A spherical combustion chamber was provided in the present experiment to measure the burning velocities of homogeneous lean mixtures of air and gaseous fuel under microgravity. A 5 m drop tower realized microgravity for about 1 s by dropping the chamber freely. The burning velocity of the mixtures was determined from the measured time histories of the chamber pressure. Methane was chosen as the test fuel, because it is the major component of natural gas and natural gas is considered to be one of the most promising candidates as alternative fuel for several application. The effects of pressure, temperature and equivalence ratio on the burning velocity were examined. The burning velocity was found to decrease with an increase in pressure and with a decrease in temperature or equivalence ratio. The addition of small amount of hydrogen was effective for increasing the burning velocity.
