The figure illustrates the effect of EGR on CO emission.It is evident from the figure that the CO emission increases with EGR. At the presence of EGR , extra CO is formed because of two reasons.First,application of EGR reduces the amount of fresh air entering the cylinder.So,insufficient oxygen burns with carbon and form CO.Again,when EGR is applied,there are more CO2 inside the combustion chamber.These CO2 absorb the heat inside the cylinder.This results in dissociation of CO2 and formation of extra CO.Thus CO emission increases with increase in percentage of EGR.