A study on autoignition characteristics of H_2-O_2 mixtures with diluents of Ar/N_2 in rapid compression machine for argon power cycle engines

摘要

The autoignition features of H-2-O-2 are crucial for Argon Power Cycle (APC) engines to understand the abnormal combustion in spark-ignition mode and to realize stable ignition in compression-ignition mode. A well-validated H-2-O-2 mechanism is a cornerstone to all hydrocarbon reaction kinetics emphasizing its importance in fundamental research. Here measurements of the ignition delay times of H-2-O-2 mixtures have been conducted in a rapid compression machine at 1.0, 3.0, and 5.0 MPa, 903 similar to 1042 K, with excess oxygen ratio of 1.0, 2.0, and 4.0, dilution ratio of 70%, 80%, and 90%, with argon ratio in the diluent of 50%, 60%, 70%, and 75%. 394 data points and 85 data sets were consequently obtained. A comprehensive comparison between 17 selected literature mechanisms was then performed. Results show that the ignition delay time of H-2 is very sensitive to the temperature, especially near the ignition limit. The argon ratio in the diluent has a remarkable effect on the ignition delay. High pressure accelerates the autoignition, while both a high dilution ratio and a high excess oxygen ratio inhibit the autoignition. This research work suggests that a combination of highly diluted and ultra-lean combustion may inhibit knock in APC engines. H + O-2 (+M) = HO2 (+M) and H + O-2 = O + OH are the most sensitive reactions at 1.0 MPa over 950 K, while 2OH (+M) = H2O2 (+M) and H + H2O2 = H-2 + HO2 are the most sensitive reactions at both 3.0 and 5.0 MPa.