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In order to achieve lower emissions and extensive load in the homogeneous charge compression ignition (HCCI) engine system, a novel fuel design concept that high-octane number fuel and high-cetane number fuel are mixed real-time to control HCCI combustion is proposed in this study. HCCI combustion fueled with iso-octane/n-heptane mixtures controlled real-time on a single-cylinder HCCI combustion engine is studied. The test results show that the equivalence ratio of n-heptane in mixtures decides ignition and controls the combustion phase of HCCI combustion. The addition of iso-octane extends knocking limit in equivalence ratio somewhat, but knocking occurrence mainly depends on the total concentration of mixture. Although operating range in equivalence ratio becomes narrow with the increasing proportion of iso-octane, the maximum load of HCCI combustion fueled with iso-octane/n-heptane mixtures controlled real-time is increased about 80% more than that of pure n-heptane. When iso-octane/ n-heptane mixtures are controlled in optimized method, it is proved that the load of HCCI combustion can be fully extended and emissions can be decreased remarkably, while at the same time the higher indicated thermal efficiencies are obtained over the extensive operation range.HCCI combustion is receiving increasing attention for its potential to improve both the efficiency and emissions of the engine [1] . In an HCCI combustion engine, the homogenous fuel-air mixture is compressed to attain auto-ignition close to top dead center (TDC). As the ignition process depends on a spontaneous autoignition at many points and HCCI combustion has no flame propagation, the whole bulk burns almost simultaneously and the combustion rate becomes very fast.Highly diluted mixtures are necessary to avoid knocking. Compared with conventional engines, it is fundamentally more challenging to control the start of combustion and the rate of heat release over a wide range of engine operating conditions [1][2][3] , because the ignition is sensitive to very small changes in temperature in HCCI combustion mode, while conventional engines have a direct control over the start of ignition through a spark for spark ignition mode and fuel injection timing for diesel engines.The ignition timing and combustion rate significantly depend on the interaction between the chemical kinetics of the fuel-air-residual gas mixture and their temperature-pressure history during the compression process. Two primary factors to influence HCCI combustion can be deduced. First, the environmental conditions such as pressure, temperature and components of air-residual gas mixture are important to HCCI combustion. Hence, exhaust gas recirculation (EGR), variable compression ratio (VCR) and variable valve timing (VVT) [4][5][6] measures that can influence the environmental condition of HCCI combustion, have led to some improvement on controlling the ignition timing and combustion rate of HCCI combustion.On the other hand, the fuel properties are more important to HCCI combustion. Fuel...

This paper investigated the effects of methanol additive on autoignition and combustion rate of homogeneous charge compression ignition (HCCI) combustion using n-heptane. n-Heptane and 10–40 per cent (v/v) methanol/n-heptane blend fuels were injected into the intake port. The combustion characteristics and emissions of HCCI combustion for different methanol/n-heptane blend fuels at 1800r/min were recorded and analysed. The results show that the ignition timing of low- and high-temperature reaction is delayed and the maximum heat release during the low-temperature stage decreases with the increase in methanol addition in n-heptane. Sequentially, both the maximum and minimum accepted equivalence ratio increase, but the maximum engine load could not be further expanded beyond 40 per cent and above methanol/n-heptane fuels. For 20 and 30 per cent methanol/ n-heptane blend fuels, the combustion phasing of the high-temperature reaction occurs between -5-5° CA ATDC (crank angle after top dead centre) and the combustion events accomplished during the expanding stroke. With regard to the emissions, 10 and 20 per cent methanol addition shows little effect on CO and HC emissions, but substantially increases for 30 and 40 per cent methanol/n-heptane blend fuels. NOx emissions are greatly lowered for all fuels.