Controls-oriented modelling and LQR control of natural gas HCCI engines

Homogeneous charge compression ignition (HCCI) engines have been proposed as a solution to designing efficient engines that follow emission regulations set by the US Environmental Protection Agency. The main idea behind HCCI engines is to combust a lean, homogeneous air-fuel mixture using compression. However, due to the fact that HCCI combustion is triggered by auto-ignition of the mixture during compression, there is no direct method of controlling combustion timing to ensure maximum efficiency. Therefore, the goal of this paper is to develop a control strategy for ignition timing of natural gas HCCI engines at steady-state conditions. To model the engine, a controls-oriented model is developed based on the modified knock integral model and is validated using a model developed by GT-power. Furthermore, a linear quadratic regulator is designed to control the engine timing. Simulation results show that the control system can track engine timing within 0.5% of its target value.