Numerical simulation of dimethyl ether/natural gas blend fuel HCCI combustion to investigate the effects of operational parameters on combustion and emissions

Abstract

Homogeneous charge compression ignition (HCCI) combustion phasing control is one of the most difficult challenges of operating this new concept of combustion. In this study, a dimethyl ether (DME)/natural gas (NG) blend fuel HCCI engine is simulated to investigate the effect of DME additive on the control of a NG HCCI start of combustion (SOC) timing. The studies are carried out in two sections. Firstly, different mole fractions of DME from 0 to 0.25% are thoroughly examined. In the second part, the effect of general equivalence ratio on the combustion phasing is studied. Moreover, in both sections, the studies are mainly focused on the influence of these two parameter variations on the SOC timing, auto-ignition temperature, heat flux, and heat capacity ratio. A 3D computational fluid dynamic AVL FIRE code coupled with CHEMKIN is adopted to simulate the HCCI combustion. Results showed that while DME amount increases in the mixture, a two-stage heat release rate would appear. DME additive can advance SOC and reduce requiring inlet temperature. Adding only 5% of DME would lead to 6.7-CAD change in SOC. Heat capacity ratio would lead to higher in-cylinder temperature during compression stroke, while equivalence ratio rises. 2.4 CAD change in SOC occurred for increasing equivalence ratio from 0.25 to 0.4.