Fuel reactivity as a means to control DI-HCCI combustion engine

The homogeneous charge compression ignition (HCCI) is an advantageous combustion concept for internal combustion engines in terms of efficiency and pollutant emissions. This combustion strategy is one of the main types of low temperature combustion (LTC) concepts. It is a spontaneous multi-point combustion of a highly diluted premixed fuel-air mixture. However, its limited operating range suppressed its successful utilization. One applicable method to use this combustion concept in engines is to combine it with other combustion strategies while each combustion concept come into work during its optimum operating range. The idea of an HCCI combustion engine involving direct fuel injection into the combustion chamber is an applicable strategy aiming at this target. In the HCCI engines there is no direct control method for the time of auto-ignition. The octane number or fuel auto-ignitability characteristic is one of the most influential parameters on the combustion timing. Therefore, this study investigates the effect of the octane number on the direct injection (DI) HCCI combustion. The mathematical investigations are based on a novel two-stage combustion model. The combustion is predicted with the single-zone model from the intake valve closing to the end of injection. Thereupon, it is predicted by the multi-zone model. The results indicate that the octane number has profound effects on combustion phasing and delivered power. Therefore, cycle-by-cycle and cylinder-to-cylinder control of the combustion phasing by octane number adjustment is possible.