Combustion Timing Control of Homogeneous Charge Compression Ignition Engines

Abstract

Homogeneous Charge Compression Ignition (HCCI) Engines hold promises of being the next generation of internal combustion engines due to their ability to produce high thermal efficiencies, in addition to low nitric oxides (NOx) and particulate matter (PM). HCCI combustion is achieved through the auto-ignition of a compressed homogeneous fuel-air mixture, thus making it a "fusion" between spark-ignition and compression-ignition engines. The main challenge experienced when developing HCCI engines is the absence of a combustion trigger hence making it difficult to control its combustion timing. The aim of this research project is to develop a natural gas HCCI engine to improve the performance of stationary power plants in Qatar. Since HCCI primarily depends on temperature and chemical composition of the mixture, exhaust gas recirculation (EGR) and adjusting intake temperature are the techniques that will be used to control ignition timing. Previously, a simulation model was developed using a highly sophisticated program, GT-Power. It was noticed that simulation time for such a model was high. Therefore a simple, non-linear model was developed to capture the main thermodynamical features of the HCCI engine. In this oral presentation, we will explain how the model was developed as well as the optimization technique used to adjust an experimental correlation to predict ignition timing. We will show that performance data produced by our model is in accordance with the data acquired from GT-Power. In addition, several methods were exhausted to further simplify the model and produce a linear version that could be used in linear control schemes. Data from the finalized linear model were compared to the initial non-linear model and proved to be a sufficient approximation. A Linear Quadratic Regulator Controller scheme will be used on our final linear model to control the EGR ratio and intake temperature, which will ultimately control the combustion timing. Finally, a block diagram of the proposed control scheme was developed. Further work for validation and implementation of the proposed scheme will be discussed.