the

Results
This section presents the outcomes of tests carried out at two different loads (4.16 and 5.2 kW) operating at 1500 rpm for four injection pressures (205, 220, 240, and 260 bar) and nozzle geometry (a three, four, five, and six-hole injector with 0.2, 0.25 and 0.3 mm) on the performance of an engine fueled with SuOME. All the readings recorded from the instruments with the total uncertainty of ±2.3% were calculated based on the square root method.

Effect of Fuel Injector Pressure
Baseline fuel injection pressure was 205 bar for diesel as prescribed by the engine supplier. However, to study the impact of injection pressure on SuOME mode of operation on engine performance, the injection pressure was varied from 205 to 260 bars. An optimum fuel injection pressure was fixed for SuOME for further studies based on the performance, emission, and combustion parameters. The optimum result was also compared with diesel with a standard manufacturer mode of injection pressure of 205 bar.

Brake Thermal Efficiency
The variation in brake thermal efficiency on a partial and full load for SuOME for different fuel injection pressures is shown in Figure 3. Higher brake thermal efficiency is observed from the engine during an 80% load of full load compared to full load for all the injection pressures and diesel. Based on the results, the highest brake thermal efficiency for SuOME mode of operation is 27.25% at 240 bar. A further increase in injection pressure resulted in a drop in brake thermal efficiency, and this may be attributed to the fact that as the injection pressure increased, the droplet size reduced and hence suffered in penetrating deeper into the combustion chamber [57,58]. However, due to the higher viscosity of SuOME than diesel, reduced BTE was recorded for SuOME. performance, emission, and combustion parameters. The optimum result was also compared with diesel with a standard manufacturer mode of injection pressure of 205 bar.

Brake Thermal Efficiency
The variation in brake thermal efficiency on a partial and full load for SuOME for different fuel injection pressures is shown in Figure 3. Higher brake thermal efficiency is observed from the engine during an 80% load of full load compared to full load for all the injection pressures and diesel. Based on the results, the highest brake thermal efficiency for SuOME mode of operation is 27.25% at 240 bar. A further increase in injection pressure resulted in a drop in brake thermal efficiency, and this may be attributed to the fact that as the injection pressure increased, the droplet size reduced and hence suffered in penetrating deeper into the combustion chamber [57,58]. However, due to the higher viscosity of SuOME than diesel, reduced BTE was recorded for SuOME. The emission of unburnt HC on different power for SuOME is shown in Figure 4a. A noticeable drop has been observed at 240 bar injection using a standard injector because of enhanced atomization of SuOME and better combustion for injected fuel. Ignition delay viz., the physical delay also reduced due to an increase in injection pressure. HC was reduced by 47 to 41 ppm by increasing the injection pressure from 205 to 240 bar at a 4.16 kW load. Increasing the injection pressure further, the HC level raised to 42 ppm. This may be due to a top portion of the injected fuel burning in the combustion diffusion phase based on a smaller fuel spray and reduced ignition delay. Hence, it can be concluded that HC emissions are less at 240 bar operation with a three-hole injector, and this is due to superb atomization and increased combustion of SuOME rather than other injection pressure. The emission of unburnt HC on different power for SuOME is shown in Figure 4a. A noticeable drop has been observed at 240 bar injection using a standard injector because of enhanced atomization of SuOME and better combustion for injected fuel. Ignition delay viz., the physical delay also reduced due to an increase in injection pressure. HC was reduced by 47 to 41 ppm by increasing the injection pressure from 205 to 240 bar at a 4.16 kW load. Increasing the injection pressure further, the HC level raised to 42 ppm. This may be due to a top portion of the injected fuel burning in the combustion diffusion phase based on a smaller fuel spray and reduced ignition delay. Hence, it can be concluded that HC emissions are less at 240 bar operation with a three-hole injector, and this is due to superb atomization and increased combustion of SuOME rather than other injection pressure.   Figure 4b shows CO emissions for a partial and full load for SuOME and diesel. CO emissions were also raised as the load increased, which could be incomplete combustion at full load. Both CO and HC emissions followed similar trends with reduced CO emissions at 240 bar of fuel injection than 205 bar for SuOME. CO emission at 240 bar injection pressure was 0.14% at 4.16 kW. However, CO emissions for diesel were further lesser than SuOME at 240 bar injection pressure. This may be due to the complete combustion of diesel because it has a more volatile nature than SuOME [27]. Figure 4c shows how injection pressure on smoke opacity with BP operated, using diesel and SuOME. Smoke levels were observed to fall with increased IOP compared to the standard injector opening pressure for SuOME. This trend may be attributed to improved air-fuel mixture resulting from higher atomization of SuOME. The lowest smoke level of 49 HSU has been observed at an IOP of 240 bar at 80% load. With a further increase in the IOP to 260 bar, the fuel tended to suffer in finding the fresh air for combustion [16]. Smoke opacity for IP of 205, 220, 240, and 260 bar were 58, 54, 49, and 51  Figure 4b shows CO emissions for a partial and full load for SuOME and diesel. CO emissions were also raised as the load increased, which could be incomplete combustion at full load. Both CO and HC emissions followed similar trends with reduced CO emissions at 240 bar of fuel injection than 205 bar for SuOME. CO emission at 240 bar injection pressure was 0.14% at 4.16 kW. However, CO emissions for diesel were further lesser than SuOME at 240 bar injection pressure. This may be due to the complete combustion of diesel because it has a more volatile nature than SuOME [27]. Figure 4c shows how injection pressure on smoke opacity with BP operated, using diesel and SuOME. Smoke levels were observed to fall with increased IOP compared to the standard injector opening pressure for SuOME. This trend may be attributed to improved air-fuel mixture resulting from higher atomization of SuOME. The lowest smoke level of 49 HSU has been observed at an IOP of 240 bar at 80% load. With a further increase in the IOP to 260 bar, the fuel tended to suffer in finding the fresh air for combustion [16]. Smoke opacity for IP of 205, 220, 240, and 260 bar were 58, 54, 49, and 51 HSU, respectively, for 80% load operated using SuOME. However, the smoke opacity for diesel was 43 HSU and was lesser than SuOME due to the fuel's complete reaction.

