Numerical studies of an impingement-conditioned small direct-injection diesel engine

Numerical studies are performed to identify an optimal range of geometric p arameters in connection with the design of an impingement-conditioned small direct-injection diesel engine. The parametric studies were made in a pres sure chamber with a circular protrusion on to which sprays are directed to impinge. Computational runs were made for 24 cases carefully chosen to allo w examination of the effects on post-impingement spray characteristics of t he following parameters: (a) the nozzle-plate distance and (b) the size and geometry pattern of the protrusion. An optimal range of these parameters h as been identified through an analysis of the calculated results in terms o f vapour concentration, the Sauter mean diameter of the wall spray and the dispersed wall spray volume. The results obtained also reveal that, by just changing the size of the impingement surface and the impingement distance, local fuel vaporization efficiency can be increased as high as 40 per cent under the same injection and ambient conditions. This raises the possibili ty that spray impingement may be conditioned in a manner ensuring good fuel distribution and a sufficient fuel-air mixing rate without even resorting to swirling air, thus improving substantially the engine efficiency.