Comparison of a Detailed and a Reduced Ethanol Oxidation Mechanism in HCCI Combustion Using a Multi-Zone Model

ABSTRACT

The subject of the present study is the comparison of a detailed and a reduced ethanol oxidation mechanism. The main scope is to determine whether the reduction of species and reactions, which reduces the simulation time, affects the prediction of performance and emissions from a multi-zone model. The numerical study is conducted using a previously published multi-zone model, which incorporates chemical kinetics for the estimation of reaction rates. The model also includes sub-models for the description of heat transfer, mass transfer and crevice flow, and produces a temperature distribution within the combustion chamber. The cases simulated and examined involve ethanol HCCI combustion in a reciprocating internal combustion engine with various equivalence ratios. At each load two simulations are conducted with the multi-zone model, i.e. one with each oxidation mechanism, and the results are compared to the corresponding experimental results. The comparison of the two oxidation mechanisms includes simulation times, pressure traces, heat release rates, composition and quantity of unburned hydrocarbons emissions, including their composition, carbon monoxide and nitrogen oxides emissions. The reduced model decreases the simulation time by 50%. The two mechanisms produce almost identical results as regards ignition timing. The pollutant emissions predicted are essentially the same for the two mechanisms, with the greatest difference occurring between predicted CO emissions (~9%) at the low load cases.