Discussion of Transient Response Optimization Strategies of Turbocharged Diesel Engine under EGR Step Change Operation

Due to the high cost of engine bench test under transient operations, a transient simulation platform of turbocharged diesel engine with EGR (Exhaust Gas Recirculation) loop was established. Based on this simulation platform, in order to reduce NOx emissions and control the smoothness of combustion process organization of HCCI (Homogeneous Charge Compression Ignition) combustion mode, four control strategies under EGR step change transient operation were discussed, which were the linear control strategy, the upcast control strategy, the sunken control strategy and the compositive control strategy. From the aspect of transient response of combustion boundary parameters, the upcast and the compositive control strategy are superior to the linear and the sunken. The response time of EGR mass flow rate of the upcast control strategy is 40% shorter than the linear, and it is 57% shorter than the sunken. In order to avoid torque ripple during transient process, the compositive and the linear control strategy are superior to the upcast and the sunken. The torque ripple of the compositive control strategy is 18% lower than the upcast. In terms of reducing NOx emissions during transient process, at one time, NOx emissions of the upcast and the compositive control strategy are 11% and 6% less than that of the linear. Reducing the same 12% of the NOx emissions, the upcast and the compositive control strategy can shorten 38% and 19% response time than that of the linear. From the purpose of reducing Soot emission during transient process, at one time, Soot emission of the linear and the compositive control strategy are 23% and 11% less than the upcast. Reach the same Soot emission value, the time of the linear and the compositive control strategy is slower by 36% and 17% relative to that of the upcast.