Licentiate's Thesis

Kiijärvi, J., The Principles of Diesel Fuel Injection System Modeling and Defining Flow Parameters. Espoo 1993, Helsinki University of Technology, Internal Combustion Engine Laboratory, Report 63, 133 pp. (in Finnish, Licentiate's Thesis).

Abstract

The fuel injection into the cylinder drives the combustion in the diesel engine. For this reason the injection must be controlled well. Since there is little literature about the fuel injection models of medium-speed diesel engines, the mathematical model and experiments were applied to injection system of this type of diesel engine.

In the diesel fuel injection system the flow of the liquid is unsteady. The calculation principles for this kind of flow are presented in the theoretical section. The components of fuel injection system are modeled using elements, whose properties are described by equations. The effects of such factors as wave propagation phenomena, pipe friction and cavitation were included in the model. The properties of the liquid are functions of pressure and temperature.

A mathematical model of the medium-speed diesel engine injection system is constructed from the elements. This injection system consists of a piston driven pump, a constant volume pressure valve, a pressure pipe and an injection valve.

The mathematical model must be verified later by comparing the results of a computer program and experimental data.

In the experimental part the fictive flow coefficients of the flow passages in a medium-speed diesel engine injection valve were measured. Diesel oil was used as liquid in these experiments. The fictive flow coefficients were measured using continuous flow.

When the flow was laminar or turbulent in the injection valve holes, the fictive flow coefficient followed the model of Giffen and Muraszew. If the flow cavitated in the holes, the fictive flow coefficient could be described with Schmitt's model.

The fictive flow coefficient between needle and seat did not follow any known model. The fictive flow coefficient in this flow passage was approximated with a polynomial and an exponent function. Both functions depended on the square root of the Reynolds number. The polynomial and exponent function fitted the measuring points rather well.