fig.8 present the effects of PODE on CO and HC emissions at different loads and EGR rates. At low and medium loads, PODE15 and PODE25 have no significant effect on the reduction of CO emission compare to neat diesel because the oxygen concentration in cylinder is sufficient at these conditions, which is the key factor to oxidize the CO to CO2. Therefore, the function of the high oxygen content in the PODE blends is not conpletely exploited. However, when the operation condition shifts to high load, the available oxygen in cylinder is reduced, which affects the CO oxidization. In this case, the advantage of the high oxygen content in PODE can be effectively exhibited. Furthermore, superior volatility of PODE is also beneficial to improve the oxygen utilization in the fresh air. It clearly shows that blending PODE can dramatically reduce the CO emission, especially at high load conditions with high EGR. The HC emission is higher for all fuels at low load than at high load because of the over-lean mixture and low in-cylinder temperature. At medium or high load, HC emission is extremely low due to the high combustion temperature and high cylinder wall temperature, thus the incomplete combustion and wall quenching phenomenon can be reduced. Therefore, the high oxygen content of PODE blends can hardly present its capability to reduce HC emission at this condition.