The effect of initial pressure on explosions of hydrogen-enriched methane/air mixtures

The evaluation of safety parameters for binary and ternary mixtures of hydrogen and light hydro-carbons is essential for the definition of the combustion characteristics of bio-derived fuel-gas mixtures. Furthermore, with specific reference to laminar burning velocity, there is a strong need to define simple correlations, which would allow a fast prediction of global burning velocity of the mixtures starting from molar compositions and laminar burning velocity of the pure components, in analogy with Le Chatelier's rule for flammability limits. In this paper, a preliminary experimental and numerical study is performed for the assessment of safety parameters for mixtures of methane, propane and hydrogen with air at initial ambient pressure. Explosion tests have been conducted in a reinforced 5 liters steel vessel. The PREMIX module of the CHEMKIN package, coupled to the Marinov detailed reaction scheme, has been used to compute the un-stretched laminar burning velocity. For model validation, results have been compared to experimental data.

Hydrogen-enrichment has been proposed as a useful method to overcome drawbacks (local flame extinction, combustion instabilities, lower power output, etc.) associated to turbulent premixed combustion of natural gas in both stationary and mobile systems. For the safe use of hydrogen-enriched hydrocarbon fuels, explosion data are needed. In this work, experimental tests were performed to evaluate the explosion parameters for stoichiometric hydrogen-methane blends in air, with the hydrogen molar content in the fuel varying from 30% up to 70%, at different initial pressures (1, 3 and 6 bar). Results allow quantifying the combined effects of hydrogen presence and initial pressure on maximum pressure, maximum rate of pressure rise and burning velocity.