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

摘要

Numerical studies are performed to identify an optimal range of geometric parameters in connection with the design of an impingement-conditioned small direct-injection diesel engine. The parametric studies were made in a pressure chamber with acircular protrusion on to which sprays are directed to impinge. Computational runs were made for 24 cases carefully chosen to allow examination of the effects on post-impingement spray characteristics of the following parameters: (a) the nozzle-platedistance and (b) the size and geometry pattern of the protrusion. An optimal range of these parameters has been identified through an analysis of the calculated results in terms of vapour concentration, the Sauter mean diameter of the wall spray and thedispersed 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 andambient conditions. This raises the possibility 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 engineefficiency.