Results are presented of ignition delay measurements, over the temperature range 1073-2211 K, obtained by monitoring CH emission from ethylene and propane mixtures. The relative influence of argon and nitrogen as diluents is also investigated. Comparisons with other experimental data are made and the validity of chemical kinetic reaction mechanisms discussed. Spark schlieren photographs of the reflection and subsequent ignition processes are also presented, and the effects of varying the diluent and degree of dilution away from ideal conditions investigated. In some cases, acceleration of the reaction wave has been observed, with transition to detonation occurring a short time later.