The Effect of Exhaust Throttling on HCCI - Alternative Way to Control EGR and In-Cylinder Flow

Homogeneous Charge Compression Ignition (HCCI) has emerged as a promising technology for reduction of exhaust emissions and improvement of fuel economy of internal combustion engines. There are generally two proposed methods of realizing the HCCI operation. The first is through the control of gas temperature in the cylinder and the second is through the control of chemical reactivity of the fuel and air mixture. EGR trapping, i.e., recycling a large quantity of hot burned gases by using special valve-train events (e.g. negative valve overlap), seems to be practical for many engine configurations and can be combined with any of the other HCCI enabling technologies. While this method has been widely researched, it is understood that the operating window of the HCCI engine with negative valve overlap is constrained, and the upper and lower load boundaries are greatly affected by the in-cylinder temperature. Boosting has been found very effective in increasing the upper load boundary of HCCI but very little has been published about the effect of raised exhaust back pressure when a turbocharger is used. This paper presents a study of the effect of increased exhaust back pressure on gas exchange processes in a HCCI engine with an exhaust throttling valve. The work has included 1-D gas dynamic modelling using Ricardo WAVE™ and experiment on a Ford/Jaguar V6 HCCI engine with a fitted exhaust throttling orifice. Appropriate boundary and initial conditions in the engine have been created and information from the 1-D simulations is visualized.