Simultaneous dynamic optimization of valves timing and waste gate to improve the load step transient response of a turbocharged spark ignition engine

Abstract

A result of adding a turbocharger for downsizing of spark ignition engines is slower transient response of the engine in comparison to the naturally aspirated engine. Until recently, it was impossible to use turbocharger in spark ignition engines due to self-ignition problems. However, with the waste gate technology, the turbine speed and hence the boost pressure level are regulated for reduction of self-ignition and increase of torque. In this paper, the engine simulation is done in one-dimensional software GT-POWER and the torque transient response is being focused. For optimization, the coupling between two softwares GT-POWER and MATLAB SIMULINK is used to find an appropriate setting to utilize variable valve timing and waste gate technologies simultaneously during the transient. Variable valve timing in this study refers to opening and closing timings of inlet and exhaust valves. The optimization target is to maximize the torque integral during time interval of the transient. The transient in this paper is the one in which the engine speed is constant and the load increases rapidly and suddenly to a special value (step increase of load). Improved genetic algorithm is used for optimization. With this optimization, the mean improvement percentage in torque integral is about 6.46% for speed 1900 rpm and about 9.33% for speed 2500 rpm. The studied engine is 1.65 L EF7-TC which is a spark ignition engine equipped with turbocharger.