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A computational and experimental study has been carried out to assess the high load efficiency and emissions potential of a combustion system designed to operate on low octane gasoline (or naphtha). The “naphtha engine” concept utilizes spark ignition at low load, HCCI at intermediate load, and compression ignition at high load; this paper focuses on high load (compression ignition) operation. Experiments were carried out in a single cylinder diesel engine with compression ratio of 16 and a common rail injector/fuel delivery system. Three fuels were examined: a light naphtha (RON∼59, CN∼34), heavy naphtha (RON∼66, CN∼31), and heavy naphtha additized with cetane improver (CN∼40). With single fuel injection near top dead center (TDC) (diesel-like combustion), excessive combustion noise is generated as the load increases. This noise limits the maximum power, in agreement with the CFD predictions. The noise-limited maximum power increases somewhat with the use of single pilot injection.

The effects of fuel octane have been assessed on the efficiency and emissions of a high compression ratio (ε=13) spark ignition direct injection (SIDI) engine. Under low load stratified operation (1200 rpm, ∼20% load), a low octane fuel (RON=84, comprised of toluene, iso-octane, and n-heptane) yielded higher brake thermal efficiency and significantly lower hydrocarbon emissions than a base gasoline (RON=91). The indicator diagram for the low octane fuel showed evidence for two stage heat release, suggesting the presence of spark induced compression ignition (SICI). These results suggest that higher efficiency under low load stratified conditions can be obtained with lower octane fuels that undergo SICI combustion. The effect of fuel octane under high load was assessed at WOT with a high RON model fuel (RON=103, comprised of toluene, iso-octane, and n-heptane).

A two-color high speed shutter TV camera system has been developed as a new sensing device for measuring the flame temperature in engines. The TV camera system can measure the radiant intensities of high temperature substances accurately and rapidly. And, the two-dimensional temperature distribution can be easily calculated from the radiant intensities by using an image processor. This system is applicable to measurement of flame temperatures in diesel and gasoline engines. The relation between the progress of combustion phenomena and the measured temperature distribution is clearly explained. It is confirmed that the system is effective for measurement of the flame temperature distribution in engines.