The combined effect of split fueling strategy and EGR on the combustion, performance, and emission characteristics of a CRDI biofuel engine

The current research investigates the impact of a split fueling strategy combined with several flow rates of exhaust gas recirculation (EGR) on the combustion and emission characteristics of a diesel engine running on B20 waste cooking oil (WCO) biodiesel. A four‐stroke single‐cylinder common rail direct injection engine was employed for experiments. It operates with a B20 blend of WCO biodiesel at 600 bar pressure for varying pilot fueling conditions of 10%, 20%, and 30%. The B20 blend with 30% pilot fuel injection (B20P30) showed excellent performance and emission characteristics compared with B20 blend with 10% pilot fuel injection (B20P10) and B20 with 20% pilot fuel injection (B20P20). However, B20P30 had greater levels of nitrogen oxide (NOx) emissions than those by diesel. EGR discharge levels in 5% increments, ranging from 0% to 15% were introduced to address this issue. The experimental findings revealed that both cylinder peak pressure and heat release rate showed a reduction when the EGR flow rate was enhanced. The recirculation of exhaust gas into the combustion chamber led to a slight increase in the emission levels of hydrocarbon (HC), carbon monoxide (CO), and smoke, as well as a decrease in carbon dioxide (CO2). Nevertheless, the introduction of EGR significantly decreased NOx emissions by 22.94%, 35.05%, and 47.96% for EGR flow rates of 5%, 10%, and 15%, respectively, when compared with the engine operating without EGR. Overall, the two‐stage fueling strategy, B20P30 blended with 10% EGR corroborated to be beneficial in reducing NOx emissions with minimal performance penalties. Although there was a slight uptick in certain emissions, the overall trade‐off between emission reduction and performance was favorable. The culmination of this study is targeting the objectives of sustainable development goal 7 (clean energy) and goal 13 (climate action) to be achieved by 2030.

