On the Relative Roles of Fuel Spray Kinetic Energy and Engine Speed in Determining Mixing Rates in D.I. Diesel Engines

Abstract

This paper describes an attempt to separate out and to quantify the relative importance of fuel injection characteristics and in-cylinder air motion as factors influencing the rate of fuel-air mixing and of combustion in high-speed D.I. diesel engines, where bulk swirling air motion is absent. Tests on a 121 mm bore × 139 mm stroke, 1.6 liter, single-cylinder engine at constant engine speed reveal substantially shorter fuel-air mixing times as the mean fuel injection kinetic energy (M.I.K.E.) is increased. Also, tests at constant injection kinetic energy but with varying engine speed (involving different fuel injection system builds at each speed) show that fuel-air mixing times are reduced at higher engine speeds. From these trends it is concluded that, while injection kinetic energy is the dominant factor in determining fuel-air mixing rates in D.I. diesels, small-scale turbulent air motions, the intensity and structure of which are related to engine speed, also exert an important influence on the mixing rate.