Practical combustion devices frequently rely upon forced ignition of turbulent fuel/oxidizer mixtures that also contain the product species of combustion. Examples of this include engines that use exhaust gas recirculation (EGR), inter-turbine burners in aircraft engines, and other systems the utilize staged combustion. In this work, the effects of major combustion product species (i.e., N2, CO2, H2O, and NO) on forced ignition of CH4/air mixtures were identified and quantified. Additionally, turbulent flame speed measurements of premixed, jet-A/air mixtures were obtained with and without dilution with the same species. The equivalence ratios, adiabatic flame temperatures, and concentrations of individual diluents in mixtures were systematically changed to highlight the effects of changes in mixture composition, kinetics, and radiation heat loss. Addition of N2, CO2, and H2O to the unburned mixture was found to reduce the probability of forced ignition in CH4/air mixtures, the growth rate of ignition kernels, and the turbulent flame speed of jet-A/air mixtures. Dilution with N2 had the smallest effect on all parameters, and dilution with CO2 had the largest effect. Laminar flame calculations were used to provide insight into the changes in chemistry induced by particular diluent species, and the ways in which these changes impact forced ignition and turbulent flame propagation.