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.