Air-Assisted Direct Firing for SI Combustion Engines

The conception, design, simulation, and experimental evaluation of a novel SI combustion system will be presented in this paper. First, a new one-cylinder research engine was designed based on the combination of a port fuel injection engine with a centrally located direct minimal fuel-air mixture injection system. This combustion system is designed for low and mediate load conditions for moderate engine speeds, and aids the ignition process even when very high exhaust gas recirculation rates are present. It is also expected that the ignition stability under full load and under warm-up conditions will be improved significantly. The engine hardware fulfills the requirements of the MBtech “Integrated Combustion Development Process”, which allows operation of the research engine at all engine loads and speeds, while still supporting full optical access. A new additional injector is integrated on a four-valve cylinder head on a pent-roof combustion domain. This injector provides a minimal amount of fuel-air mixture under moderate pressure, in order to facilitate the ignition process in the presence of high EGR rates. Numerical simulation of the in-cylinder mixture formation process helps to improve the experimental setup for the combustion process as well as the injector layout design. For the proposed firing system, the thermodynamical results show promising improvements in fuel consumption and firing stability, while maintaining all of the advantages of the classic homogeneous SI combustion process.