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A series of engine experiments have been performed to explore the impact intake temperature, engine speed and fuel composition on the HCCI operating range of a CFR engine. The experimental matrix covers a range of engine speeds 600 - 2000 RPM), intake temperatures (300 K - 400 K), and four different fuels. Three of the fuels had different chemical composition but had equivalent research octane numbers of 91.8. The fourth fuel, a blend of primary reference fuels had a research octane number of 70. The acceptable HCCI operating range of the engine was defined through two criteria; the rate of pressure rise needed to be less than 10 MPa per crank angle and the covariance of the indicated mean effective pressure needed to be less than 10 percent. Using these limits the HCCI operating range for the engine was evaluated for the experimental matrix. Data for emissions, and fuel consumption as well as in-cylinder pressure were recorded.

A single cylinder CFR research engine has been run in HCCI combustion mode for a range of temperatures and fuel compositions. The data indicate that the best HCCI operation, as measured by a combination of successful combustion with low ISFC, occurs at or near the rich limit of operation. Analysis of the pressure and heat release histories indicated the presence, or absence, and impact of the fuel's NTC ignition behavior on establishing successful HCCI operation. The auto-ignition trends observed were in complete agreement with previous results found in the literature. Furthermore, analysis of the importance of the fuel's octane sensitivity, through assessment of an octane index, successfully explained the changes in the fuels auto-ignition tendency with changes in engine operating conditions.