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Reduced emissions from the spark-ignition engine, when fueled by gasoline containing small amounts of MTBE, have led us to explore similar positive results in compression-ignition (CI) engine combustion by adding this oxygenate compound to Diesel fuel. This study was performed in two separate laboratories by employing the respective experimental apparatus. When a pre-chamber type CI engine was operated by using Diesel fuel mixed with several volume portions of MTBE, including 5, 10 and 15%, several positive results were obtained, as compared with those from the baseline neat Diesel-fueled operations: (1) The engine delivers overall comparable or better performance characteristics; (2) The brake thermal efficiency is higher at the advanced and late injection times; (3) Some considerable reduction of both soot and NOx emissions is found; (4) The ignition delay increases but the combustion duration decreases.

Effects of the intake air oxygen enrichment (IOE) on the combustion processes and performance of a spark ignition (SI) engine were investigated when the engine was operated under part load conditions both after and during the warm-up period. The study was performed by comparing the direct measurements of engine performance and emission characteristics with instantaneous digital imaging of in-cylinder reaction processes obtained using our high-speed dual-spectra infrared imaging system developed at Rutgers. The IOE under the partial load operations of an SI engine produced some comparable improvements in the thermal efficiency and mean effective pressure to those from the full load operations. Although no dramatic reduction of unburned hydrocarbon emissions with the IOE was realized in the present measurement, the insignificant increase of Nox under the same condition is noteworthy.

Many recent publications indicate that spark ignition (SI) engines equipped with the conventional port-injection fuel system (PIF) seem to have serious fuel-maldistribution problems, including the formation of liquid layers over the combustion chamber surfaces. It is reasonable to expect that such a maldistribution is an unfavorable condition for the flame propagation in the cylinder. The in-cylinder flame behaviors of a PIF-SI engine as fueled with gasoline are investigated by using the Rutgers high-speed spectral infrared imaging system. These results are then compared with those obtained from the same engine operated by gaseous fuels and other simple fuels. The results from the engine operated by gasoline reveal slowly burning fuel-rich local pockets under both fully warmed and room-temperature conditions. The local pockets seem to stem from the liquid layers formed over the surfaces during the intake period.