Nitrogen Oxide
The emission of NO x for 80 and 100% load for SuOME fuel and diesel is shown in Figure 4d. The figure shows that NO x emission was uppermost at 220 bar injection pressure; the possible reason is the optimum oxygen content supply. The NO x emission decreased with an increase in injection pressure. The highest and lowest NO x emission ranged from 1080 and 960 ppm, respectively. At 4.16 kW, the NO x emission was 0.094, 0.091, 0.087, 0.089, and 0.068 g/kWh, and the corresponding injection pressure 205, 220, 240, 260 bar for SuOME and 205 bar for diesel.

Influence of Number of Injector Holes and Their Orifice Diameter
This section shows the effect of different numbers of injector holes and their orifice diameter on the performance of SuOME fueled engines. To study the effect of the number of injector holes, a three, four, five, and six-hole injector was used, and based on the results, a six-hole injector was optimized. A six-hole injector was used with a varied orifice diameter of 0.3, 0.25, and 0.2 mm to study the effect of the nozzle orifice diameter.

Brake Thermal Efficiency
The variation of BTE for SuOME injected with three, four, five and six-hole injectors of orifice diameter 0.3 mm is shown in Figure 5a. Figure 5b shows the variation of BTE of six-hole injectors having an orifice diameter of 0.3, 0.25, and 0.2 mm. As the number of holes increases, the amount of high viscous fuel injected will increase. Hence a 3.2% increase in BTE with a six-hole injector has been recorded compared to the three-hole injector, which operated at 240 bar of injection pressure with SuOME. On the other side, as the orifice size reduced from 0.3 to 0.2 mm, enhanced fuel-air mixture formation occurred inside the CC, which tends to increase the combustion rate and hence, there was a higher BTE [20,59]. However, increasing the number of orifice holes to more than six is practically impossible, and reducing the orifice diameter to less than 0.2 mm nullified the above effect as the injected fuel moves much faster than air. This tends to reduce mixture formation and results in a reduction in engine performance [58,60,61]. HSU, respectively, for 80% load operated using SuOME. However, the smoke opacity for diesel was 43 HSU and was lesser than SuOME due to the fuel's complete reaction.