fuels, biodiesel has gained significant recognition due to its positive environmental impact.Biodiesel exhibits characteristics such as density and calorific value similar to diesel fuel.It can be employed as a substitute fuel and necessitates the least modifications in an engine.Although organic plant-based edible oils are widely employed for cooking and frying different food products, the practice of reusing these oils at high temperatures can lead to the formation of harmful compounds that pose risks to human health. 2Nevertheless, low-cost feedstock, such as waste cooking oil (WCO), can be a very handy fuel by making biodiesel's price competitive with petroleum diesel fuel.This creates an advantageous opportunity for leveraging WCO as a production feedstock. 3Reusing WCO as biodiesel can significantly reduce the costs associated with waste disposal, oily wastewater treatment, and biodiesel production. 46][7][8] These strategies encompass controlled fueling, fueling pressure, split fueling, geometrically modified combustion chambers, usage of oxygenated fuels, and recirculation of exhaust gas.The use of the split fueling technique in conjunction with exhaust gas recirculation (EGR) has emerged as an innovative and highly effective technique in compression-ignition engines to tackle nitrogen oxides (NO x ) and smoke. 9This cutting-edge approach has proven promising in mitigating the environmental impact of such emissions.Gautam et al. 10 examined the re-use of tailpipe gas combined with multiple fueling techniques in compression ignition (CI) engines using diesel fuel.Several experiments were conducted for pilot fueling rates of 10%, main fueling rates of 90%, EGR flow rates of 5% and 10%, and fueling pressures of 200, 230, 250, 300, and 350 bar.The studies unveiled that the NO x and smoke levels decrease at higher EGR flow rates with split fueling, but there is a marginal penalty in engine thermal efficiency.Roh et al. 11 reported that with an escalating EGR discharge rate, the combustion pressure of the dimethyl ether (DME)-biodiesel blend demonstrates a slight decrease.Implementation of pilot fueling and EGR resulted in a notable dwindles in NO x emissions, though increases in CO and hydrocarbon (HC) emissions.
Jayabal et al. 12 investigated the oxygenated additives (dimethyl carbonate and n-butanol) with sapota methyl ester blends for different EGR discharge rates (5, 10, and 15%) and diesel fueling timing (21⁰, 23⁰, and 25⁰ CA bTDC).EGR discharge rates drastically reduced NO x and smoke pollutants.However, this leads to a lower brake thermal efficiency (BTE) and heat release rate (HRR).Bragadeshwaran et al. 13 investigated the engine characteristics under varying conditions of fueling timing and EGR volume rate using lemon peel oil (LPO) as a biofuel in CI engines.They documented that a 46% alleviation in NO x emission resulted in a higher EGR flow rate.Lower EGR discharge rates marginally lowered the smoke level, whereas higher EGR discharge rates increased the smoke levels.Kulandaivel et al. 14 probed the combined impact of retarded fueling timing and EGR discharge rate using high-density polyethylene (HDPE)oil-diesel blends.Reduction in fueling timing and re-use of tailpipe gas flow levels have lowered BTE and NO x emission levels, though it has led to an increase in smoke emissions.Esakki et al. 15 in their study of the leather industry waste fat biodiesel with varying blend ratios (10, 20, and 30) with EGR flow rates (5%, 10%, and 15%) observed a reduction of 87.59% in NO x emissions in the B30 blend with an EGR 15% rate and smoke opacity increased with escalating EGR levels.Qi et al. 16 evaluated the engine parameters of ternary blends (diesel + palmoil + ethanol) in CI engines and noticed that dual fueling techniques and EGR utilization effectively reduced both NO x and soot emissions while incurring a minor impact on performance.Raja et al. 17 studied the ternary (Prosopis juliflora biodiesel + isopropanol + diesel) blends in conjunction with EGR flow rate (10%, 20%, and 30%) to evaluate the engine characteristics.They revealed that the implementation of a 30% EGR led to significant reductions in both NO x and smoke emissions.These reductions were achieved simultaneously, albeit with a minor trade-off in engine performance.Choi et al. 18 disclosed that increasing the re-use of tailpipe gas rate in the engine had negative consequences on performance, including delayed cylinder pressure and combustion phasing.Additionally, the higher re-use rate of tailpipe gases resulted in a diminishing oxidation rate of particulate matter (PM), resulting in increased PM emissions.Furthermore, the study established an association between NO x and PM emissions, indicating the interconnected nature of these pollutants.
Liang et al. 19 tested the engine parameters of ternary (biodiesel + n-pentanol + diesel) blends on a CI engine.They observed that at moderate EGR rates, double and triple fuels produce marginally higher HC emissions.High EGR rates led to a reduction in NO x and PM simultaneously but an enhancement in CO and HC emissions.Rami Reddy et al. 20 studied the varying fueling timings and EGR flow rates (5% and 10%) of waste mango seed biodiesel.Implementing EGR rates of 5% and 10% at an advanced fueling timing resulted in appreciable reductions in NO x emissions, with a decrease of 48.38% and 54.83%, respectively.However, this reduction in NO x was accompanied by a corresponding increase in smoke emissions, with corresponding values of 38% and 42%, respectively.The initiation of the EGR volume rate involves a trade-off, as it aids in higher HC emissions while simultaneously reducing CO emission levels.Ramalingam et al. 21evaluated the EGR volume rate and dual fuel approach on a premixed charge CI engine using Moringa oleifera methyl ester.With a gradual increase in the EGR rate (from 10% to 30%), a notable decrease in nitric oxide emissions was noticed.Specifically, marginal increases were observed in brake-specific fuel consumption (BSFC), CO, and unburned-HC emissions.Senthil Kumar et al. 22 reviewed the fueling parameters and EGR volume rate on a CI engine using a cashew nut shell biodiesel blend.Studies were conducted using three types of fuel blends: diesel, B5, and B10.These trials involved varying percentages of EGR flow rate (5%, 10%, 15%, 20%) while maintaining a fueling timing of 10.2°bTDC and 15% split volume.A noticeable reduction in BTE and NO x emissions is viewed with a substantial increase in the EGR discharge rate.However, a minor elevation in smoke levels is a trade-off.Dual impact of fueling pressure and EGR volume rate of the Juliflora biodiesel was studied in a CI engine previously. 23It showed that applying EGR rates (10% and 20%) to the B20 blend resulted in a significant diminishment in NO x emissions by 22.32% and 17.71%, respectively, when compared to B20 and diesel fuel.Nevertheless, the implementation of EGR at rates of 10% and 20% led to a minor decline in BTE, cylinder pressure, and HRR.Gowthama et al. 24 tested the application at the start of fueling and EGR (10%, 15%, and 20%) on combi-fuel (isobutanol + diesel and WCO biodiesel) and reported that NO x emissions diminish by prolonging the start of injection (SOI) and augmenting the EGR.The performance of palmyra oil methyl ester (POME) blends was examined. 25These blends consisted of 10%, 20%, and 30% volume fractions.The study focused on varying the EGR volume rates at 6% and 12%.For the compression ratios of 16:1, 18:1, and 20:1conditions, the BTE of 22.89%, 23.41%, and 24.59%, respectively, were obtained.Moreover, for the POME20 blend with a CR 20, the BTE value diminishes at 6% (24.01%) and 12% (22.09%)EGR conditions.Chaitanya et al. 26 investigated the use of 1-pentanol blended (10%, 20%, and 30% by volume) with waste plastic oil in CI engines using recycled exhaust gas rates (10% and 20%).Adoption of EGR up to 20% at 60% engine capacity was found to have significantly mitigated NO x (234 ppm) emissions.Exhaust HC emissions (5.1 ppm) and CO emissions (0.07%) increased marginally.Prasada Rao et al. 27 evaluated the dual outcome of compression ratio and recycling of exhaust gas of palmyra biodiesel blend in CI engine.They manifested that an increment in the compression ratio (18 ̶ 20) led to a dwindling of HC (29.5%) and CO (27.8%) pollutants while augmenting in BTE (7.4%) and NO x (7.9%) compared with a compression ratio of 16.Further addition of EGR downturned the NO x emission (15.1% and 23% for 5% and 10% EGR, respectively) compared with 0% EGR.Su et al. 28 tested the blend (diesel + cyclohexanol) fuels for varying recycled exhaust gas and dual fueling approach.They revealed that emissions of NO x showed a gradual decrease, while the particulate number concentrations increased as the EGR rates were raised for the tested fuels.However, when using a fuel mixture of 80% diesel and 20% biodiesel with an EGR ratio of 8%, both the particulate number and NO x emissions of the diesel engine were reduced effectively, particularly at medium and high loads.Öztürk et al. 29 observed that despite the positive reduction in NO x emissions, the excessive utilization of EGR contributed to a notable escalation in smoke and CO emissions.
Many researchers investigated the impact of two-stage fueling in a common rail direct injection (CRDI) engine and reported engine characteristics.The study related to the combined influence of two-stage fuel injection and EGR on a CRDI engine fueled with WCO biodiesel is scanty.The current study aimed to evaluate the effect of two-stage fueling technique with EGR rates in CRDI engines using a WCO B20 blend at a nozzle fueling pressure of 600 bar.The pilot fueling timing was kept at 33°bTDC, and the standard main fueling timing was maintained at 23°bTDC.The initial tests were conducted to consider the optimum pilot fueling quantity of the B20 blend of WCO biodiesel at 600 bar (B20P10, B20P20, B20P30) and under varying load conditions ranging from 0% to 100% with a 25% interval at a steady speed of 1500 rpm.Table 1 shows results along with other pilot-fueling quantities; it is evident that B20P30 yielded excellent performance and emissions.Thus, the present study relies on the B20 blend with 30% pilot fueling at 600 bar with EGR rate variations (5%, 10%, and 15%).All the test findings of WCO B20 under the combined impact of the split fueling approach and EGR rate were correlated with diesel mineral fuel at 10% pilot fueling and B20 with 30% pilot fuel injection (B20P30) without EGR.

