Simulation Study of Sparked-Spray Induced Combustion at Ultra-Lean Conditions in a GDI Engine

Abstract

<div class="section abstract"><div class="htmlview paragraph">Ultra-lean combustion of GDI engine could achieve higher thermal efficiency and lower NOx emissions, but it also faces challenges such as ignition difficulties and low-speed flame propagation. In this paper, the sparked-spray is proposed as a novel ignition method, which employs the spark to ignite the fuel spray by the cooperative timing control of in-cylinder fuel injection and spark ignition and form a jet flame. Then the jet flame fronts propagate in the ultra-lean premixed mixture in the cylinder. This combustion mode is named Sparked-Spray Induced Combustion (SSIC) in this paper.</div><div class="htmlview paragraph">Based on a 3-cylinder 1.0L GDI engine, a 3D simulation model is established in the CONVERGE to study the effects of ignition strategy, compression ratio, and injection timing on SSIC with a global equivalence ratio of 0.50. The results show it is easier to form the jet flame when sparking at the spray front because the fuel has better atomization and lower turbulent kinetic energy at the spray front. The jet flame will be stronger if the ignition position is further from the injector, leading to shortened combustion duration and lower CO, Soot and HC emissions, but higher NOx emissions due to the increase of combustion temperature. With the increase of compression ratio, flame propagation speed is faster, thermal efficiency is higher (46.6% at compression ratio 14), and the emissions of CO, Soot and HC are decreased significantly, but NOx emissions are increased. At the compression ratio of 14, with the advance of injection timing, the thermal efficiency increased firstly and then decreased (47.3% at injection timing -30°CA ATDC), while HC, CO, Soot and NO_X emissions all decreased.</div></div>