COMPARATIVE ASSESSMENT OF THE EMISSION CHARACTERISTICS OF FIRST, SECOND AND THIRD GENERATION BIODIESELS AS FUEL IN A DIESEL ENGINE

The present study aims to investigate emission characteristics with the B20 blend level of first, second and third generation biodiesels. The engine, a naturally aspirated, single cylinder, diesel engine, was operated at 1500 rpm engine speed and at different engine loads with intervals of 25%. Also, the engine is analyzed by Diesel-RK mathematical tool and emission characteristics such as smoke, carbon dioxides (CO2), particulate matter (PM), nitric oxide (NO) and summary of emission (SE) were obtained. Numerical simulation is performed using pure diesel (D100), first, second and third generation B20 (80% diesel + 20% biodiesel). Results of reduction in emissions for biodiesel blend were found to be lower than diesel fuel as smoke (BSN) by 54.68% for jojoba, PM by 4.8% for coconut, 52.0% for jojoba and 7.1% for fish oil, NO by 38.2% for jatropha curcas, and SE by 8.8% for soybean, 12.9% for jatropha curcas and 8.8% for spirulina but carbon dioxides was found to be higher by 0.38% for rapeseed, 0.61% for fish oil. The blend of B20 shows a decrease in emissions at 1500 rpm with 100% engine load. The numerical results are verified against experimental results conducted under the same operating conditions.


INTRODUCTION
Biodiesel is an alternative and renewable fuel for compression ignition engine, can be formed from different categories of edible and non-edible vegetable oils from first, second and third generation renewable fuel. The special effects on exhaust gas emissions such as smoke, unburnt hydrocarbon (UHC), carbon monoxide (CO), carbon dioxides (CO2), Nitric oxide (NO) and particulate matter (PM) emissions and slightly reduced engine performance using biodiesel as an alternative fuel in place of petroleum fuel [1][2][3]. The effect of emission parameter on a direct injection diesel engine using five different categories of biodiesel is investigated. The results show reduction in NOX by 31.2% of chicken fats, PM emission by 93.78% for poultry fats and reductions in smoke emission by 93.8% for sunflower at full load condition [20]. The effect of microalgae Chlorella protothecoides with diesel is evaluated and compared on a 4-stroke, single-cylinder air-cooled diesel engine at different engine speeds. Results found are reduction in performance with brake power by 7.0%, torque by 4.9%, exhaust gas temperature by 6.1% and emission of CO by 28%, CO2 by 4.2% and NOX by 7.4%, but increase in fuel consumption by 10.2% and O2 by 15.8% for microalgae chlorella protothecoides (B100) as compared to diesel (D0) [21].
Investigated the effect of ternary blends (diesel + cotton oil + n-butanol) as a volume basis at different engine speed (1800 rpm to 4400 rpm) on a direct injection turbocharged diesel engine. The results show that reduction in thermal brake efficiency (BTE), brake power (BP), brake torque (BT), and exhaust gas temperature (EGT), but increase of fuel consumption with increasing blend ratio of n-butanol. The emission parameters show the reduction in CO, UHC, but increase in oxides of nitrogen (NO and NO2). Higher reduction in CO and UHC emissions in 30% diesel + 10% cotton oil + 60% n-butanol and 20% Diesel +20% cotton oils + 60% n-butanol blends and increase of fuel consumption [22]. The utilization of 10%, 15%, and 20% pentanol and Calophyllum inophyllum (CI) biodiesel blend on a water-cooled, direct-injection diesel engine is investigated for performance, emission, and combustion parameters at different engine speeds (1200 rpm to 2400 rpm). The results show that the addition of pentanol with CI 20 in blend improved fuel properties. Also, thermal efficiency and engine power are higher and fuel consumptions lowered by using 15% and 20% blends of pentanol as compared to CI20. The emission parameters are slightly increase, such as NO, CO and UHC for 15% and 20% blends of pentanol and a significant 212 reduction in smoke emission but better than CI 20 blend ratio [23]. Evaluated effects of water (5, 10 and 15%) and biodiesel (10,20,30 and 40%) addition with diesel at engine speeds (1000, 2100 and 3000 rpm) with a load of 20%, 50% and 80%. The thermal efficiency, fuel consumption, carbon monoxide emissions increase and exhaust gas temperature, smoke emission and NOX are reduced emission with increasing water percentage [25].
A number of studies was carried out investigating the blend ratio of diesel and biofuels on CI engine combustion, performance and emission at different operating conditions. In this respect, the present study carried out to investigate the emission characteristics and comparison of emulsion B20 (80% diesel+20% biodiesel) of a diesel engine by using three different categories of biofuels from first, second and third generation. Thus, the primary ambition of present investigation is to emphasize the enormous potential of biodiesel as the renewable energy source in the transport industry and potential to avoid the energy and environment crisis.