Nitrogen Oxide
The emission of NOx for 80 and 100% load for SuOME fuel and diesel is shown in Figure 4d. The figure shows that NOx emission was uppermost at 220 bar injection pressure; the possible reason is the optimum oxygen content supply. The NOx emission decreased with an increase in injection pressure. The highest and lowest NOx emission ranged from 1080 and 960 ppm, respectively. At 4.16 kW, the NOx emission was 0.094, 0.091, 0.087, 0.089, and 0.068 g/kWh, and the corresponding injection pressure 205, 220, 240, 260 bar for SuOME and 205 bar for diesel.

Influence of Number of Injector Holes and Their Orifice Diameter
This section shows the effect of different numbers of injector holes and their orifice diameter on the performance of SuOME fueled engines. To study the effect of the number of injector holes, a three, four, five, and six-hole injector was used, and based on the results, a six-hole injector was optimized. A six-hole injector was used with a varied orifice diameter of 0.3, 0.25, and 0.2 mm to study the effect of the nozzle orifice diameter.

Brake Thermal Efficiency
The variation of BTE for SuOME injected with three, four, five and six-hole injectors of orifice diameter 0.3 mm is shown in Figure 5a. Figure 5b shows the variation of BTE of six-hole injectors having an orifice diameter of 0.3, 0.25, and 0.2 mm. As the number of holes increases, the amount of high viscous fuel injected will increase. Hence a 3.2% increase in BTE with a six-hole injector has been recorded compared to the three-hole injector, which operated at 240 bar of injection pressure with SuOME. On the other side, as the orifice size reduced from 0.3 to 0.2 mm, enhanced fuel-air mixture formation occurred inside the CC, which tends to increase the combustion rate and hence, there was a higher BTE [20,59]. However, increasing the number of orifice holes to more than six is practically impossible, and reducing the orifice diameter to less than 0.2 mm nullified the above effect as the injected fuel moves much faster than air. This tends to reduce mixture formation and results in a reduction in engine performance [58,60,61].

Unburnt Hydrocarbon and Carbon Monoxide Emissions
Variation of HC and CO emissions for SuOME fuel injected with three, four, five, and six holes with an orifice diameter of 0.3 mm and the effect of injector orifice diameter for six-hole injectors is shown in Figure 6a,b and Figure 6c,d, respectively. HC and CO emissions from six-hole injectors for SuOME are 38 ppm and 0.121%, whereas HC and CO emissions from three-hole injectors for SuOME fuel are 42 ppm and 0.142%. Based on the emissions of HC and CO, a six-hole injector was used for further studying the effect of the orifice hole diameter. HC and CO emissions from the 0.3, 0.25, and 0.2 mm orifice diameters were 38, 37, and 36 ppm and 0.121, 0.111, and 0.09%, respectively. For the same power to develop, more SuOME needed to be injected, and hence higher HC and CO were observed than diesel. However, larger hole diameters tended to deposit injected fuel onto the walls of the combustion chambers [27,46]. Hence HC and CO were greater with a standard injector.

Smoke Opacity
The influence of the number of injector holes on smoke opacity is shown in Figure 6e. As the number of holes increases in the injector nozzle, the smoke opacity of SuOME operated engine reduces. Smoke opacity for SuOME mode of operation using three, four, five, and six-hole injectors with 0.3 mm diameter was 51, 51, 50, and 49.5, respectively. This may be attributed to the fact that holes directly affect increased the fuel-air mixture formation and reduced smoke [62,63]. Higher smoke emission was observed with three, four, and five-hole nozzles due to the improper fuel-air mixture. Another reason for the reduced smoke emissions may be due to the higher BTE [36].
The influence of injector orifice diameter on smoke opacity for SuOME fueled CI engine is presented in Figure 6f. Compared to the six-hole with an 0.3 mm orifice diameter, smoke opacity from an 0.2 mm diameter showed reduced smoke opacity. By reducing the injector orifice diameter from 0.3 to 0.2 mm diameter, smoke emission was reduced by 10%. This may be attributed to the fact that as the orifice's diameter reduced the atomization of fuel, a more delicate spray of highly viscous SuOME resulted in nearly complete combustion of supplied fuel, with higher BTE and reduced smoke opacity [2].

