The background for this master thesis is the need for lower emissions, especially NOx , COx, SOx and CxHy emissions. To meet stringent vehicular emission norms worldwide, various exhaust treatment techniques have been employed in modern engines. Oxides of nitrogen (NOx) are formed during combustion inside cylinder which is responsible for major respiratory problems in human beings. NOx also contributes to global warming and acid rain formation. Different reduction methods are described and evaluated in this study. This thesis presents a brief review of phase change material on the effect of exhaust emission concentration of internal combustion diesel engines based on the reports of different researchers available in the literature. The focus is on the “phase change materials (PCMS) NOx reduction technologies”. The evaluation consists of a literature study, modeling and simulations of phase change materials in combustion analysis and comparing the result of combustion with and without adding the PCMs. The comparison consists of engine performance, emission reduction in percent (%), material availability, and cost. Hence by introducing the paraffin wax near to the cylinder head of the exhaust port, NO emission is reduced by 45% when we compared to NO emission without paraffin wax.