CONTROL OF COMBUSTION IN DIESEL ENGINES USING GASOLINE FUMIGATION

Abstract

This study is made to identify the most favorable conditions for dual fuel mode of operation of diesel engines using gasoline fumigation technique. Diesel has been used as main fuel and Gasoline as a combustion improver. The selected approach is to improve the brake thermal efficiency through improving the combustion efficiency. This has helped in both aspects of improving thermal efficiency and on the other hand reducing incomplete combustion products and thus improving emission level. The experiments are conducted in two stages, first by running a pilot test in a variable speed multi cylinder diesel engine. Air has been fumigated by gasoline and the effect on part and full load have been defined. The point of higher engine loads was found in need of more development. The second stage is the main test running where a single cylinder constant speed direct injection diesel engine has been modified to run on gasoline fumigated mode. Performance has been scrutinized throughout the engine load range using four different modes of running. First the baseline performance was recorded with the original engine settings using diesel alone as fuel (D). Then by using a single jet carburetor, gasoline fumes has been generated at the air intake manifold producing a lean mixture homogenously ready to enter combustion chamber in the induction stroke. Two fuel jet sizes were used to produce two different mixture strengths. The fuel jets produced fumigation A/F of 242:1 (D+GI) and 61:1(D+GII). The obtained effect with (D+GII) showed an increase in thermal efficiency by 10% and a significant decrease in CO and NOX emissions. In order to reduce HC to a level below that of diesel fuel mode, the fuel injection timing found need to be retarded by 2o(D+GIII). This produced the optimum performance with the same increase in thermal efficiency and a significant decrease in CO (by 73%) and HC by 25% and NOX decreased as well by 7.5%. Gasoline fumigated diesel (GFD) combustion; using simple single jet carburetor gave better result when compared to the current research which is using the method of port injection of gasoline.