Experimental investigation of a premixed compression ignition engine

Premixed compression-ignition (PCI) combustion techniques using low-cetane fuels, including Dieseline (mixture of diesel-gasoline) and naphtha, were investigated in a light-duty multi-cylinder CI-engine focusing mainly on reducing emissions while maintaining or improving the brake-thermal-efficiency. Different fuel-injection and intake/exhaust handling strategies were investigated in a wide engine operating load range from 1.4 to 17.3 bar BMEP. Moreover, an out-cylinder emission reduction technique through using a diesel-oxidation-catalyst (DOC) was investigated. Hot (uncooled) exhaust-gas-recirculation (EGR) combined with low fuel-injection-pressure (as low as 150 bar) significantly enhanced combustion-performance (COV99% with respect to the diesel-CI baseline, in terms of number and mass, while maintaining brake-specific-NOx below 0.4 g/kWh. At loads more than 6 bar BMEP, double-injection strategy advanced combustion-phasing, where the first injection-event was shown to be significantly influential. Due to narrower boiling-range of naphtha compared to Dieseline, naphtha PCI resulted in high-COV at low loads, while it resulted in rapid-combustion at medium/high loads. Utilisation of the hot-EGR is a “win-win” strategy to enhance the combustion-process of the PCI-engine and reduction of the volatile/semi-volatile compounds using the DOC