| Fuel preparation and properties
Procurement of the WCO biodiesel is sourced from the nearby bio-energy development park, Nitte.WCO was acquired from hotels, restaurants, and food processing facilities.To eliminate the moisture content, the oil is heated to 100°C after being further treated and filtered to remove any leftover food particles.The utilization of single-step transesterification was employed due to the low concentration of free fatty acid content.During the transesterification process, the reaction temperature is carefully maintained at 63°C, while the presence of a NaOH catalyst and a mixing rate of 2800 rpm are ensured.After the completion of transesterification, both the crude biodiesel and glycerol are separated.The raw biodiesel is next cleaned by washing it in warm water to ensure that all contaminants are removed, and it is dried at 110°C to remove any moisture present.Table 2 shows the physicochemical properties of the fuel.

| Fourier transform infrared spectroscopy (FTIR) analysis
FTIR is an analytical technique used to identify organic and inorganic compounds within a given sample.The FTIR analysis is typically carried out using the Perkin Elmer Spectrum Two instrument.In FTIR, molecules absorb infrared light associated with their molecular bonds.This technique compares the infrared emission from the sample to a reference background spectrum.The ratio between the sample's emitted spectrum and the background spectrum provides the sample's absorption spectrum.Figure 1 indicates the WCO biodiesel's (B100) FTIR spectrum.In FTIR images, a plot of wave number (cm −1 ) against transmittance (%T) reveals absorption regions in the spectrum corresponding to specific molecular bonds in the sample, such as O-H (3000-3700 cm −1 ), C-H (2700-3000 cm −1 ), F I G U R E 1 Fourier transform infrared spectroscopy spectrum of waste cooking oil biodiesel.
C═O (1500-1800 cm −1 ), and C-O (600-1400 cm −1 ).The WCO biodiesel's FTIR spectrum showed the alkane C-H bond stretching vibration is associated with a wave number of 2923 and 2853 cm −1 indicates the presence of CH 2 and CH 3 groups.The C═O bond is associated with a wave number of 1741 cm −1 confirms ester linkage and C-O bond stretching vibration lies on the wave number of 1195.8 cm −1 , due to ester groups.Hence, the inclusion of oxygen in biodiesel exhibits the capacity to augment the efficiency and efficacy of the combustion procedure, leading to a more environmentally friendly consequence. 30The C-H bond bending vibration is associated with a wave number of 1435.9 cm −1 , due to the presence of CH 3 groups.The wave number of 722.4 cm −1 indicates out-ofplane bending of C-H bonds of aliphatic HCs.

