The upper explosion limit of lower alkanes and alkenes in air at elevated pressures and temperatures

The upper explosion limit (UEL) of ethane–air, propane–air, n-butane–air, ethylene–air and propylene–air mixtures is determined experimentally at initial pressures up to 30 bar and temperatures up to 250 °C. The experiments are performed in a closed spherical vessel with an internal diameter of 200 mm. The mixtures are ignited by fusing a coiled tungsten wire, placed at the centre of the vessel, by electric current. Flame propagation is said to have taken place if there is a pressure rise of at least 1% of the initial pressure after ignition of the mixture. In the pressure–temperature range investigated, a linear dependence of UEL on temperature and a bilinear dependence on pressure are found except in the vicinity of the auto-ignition range. A comparison of the UEL data of the lower alkanes shows that the UEL expressed as equivalence ratio (the actual fuel/air ratio divided by the stoichiometric fuel/air ratio) increases with increasing carbon number in the homologous series of alkanes.