Laminar flame speeds of lean H_2/O_2/He at low and elevated pressures

摘要

Laminar flame speed is one of the most important combustion properties of a combustible mixture. It is an important target for chemical mechanism validation and development, especially at low and elevated pressure conditions. In this study, the laminar flame speeds of lean hydrogen/oxygen/helium mixtures were measured at low and elevated pressures up to 7 atm using a dual-chambered high pressure combustion facility. Similar to experiments, numerical simulations of outwardly spherical flame propagation were conducted. Four chemical mechanisms for hydrogen available in the literature were considered in simulation and their performance in terms of predicting the stretched flame speeds, laminar flame speeds were examined through comparison between experimental and numerical results. It was found that at low pressures, especially at P<0.7 atm, the present experimental results of laminar flame speed are much higher than those predicted by these four chemical mechanisms. The laminar flame speed measured in experiments decreases as the pressure increases. However, the predicted laminar flame speed first increases and then decreases as the pressure increases. At high pressures, the experimental laminar flame speeds agree well with those predicted by chemical mechanisms. It was also found that the overall reaction order n at low pressure is above 2, while it is negative at high pressure.