Detonation behaviors in stoichiometric CH4-H2-O2 under different initial pressures conditions

In this study, the detonation behaviors (i.e., detonation limit, detonation overpressure, mean velocity, velocity deficit, and cell sizes) of CH4-H2-O2 mixtures in a small-bore tube at different initial pressures (ranging from 6 kPa to 300 kPa) were investigated. Mixtures with different proportions of H2 in the total fuel (0, 10%, 20%, 25%, 30%, 50%, 75%, 100%) were tested. Steady one-dimensional ZND calculations are used to obtain detonation parameters such as induction zone length, stability parameters, and cell sizes. Results indicate that increasing the hydrogen fraction decreases the detonation limit. The addition of hydrogen can reduce velocity deficit, especially near the detonation limit pressure. Velocity deficits were found to be within 3.5% when the initial pressure higher than 50 kPa. Higher initial pressure may result in the mean detonation velocity surpassing the theoretical CJ velocity. The detonation overpressure increases with the initial pressure and decreases with hydrogen frac-tion. The influence of initial pressure on cell sizes weakens as hydrogen fraction increases. Besides, the induction zone length and stability parameter decrease as hydrogen fraction increases Notably, the stability parameter of mixtures with different hydrogen fractions shows different trends as the initial pressure increases. A linear relationship between actual measured cell sizes and induction zone length is given as lambda = 24.56 Delta i for hydrogen -methane-oxygen mixtures with the initial pressure range of 100 to 300 kPa. If experimental measurement error is considered, the prediction of the Ng model has reasonable accuracy.