a photocatalytic ignition system is provided that basically comprises an ignition chamber , a photocatalyst and a light source . the ignition chamber is configured to receive an air fuel mixture . the photocatalyst is arranged in the ignition chamber to contact an air fuel mixture . the light source is arranged to shine light on the photocatalyst . the photocatalyst includes a photocatalytic material having an oxygen absorbing and a desorbing function . the photocatalytic ignition system is capable of igniting a lean air fuel mixture with a greatly reduced amount of light energy .