Experimental investigation of the combustion characteristics of Mahua oil biodiesel-diesel blend using a DI diesel engine modified with EGR and nozzle hole orifice diameter

Article history: Received 12 June 2018 Received in revised form 10 August 2018 Accepted 12 August 2018 Available online 1 September 2018


Introduction
Growing interests in achieving higher power with better fuel economy at a lesser maintenance cost have been the driving force behind the increasing number of compression ignition (CI) engine vehicles.In line with that, engine manufacturers constantly strive to further develop the CI engine technology to more efficiently meet the above-mentioned objectives.It should be mentioned that among these objectives, reducing exhaust gas emissions in order to meet the increasingly stringent emissions standards/policies is of utmost importance.Therefore, different engine modifications, methods/approaches for exhaust gas after-treatment, and strategies leading to more optimized combustion such as the application of more environmentally-friendly fuels/fuel additives have attracted a great deal of attention (Hussain et al., 2012; Vijay Kumar et al., 2018a).A number of these solutions are discussed herein.

Biodiesel
Biodiesel is defined as the mono-alkyl esters of long chain fatty acids resulting from vegetable oils or animal fats (Venkanna and Reddy, 2009; Vijay Kumar et al., 2017a).The critical properties of biodiesel, such as being nontoxic, high cetane number, oxygen content, absence of sulfur, high inherent lubricity, and being biodegradable, make this alternative fuel an ideal replacement for mineral diesel.Biodiesel can be used in neat form or with diesel at different blending ratios with no or little engine modification.Nevertheless, engine manufacturers recommend biodiesel blending ratios of up to 20% for the existing diesel engines (Mo et al., 2016).
In spite of the above-mentioned advantages, biodiesel is associated with a number of disadvantages as well including lower volumetric energy capacity, lower oxidative stability, inferior cold flow properties, higher kinematic viscosity, and higher NOx emissions (Can et al., 2016).Moreover, the widespread use of edible vegetable oil for biodiesel production has sparked much concern over the growing food vs. fuel competition over food resources/water/land. Additionally, edible oils could be more costly to use as biodiesel feedstock jeopardizing the economic viability of the biodiesel production process.Hence, the application of non-edible oil crops such as Sterculia foetida, Soapnut, Jatropha, Mahua, Pongamia, Polanga, Neem, etc. has been offered to overcome these challenges (Sahoo et al., 2007;Kumar and Sharma, 2011).Table 1 tabulates the estimated oil yields of mahor non-edible oil crops used as biodiesel feedstock.
While the application of many of the non-edible oil crops as biodiesel feedstock is still being assessed, these crops in general offer the following advantages (Atabani et al., 2013): The cultivation of non-edible oil feedstock requires non-agricultural and marginal land with little fertilizer and irrigation requirements.

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Non-edible oil crops can also be grown in semi-arid zones with an annual precipitation of around 200 mm.

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Following oil extraction, the seed cakes can be used as fertilizer for soil improvement and/or biopesticide (Vijay Kumar et al., 2018b).

Biodiesel application without engine modifications
Many research studies have recommended the application of biodiesels produced from different oil feedstock without requiring any engine modifications.For instance, Polanga oil methyl ester (POME) and its blends were combusted at varying loads by Sahoo et al. (2007).The authors claimed more favorable engine performance parameters such as brake thermal efficiency (BTE) and brake specific energy consumption (BSEC) using POME blends compared with neat diesel.They also argued that smoke opacity and hydrocarbon (HC) emissions were decreased in response to POME inclusion while NOx was increased owing to the oxygen content of biodiesel (Sahoo et al., 2007).Similar results were reported by Mofijur et al. (2013) who investigated two blending ration of biodiesel into diesel, i.e., B10 and B20.They indicated that the average BSFC values obtained for B10 (278.46 g/kWh) and B20 (281.9 g/kWh) were higher than that of neat diesel (273.5 g/kWh).
Whereas, compared to neat diesel, B10 and B20 led to lower CO (16% and 25%, respectively) and HC (3.84% and 10.25%, respectively) emissions, but a slightly higher NOx emissions (3% and 6%, respectively (Mofijur et al., 2013).In a different study, Karanja biodiesel and its blends were found compatible with the existing diesel engines (Chauhan et al., 2013).From the unfavorable combustion characteristics point of view, it was found that compared with neat diesel, Karanja biodiesel blends led to 3-5% less BTE, lower in-cylinder pressure, and lower heat release rate (HRR), but increased NOx emissions (Chauhan et al., 2013).Raheman and Phadatare (2004) as well as Agarwal and Dhar (2013) also studied the combustion characteristics of Karanja biodiesel and claimed reductions in emissions, i.e., CO, HC, and smoke.
These findings were in line with those of the other investigations on biodiesel produced from other oil feedstocks such Pongamia Pinnata biodiesel (Sureshkumar et al., 2008), Mahua oil biodiesel (Raheman and Ghadge, 2007;Vijay Kumar et al., 2017b), mango seed oil biodiesel (Vijayaraj and Sathiyagnanam, 2016), palm and Jatropha biodiesel (Rahman et al., 2014), etc.Overall, these studies are unanimous in concluding that biodiesel can be used by up to 20% (i.e., B20) in the existing diesel engines without modifications and that it could lead to reduced emissions (except NOx).

