Effects of Throat Shape on Combustion Improvement in a Swirl-Chamber Diesel Engine with Electronically Controlled Multi Hole Injector

Abstract

<div class="section abstract"><div class="htmlview paragraph">In-Direct Injection (IDI) system are mainly used in off-road diesel engines with output of less than 19 kW. These engines generally employ a mechanical injection system. Since it is difficult for these engines to flexibly control the injection timing and injection quantity, there are restrictions on improving fuel efficiency and emission performance.</div><div class="htmlview paragraph">Therefore, we have developed an electronically controlled fuel injection system that is optimal for small diesel engines. We adopted injectors used in relatively inexpensive direct-injection gasoline engines for automobiles, instead of injectors for common rail systems, which are often used in diesel engines. The adopted injector is a multi-hole nozzle, and its spray behavior is different from that of the pintle nozzle used in swirl-chamber diesel engines. In swirl-chamber diesel engines, not only the injector type, but also the shape of the throat connecting the swirl-chamber and main chamber influences the formation of the fuel-air mixture.</div><div class="htmlview paragraph">In this research, 3D Computational Fluid Dynamics (CFD) was used to understand fuel-air mixture formation and to optimize the shape of throat. A spray model that can express the dynamic behavior of droplets is necessary for proper spray and combustion analysis. The spray behavior from the multi-hole nozzle was measured using a constant volume chamber. The spray model was validated based on the measurement data. The optimum combustion chamber shape for fuel-air mixture formation was investigated by in-cylinder combustion analysis using the calibrated spray model. As a result, it was shown that the diffusion combustion in the main chamber can be improved by adjusting the cone angle and the area of the throat.</div></div>