Hydrogen autoignition at pressures above the second explosion limit (0.6–4.0 MPa)

The investigation of high-pressure autoignition of combustible mixtures is of importance in providing both practical information in the design of combustion systems and fundamental measurements to verify and develop chemical kinetic models. The autoignition characteristics of hydrogen-oxygen mixtures at low pressures have been explored extensively, whereas few measurements have been made at high pressures. The present measurements extend the range of pressures up to 4 MPa, where few measurements have yet been reported. Using a rapid compression machine equipped with a specially designed piston head, hydrogen autoignition pressure traces were measured at pressures above the second explosion limit (p=0.6–4 MPa, T=950–1050 K). The measured pressure records show a more gradual pressure increase during induction time in this regime than in the low-pressure regime, indicating that the energy release becomes significant at conditions over the second explosion limit. By comparing the measurements and a thermodynamic model which incorporates the heat transfer and energy release, a modified reaction rate constant for H₂O₂+H=HO₂+H₂, one of the most important reactions for hydrogen oxidation at high pressure, and the reaction with the largest uncertainty, is suggested in this work as k₁₇=2.3 . 10¹³exp(−4000/T) cm³/mol-s. The modeled pressure history with the modified reaction rate agrees well with the measured values during the induction period over the range of conditions tested. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 385–406, 1998