Biodiesel application along engine modifications
Some research works have been focused on investigating the effects of various engine modifications, e.g., compression ratio (CR), injection timing (IT), pressure opening, etc. on diesel engines powered by biodiesel-diesel blends.For instance, Ganapathy et al. (2011) claimed reductions in BSFC as well as HC, CO, and smoke emissions by applying variations in injection timing when using Jatropha biodiesel.They also argued that HRR, pressure, and BTE could be increased while NOx emissions could be reduced through such variations.In a different study, Gnanase Karan et al. (2016) studied the combustion characteristics of a diesel engine running on fish oil biodiesel and its blends at different injection timings, i.e., 21° bTDC, 24° bTDC, and 27° bTDC.They reported shorter ignition delays (ID) and lower HRRs for biodiesel blends.They also argued that through the retardation of IT, a number of emission and combustion parameters including NOx, HC, CO, peak pressure, ID, combustion duration, and HRR were decreased while advancement in IT led to opposite results (Gnanase Karan et al., 2016).
Variations in ignition pressure (IP) has also taken into account by a number of investigations.For instance, Channapattana et al. (2015) and Shehata et al. (2015) studied the effects of varying IPs on the combustion characteristics of Honne biodiesel and corn/soybean biodiesel blends, respectively.These authors concluded increases in NOx emissions and decreases in HC, CO, and smoke opacity in response to increasing IP.In a recent investigation, Dubey and Gupta (2018) took into consideration the effects of increasing compression ratio (CR) (i.e., 15.5:1, 17:1, 18.5:1, and 20:1) on the performance and emissions profile of a dual biofuel (Jatropha biodiesel and turpentine oil).They claimed that at the CR of 20:1, the investigated biofuel led to the most favorable results, i.e., increased BTE by 2.17% as well as decreased CO, HC, NOx emissions, and smoke opacity by 13.04%, 17.5%, 4.21%, and 30.8%, respectively (Dubey and Gupta, 2018).Lower HC and CO emissions were also recorded by Sivaramakrishnan (2018) through optimizing IP at 200 bar and CR at 18:1 when combusting a 25% blend of Karanja biodiesel.Similar results were also reported by Jindal et al. (2010) who claimed that higher CRs and higher IPs improved the engine performance of a diesel engine running on Jatropha biodiesel.

Biodiesel application with after-treatment technologies
Efforts to reduce the NOx emissions associated with the application of biodiesel have been intensified over the last decade.In line with that, selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) have been offered as proven technologies for reducing NOx emissions.For instance, in a study, Hussain et al. (2012) investigated the effect of EGR (10%, 15%, 20% and 25%) on a 3-cylinder, constant speed, and air-cooled CI diesel engine and concluded that at lower loads, higher rates of EGR could be applied without negatively affecting the fuel economy and efficiency, while leading to reduced NOx.Duraisamy et al. (2011) combusted Jatropha biodiesel using EGR and argued that EGR of 15% was optimal in terms performance improvement and reduction in NOx emission.Similar findings verifying the favorable impacts of EGR have also been reported by other studies (Kusaka et al., 2000;Rajan and Senthilkumar, 2009;Bani et al., 2010;Fontana and Galloni, 2010;Mani et al., 2010).These improvements in response to EGR application could be explained by the resultant high intake temperature, which improves flame propagation in the combustion chamber (Sasaki et al., 1998).
In our recently published report, the combination of Mahua oil biodiesel blend (B20) application with engine modification, i.e., the implementation of smaller orifice nozzle hole diameter (NHD), was shown to lead to improved combustion characteristics (Vijay Kumar et al., 2018b).However, the combined strategy also led to NOx augmentation as its only drawback observed.These outcomes could be ascribed to the more efficient atomization of the fuel particles triggered by the smaller orifice NHD and the consequently more effective fuel combustion taking place in the combustion chamber on one hand and the high oxygen content of the fuel blend on the other hand (Vijay Kumar et al., 2018b).In light of that, the present study was set to overcome the shortcoming of the investigated strategy or in better words, to reduce NOx emissions by employing EGR while using Mahua oil biodiesel blend and small orifice NHD.

