 Engine design can then be optimised with the recorded data and the visualisation of the combustion cycle.The flow and direction of the gas particles can be improved by changing shape and sizes of the chamber, valves, spark plug, injectors and pistons resulting in improved combustion and performance and in reduced emissions.Engine heads with two spark plug holes per cylinder can be used to record the velocity and direction of the movement of gas particles in an engine running under live, firing conditions.