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An improvement of thermal efficiency of internal combustion engines is strongly required. Meanwhile, from the viewpoint of refinery, CO2 emissions and gasoline price decrease when lower octane gasoline can be used for vehicles. If lower octane gasoline is used for current vehicles, fuel consumption rate would increase due to abnormal combustion. However, if a Homogeneous Charge Compression Ignition (HCCI) engine were to be used, the effect of octane number on engine performance would be relatively small and it has been revealed that the thermal efficiency is almost unchanged. In this study, the engine performance estimation of HCCI combustion using lower octane gasoline as a vision of the future engine was achieved. To quantitatively investigate the fuel consumption performance of a gasoline HCCI engine using lower octane fuel, the estimation of fuel consumption under different driving test cycles with different transmissions is carried out using 1D engine simulation code.

In this study, the effect of the low octane number fuel on HCCI engine performance was experimentally investigated using a slightly modified commercial four-cylinder gasoline engine. To operate the engine in HCCI strategy with wide operational range, the blowdwon supercharging (BDSC) system proposed by the authors was applied in the test engine. Research octane number (RON) of test fuels was varied from 90 to 78.5 as an experimental parameter. Experimental results showed that in the range of the present study, HCCI operational range, brake thermal efficiency and exhaust emissions during HCCI operation were little affected by the RON of the test fuels. In contrast, during SI operation, thermal efficiency was deteriorated with lower RON fuel because of knocking.