The NOx and soot emissions of diesel, PODE15 and PODE25 at different loads are shown in Fig.9. Theoretically, the presence of oxygen in diesel/PODE blends has the tendency to increase the NOx emission. However, the experimental results show that blending PODE can actually reduce the NOx emission under low and medium loads because of lower CN and lower LHV of diesel/PODE blends resulting in lower peak HRR and lower premixed combustion ratio. Previous studies also made conclusions that higher peak HRR generally produces more NOx emission and fuel with high CN is beneficial to NOx reduction because of shorter ignition delay resulting in lower premixed combustion fraction. With the increase of load, the differences of peak HRR and ignition delay between these fuels are getting smaller, resulting in quite close NOx emission between diesel, PODE15 and PODE25. Moreover, when the EGR is increased to a relative higher level at low or medium load, the difference of NOx emission between these fuels are getting smaller. While at high load, the difference of fuel properties has almost no effects on NOx emssion between these fuels are getting smaller. While at high load, the difference of fuel properties has almost no effects on NOx emission. It is said that EGR is the primary factor while the difference of fuel properties is the secondary factor that effects the NOx emission at low excess air ratio conditions. The conclusion was also made by Ruggero et al.