Abstract: Air pollution is one of main challenging issues now a days that some researchers has been trying to solved. There are so many aspects that can cause air pollution and the biggest one is from marine transportation. The emissions from marine transportation are mostly from the engine propulsion which is using diesel engine as their driver. Diesel consumption is responsible for serious air pollution which includes Nitrogen Oxides (NOx), Hydrocarbon (HC), Carbon monoxide (CO) and some Particulate Matter (PM). Therefore, efforts to tackle harmful gases from diesel engines is very important because with such efforts can prevent the pollution level increases. In general, an engine will operate when completed elements of combustion that include air, fuel and heat. This composition is called air/fuel ratio which shows a comparison the amount of air and fuel to be incorporated into the engine combustion chamber. Due to the large impact of air/fuel ratio to engine output generated in this study will be explained in more detail whatever the impact of the effect of the composition of the air/fuel ratio both the engine and the output of the engine, especially, the effect of the emission