Experiment Method
The engine was operated with different engine load with a step of 25% and regular diesel at 1500 rpm constant speed to achieve an engine steady state condition. After achieving the steady-state condition and with three-times repeatability of readings, data were recorded into the data-acquisition system. After completing the test for one test fuel, the engine was run after a few minutes to ensure the achievement the steady-state condition and prediction of test results considering average of three times reading for diesel fuel. Test engine is illustrated in Fig. 1 and Test conditions are shown in Table 5. The single cylinder diesel engine connected eddy current dynamometer in present study for proposed tool validation. An eddy current dynamometer of 10 kg capacity with maximum output of 3.5 kW is used for this study.  Diesel, biodiesel

Uncertainty Analysis Of Experiment And Numerical Results
The uncertainty of instruments and impact of the varying environmental condition. The uncertainties of the instruments are temperature sensor (±0. 15), pressure sensor (±0. 5), speed sensor (±1. 0), crank angle encoder (±0.  Table 6. The overall uncertainty in the experimental setup measurement is 2.2% of the measured value.

Conservation Of Species
In The species conservation equation considering the evaluation and destruction of each species has been considered on mass fraction basis, which is described in the following equations (1-2) [39]:

Conservation Of Energy
General conservation of energy equation written by Fivelend and Assanis for a thermodynamic system is shown in equation (3):

Heat Model
Multi-zone combustion model used in Diesel-RK model where combustion cylinder heat release rate is defined in four phases are in equation (4-7): Ignition delay period model Premixed combustion period model Controlled combustion period model Burning period model Nox Formation Model NOX emission produced within the combustion chamber in diesel engine are grouped in form of nitric oxide (NO) and nitrogen dioxide (NO2) using equation (8)(9)(10)(11)(12): Journal of Thermal Engineering, Research Article, Vol. 6, No. 6, Special Issue 12, pp. 211-225, December, 2020

Smoke (Bsn) Model and Particulate Matter (Pm) Formation Model
PM emission by Alkidas method is selecting for calculation of particulate matter emission which is given in equation (12). PM emission consists of list of species. Soot has a dominant fraction. PM emission as a function of soot emission [15]:

RESULTS AND DISCUSSION
The comparison of the in-cylinder pressure, heat release rate (HRR), smoke emission between experimental results and numerical results are demonstrated in Figure (2-4). In the experiment and numerical analysis the same operating conditions as shown in Table 5. The trend of results curve was similar during the intake, compression, combustion and exhaust processes and percentage of error deviation between experiment and numerical results as shown in Table 7. The numerical analysis performed using commercial solver Diesel-RK results show that higher cylinder pressure by 4.3%, reduction in maximum heat release rate by 5.9% and smoke emission by 4.6%. The numerical results and experimental results percentage difference acceptable range. The necessary changes are made in the manuscript at section 3.1 validation simulation tool.