| Engine test setup
The experimental test was conducted on a single-cylinder compression-ignition CRDI engine that generates 3.5 kW of rated power at a steady speed of 1500 rpm.The engine test rig was loaded with an eddy-current dynamometer with water cooling.The test setup consists of high-pressure fueling system and a programmable electronic control unit (ECU) for monitoring the fuel timing, quantity, and pressure.A standard burette, a rotameter, and an air-stream sensor were used to determine the flow rates of fuel, cooling water, and air inflow, respectively.Tailpipe emissions and smoke concentrations were determined using Digas 5-Gas Analyzer and a standard Smoke Meter, respectively.Pressure sensing probe transducer and crankshaft position encoder were employed to measure cylinder pressure and crankshaft angle, respectively.The schematic diagram of the research engine is depicted in Figure 2. The details of the engine setup are outlined in Table 3.
To reduce tailpipe NO x emissions from engines, EGR was used.Figure 3A,B show EGR setup.EGR valves were used to adjust the flow rate of EGR at various ratios (i.e., 5%, 10%, and 15%) which are combined with intake air at the entrance manifold.The EGR rate 20 is determined using the following equation:  | 1539 Percentage of EGR = Volume of EGR Total intake air into the cyliner × 100. (1) Table 4 shows the test conditions.To improve the precision of the testing results, an uncertainty inspection was necessary.Table 5 displays the measuring device's accuracy and uncertainty.The overall amount of uncertainty was ±2.19%.Before fuel testing, the diesel engine was allowed to operate for approximately 10 min to burn off any remaining fuel quantity from the preceding test.Once fresh fuel reached a stable state, its measurements were recorded.Individual test trials comprised 25 cycles and the recorded data's mean value was noted.

| RESULTS AND DISCUSSION
To examine the engine characteristics, a detailed investigation was carried out by using a B20 blend of WCO biodiesel fuel.The study encompassed the variation of EGR flow rates in 5% increments, ranging from 0% to 15%.Additionally, a split fueling approach incorporating both pilot and main fueling was implemented.The following section presents a detailed analysis of the performance, combustion behavior, and emission parameters of the CI engine observed throughout the experimental study.

| BTE
Figure 4 shows the results of the EGR flow rate on BTE for B20 blends at 600 bar.It has been noted that without EGR, BTE showed an increase of B20 at 30% pilot fueling quantity at maximum load, which is 1.72% higher than DieselP10.The oxygen concentration in biodiesel blends is the key reason.Dhar et al. obtained similar test results for B10 and B20 Karanja biodiesel blends 31 with a high amount of exhaust gas intake resulting in lower BTE, whereas a low amount of exhaust gas intake exhibiting higher BTE.At 30% pilot fuel quantity, increasing the exhaust gas percentage for B20 blends reduces BTE.At optimum load, values of BTE for B20 blend at 30% pilot fueling quantity for recirculation of exhaust gas of 0%, 5%, 10%, and 15% were 34.90%, 33.18%, 32.46%, and 31.33%,respectively.This shows that the lower BTE is because there is less oxygen in the air due to the exhaust flue gas.Adopting EGR will lower the air-fuel ratio, cylinder pressure, and temperature, causing improper combustion and leading to a reduction in BTE.The addition of EGR raises the specific heat capacity, lowering the BTE.Naresh et al. 32 noticed a similar trend.It is seen that the BTE of B20 with 30% pilot fueling at 15% exhaust gas intake rate was 10.23% lower than 0% EGR.

| BSFC
The influence of EGR flow rate on BSFC for B20 blends at 600 bar is shown in Figure 5.It was observed that BSFC reduces as the load rises for all the fuel samples.At optimum load, the BSFC for DieselP10 was reported as 0.23 kg/kWh, and in B20 blends at 30% pilot fueling quantity with an EGR flow rate of 0% was reported as 0.24 kg/kWh.When correlated to DieselP10, the specific fuel consumption of the B20 blend with a 30% pilot fueling without EGR rose to 4.34%.This signifies that the oxygen-rich biodiesel blend burns completely, resulting in high temperatures.
The low calorific value of the biodiesel blend tends to inject more fuel into the engine to deliver the required power.Susanth et al. 33 showed a similar pattern of declining BSFC as pilot F I G U R E 4 brake thermal efficiency for various exhaust gas recirculation (EGR) flow rates.
fueling for biodiesel blends increased.The experimental results found that the EGR flow rate from 0% to 15% increased the BSFC.At optimum loads, BSFC values for a B20 blend at 30% pilot fueling quantity for recirculation of exhaust gas of 0%, 5%, 10%, and 15% were 0.24, 0.25, 0.26, and 0.28 kg/kWh, respectively.Re-use of exhaust gas, which has a lower oxygen concentration and lower heating value of the biodiesel blend, causes a dilution effect and results in improper combustion. 32A maximal BSFC of 0.28 kg/kWh and a minimal BSFC of 0.24 kg/kWh were achieved for B20P30@15% EGR and B20P30@0% EGR, respectively.