Unburnt Hydrocarbon and Carbon Monoxide Emissions
Variation of HC and CO emissions for SuOME fuel injected with three, four, five, and six holes with an orifice diameter of 0.3 mm and the effect of injector orifice diameter for six-hole injectors is shown in Figure 6a,b and Figure 6c,d, respectively. HC and CO emissions from six-hole injectors for SuOME are 38 ppm and 0.121%, whereas HC and CO emissions from three-hole injectors for SuOME fuel are 42 ppm and 0.142%. Based on the emissions of HC and CO, a six-hole injector was used for further studying the effect of the orifice hole diameter. HC and CO emissions from the 0.3, 0.25, and 0.2 mm orifice diameters were 38, 37, and 36 ppm and 0.121, 0.111, and 0.09%, respectively. For the same power to develop, more SuOME needed to be injected, and hence higher HC and CO were observed than diesel. However, larger hole diameters tended to deposit injected fuel onto the walls of the combustion chambers [27,46]. Hence HC and CO were greater with a standard injector.

Smoke Opacity
The influence of the number of injector holes on smoke opacity is shown in Figure  6e. As the number of holes increases in the injector nozzle, the smoke opacity of SuOME operated engine reduces. Smoke opacity for SuOME mode of operation using three, four, five, and six-hole injectors with 0.3 mm diameter was 51, 51, 50, and 49.5, respectively. This may be attributed to the fact that holes directly affect increased the fuel-air mixture formation and reduced smoke [62,63]. Higher smoke emission was observed with three, four, and five-hole nozzles due to the improper fuel-air mixture. Another reason for the reduced smoke emissions may be due to the higher BTE [36].
The influence of injector orifice diameter on smoke opacity for SuOME fueled CI engine is presented in Figure 6f. Compared to the six-hole with an 0.3 mm orifice diameter, smoke opacity from an 0.2 mm diameter showed reduced smoke opacity. By reducing the injector orifice diameter from 0.3 to 0.2 mm diameter, smoke emission was reduced by 10%. This may be attributed to the fact that as the orifice's diameter reduced the atomization of fuel, a more delicate spray of highly viscous SuOME resulted in nearly complete combustion of supplied fuel, with higher BTE and reduced smoke opacity [2].

Nitrogen Oxide
Variations of emissions of oxides of nitrogen with three, four, five, and six-hole injector and six-hole injectors with an orifice diameter of 0.3, 0.25, and 0.2 mm for a SuOME operated engine are shown in Figure 6g,h, respectively. NO x emissions depended on combustion temperature in the adiabatic flam region. Higher NO x was observed with the diesel mode of operation due to the higher combustion temperature of low volatile diesel than SuOME [27]. NO x emission was higher for a six-hole injector with an orifice diameter of 0.2 mm than a three-hole injector with a 0.3 mm orifice diameter by 12 ppm. This increase in NO x for small hole injectors was due to superior combustion and increased heat release rate inside the combustion chamber at premixed combustion [64]. Figure 7a shows the in-cylinder pressure for diesel and SuOME for six-hole injectors with a 0.3, 0.25, and 0.2 mm orifice diameter. The data for cylinder pressures for different crank angles are obtained from an average of 500 cycles for SuOME, diesel fuel only for 80% loading of full load. SuOME with an injector orifice diameter of 0.2 mm showed peak pressure near to the diesel mode of operation. Peak pressure with other injectors recorded reduced in-cylinder peak pressure.

Nitrogen Oxide
Variations of emissions of oxides of nitrogen with three, four, five, and six-hole injector and six-hole injectors with an orifice diameter of 0.3, 0.25, and 0.2 mm for a SuOME operated engine are shown in Figure 6g,h, respectively. NOx emissions depended on combustion temperature in the adiabatic flam region. Higher NOx was observed with the diesel mode of operation due to the higher combustion temperature of low volatile diesel than SuOME [27]. NOx emission was higher for a six-hole injector with an orifice diameter of 0.2 mm than a three-hole injector with a 0.3 mm orifice diameter by 12 ppm. This increase in NOx for small hole injectors was due to superior combustion and increased heat release rate inside the combustion chamber at premixed combustion [64]. Figure 7a shows the in-cylinder pressure for diesel and SuOME for six-hole injectors with a 0.3, 0.25, and 0.2 mm orifice diameter. The data for cylinder pressures for different crank angles are obtained from an average of 500 cycles for SuOME, diesel fuel only for 80% loading of full load. SuOME with an injector orifice diameter of 0.2 mm showed peak pressure near to the diesel mode of operation. Peak pressure with other injectors recorded reduced in-cylinder peak pressure.  The variation of heat release rate with SuOME and diesel fuel for different injectors are shown in Figure 7b. A higher heat release rate was observed from diesel compared to SuOME. This may be attributed to diesel fuel burning in the premixed phase because of the higher volatility of SuOME. A higher performance for diesel was also observed mainly due to this reason. A higher peak was observed for SuOME than diesel under diffusion during the phase [65]. Hence combustion rates were higher during later stages of combustion with SuOME. Hence, it produced increased exhaust emissions and reduced brake thermal efficiency. Due to the later combustion, NOx emissions from SuOME were lower than emissions from diesel [27,33,46].

