Mixture formation enhancement in a direct-injection spark-ignition engine using horizontal injection

Abstract

In a direct-injection gasoline engine, combustion instability can increase because of the formation of an inhomogeneous mixture under stoichiometric conditions, a slow combustion rate under lean conditions, and misfires. Effective methods of dealing with combustion instability include enhancing tumble, increasing turbulence intensity, and enhancing stratification, and increasing flow velocity near the spark plug. Many studies have been conducted to enhance in-cylinder flows, but they have been limited to geometry modification or multi-injection. In this study, we adopt a horizontal injection strategy, as opposed to simple multiple injection in previous studies, to enhance in-cylinder flows. We examine the effect of horizontal injection on tumble by using a horizontal injector with an upward spray pattern and computational fluid dynamics. The tumble ratio and turbulence kinetic energy of the horizontal injector are compared to those of a conventional injector, which has a downward spray pattern. In addition, the effects of double injection on stratification and velocity near the spark plug at the end of compression are compared to that under single injection in terms of the equivalence ratio and average velocity near the spark plug. An injection pressure of 35 MPa is utilized. The total mass injected is 30 mg, and it is split into masses of 27 mg and 3 mg when using double injection. The CONVERGE v2.4 software application is used to reduce computational costs. The spray model is validated through a Schlieren visualization of the pent roof combustion chamber, in which a high-temperature and high-pressure environment are simulated. The results indicate that horizontal injection enhances the tumble ratio and turbulence intensity by 22% and 26%, respectively, compared to those achieved with conventional, downward-spray injection. While double injection fails to enhance the tumble ratio and turbulence kinetic energy because the second injection mass is small, the velocity and stratification near the spark plug at the end of the compression strike are enhanced from-2 and 13.8 m/s to 11.5 and 18.6 m/s, respectively, because of double injection.