The experimental results for CO2 are shown in Fig. 3a, the levels of CO2 in exhaust gas of all the fuels increased with increasing loads. This is because more supplied fuel was combusted with the richer mixture at the higher loads. Therefore, more CO2 was produced and its concentration in exhaust gas increased. Fig. 3a shows that the levels of CO2 for all the fuels were quite similar; however, in comparison, the levels of CO2 for DgMCPO20 and EMCPO30 were slightly lower than that of diesel (1.9% and 1.2%, respectively).