Understanding diesel injection characteristics in winter conditions

Abstract

Starting and operating of diesel engines in cold conditions is a common and important problem. Many factors such as ambient conditions, fuel properties, fuel injection, cranking speed, etc, affect cold engine functionality. In order to improve diesel engine cold start, it is essential to understand better these problems. In this paper the injection development at cold temperatures is studied, since it is an important parameter that affects the fuel interaction with the air, so the future combustion process would also be influenced. In particular, a hydraulic characterization of diesel injection is made, using specialized test rigs that simulate real engine in-cylinder air pressure and density; the fuel is injected from three axi-symmetric convergent nozzles at several injection pressures (30, 50, 80, 120 and 180 MPa), two chamber densities and two temperatures of 255 K (winter) and 298 K (reference). In order to achieve winter cold conditions, the facilities are introduced into a specialized climatic room with optical access, where the temperature and humidity are carefully controlled. Then, an extended analysis is carried out, based on mass flow, momentum and visualization measurements, obtaining real values of Reynolds numbers, drag coefficients and effective velocity in the outlet orifice, used to validate theoretical correlations. Results showed that winter temperature changes significantly fuel properties, affecting the spray development, producing a smaller injected mass and shorter spray momentum and penetration. Copyright © 2009 SAE International.