Engine manufactures are currently seeking to develop spark ignition engines that are more fuel efficient, more refined and produce lower amounts of polluting emissions. To achieve these objectives an improved understanding of the factors governing the combustion process is required. Engine in-cylinder fluid motion is known to fundamentally affect fuel–air mixture preparation and flame propagation. Therefore, characterisation and quantification of the in-cylinder flow is an important step in the process of achieving the conditions necessary for optimal combustion. This thesis reports the application of two-colour Particle Image Velocimetry (PIV) to measure extended velocity fields within the combustion chamber of a firing production geometry optical engine. Two-colour PIV was used to obtain high spatial resolution fluid velocity maps for a range of crank angles and engine conditions. PIV measurements were obtained in the unburned gas ahead of the propagating flame and a combustible seeding material was used to clearly define the burned gas region. Data is presented for both the normal 2-valve running conditions and with one inlet port deactivated for both open-valve and closed-valve fuel injection timing.