This figure demonstrates the effect of EGR on NOx emission.It is obvious from the figure that the amount of NOx emission decreases as the percentage of EGR increases. For the same load and speed, NOx emission decreases with increase in percentage of EGR. When EGR increases, availability of O2 decreases.At the same time the temperature inside the cylinder decreases which is required to be at high level for the formation of NOx .Because of these two reasons NOx formation decreases.Thus the amount of NOx emission decreases with increase in percentage of EGR.