IGNITION DELAY CHARACTERISTICS OF METHANE FUELS

A comprehensive literature search and a series of shock-tube experimen ts were undertaken to determine the ignition delay times for mixtures of methane with ethane, propane or butane, and for a typical natural g as fuel. Ignition delay experiments were conducted at equivalence rati os of 0.45-1.25 for temperatures 1300-2000 K and pressures 3-15 atm. T he combined data were used to develop general correlations for predict ing the ignition delays of binary methane-hydrocarbon mixtures and mul ticomponent natural gas mixtures in terms of temperature and the initi al fuel and oxygen concentrations. For natural gas, the ignition delay was correlated by the empirical expression t = 1.77 x 10(-4) exp (186 93/T)[O-2](-1.05)[CH4](0.66)[HC](-0.39) in which concentrations are ex pressed in molecules per cubic cm and the [HC] factor represents the t otal molar concentration of all non-methane hydrocarbons. Chemical kin etic modeling was also performed to define the ignition mechanisms, an d to permit extrapolation of data and prediction of the effects of usi ng vitiated air for combustor testing.