Experimental investigation on velocity inside a diesel spray after impingement on a wall

Abstract

Recently, a combustion chamber of a high speed diesel engine has been downsized in order to improve fuel economy. Moreover, injection pressure of the diesel fuel tends to increase due to promotion of fuel atomization. Therefore, the diesel spray flame impinges on a cavity wall of a combustion chamber in recent diesel engines. It results that promotion of heat loss from the engine occurred due to the heat transfer between the impingement spray flame and the cavity wall. Therefore, it is necessary to understand the impingement phenomenon of the diesel spray flame for improvement of the thermal efficiency. In order to understand the impingement mechanism between the spray flame and the wall, velocity measurement of an impingement diesel spray flame is required. Moreover, the heat transfer strongly depends on the flow characteristics of the impingement spray flame. Velocity information of the impingement spray might provide heat transfer mechanism between the spray and the wall although the diesel spray was not a flame. In this study, velocity field of an impingement diesel spray was measured with time-resolved PIV. Effect of ambient gas density, injection pressure and impingement angle on flow characteristics of the impingement diesel spray was investigated. Moreover, velocity of the diesel spray just before impingement on the wall was measured in order to investigate dependence of the impinging spray velocity on the post-impingement spray velocity. As the result, averaged radial peak velocities of the post-impingement diesel spray decreased with an increase of ambient gas density. Moreover, dependence of the impinging spray velocity on the averaged peak velocities of the post-impingement spray was clarified.