| In-cylinder pressure
Figure 6 indicates the effect of the EGR rate on engine cylinder gas pressure for B20 blends at 600 bar.At peak load, the maximum in-cylinder for DieselP10 and B20P30M70 without EGR was 68.86 and 71.89 bar, respectively.This shows that the maximum cylinder gas pressure for the B20 blend with a 30% pilot fueling quantity is 4.40% higher than for diesel fuel, with a 10% pilot fueling quantity at 0% EGR.Pilot fueling accelerates early combustion and minimizes the delay period for ignition, which aids in escalating the cylinder pressure and ensures complete combustion. 34Bhowmick et al. 35 observed similar trends.With an increment in EGR flow rate, it was noted that cylinder pressure decreased.At optimum loads, the maximum cylinder gas pressure for a B20 blend at 30% pilot fueling quantity for recirculation of exhaust gas of 5%, 10%, and 15% were 70.42, 69.82, and 67.47 bar, respectively.
Furthermore, the gas peak pressure for all the samples of test fuel was obtained at 5°aTDC.The experimental outcomes indicate that the maximum cylinder gas pressure for EGR flow rates of 5%, 10%, and 15% was reduced by 2.04%, 2.88%, and 6.14%, respectively, compared with 0% EGR.The addition of tailpipe flue gases to the combustion chamber reduces the volume of oxygen in the chamber, which makes the partial burning process and lowers the pressure and temperature of the combustion.Also, addition of EGR increases the specific heat capacity of the intake exhaust gas while decreasing gas peak pressure. 36I G U R E 5 Brake-specific fuel consumption for various exhaust gas recirculation (EGR) flow rates.
The rate of heat release is an essential parameter in combustion analysis in a split fueling approach with engine exhaust flue gas recirculation.Figure 7 indicates the effect of the EGR flow rate on NHRR for B20 blends at 600 bar.Pilot fueling has been shown to F I G U R E 6 In-cylinder pressure for various exhaust gas recirculation (EGR) flow rates.
F I G U R E 7 Net heat release rate for various exhaust gas recirculation (EGR) flow rates.enhance the HRR.At peak load, the highest HRR for DieselP10 and B20P30 without EGR was 72.45 and 75.23 J/°CA, respectively.For DieselP10 and B20P30M70 with 0% EGR, the maximum NHRR occurred at 8°bTDC, and 7°bTDC, respectively.Because of the pilot fueling strategy and immanent oxygen concentration in biodiesel, the ignition delay period is reduced, resulting in complete combustion and a greater amount of heat release during combustion. 34t optimum load, the maximum net HRR for a B20 blend at 30% pilot fueling quantity for recirculation of exhaust gas of 5%, 10%, and 15% were 74.10, 73.24, and 73.17 J/°CA.In contrast to the B20 blend at 0% EGR, the introduction of exhaust flue gases diminished the NHRR for EGR percentage rates of 5%, 10%, and 15% by 1.50%, 2.64%, and 2.74%, respectively.Re-use of exhaust flue gases with incoming fresh air lowers the oxygen content, resulting in incomplete combustion.Because of incomplete combustion, both the rate of combustion and the rate at which heat is released are low, this result corroborates previous findings. 10,375 | Cumulative heat release rate (CHRR) Figure 8 shows the impact of the EGR flow rate on CHRR for B20 blends at 600 bar.Without EGR, the cumulative HRRs for DieselP10 and B20P30 at peak load were 1.29 and 1.37 kJ, respectively.When compared to DieselP10, B20P30 is seen to produce a 6.2% greater CHRR value.The pilot fueling approach and immanent oxygen concentration in biodiesel blends reduce the ignition delay, resulting in complete combustion and an increase in HRR.34 At optimum load, the CHRR for a B20 blend at 30% pilot fueling quantity for recirculation of exhaust gas of 5%, 10%, and 15% was 1.34, 1.23, and 1.17 kJ, respectively.As the EGR discharge rate rises, the CHRR declines drastically for B20 at 30% pilot injection.Low oxygen content in the combustion chamber leads to incomplete combustion, which reduces the combustion temperature and heat release rate.33 F I G U R E 8 Cumulative heat release rate for various exhaust gas recirculation (EGR) flow rates.
The term "period of ignition delay" (PID) pertains to the time interval that arises between the initiation of fuel injection and the commencement of combustion.PID is an important parameter, which affects the efficiency of combustion engine.The length of the ignition delay period depends on parameters such as fuel composition, temperature, engine speed, compression ratio, and engine load.
Figure 9 illustrates the impact of EGR flow rate on the PID for B20 blends at 600 bar, in relation to the fluctuation in load conditions.In the absence of EGR, the ignition delay periods for DieselP10 and B20P30 fuels under peak load conditions were measured to be 12.02°CA and 11°CA, respectively.Whereas in DieselP10, it is seen that the injected fuel quantity at the pilot fueling timing is relatively small, resulting in an inadequate air-fuel mixture strength that is insufficient to initiate the burning process.The accumulation of the flammable mixture within the engine cylinder leads to boosts in the delay period following the main fueling timing.Also, it has been noted in the B20 blend, 30% pilot fueling and without the incorporation of EGR, that the combustion resulting from pilot fueling has a significant impact on the subsequent combustion of the main fueling.This impact ultimately leads to a decline in the overall ignition delay.The ignition delay duration for a B20 blend with a pilot fueling amount of 30% and EGR rates of 5%, 10%, and 15% were found to be 12.2°CA, 12.6°CA, and 12.8°CA, respectively.The introduction of exhaust gas into the cylinder displaces fresh air, leading to a gradual reduction in oxygen levels.This loss in oxygen directly hampers the main combustion process, ultimately causing an elevation in the period of ignition delay.The aforementioned phenomenon is the result of the absorption of thermal energy by massic thermal capacity of exhaust gas present within the engine cylinder.Consequently, this leads to a subsequent prolongation in the achievement of the self-ignition temperature by the particles constituting the fuel charge.The results are consistent with the previous research. 38I G U R E 9 Period of ignition delay for various exhaust gas recirculation (EGR) flow rates.
Figure 10 indicates the impacts of the EGR rate on CD for B20 blends at 600 bar with respect to the variation in load conditions.CD refers to the time period required for the mixture of air and fuel to undergo complete burning within the cylinder of the engine during the combustion stroke.The burning time for DieselP10 and B20P30 fuels at peak load conditions was measured to be 68°CA and 64°CA, respectively, in the absence of EGR.This has been noticed that in the B20 blend, which has 30% pilot fuel and no EGR, the initial ignition of the pilot fuel will produce heat, which in turn speeds up the vaporization of the main fuel, resulting in a shorter CD. 39 It is noted that there is a gradual augmentation in the duration of combustion as the load is increased.The observed phenomena can be ascribed to the presence of delayed ignition.The findings revealed the length of combustion for a B20 blend with a pilot fueling proportion of 30% and varying rates of EGR (EGR) at 5%, 10%, and 15%.The observed CDs were 66°CA, 67°C A, and 68°CA, respectively.It is evident that the increments in the quantity of EGR flow rates lead to prolonging the CD owing to the elongation of the ignition delay intervals.The main reason for the slower flame speed and longer combustion time is the lower oxygen concentration and the intake dilution effect resulting from EGR.

