A fuel injection system have been evaluated prior to application in a rotary “Wankel” engine; the objective being to improve combustion efficiency and engine performance. Incomplete combustion produces various air pollutants such as carbon monoxide, nitrogen oxide, and nitrogen dioxide. Factors such as particle size distribution and injection- sparkling timing play an important role in improving the thermal efficiency of an engine. Fuel particle size is directly related to the design and quality of the atomiser. The more effective a fuel atomiser is, the smaller droplets it produces, thus increasing the fuel surface and evaporation rates. Increasing the burning range leads to a higher released power rates and lower exhausted pollutant emissions. High-power lasers and high-resolution CCD cameras are employed to perform the experimental work. Image processing is applied to investigate the spray behaviour and characteristic including spray profile, spray-cone angle, spray tip penetration and velocity, and spray development process. Microscopic characteristics of the fuel spray have been investigated as well using long distance microscopes. This includes particle size distribution and particle velocity (PIV).