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Ignition Characteristics of Ethane and Its Roles in Natural Gas for HCCI Engine Operation
Abstract:
The ignition characteristics of each component of natural gas and the chemical kinetic factors determining those characteristics were investigated using detailed chemical kinetic calculations. Ethane (C2H6) showed a relatively short ignition delay time with high initial temperature; the heat release profile was slow in the early stage of the ignition process and rapid during the late stage. Furthermore, the ignition delay time of C2H6 showed very low dependence on O2 concentration. In the ignition process of C2H6, HO2 is generated effectively by several reaction paths, and H2O2 is generated from HO2 and accumulated with a higher concentration, which promotes the OH formation rate of H2O2 (+ M) = OH + OH (+ M). The ignition characteristics for C2H6 can be explained by H2O2 decomposition governing OH formation at any initial temperature.
Furthermore, the relation between the operating characteristics of an HCCI engine and the ignition characteristics of C2H6, and its roles in CH4-based blended fuels for HCCI engine operation were investigated through engine tests. The CH4/C2H6 showed high ignition stability during the expansion stroke, high anti-knocking properties, and high EGR tolerance. These results revealed that C2H6 plays a significant role in expanding the operation range. Finally, engine operation tests at maximum loads, with and without EGR, indicated that CH4/C2H6 provides greater indicated thermal efficiency compared to CH4/n-C4H10, regardless of EGR rate and ignition timing. These results suggest that, in terms of thermal efficiency at the maximum load, anti-knocking properties are the most important ignition characteristics of C2H6.