| Volumetric efficiency
Volumetric efficiency is a critical parameter in diesel engines as it directly impacts the engine's performance and efficiency.Several factors can influence the volumetric efficiency of a diesel engine, including valve timing, intake valve closure timing, compression ratio, fuel type, and engine speed.
The influence of the EGR flow rate on volumetric efficiency is shown in Figure 11.From the graph, the volumetric efficiency of a B20 blend with a pilot fueling proportion of 30% and F I G U R E 10 Combustion duration for various exhaust gas recirculation (EGR) flow rates.
varying EGR rates of 0%, 5%, 10%, and 15% is 71%, 68.1%, 66.07%, and 62.7%, respectively.It is evident that the augmentation of the EGR flow rate steers to a decline in volumetric efficiency.The incorporation of EGR causes de-escalations in the intake air mass flow, consequently resulting in a decrease in volumetric efficiency.The results obtained are consistent with previous findings documented. 40

| HC
The influence of the EGR rate on cylinder gas pressure for B20 blends at 600 bars is shown in Figure 12.Without EGR, the HC emissions for DieselP10 and B20P30 at peak load were 30 and 25 ppm, respectively.When compared to DieselP10, the B20 blend at 30% pilot fueling quantity is estimated to have 16% reduced HC emissions.This demonstrates that the inherent oxygen content in biodiesel and the pilot fueling technique enhance combustion temperature, which fosters the main fueling vaporization and results in efficient combustion. 41At maximum load, the HC emissions for a B20 blend with a 30% pilot fueling amount were 27, 28, and 29 ppm for engine flue gas recirculation rates of 5%, 10%, and 15%, respectively.HC emissions for B20 blend at a pilot fueling quantity of 30% at different EGR flow rates of 5%, 10%, and 15% are reduced by 8%, 12%, and 16%, respectively, compared with 0% EGR.This demonstrates that an increase in the EGR discharge rate marginally increases the release of HCs.The main reasons are lower oxygen content and a longer ignition delay.HC emissions occur as a result of low combustion rates. 42

