Optimizing injector nozzle hole layout of a direct-injection spark-ignition engine for wide open throttle condition

Abstract

The direct-injection concept in gasoline engines induces emission problems due to wall impingement of fuel and lack of mixing time, compared to port-fuel-injection engines. One of the solutions for these problems is optimization of the spray pattern. In this study, injector nozzle arrangement and injection timing were optimized under the wide-open-throttle condition using computational fluid dynamics. An injection pressure of 33 MPa was utilized. Mixture homogeneity, turbulent kinetic energy, and fuel film mass were monitored to evaluate the intermediate optimal design. These variables comprise the objective function. The nozzle arrangement was restricted to consider the processability and reduce computational costs. The KIVA-3V release 2 code was combined with the optimization tool. Depending on the design, the amount of leaking along the outflow to the intake port at the end of the intake process varies, however the injection quantity was maintained for simplification of optimization process. After optimization, the vapor fuel mass fraction in the intake port was considered to form a stoichiometric mixture, and mixture formation and combustion processes were analyzed. The optimal design had a narrower pattern than the reference design and targeted the downward direction when mounted on the engine because it is easy to increase in-cylinder turbulence intensity. The optimal design showed that the mixture homogeneity increased by 0.86% based on homogeneity index and the fuel film mass decreased by 51%, while the turbulent kinetic energy showed no significant change. The exhaust emissions (carbon monoxide, hydrocarbon, soot, nitrogen oxide) were reduced, while the indicated mean effective pressure remained constant.