The Simulation Of The Combustion AndEmission Characteristics Of A Diesel/Ethanol Reactivity Controlled Compression Ignition (RCCI) Engine

To overcome the problems associated with premixed charge compression ignition (PCCI) combustion such as the formation of homogeneous mixture and ignition control, the fuel reactivity controlled compression ignition (RCCI) has been proposed recently. In this combustion strategy, the diesel is injected into cylinder, while the fuel with high octane number and low boiling point is injected into intake port, so the stratified distribution of fuel reactivity is formed which leads to stratified combustion when be ignited by compression.To investigate the combustion and emission characteristics of a diesel/ethanol RCCI engine, a diesel/ethanol dual fuel chemical kinetic mechanism was developed in this study, which used a detailed mechanism of ethanol and a n-heptane simplified mechanism, and added a nitrogen oxides (NOX) formation mechanism, and the thermodynamic data of soot precursor and soot on this basis.The chemical kinetics code CHEMKIN was implemented into the KIVA-3V code advanced by American national laboratory, Los Alamos, so that the chemical reaction and flow were coupled. A multi-dimensional numerical model was established and verified by comparing the numerical simulation results with experimental results of diesel PCCI and ethanol homogeneous charge compression ignition (HCCI) combustion.The effects of start of injection (SOI) of diesel, mass fraction of premixed ethanol, initial in-cylinder temperature, initial in-cylinder pressure, speed of engine and concentration of mixed gas on engine combustion and emissions were investigated in this paper. The results show that both SOI and ethanol mass fraction have a significant impact on combustion and emissions, while the effect of initial in-cylinder temperature is not so significant. Increased ethanol fraction makes the cylinder peak pressure decreased and ignition timing delayed, while NOX、soot、carbon monoxide (CO) and hydrocarbon (HC) have a downward trend. With the diesel injection timing advance, the maximum cylinder explosion pressure rose, and ignition timing advanced. When the injection advance angle increases to a certain value (more than25°CA), ignition timing was postponed with the injection advancing. Advanced SOI is favorable to HC and soot reduction, yet not to the decrease of NOX and CO. Both increasing ethanol fraction and advancing the SOI are beneficial to improve fuel economy and avoid engine knock. Using intake boosting can increase peak cylinder pressure and temperature and advance ignition timing with decreased soot, CO and HC emissions and increased NOX emission. Engine speed has little effect on the combustion process, NOX, soot and HC emissions is essentially a downward trend with the increased engine speed, while CO emission has an upward trend. When the cylinder mixture concentration increases, peak cylinder combustion pressure and in-cylinder combustion temperature first increase and then decrease with delayed ignition timing.