| Carbon monoxide (CO)
Figure 13 represents the impact of the EGR rate on CO emission for B20 blends at 600 bar.The CO emissions for DieselP10 and B20P30 at peak load were 0.38% vol.and 0.30% vol., respectively, without EGR.CO emissions rise slightly at lower loads.This is primarily caused by a lower conversion of CO into carbon dioxide.With an increase in load conditions, CO levels decrease due to the availability of O 2 gas and high combustion temperatures.At peak load, CO levels rise as a result of a reduction in resident time, which shortens the time needed for CO to oxidize. 43At maximum load, a B20 blend at 30% pilot fueling generates carbon monoxide emissions of 0.32%, 0.34%, and 0.36% for engine flue gas recirculation rates of 5%, 10%, and 15%, respectively.Carbon monoxide emissions for B20 blend at pilot fueling quantity of 30% at different EGR flow rates of 5%, 10%, and 15% are increased by 8.6%, 13.3%, and 20%, respectively, compared with 0% EGR.The formation of carbon monoxide relies on the oxygen content, air-fuel ratio, and combustion temperature.Low O 2 content accelerates the formation of carbon monoxide.The thermal atmosphere inside the cylinder is amply reduced by the implementation of EGR due to the reduced supply of oxygen in the combustion chamber.A high rate of exhaust gas intake into the cylinder lowers the combustion rate, causing lower thermal combustion, which results in high levels of CO emissions. 4411 | Nitrogen oxide (NO x ) Figure 14 demonstrates the impact of the EGR rate on NO x emission for B20 blends at 600 bar.Without EGR, the NO x emissions for DieselP10 and B20P30 at peak load were 1322 and 1643 ppm, respectively.When compared to a diesel with a 10% pilot fueling quantity, it has been found that a B20 blend at 30% pilot fueling quantity emits more NO x emissions.Combustion temperature witnesses a rise mainly because of the inbuilt oxygen content of the B20 blend and increased fuel consumption.35 The formation of nitrogen oxides occurs mainly at high cylinder temperatures.45 For recirculation of exhaust gas rates of 5%, 10%, and 15%, the nitrogen oxide emissions for a B20 blend at 30% pilot fueling quantity were 1266 ppm, 1067, and 855 ppm, respectively, at maximum load.NO x emissions are observed to decrease as exhaust flue gas rates increase.Exhaust flue gases replace fresh intake air in the combustion chamber and lower the oxygen content, which degrades the thermal atmosphere in the chamber.Because of an endothermic process, the dissociation of H 2 O and CO 2 lowers the combustion temperature.Low combustion temperatures favor low emissions of NO x .36 Higher EGR flow rates of 5%, 10%, and 15% reduce nitrogen oxide emissions by 22%, 35%, and 47.9%, respectively, compared with B20P30 at 0% EGR.
F I G U R E 14 Nitrogen oxide (NO x ) emission for various exhaust gas recirculation (EGR) flow rates.
The significance of the EGR rate on smoke opacity for B20 blends at 600 bar is presented in Figure 15.At peak load, the smoke opacity for DieselP10 and B20P30 without EGR was 43.8% and 29.3%, respectively.Further, as engine load increases, smoke opacity also rises.It is also observed that smoke opacity increases with a rise in engine load.The pilot fueling method and the biodiesel's immanent oxygen content contribute to raising the combustion temperature.Higher combustion temperature lowers the smoke opacity emissions. 46The opacity of smoke increases as the load increases; it occurs primarily due to the engine maintaining its output and thus requiring more fuel to be injected.
For recirculation of exhaust gas flow rates of 5%, 10%, and 15%, the smoke opacity for a B20 blend at 30% pilot fueling quantity was 31.8%,33.3%, and 34.1%, respectively, at maximum load.The higher EGR flow rates of 5%, 10%, and 15% increased the smoke opacity by 8.53%, 13.65%, and 16.38%, respectively, compared to B20P30 at 0% EGR.The introduction of tailpipe flue gas into the combustion chamber by replacing the fresh air results in a lower amount of oxygen content and an increased equivalence ratio, which tends to lead to improper combustion.Improper combustion diminishes the combustion temperature, resulting in higher smoke opacity. 15

