A study of alternative fuels in S I engines for fuel efficiency and exhaust emission control

Abstract

The rapid depletion of petroleum fuels, their ever-increasing cost and increasing global concern for environmental pollution caused by the petroleum fuels have led to an intensive search for alternative fuels in internal combustion engines. This search has led to the recognition of several alternative fuels, which can be successfully used in spark ignition engines. However, the choice of an alternative fuel in a particular country will be governed by the availability of resources and economics apart from how efficiently a particular alternative fuel can be used in engines. Alternative fuels like ethanol and compressed natural gas can be attractive in India because of the country's wide agricultural base and large coal reserves. Ethanol can be produced from the fermentation of sugar cane, corn and grain stocks that are also renewable energy sources. Apart from natural gas reserves methane, which is one of its principal constituent, can also be produced from coal and biomass conversion thus making it much more available energy base. Hence, in the present thesis, experimental and theoretical investigations that were undertaken to visualize the potential of ethanol and compressed natural gas as spark ignition engine alternative fuels and reducing the harmful emissions are reported. Experimental results of a single cylinder engine operated on gasoline, E-85 (85 percent ethanol and 15 percent gasoline by volume) and other ethanol-gasoline blends (E-20, E-10) at similar equivalence ratio, engine speed, bmep and compression ratio of 8.0 (nominal compression ratio of Indian 4-stroke gasoline operated vehicles) are reported. The results of these fuels are compared at similar equivalence ratios. WOT and constant speed performances were also compared. The performance of E-85 at different ignition timings and compression ratios are also presented. Other results presented include, the effect of intake air temperature, performance at idling, performance of catalytic converter and pressure crank angle history. Similar works were also carried out with the variation of equivalence ratio and engine speed using CNG and the results were compared with gasoline. Experimental work was also carried out to . evaluate the performance of CNG using dual spark plugs.The results showed that at a given equivalence ratio, ethanol fueling resulted in 2-3 percent greater thermal efficiency, up to 50% lower CO and 26 percent lower NOx emissions. However, bsfc and hydrocarbons emissions were higher with E-85 as compared to gasoline operation. It was observed that MBT timings for E-85 operation were 4-6 degrees less advanced than gasoline operation depending on equivalence ratios. At WOT, ethanol (E-85) fueling resulted in higher power and efficiency by 4-7% and 3-5% respectively as compared to gasoline. With gasoline an ignition timing of 20 degrees before top dead centre gave lowest fuel consumption while for E-85, an ignition timing of 16 degrees bTDC gave minimum fuel consumptions. An intake air temperature of 50 deg. centrigrade resulted in best performance with E-85 because of improved mixture formation. Increased compression ratio from 8 to 10 and 12 increased thermal efficiency by 3 and 8 percent respectively. It also increased exhaust emissions of NOx and HC by 15 and 40 percent respectively. Increased idling speed increased fuel consumption and decreased CO and HC emissions. Stable operation at idling was achieved at 900 rev./min. for both gasoline and E-85. The analysis of pressure-crank angle diagram at half throttle operation and WOT showed that with ethanol (E-85), pressure increased more rapidly. Peak pressures were also higher with E-85. A reasonably satisfactory correlation was found between theoretically predicted and experimentally obtained results on engine performance Single cylinder engine operation with CNG showed 3 to 5 percent higher thermal efficiency and 15 percent lower b f c as compared to gasoline. Also CO emissions were lower by 30 - 80 percent in rich zone and NOx by about 12 percent at an equivalence of 1.0. At WOT CNG operation resulted in 10 to 12 percent lower power, however, thermal efficiency and bfc was better with CNG as compared to gasoline. Dual spark plug operation increased power output by 3 to 5 percent.