BURNING VELOCITY OF METHANE-AIR FLAMES

Burning velocity measurements using stationary flames have been refined to give results with a mean error as low as ± 1 per cent. The method employs nozzle burners and a single pass schlieren system. Precautions have been taken to minimize errors at each stage of the experiments and calculations. The influence of burner design and the use of approximations in burning velocity measurements have also been investigated. The maximum burning velocity of methane in air at 25°C and 760 mm of mercury is concluded to be 39·6 ± 0·4 cm/sec at a methane concentration of 10·16 ± 0·06 per cent by volume. The effects of the following additives on methane-air burning velocities are reported: nitrogen, carbon dioxide, water vapour, methanol, acetaldehyde, formaldehyde, nitromethane, nitrogen dioxide and hydrogen peroxide. The retarding effects on burning velocity of the first three additives were in the order nitrogen < water vapour < carbon dioxide. These effects could be explained on the grounds of dilution and heat abstraction. No additive produced any flame-promoting effect and the burning velocity results obtained could be explained by the thermal properties of the additives or by their actions as fuels or oxidants. Nitromethane was found to be capable of acting simultaneously as both a fuel and an oxidant. © 1969.