Numerical Study of Boosting Configurations and Valve Strategies for High Load HCCI Engine in Wide Range of Engine Speed

Nowadays, the main potential of the HCCI engine, i.e. high efficiency with low NO_x and soot emissions, is a well-known fact. Main limitations that prevent the commercial application of the HCCI engine are the control of combustion timing and low power density. Higher power density could be achieved by boosting the engine, but low exhaust temperatures associated with the HCCI combustion require a different approach when trying to achieve a boosted HCCI engine. This paper presents a numerical study on two boosting configurations that will enable high boost levels and high load, as a consequence, in the Ethanol fueled HCCI engine, in the engine speed range of 1000 - 4000 rpm. For the purposes of this study, a four-cylinder HCCI engine model has been made in the cycle-simulation software. The model includes the entire engine geometry and all elements necessary for representing the entire engine flow path. Instead of using the available, but computationally very demanding six-zone HCCI combustion model which uses detailed chemical kinetics, a specially developed and much faster model was used for combustion. This model is based on a Vibe function whose parameters depend on in-cylinder conditions: pressure, temperature, mixture composition, and engine speed. The model is trained with the results of the previously validated single cylinder model that uses a six-zone HCCI model with detailed chemical kinetics. The best solution for achieving high boost with high efficiency has been reached from the results of a multi cylinder model with two different boosting configurations.