Biodiesel preparation
Biodiesel was produced as described in our previous report (Vijay Kumar et al., 2018b).Briefly, inedible Mahua oil was transesterified through a two-step procedure.This strategy was employed owing to the high free fatty acids (FFA) of this oil feedstock, i.e., 21%.In the first step, the FFA content was reduced through mixing 0.35 v/v of methanol and 1% v/v of concentrated H2SO4 with the pre-heated Mahua oil at 60 °C for 1 h.Subsequently, the resultant oil was transesterified by using 0.25 v/v of methanol and 0.7% w/v of KOH at 60 °C for 1 h.Following glycerin decantation, crude biodiesel was washed with 50 °C distilled water three times.Finally, anhydrous CaCl2 was added to the resultant product, heated gently at 50 °C while shaken vigorously.Dry purified Mahua oil biodiesel was obtained after CaCl2 separation and blended with diesel to obtain B20 fuel.
Fuel properties of diesel, Mahua oil biodiesel and its 20% blend with diesel (B20) are presented and compared in Table 2.The chemical compositions of diesel and Mahua oil biodiesel are tabulated in Table 3.

Engine modifications with fuel injector nozzle and EGR
First, the injection nozzle system of a diesel engine was modified to smaller orifice diameter in order to improve the performance and to reduce the harmful emissions as reported previously (Vijay Kumar et al., 2018b).Briefly, the reduction of NHD significantly affected the air-fuel mixture formation, atomization, and evaporation leading to improved BTE, BSFC, and HRR and reduced emissions (except NOx) in the investigated CI engine.Subsequently, to overcome the challenge associated with the NHD modification, the coupling of a partially-cooled EGR system to the diesel engine was investigated.
Parametric details of the fuel injection systems used including the differences between the base and modified nozzle orifice diameters are presented in Table 4.For better understanding, cross-sectional views of the nozzle hole geometries are also shown in Figure 1.

Diesel engine setup
A computerized single cylinder diesel engine was employed to study the effects of reduced nozzle orifice diameter and EGR on the combustion (performance and emissions) characteristics of Mahua oil biodiesel blend.The specifications of the engine used is shown in Table 5.The engine was coupled to an eddy current dynamometer for loading the engine.For EGR, appropriate plumbing was done.To maintain the re-circulated exhaust gases partially cool, a water cooler was used while no insulation was considered on the pipeline to allow the escape of the heat.A control valve was installed to regulate the EGR percentage.An EGR mixture chamber was also provided to mix the exhaust gases with fresh air.The flow rate of the intake fresh air was monitored by an orifice meter.A schematic presentation of the engine setup coupled with the EGR system is shown in Figure 2.For EGR setupThe EGR (%) was calculated according to the following equation (Eq.1).

EGR rate (
Where, Qwithout EGR is the airflow rate without EGR, i.e., 26 kg/h and QEGR is the EGR flow rates investigated, i.e., 2.6 kg/h, 5.2 kg/h, and 7.8 kg/h.An AVL gas analyzer was used to measure CO, NOx, and HC.The exhaust gas smoke opacity was measured by an AVL smoke opacity meter.

Measuring devices; ranges, accuracies, and percentage uncertainties
The ranges and accuracies of the measuring devices used in the present investigation are shown in 6.While the percentage uncertainties of   7 and 8, respectively.