Emission Parameters
The numerical results in this paper shows the effects of biodiesels (B20) as characterized by, first, second and third generation biofuels, on the emission characteristics when used as fuel for a direct-injection diesel engine. This section details the related emission characteristics for diesel engine such as smoke, PM, CO2, NO and summary of emission. Figure 5 shows the variation of smoke emissions with load for first, second and third generation biodiesel. The smoke emission is affected by advancing injection timing, fuel mixing rate, viscosity, oxygen contents, incomplete combustion, the temperature of the combustion zone, engine load, speed, injection pressure [2,12,20,23,25]. At full load, smoke emission (BSN) is found to be 3.2 for diesel, 3.05, 3.1, 3.12, 3.1 for first-generation biodiesels coconut, palm, rapeseed, and soybean, respectively, 2.85, 3.45, 1.45, 2.89 for second generation biodiesels cottonseed, jatropha, jojoba, and Karanja respectively and 3.05, 3.08, 3.1, 3.06 for third generation biodiesel fish oil, microalgae spirulina, waste oil and animal fats respectively. The minimum smoke emission observed, is 1.45 BSN for jojoba biodiesel, and is about 54.68% as compared to diesel fuel and other biodiesels. For all the tested biodiesels lesser smoke emissions are obtained as compared to regular diesel fuel. Well, it is the cause due to advanced injection timing and a higher percentage of oxygen contents within biodiesel [30][31][32][33]. The fuel-air mixture preparation is good in premixed combustion phase due to oxygen contents, which results in better combustion and low smoke emission [42]. Carbon Dioxide Emission Figure 6 shows the variation of carbon dioxide (CO2) with load for first, second and third generation biodiesels. The CO2 emission is affected by the heating value of fuel, exhaust gas temperature, oxygen contents, complete combustion, engine load, speed [13,19,21]. At CR17.5 on full load condition, CO2 emissions (g/kWh) are found 825.5 for diesel, 839.5 for coconut, 844.57 for palm, 828.65 for rapeseed, 836.1 for soybean of the first generation biodiesels, respectively, 846.7 for cottonseed, 823.46 for jatropha, 883.7 for jojoba, 857.6 for Karanja, of the second generation biodiesels respectively and 830.55 for fish oil, 836.24 for microalgae spirulina, 835.46 for waste oil and 834.87 for animal fats of the third generation biodiesel respectively. The CO2 emissions are obtained higher by 0.38% for rapeseed, and 0.61% for fish oil, but are reduced for jatropha curcas by 0.27% within blend of B20 as compared to diesel fuel. For all tested biodiesel obtained CO2 emissions are higher as compared to regular diesel fuel, but lesser only for jatropha curcas, due to complete combustion and higher oxygen percentage within the combustion chamber, as compared to diesel fuel. The fuel-air mixture preparation is good in premixed combustion phase due to oxygen contents which results in better combustion and higher CO2 emission [34][35][36]. Particulate Matter Emission Figure 7 shows the specific particulate matter (PM) emission changes at different load for three tested generation biodiesel (B20) samples and diesel. The PM emission is affected by oxygen contents, engine load and speed, injection timing, improper combustion, combustion temperature, and air-fuel mixing rate [1,5,19,20,27]. The PM emission produced in the combustion chamber due to the improper combustion process. High combustion flame temperature, injection timing, percentage of oxygen, speed and load lead to lower PM emission [37][38][39][40][41]. At CR17.5 with high fuel injection pressure of 220 bar on full load condition, the PM (g/kWh) was found to be 0.798 for diesel, 0.759 for coconut, 0.776 for palm, 0.772 for rapeseed, 0.767 for soybean (first generation), 0.698 for cottonseed, 0.891 jatropha curcas, 0.383 for jojoba, 0.72 Karanja (second generation) and 0.742 from fish oil, 0.767 spirulina, 0.772 for waste oil, and 0.756 for animal fats (third generation). The minimum PM emission were found to be 4.8% for coconut (first generation), 52.0% for jojoba (second generation) and 7.1% of fish oil (third generation) within a blend of B20 compared to diesel fuel. For all tested biodiesels, lower PM emissions are obtained as compared to regular diesel fuel, due to complete combustion and higher oxygen percentage, compared to diesel fuel. The fuel-air mixture preparation is good in premixed combustion phase due to oxygen contents which results in better combustion and lowered PM emission.

