Air Motion in a Four-Stroke Direct Injection Diesel Engine

This paper presents the results of a study of the air motion in a motored four-stroke direct injection diesel engine using hot-wire anemometry.The effects of engine speed, valve masking and supercharging on mean air swirl have been studied. A theoretical analysis is developed for the mean air swirl which in general shows good agreement with the experiments reported here and with the measurements of other workers on similarly sized engines.The problem of ‘squish’ has been investigated and it is shown to be the radial component of the spiralling swirl flow entering the combustion chamber. Reasonable agreement has been found between measurement of the radial flow component at the edge of the combustion bowl and a theoretical analysis that considers the bulk radial flow of air to the combustion bowl during the last 30°-40° b.t.d.c. of the compression period.