Parameter Percentage uncertainties
Brake power ± 0.5 Brake specific fuel consumption ± 1.5 Brake thermal efficiency ± 1.0

Experimental testing procedure
As mentioned earlier (see Section 2.2), the present work was aimed at overcoming the shortcoming observed in our previous investigation using Mahua oil biodiesel blend, i.e., increased NOx emissions in response to reduction in orifice NHD (Vijay Kumar et al., 2018b).More specifically, the two different fuels, i.e., neat diesel and B20 (20% v of Mahua oil biodiesel + 80% v of diesel) were used.Moreover, the base nozzle hole orifice diameter (Ø = 0.280 mm) and modified nozzle hole orifice diameter (Ø = 0.20 mm) were taken into account.Finally, the effect of EGR with three different rates (i.e., 10%, 20%, and 30%) was investigated.Baseline data were obtained by operating the engine at different loads with diesel fuel and base NHD and the experimental data were analyzed and compared with the baseline data.

Brake specific fuel consumption and brake thermal efficiency
The variations in BSFC and BTE vs. full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate are shown in Figure 3.As can be seen, there was a negative correlation between BSFC and BP.It should be noted that BSFC trend generally depends on density, viscosity, calorific value, and chemical composition of a given fuel.As revealed in our previous report, the smaller orifice NHD, i.e., 0.20 mm, led to significantly less BSFC with both diesel and B20 because of the higher mixing rate achieved (Vijay Kumar et al., 2018b).In the present study, BSFC was reduced by implementing the EGR rate of 10% for both B20 and diesel fuel probably due to the returning of HC and that the partially-cooled EGR acted as a pre-heater of the intake mixture.Further increments of EGR rate, i.e., 20% and 30%, resulted in increases in BSFC at both lower and higher loads (Fig. 3) due to the lack of sufficient O2 in the combustion chamber leading to incomplete combustion.
There was a positive correlation between BTE and BP.When combusting neat diesel fuel, BTE was slightly increased by using the 0.20 mm nozzle hole orifice diameter with.While in the case of B20 and the modified orifice diameter, the increases observed in BTE in response to increasing BP were more pronounced.This could be ascribed to the presence of O2 in biodiesel enhancing the combustion process and heat release.On the other hand, the small orifice NHD of 0.20 mm improved fuel vaporization and atomization.Using the modified nozzle orifice diameter and the partiallycooled EGR of 10%, BTE was slightly increased for both B20 and diesel fuel.This could be explained by the re-burning of HC in the combustion chamber with EGR.At high loads, BTE is generally decreased due to introduction of a rich fuel mixture generating higher levels of CO2 and soot which could in turn lead to incomplete combustion.In line with that and as can also be seen in Figure 3, at higher loads and by suing higher EGR rates of 20% and 30%, the re-burning of HC was much significant.Moreover, through the application high EGR rates, the in-cylinder temperature would be reduced and late HRR would occur leading to reduced peak pressure at different loads and consequently decreased BTE.

Maximum in-cylinder pressure
The variations of maximum pressure at different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate are shown in Figure 5.The usage of biodiesel blend and diesel fuel with smaller orifice diameter reduced the ID period and led to increases in the pressure in the combustion chamber.As can be observed as BP was increased, the peak pressure increased as well.Comparing diesel and biodiesel blend at different EGR rates with the modified orifice diameter, it could be concluded that the application of EGR with B20 seemed to be more promising (Fig. 5) probably due to the O2 concentration of the biodiesel-containing blend (Lai et al., 2011).

In-cylinder gas temperature
The variations in the in-cylinder gas temperature with respect to different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate are shown in Figure 6.The in-cylinder gas temperature trend indicated that as the BP was increased, the gas temperature rose as well.Furthermore, the temperature was increased by reducing the orifice diameter using B20.This was ascribed to both the oxygen content of biodiesel (Lai et al., 2011) and the more efficient spraying of the fuel leading to more favorable atomization of the fuel particles and consequently more complete combustion process.When the diesel engine was operated with partially-cooled EGR, the temperature was reduced under all operating conditions.More specifically, there was a negative correlation between the in-cylinder gas temperature and the EGR rates.This could be explained by the decreasing O2 availability and increasing specific heat of intake mixture in response to increasing EGR rates.