Figure 7.
Comparison of variation of PM emission from first, second and third generation biodiesel at different engine load for B20 Nitric Oxide Emission Figure 8 shows the specific nitric oxide (NO) emission changes at different loads for the three generation biodiesel (B20) samples and diesel. The NO emission is affected by engine load and speed, in-cylinder peak pressure and temperature, calorific value of fuel, viscosity, injection timing, oxygen content, and cetane number [3, 12, 13, 18, and 27]. The NO emission is produced within the cylinder due to high temperatures during the combustion process. At CR17.5 with the full load condition, the NO (g/kWh) was found to be 16  221 of B20, compared to diesel fuel. The NO emission was found higher 41.16% for jojoba and 8.5% for fish oil, compared to diesel, due to higher oxygen and viscosity, compared to diesel [43][44][45].

Figure 8.
Comparison of variation of NO emission from first, second and third generation biodiesel at different engine load for B20 Summary of Emissions Figure 9 shows the changes in summary of emission (SE) at different loads for three biodiesel generation (B20) samples and diesel. The SE is affected by engine load, combustion temperature, viscosity, oxygen contents. At CR17.5 with the full load condition, the SE was found 5.1 for diesel, 4.91 for coconut, 4.83 for palm, 4.92 for rapeseed, 4.65 for soybean (first generation), 5.66 for cottonseed, 4.44 jatropha curcas, 5.32 for jojoba, 5.63 for Karanja (second generation) and 5.1 for fish oil, 4.65 for spirulina, 4.87 for waste oil, and 5.1 for animal fats (third generation) respectively. The minimum SE emissions were found to be 8.8% for soybean (first generation), 12.9% for jatropha curcas (second generation) and 8.8% for spirulina (third generation) within a blend of B20, compared to diesel, due to higher oxygen and complete combustion, as compared to diesel. Should be clarified from figure 9, the SEs decrease with increase in engine load, shown at the right hand side of 25%.  Figure 9. Comparison of variation of SE emissions from first, second and third generation biodiesels at different engine loads for B20

CONCLUSION
The effects of first, second and third generation biodiesel blends and diesel on the emission characteristics is investigated. The proposed Diesel-RK model will reproduce the smoke, PM CO2, NO and SE trends of different fuels obtained in the single cylinder diesel engine. The critical decisions are as follows.
• Similar numerical and experimental results for tool validation, the numerical results show that reduction in heat release rate and smoke emission, but higher cylinder pressures as compared for diesel. • The smoke emission is observed to be lower for biodiesel than diesel and increases with an increase in engine load. • NO emission is lower by 12.0%, 38.2% and 12.01% for soybean, jatropha curcas and spirulina biodiesel, respectively, but higher by 41.16% for jojoba and 8.5% of fish oil, as compared to diesel. It is also observed that the increase of engine load increases the NO emissions at 1500 rpm and CR17.5. • Similarly, PM and SE emissions were also lower for testing of first, second and third generation biodiesel than diesel. Engine load can further decrease these emissions. • Biodiesels showed higher CO2 emissions by 0.38% for rapeseed, 0.61% of fish oil, but the reduction for jatropha curcas about by 0.27% within a blend of B20, compared to diesel fuel due to complete combustion as compared to diesel. The numerical analysis results show that soybean (first generation), jatropha curcas (second generation) and spirulina (third generation) biodiesel superior fuel for compression ignition engine due to lower NO emission obtained. Pure diesel B20 80 diesel + 20 biodiesel BC20