Lean Combustion Chemical-Kinetics Studies of an Ethanol Four-Stroke Radical-Ignition DI-Diesel Engine

This study explores the potential for ethanol use in the DI-HCRI (direct-injection homogeneous-combustion radical-ignition) diesel engine with its periphery-mounted secondary radical-generation chambers (mini-chambers). The aim of this simulation study is to determine whether HCRI alone can extend the lean burn region of this four-stroke ethanol engine to include low NO_x operations at normal diesel compression ratios. The simulation employs a highly modified variant of an earlier single-phase full-kinetics formulation and a new chemical-kinetics mechanism with 57 species and 371 reactions. The fuel is injected in the liquid phase within both of the separate-but-connected open systems representing the main and mini chambers. Thus a droplet spray model is included in this full chemical-kinetics formulation to account for the vaporization and mixing of the liquid fuel in both chambers. Though the formulation is chemical-kinetics focused, it provides a fairly serious qualitative accounting for the regional effects of heat transfer, mass transfer and momentum transfer. It also accounts for the effects of turbulence on the exchange of mass and energy between the chambers. The multi-dimensional fuel droplet-spray computations are conducted in “virtual” space and incorporated directly into the one-dimensional (in time) full chemical-kinetics computations. The work adds veracity to earlier experimental ethanol RI results and represents a significant incremental step toward the refinement and validation of a two-phase radical ignition (RI) chemical-kinetics simulation model. This is the first RI full chemical-kinetics study with a fuel containing more than a single carbon atom.