Heat release rate
The variations in HRR against crank angle at full load condition for different combinations of nozzle orifice diameter, fuel type, and EGR rate are shown in Figure 7. HRR is mainly dependent on ID, heating value of fuel, and air-fuel mixing.In fact, HRR is used to identify the differences in the combustion rates of fuels, the fraction of fuel burnt in the premixed process, and the SOC.The HRR for B20 with 0.20 mm nozzle orifice diameter was found to be lower with the early SOC (Fig. 7).
As the EGR rate was increased for diesel and B20, the HRR was increased as well due to the late SOC which was caused by the recirculation of CO2, soot, and H2O.Overall, the EGR rate of 10% with B20 seemed to be more promising than the other EGR rates (Fig. 7).868

Combustion parameters analysis 3.2.1. In-cylinder pressure
The variations recorded in in-cylinder pressure against crank angle at full load condition for different combinations of nozzle orifice diameter, fuel type, and EGR rate are shown in Figure 4.The application of biodiesel blend and diesel fuel with smaller orifice diameter reduced the ID period because of the lower heat capacity as well as the increased O2 content and cetane number.The peak pressure was decreased with the application of EGR rates.It should be quoted that EGR is mainly composed of CO2, soot, and H2O resulting in reduced O2 concentration in the combustion chamber.The EGR function and the associated dilution and thermal effects led to slower chemical reactions and consequently, delayed start of combustion (SOC) and lengthier ID period.The latter intensified the premixed combustion phase.The variations in CO emission at different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate are shown in Figure 8. CO is mainly formed due to incomplete combustion.This takes place when there is not enough O2 present to react with fuel.By using the modified 0.20 mm nozzle orifice diameter with B20, CO emissions were reduced due to the better atomization of the fuel.Through the application of the partially-cooled EGR, the CO emissions were increased.More specifically, these increments in CO emissions were proportional with increasing EGR rates.The reason behind increased CO emissions was the low in-cylinder temperature and reduced peak pressure mainly caused by the recirculation of high amounts of unburnt soot, CO2, H2O, as well as O2 deficiency (Duraisamy et al., 2011).

Hydrocarbon
The variations of unburned HC at different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate are shown in Figure 9. HC emissions originate from the presence of too many fuel particles left unburned in the combustion chamber due to incomplete combustion.It also appears in the inner layers during the diffusion flame where there is more fuel than air.As presented, HC emissions were substantially reduced by using the modified orifice diameter with both diesel and B20 fuel (Fig. 9).This was mainly ascribed to the more atomization of the fuel and proper air-fuel mixing in the combustion chamber.When EGR was used in combination with the modified orifice diameter and both B20 and diesel, increases in HC were recorded.At high loads and by suing the EGR rate of 30%, HC emissions were drastically increased due to the reductions in incylinder temperature and pressure reduction.This was because of higher deficiency of O2 leading the rich fuel mixture inside the combustion chamber

Oxides of nitrogen
The variations of NOx at different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate are shown in Figure 10.NOx is generally formed when N2 and O2 react at high temperatures in the combustion process.The NOx emissions measured for the modified orifice diameter stood higher.Using the biodiesel blend, NOx must have been formed mainly in the premixed combustion and in the outer layers of the diffusion flame, where the temperature is high and there is a lot of O2 presents (i.e., the O2 contained in the B20).As shown in Figure 10, the application of the EGR substantially reduced the NOx emissions.This was in line with the findings of the previous studies indicating that increasing EGR rates led to reduced NOx formation (Sasaki et al., 1998;Mani et al., 2010).These results could be ascribed to the effect of EGE in decreasing O2 concentration and flame temperature in the combustible mixture.This was also in line with the results obtained on in-cylinder temperature (Figure 10) implying reduced tepmretures in response to increasing EGR rates.

