A chemical kinetics based investigation on laminar burning velocity and knock occurrence in a spark-ignition engine fueled with ethanol–water blends. (15th November 2020) - Fagundez, J.L.S.
Highlights: NUI Galway and 40-Skeletal mechanisms predicted auto-ignition in ethanol fuels. Ethanol fuels with more water content had increased mixture reactivity. Knocking combustion rarely occurs in wet ethanol fuels with water up to 20% (v/v). Unburned hydrocarbon emissions increased due to the lower in-cylinder temperature. CO2 emissions drop for wet ethanol fuels due to hydrocarbons partial oxidation. Abstract: Tests were conducted on a spark ignition engine fueled with ethanol fuels with water content up to 30% by volume. Engine experiments, along with the determination of in-cylinder state variables by GT-Power® computational routines, allowed to identify representative engine operating conditions for ethanol oxidation. Reactor simulations with Cantera® in Python environment were performed and four kinetic mechanisms with different levels of detail were applied to solve the ethanol – water – air mixture oxidation process: Marinov, UC San Diego, NUI Galway and a 40-species Skeletal. Boundary conditions for mixture auto-ignition assessment through Livengood-Wu integral indicated higher risk of knock occurrence for E96 fuel, with medium to high risk for E90 and E80 fuels using the NUI Galway mechanism and the simplest 40-species Skeletal mechanism. However, UC San Diego and Marinov mechanisms underpredicted the ignition carriers concentration and arrived at results in disagreement with what was verified experimentally. With oxidation evaluated through flame development, high water content impaired the laminar burning velocity, enlarging combustion duration due to the lower in-cylinder temperature and reducing combustion efficiency. However, knock tendency was reduced, allowing further advance in spark timing with wet ethanol fuels to without expressive increase on pressure rise rate, enabling higher indicated efficiencies with lower CO2 emissions.