Experimental Studies on Partial Substitution of Diesel With Bioethanol (Derived From Madhuca Indica Flowers) Using Different Techniques

Abstract

Use of renewable energy from biomass sources for CI engines can greatly reduce the air pollution, and dependency on the import of crude oil in a country. In the recent days, the use of ethanol for automotive power applications has gained more importance, as it can be used in both SI and CI engines and reduce the greenhouse gas (GHG) emissions. Different feedstocks have been explored for production of ethanol in a large quantity. In this research study, bioethanol from the Madhuca Indica flowers as an alternative fuel for compression ignition (CI) engines has been proposed. As a first step of the research study, bioethanol obtained from the Madhuca Indica flowers was characterized for its suitability as an alternative fuel for CI engines. For this purpose, the presence of group compounds in bioethanol were identified by using the Fourier transform infrared spectroscopy (FTIR) and Gas chromatograph-mass spectrometer (GC-MS), and analysed. Also, the physico-chemical properties of bioethanol were determined and compared with those of the diesel properties. Seven modules of work have been carried out in this research work to establish the results of using bioethanol as an alternative fuel in a CI engine. For this purpose, a single cylinder, four stroke, air cooled, DI diesel engine was used for this investigation. Bioethanol has a low cetane number and thus it cannot be directly used in CI engines. Therefore, initially in the first four modules, bioethanol was used with diesel in the engine by adopting four techniques viz. i) in the form of emulsion, ii) addition of an ignition improver to an optimum bioethanol-diesel emulsion, iii) bioethanol-DEE dual fuel mode, and iv) diesel-bioethanol dual fuel mode (fumigation). The experimental results of the combustion, performance and emissions of the engine run on bioethanol in these techniques were evaluated, and compared with those of diesel operation in the same engine.
In the first module of work, bioethanol was emulsified with diesel in a step of 5% to 15% by volume with the help of a surfactant Span 80. The stability of the emulsion was checked for 15 days under normal atmospheric conditions. The bioethanol-diesel emulsion was designated as BMDE5, BMDE10 and BMDE15, where the numeric values were the volume percentages of bioethanol. Up to 15% bioethanol in the emulsion was used for the experimental investigation by considering the miscibility, minimum calorific value and cetane number of fuel which would not affect the performance and combustion parameters of the engine. The experiments were carried out with the three different bioethanol-diesel emulsions in the diesel engine and results were compared with the diesel data. The results
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indicated that the ignition delay of engine run on the bioethanol-diesel emulsions was found to be longer by about 1 to 2 °CA than that of the diesel operation at full load. The maximum cylinder pressure of the engine run on the bioethanol-diesel emulsions was higher by about 2% to 3% than that of diesel at full load. The BMDE15 emulsion gave a better performance and emission than that of BMDE5, BMDE10 and diesel. The useful work and brake specific energy consumption (BSEC) for BMDE15 was observed to be higher by about 6% and 27% respectively, at full load. The nitric oxide (NO), smoke and carbon monoxide (CO) emissions were observed to be lower with a maximum reduction of 24%, 21% and 6% respectively, compared to those of diesel at full load. But, a marginal increase of hydrocarbon (HC) emission was observed, with the BMDE15 operation than that of diesel operation.
In order to reduce the ignition delay of the engine run on the optimum bioethanol-diesel emulsion (BMDE15), an ignition improver diethyl ether (DEE) was added to it in a step of 0.5% by volume and designated as DED1%, DED1.5%, DED2% and DED2.5%. The higher percentage of DEE was considered up to 2.5% for its vapour lock problem. The DED1.5% was considered to be an optimum blend which lowered the noisy operation and ignition delay of the diesel engine. At full load, the ignition delay of engine operated with DED1.5% was reduced by about 1°CA. The maximum cylinder pressure and BSEC were observed to increase by about 1.2% and 4% respectively, compared to that of diesel, at full load. The NO and smoke emissions were lower by about 11.3% and 13.7% respectively, compared to that of diesel at full load.
Further, as a third technique, bioethanol was directly used in the diesel engine with the help of an ignition improver. DEE with a flow rate of 60 g/h, 120 g/h, 180 g/h and 240 g/h was injected at 10cm distance of the intake manifold of the engine. The necessary arrangement was made for DEE injection. The upper and lower limits of the DEE flow rate were considered by the audible knocking and misfire of the engine. The bioethanol operation with the 180 g/h flow rate of DEE exhibited a shorter ignition delay, and higher cylinder pressure compared to those of 60 g/h, 120 g/h, 240 g/h flow rate of DEE and diesel at full load. The NO and smoke emissions were found to be lower by about 22.2% and 16.6% respectively, compared to those of diesel at full load.
In the fourth technique, bioethanol was fumigated at different flow rates viz., 0.24 kg/h, 0.48 kg/h, 0.96 kg/h and 1.22 kg/h with the help of electronically controlled injector at the intake manifold of the engine, whereas diesel was injected into the cylinder as a pilot fuel. The results revealed that, bioethanol fumigation at the flow rate of 0.48 kg/h and the equivalence ratio of 0.88 gave an increase in thermal efficiency of about 3% than that of diesel. At full load, the ignition delay was found to be longer by about 3 °CA and the maximum cylinder pressure was increased by about 2.1% compared to that diesel. The volumetric efficiency and brake specific fuel consumption (BSFC) was found to be lower by about 6% and 5.2% respectively, than those of diesel at full load. The NO and smoke emissions were observed to be lower by about 24.2% and 5.5% respectively, than those of diesel operation at full load.
The BMDE15 emulsion was chosen as the best among all the above mentioned techniques in terms of performance and emission point of view, when bioethanol was used with diesel. The spray pattern of the BMDE15 emulsion was studied with the help of a MATLAB programme in the fifth module of the work. Also the experimental results were validated with the help of the MATLAB programme and compared with those of diesel. From the analysis, it was proved that the spray profile of BMDE15 was found to be better compared to that of diesel at full load. The deviation between the simulated and experimental results of cylinder peak pressure, NO and smoke emissions for BMDE15 was found to be 3%, 5% and 4% respectively at full load.
Bioethanol has a poor lubricity in comparison with diesel that resulted in a power drop. In the sixth module, to improve the lubricity property of BMDE15, bioethanol was added with the volume percentage of 5% in each step up to 15%. The BEBDD10 blend improved the lubricity of the fuel without much affecting the performance and emissions of the engine. The power output of the engine run on BEBDD10 was found to be increased by about 2% compared to that of the BMDE15 operation at full load. The NO and smoke emissions were observed to be lower by about 4% and 21% compared to that of diesel at full load.
In the last module of the work, a short term endurance test was carried out; when the engine was run on both the BMDE15 and BEBDD10 fuel for 100 h. The carbon deposits, engine wear and change in the lubricating oil properties were analysed in both the cases. The decrease in the carbon deposit on the cylinder head, piston crown and nozzle tip were measured by about 40%, 38% and 25% respectively, with the BEBDD10 operation in comparison with the diesel operation. The wear in the fuel injection pump components such as plunger, pump barrel, pinion, and spring were found to be lower by about 0.4%, 0.32%, 1.7% and 1.5% respectively, with the BEBDD10 blend in comparison with BMDE15. With the BEBDD10 operation, the amount of metal debris such as Zn, Fe, Cu, Mn, Al, Pb, Ni and Cr were observed to be lower by about 13.6%, 24.5%, 25.7%, 14.6%, 11.7%, 17.3%, 15.1% and 36% respectively, compared to those of BMDE15. By overall comparison, it is concluded that the BEBDD10 operation seems to give better lubricating properties and lower material wear than those of diesel operation.