Search Results

It is found that a thin and rich mixture layer on a wall is formed after impingement of a gas jet of fuel on the wall. The measured thickness of the mixture layer is about 2 mm. and its dispersion rate after the end of injection is much lower, compared to that of a space gas jet. This phenomenon in a small D.I. diesel engine is known as “wall wetting” or “wall fuel accumulation” which has an important influence on engine fuel consumption and emissions. This paper presents a technique for enhancing the near wall mixing of an impinging jet by means of a bump on the wall. The development of a wall jet formed after an impingement of a gas jet has been investigated by simultaneously measuring the near wall velocity and concentration distribution. It has been found that a wall jet is stripped off the wall and ejected as a secondary jet when the wall jet encounters a bump of the wall.

The effects of jet impingement and turbulence structure on jet mixing rate arc investigated by using a simultaneous measurement system of concentration and velocity. It is found that, after the end of injection, dispersion of momentum of a CO2 jet Is much faster than that of concentration. The residual gas is then left in a rather quiescent atmosphere, that makes a sluggish mixing process of the residual gas. Jet impingement can create intensive air motion in the near impingement region, that promotes the mixing of the residual gas. However, the effect of jet impingement decreases as the distance from the impingement point increases.