Fuel Injection Strategies to Improve Emissions and Efficiency of High Compression Ratio Diesel Engines

Simultaneous low NOx (< 0.15 g/kWh) & soot (< 0.01 g/kWh) are attainable for enhanced premixed combustion that may lead to higher levels of hydrocarbons and carbon monoxide emissions as the engine cycles move to low temperature combustion, which is a departure from the ultra low hydrocarbon and carbon monoxide emissions, typical of the high compression ratio diesel engines. As a result, the fuel efficiency of such modes of combustion is also compromised (up to 5%). In this paper, advanced strategies for fuel injection are devised on a modern 4-cylinder common rail diesel engine modified for single cylinder research. Thermal efficiency comparisons are made between the low temperature combustion and the conventional diesel cycles. The fuel injection strategies include single injection with heavy EGR, and early multi-pulse fuel injection under low or medium engine loads respectively. The empirical studies have been conducted under independently controlled exhaust gas recirculation, intake boost, and exhaust backpressure. Multiple fuel injection pulses per cycle and heavy EGR have been applied to modulate the homogeneity history in order to improve the phasing and efficiency of the combustion process. The new low temperature combustion trade-off, that is, CO & THC vs. NOx & soot is presented in the context of the different fuel injection strategies.