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.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.