A comprehensive literature search and a series of shock-tube experiments were undertaken to determine the ignition delay times for mixtures of methane with ethane, propane or butane, and for a typical natural gas fuel. Ignition delay experiments were conducted at equivalence ratios of 0.45-1.25 for temperatures 1300-2000 K and pressures 3-15 atm. The combined data were used to develop general correlations for predicting the ignition delays of binary methane-hydrocarbon mixtures and multicomponent natural gas mixtures in terms of temperature and the initial fuel and oxygen concentrations. For natural gas, the ignition delay was correlated by the empirical expression t = 1.77 x 10(-4) exp (18693/T)[O-2](-1.05)[CH4](0.66)[HC](-0.39)
in which concentrations are expressed in molecules per cubic cm and the [HC] factor represents the total molar concentration of all non-methane hydrocarbons. Chemical kinetic modeling was also performed to define the ignition mechanisms, and to permit extrapolation of data and prediction of the effects of using vitiated air for combustor testing.