Isolating the influence of exhaust gas recirculation on the ignition and combustion reaction for combustion control of polyoxymethylene dimethyl ethers (PODEn)/gasoline under various fuel distribution conditions

Using exhaust gas recirculation (EGR) is a potential way to modulate the combustion process and improve the performance of a compression-ignition engine. In this study, the influence of EGR on the ignition and combustion reaction of polyoxymethylene dimethyl ethers (PODE_n) as a gasoline-doped fuel was isolated for combustion control under various fuel distribution conditions, including fuel homogeneous, concentration-stratification, and reactivity-stratification conditions. In addition, the effect of EGR on engine performance was also isolated from CA50 (50 % burn point). The results indicated that for P20G80 (blend of 20 % PODE_n and 80 % gasoline by volume), increasing 10 % PODE_n and simultaneously introducing 60 % EGR can realize the same CA50 control as P20G80 under homogeneous conditions. For P20G80 under concentration-stratification conditions at the start of injection (SOI) of −180 and −160 °CA ATDC, introducing a slight amount of EGR below 10 % can promote the combustion intensity, since the unburned fuel recycled from the previous cycle through the EGR increases the local fuel concentration. Under fuel reactivity-stratification conditions, compared to the test conditions without EGR, the decreasing rate of ignition delay with the retarded SOI significantly reduces with the introduction of 25 % EGR, suggesting a nonlinear effect of EGR on the ignition delay.