| Carbon dioxide (CO 2 )
During the combustion process, elevated temperatures in conjunction with the presence of oxygen precipitate the transformation of CO into CO 2 emissions within engines.Figure 16 indicates the impact of the EGR flow rate on carbon dioxide for B20 blends at 600 bar with variations in load conditions.It can be noticed from the illustration that as the load escalates, F I G U R E 15 Smoke opacity for various exhaust gas recirculation (EGR) flow rates.
the CO 2 emissions rise proportionally and are observed to occur at their peak in the scenario of full load for all the test fuel specimens.This occurrence can be ascribed to the reality that as engine load amplifies, a larger quantity of fuel is introduced into the engine cylinders, thereby leading to an escalation in in-cylinder temperature that facilitates the achievement of complete combustion.The CO 2 emissions for DieselP10 and B20P30 at peak load were 4.9% vol.and 6.9% vol., respectively, without EGR.The functioning of recirculation of exhaust gas involves the replacement of fresh air with the by-products of burnt gas.Consequently, this leads to a dilution effect, which is a phenomenon characterized by the influence of thermal and chemical that governs the ignition timing and regulates the rate of the combustion reaction.On the other hand, when the flow rates of EGR at 5%, 10%, and 15% are introduced for B20 blend with a pilot fueling quantity of 30% experiences a reduction in CO 2 emissions of 11.6%, 15.94%, and 24.6%, respectively, without EGR.The decline in CO 2 emissions from incomplete combustion is likely due to advancements in the EGR flow rate.Inevitably, there is less available oxygen, which increases the dilution effect.Previously documented findings exhibited a correlation with the outcomes obtained. 35,38

| CONCLUSIONS
In the current study, the effect of the pilot fueling approach and EGR was used to study the characteristics of WCO B20 in the CRDI engine.The fueling pressure is kept constant at 600 bar for all fuel trails, with a 30% pilot fueling and an EGR flow rate of 0%-15% in 5% increments.The following are the key findings: 1.Among the fuel variants tested, the B20P30 without EGR demonstrated a significant increase in BTE and a corresponding decrease in BSFC.The augmentation of recycled exhaust gas flow resulted in a decrease in BTE.Additionally, it was observed that higher EGR flow rates were linked to intensifying in BSFC across a range of fuel trials.2. The B20P30 fuel trial without EGR demonstrates an exacerbation in the in-cylinder pressure, net HRR, and CHRR.The utilization of EGR resulted in a reduction in in-cylinder pressure, HRR, and CHRR values in comparison to the B20P30 without EGR.This decline can be attributed to the air dilution effect caused by EGR. 3. It was found that adding recirculation exhaust gas flow rate decreased volumetric efficiency and increased both ignition delay time and combustion duration compared with the B20P30 fuel blend without EGR.4. By implementing split fueling approaches with a WCO B20 blend, notable reductions in HC, smoke, and CO emissions can be achieved in relation to the utilization of baseline diesel fuel at 10% pilot fueling quantity.It was discerned that the NO x emissions resulting from the split fueling strategies consistently exceed those observed with baseline diesel fuel at 10% pilot fueling. 5. Utilizing a B20 blend with a 30% pilot fueling method results in a substantial increase of 24.28% in the NO x compared with the standard diesel baseline.The application of EGR flow rates at 5%, 10%, and 15% resulted in reductions of NO x emissions by 22.94%, 35.05%, and 47.96% respectively, in comparison to the B20P30 without EGR.The recorded minimum NO x emission was 855 ppm, achieved with an EGR flow rate set at 15%.In contrast, the addition of recycled exhaust gas increases the level of HC, smoke, and CO emissions in comparison to diesel fuel.
Overall, it can be concluded that B20 with a 30% pilot fueling quantity accompanied by a 10% EGR flow rate and utilizing a waste biodiesel blend, can be directly employed in a CRDI diesel engine without requiring significant modifications.This dual approach ensures favorable performance and combustion characteristics comparable to those in diesel fuel.The outcome of the current study is targeting to address the twin issues such as the energy crisis and environmental pollution.This study also presents a constructive perspective on accomplishing the goals outlined in the United Nations' sustainable development agenda for attainment by the year 2030.
Utilizing a split fueling strategy in conjunction with EGR can effectively manage NO x emissions during the use of WCO biodiesel.Future research work can be carried out using WCO blends through the implementation of postfueling techniques and increased fuel pressure for mitigating smoke pollutants.

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I G U R E 11 Volumetric efficiency for various exhaust gas recirculation (EGR) flow rates.

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I G U R E 12 Hydrocarbon emission for various exhaust gas recirculation (EGR) flow rates.F I G U R E 13 Carbon monoxide (CO) emission for various exhaust gas recirculation (EGR) flow rates.

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I G U R E 16 Carbon dioxide for various exhaust gas recirculation (EGR) flow rates.
Engine parameters for different fuel samples at 600 bar.
Physicochemical properties of mineral diesel and waste cooking oil (WCO) biodiesel.
T A B L E 2 Test conditions.Accuracy and uncertainty of the measuring apparatus.
T A B L E 4 T A B L E 5