Investigations of HCCI Combustion Using Multi-Stage Direct-Injection with Synthetic Fuels

The mixture formation of a direct injection HCCI engine was optimized by a new nozzle geometry in combination with a multi-pulse injection scheme. To achieve this injection strategy, a highly flexible Piezo-Common-Rail injection system was used at the single cylinder research engine (DC BR 500, compression ratio reduced to 14:1). Optical probes for local, time resolved temperature and soot concentration measurement (Two-Color-Method) were adapted. Furthermore, a camera system was applied to detect the radiation of UV light (especially emitted by OH radicals which is an important indicator of the ignition process). So, the behaviors of different fuels in regard to the combustion process have been investigated. Diesel, SMDS and mixtures of n-heptane and iso-octane were tested with various EGR ratios, boost pressures and air/fuel ratios.