Tightened intake oxygen control for improving diesel low-temperature combustion

Abstract

The low-temperature combustion (LTC) operation in diesel engines is challenged by the higher cycle-to-cycle variation with heavy exhaust gas recirculation (EGR) and high unburnt hydrocarbon and carbon monoxide emissions. Small variations in the intake charge dilution can further decrease the combustion efficiency, which in turn escalates the successive fluctuations of the cylinder charge, adversely affecting the stability and efficiency of the LTC operation. In this work, improvements in the promptness and accuracy of combustion control as well as tightened control on the intake oxygen concentration have been combined to enhance the robustness and efficiency of the LTC operation in diesel engines. The empirical set-up consisted of a set of field programmable gate array (FPGA) modules that were coded and interlaced to execute on-the-fly combustion event modulations on either a cycle-by-cycle or within-the-same-cycle basis. The cylinder pressure traces were analysed to provide the necessary feedback for the combustion control algorithms. A methodology for estimating the indicated mean effective pressure for the current engine cycle 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 improved fuel efficiency and exhaust emissions. Moreover, a strategy for enabling load transients within narrow LTC operating corridors was implemented and shown to improve the load management of the LTC cycles. The reported techniques were in part to establish a model-based control strategy for robust diesel LTC operations.