fig7 shows the comparison of diesel,PODE15 and PODE25 on BTE and BSFC at different loads. At low load, with the increase of EGR, the prolonged ignition delay results in higher premix combustion ratio and the combustion efficiencies can be maintained at high levels because of the sufficient fresh air supply. Therefore, the BTE of all fuels depict slightly increase with the increase of EGR. At medium load, the BTEs of all fuels decrease with the increase of EGR because of the deteriorated combustion efficiency. At both low and medium loads, BTE decreases with the increase of blending ratio because of the lower premix combustion fraction, which is shown in fig5 . Moreover, with the increase of blending ratio, more cyclic fuel mass is needed to maintain the same total energy, combined with the higher fuel density, resulting in higher spray momentum, which is prone to increase the spray liquid and vapor penetrations, thus more fraction of air-fuel mixture may diffuse and burn closer to cylinder liner than diesel, which in turn may increase the heat transfer loss. At high load, the difference in BTE between diesel, PODE15 and PODE25 is getting smaller than that at low and medium loads. When the EGR is above 10%, the BTEs of diesel/PODE blends are higher than diesel because of the higher combustion efficiency and higher combustion rate in the late combustion phase. When the EGR is further increased up to 15%, the BTE decrease rate of diesel is obviously higher than those of diesel/PODE blends. Thus indicates that the advantage of high oxygen content and high volatility of PODE can fully exhibited it's capability in improving combustion efficiency and show greater BTE improvement at high load conditions with heavy EGR. Combined the synergistic effects of heat transfer loss, combustion rate and combustion efficiency, PODE15 shows the highest BTE at high EGR ratio conditions. However, it should be noted that, when the EGR is further increased, PODE25 has higher potential to improve the BTE than PODE15 because the oxygen content in the fuel may play more important role in improving combustion efficiency at such low excess air ratio conditions.