Development of Chemical Kinetic Mechanism for Dimethyl Ether (DME) with Comprehensive Polycyclic Aromatic Hydrocarbon (PAH) and NO _x Chemistry

Dimethyl ether (DME) appears to be an attractive alternative to common fossil fuels in compression ignition engines due to its smokeless combustion and fast mixture formation. However, in order to fully understand the complex combustion process of DME, there is still a remaining need to develop a comprehensive chemical kinetic mechanism that includes both soot and NO_x chemistry. In this study, a detailed DME mechanism with 305 species is developed from the basic DME mechanism of Curran et al. (2000) with addition of soot and NO_x chemistry from Howard's mechanism et al. (1999), and GRI 3.0 mechanism, respectively. Soot chemistry in Howard mechanism consisting hydrogen abstraction acetylene addition (HACA) and growth of small polycyclic aromatic hydrocarbons (PAH), assesses over a wide range of temperature and is able to predict good to fair the formation of PAH up to coronene. The comparison of ignition delay of the developed DME mechanism with results from shock-tube experiment by Pfahl et al. (1999) shows good agreement over all temperature ranges. Soot and NO formation region from the developed mechanism was also described using closed homogeneous reactor with 2 ms resident time. Here, DME reaction was discussed in terms of soot and NO formation regions over a wide range of temperature and equivalence ratio with comparison to n-heptane (diesel surrogate). Secondly, for time efficient computation, the skeletal mechanism was reduced using Path Flux Analysis (PFA) method by considering important species and reactions of higher order generations of selected species, while the other reduction methods such as Direct Relation Graph (DRG) only considers first generation. The reduced mechanism shows good accuracy with other published mechanisms.