Lean Flammability Limits of Syngas/Air Mixtures at Elevated Temperatures and Pressures

New experimental results for lean flammability limits (LFLs) of syngas/air (H-2/CO/air) mixtures have been obtained at temperatures up to 200 degrees C and pressures up to 9 bar. ASTM Standard E918 (1983) provided the framework for tests at these elevated conditions, using a 1-L pressure-rated test cylinder in which the fuel-air mixtures were prepared and then ignited. The purpose for characterizing the flammability limits for these gaseous mixtures is to facilitate development of appropriate procedures for the safe industrial use of syngas, which contains large quantities of hydrogen and carbon monoxide gas. The LFLs for each gas mixture are found to decrease linearly with increasing temperature at all test pressures. The LFL results at atmospheric pressure are consistent with previous flammability studies, while those at elevated pressures represent new flammability data. An increase in the initial test pressure results in an increase of the LFLs for each test mixture, which also serves to address the lack of syngas/air flammability data at elevated pressures. An empirical formula is derived that allows for the calculation of the LFLs of all syngas/air test mixtures in the temperature and pressure range of the current study in an effort to promote the ease of use in practical applications. Predicted LFL values obtained using Le Chatelier's mixing rule and an appropriate choice for the lower flammability limit of pure carbon monoxide are consistent with the experimentally determined values near ambient conditions of temperature and pressure.