Efficiency & Stability Improvements of Diesel Low Temperature Combustion through Tightened Intake Oxygen Control

Diesel engines operating in the low-temperature combustion (LTC) mode generally tend to produce very low levels of NOx and soot. However, the implementation of LTC is challenged by the higher cycle-to-cycle variation with heavy EGR operation and the narrower operating corridors. Small variations in the intake charge dilution can significantly increase the unburnt hydrocarbon and carbon monoxide emissions as well as escalate the consecutive cyclic fluctuations of the cylinder charge. This in turn adversely affects the robustness and efficiency of the LTC operation. However, Improvements in the promptness and accuracy of combustion control as well as tightened control on the intake oxygen concentration can enhance the robustness and efficiency of the LTC operation in diesel engines. In this work, a set of field programmable gate array (FPGA) modules were coded and interlaced to suffice on-the-fly combustion event modulations on a cycle-by-cycle basis. The cylinder pressure traces were analyzed to provide the necessary feedback for the combustion control algorithms. The combustion phasing was estimated using a computationally-efficient Pressure Departure Ratio Algorithm that helped to anchor the combustion within a narrow crank angle window for the best efficiency. The load variations were minimized by regulating the indicated mean effective pressure that helped to stabilize the LTC cycles. Engine dynamometer tests demonstrated that such systematic and prompt control algorithms were effective to optimize the LTC cycles for better fuel efficiency and exhaust emissions. The reported techniques were in part to establish a model based control strategy for robust diesel LTC operations.