Ignition Characteristics of Ethane and Its Roles in Natural Gas for HCCI Engine Operation 2015-01-0811

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.