Conclusions
A detailed experimental study on the viability of SuOME in the CI engine was carried out, and it was observed that the performance and combustion parameters were lesser than diesel. In the present study, an attempt was made to improve the performance of a SuOME operated engine by appropriately adjusting a few engine parameters such as fuel injection pressure and nozzle geometry. Injecting SuOME fuel into the cylinder up to 240 bar from 205 bar showed improved performance with reduced emissions. Further increasing the fuel injection pressure recorded unfavorable results. Further, to improve the SuOME operated engine's efficiency, a four, five, and six-hole injector was used and compared with a standard three-hole injector. Increasing the injector holes up to six holes improved the engine's performance with reduced emissions for SuOME mode.
Further study was also carried out on varying the injector orifice diameter. A further increase in engine combustion was observed by reducing the orifice diameter from 0.3 to 0.2 mm. Finally, to conclude, operating the engine by slightly varying the manufacturer standards settings such as increasing fuel injection pressure and the number of injector holes and reducing the injector orifice diameter, a direct injection CI engine can be operated by SuOME fuel to obtain a considerably increased performance of the engine. In The variation of heat release rate with SuOME and diesel fuel for different injectors are shown in Figure 7b. A higher heat release rate was observed from diesel compared to SuOME. This may be attributed to diesel fuel burning in the premixed phase because of the higher volatility of SuOME. A higher performance for diesel was also observed mainly due to this reason. A higher peak was observed for SuOME than diesel under diffusion during the phase [65]. Hence combustion rates were higher during later stages of combustion with SuOME. Hence, it produced increased exhaust emissions and reduced brake thermal efficiency. Due to the later combustion, NO x emissions from SuOME were lower than emissions from diesel [27,33,46].

Conclusions
A detailed experimental study on the viability of SuOME in the CI engine was carried out, and it was observed that the performance and combustion parameters were lesser than diesel. In the present study, an attempt was made to improve the performance of a SuOME operated engine by appropriately adjusting a few engine parameters such as fuel injection pressure and nozzle geometry. Injecting SuOME fuel into the cylinder up to 240 bar from 205 bar showed improved performance with reduced emissions. Further increasing the fuel injection pressure recorded unfavorable results. Further, to improve the SuOME operated engine's efficiency, a four, five, and six-hole injector was used and compared with a standard three-hole injector. Increasing the injector holes up to six holes improved the engine's performance with reduced emissions for SuOME mode.
Further study was also carried out on varying the injector orifice diameter. A further increase in engine combustion was observed by reducing the orifice diameter from 0.3 to 0.2 mm. Finally, to conclude, operating the engine by slightly varying the manufacturer standards settings such as increasing fuel injection pressure and the number of injector holes and reducing the injector orifice diameter, a direct injection CI engine can be operated by SuOME fuel to obtain a considerably increased performance of the engine. In future studies, the emissions and losses (combustion, exhaust, heat transfer, and pumping), and energy balance should be evaluated to optimize the combustion from emissions, and efficiencies can be carried out. For 240 bar compared to 205 bar of injection pressure (IP) for SuOME, the BTE increased by 2.35%, and smoke opacity reduced 1.45%. For the six-hole fuel injector compared to a three-hole injector, the BTE increased by 3.19%, HC reduced by 9.5%, and CO reduced by 14.7%. At 240 bar IP, for the six-hole injector with a 0.2 mm hole diameter compared to 0.3 mm hole diameter, the BTE increased by 5%, HC reduced by 5.26%, CO reduced by 25.61%, and smoke reduced by 10%, while NO x increased marginally by 0.27%. Hence, the six-hole FI, 240 IP, and 0.2 mm FI diameter holes are suitable for diesel engine operation fueled by Simarouba biodiesel.