Smoke opacity
The variations in smoke opacity at different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate are shown in Figure 11.Smoke opacity is measured to quantify the amount of particulate matter (PM) present in the exhaust gas.The modified orifice diameter reduced smoke opacity when combusting both diesel and B20.As the flow rate of EGR into the combustion chamber was increased, smoke opacity also increased.Comparing diesel and B20 at different EGR  (Fontana and Galloni, 2010).In another word, such heterogeneous mixtures do not combust entirely and result in increased HC emissions at higher loads.
Please cite this article as: Vijay Kumar M., Veeresh Babu A., Ravi Kumar P., Sudhakara Reddy S. Experimental investigation on the diesel and MME blend with DI diesel engine modified with EGR and nozzle hole orifice diameter.Biofuel Research Journal 19 (2018) 863-871.DOI: 10.18331/BRJ2018.5.3.6 rates, the latter led to more favorable results on smoke opacity because of the O2 concentration present in biodiesel (Fig. 11).In another words, EGR reduced the availability of O2 for the combustion of fuel, which in turn resulted in relatively incomplete combustion and increased formation of PM.The lower in-cylinder temperatures in response to the increasing EGR rates must have also contributed to the increases observed in smoke opacity (Rajan and Senthilkumar, 2009).

Conclusions
Experiments were conducted with neat diesel and 20% blend of Mahua oil biodiesel with base and modified NHD while different EGR rates (i.e., 10%, 20%, and 30%) were also employed to overcome the challenges faced regarding NOx emissions.Combustion characteristics of different combinations of nozzle orifice diameter, fuel type, and EGR rate were recorded and the obtained data were compared with baseline data on neat diesel.Accordingly, the following main conclusions could be drawn:

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The smaller orifice NHD of 0.20 mm was substantially beneficial in improving the engine performance parameters, i.e., BTE, BSFC, P-θ, and HRR as well as in reducing the emissions associated with both diesel and B20.However, the modification implemented led to increased NOx which was is a major drawback.These results were mainly attributed to the more efficient atomization and proper mixing of air-fuel mixtures in response to smaller orifice NHD.

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Partially-cooled EGR rate of 10% was found promising for both B20 and diesel when the proposed engine modification (i.e., smaller orifice NHD) was carried out.˗ By increasing the EGR, NOx emissions were drastically decreased at all the applied load conditions.This could be explained by the reduced O2 concentration and reduced flame temperatures in the combustible mixture as a result of EGR implementation.

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Beyond the EGR rate of 10%, the performance, combustion, and emissions characteristics deteriorated mainly due to the recirculation of high amounts of unburnt soot, CO2, H2O, as well as of O2 deficiency.

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The application of high EGR rates led to increased soot formation by decreasing the availability of O2 for fuel combustion and the consequent relatively incomplete combustion.
Overall and based on the findings of the present study, engine modification, i.e., shifting from the base orifice NHD of 0.28 mm to the modified value of 0.20 mm in the presence of partially-cooled EGR rate of 10% could be recommended as efficient combustion conditions for 20% blend of Mahua oil biodiesel and diesel.

Fig. 3 .
Fig.3.Variations in BSFC and BTE vs. full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate.

Fig. 4 .
Fig.4.Variations in in-cylinder pressure against crank angle at full load for different combinations of nozzle orifice diameter, fuel type, and EGR rate.Fig.6.Variations in the in-cylinder gas temperature with respect to different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate.

Fig. 6 .
Fig.4.Variations in in-cylinder pressure against crank angle at full load for different combinations of nozzle orifice diameter, fuel type, and EGR rate.Fig.6.Variations in the in-cylinder gas temperature with respect to different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate.

Fig. 5 . 6 3. 3 .
Fig.5.Variations of maximum pressure at different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate.

Fig. 8 .
Fig.8.variations in CO emission at different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate.

Fig. 10 .
Fig.10.Variations of NOx at different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate.

Fig. 7 .
Fig.7.Variations in HRR against crank angle at full load condition for different combinations of nozzle orifice diameter, fuel type, and EGR rate.

Fig. 9 .
Fig.9.Variations of unburned HC at different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate.

Fig. 11 .
Fig.11.Variations in smoke opacity at different percentages of full load BP for different combinations of nozzle orifice diameter, fuel type, and EGR rate.

Table 1 .
Estimated oil yields of non-edible oil crops used for biodiesel production.

Table 2 .
Fuel properties of neat diesel, Mahua oil biodiesel as well as its 20% blend with diesel (B20).*

Table 4 .
Parametric details of the fuel injection systems used. S.

Table 5 .
Specifications of the diesel engine used.

Table 6 .
Accuracies and ranges of the measuring devices used in this study.

Table 7 .
Uncertainties of the instruments used in this study.

Table 8 .
Uncertainties of the calculate parameters.