Mixture Formation and Combustion in a Spark Ignition Engine with Direct Fuel Injection

This paper presents investigations on the combustion process in a single cylinder SI engine with direct injection. Different nozzle types are examined i.e. hollow cone nozzles and hole type nozzles both with different geometry of the injected spray. These nozzle types have been compared in view of their suitability of creating a homogeneous as well as a stratified mixture in the combustion chamber. To create a homogenous mixture, the fuel was injected during the intake stroke. In order to examine the homogeneity of the mixture in the case of direct injection, the engine was driven with mixture formation generated through intake port injection. The comparison of the direct injection method with the intake port injection for homogenous mixture formation has shown only small differences in engine behavior. To create a stratified mixture in the combustion chamber, the fuel was injected at the end of the compression stroke. In the case of a low swirl level, the hollow cone nozzle with a cone angle of 120° leads to a stratified mixture. With this nozzle the engine could be driven until relative air/fuel ratios of about four. With the six-hole nozzle (120° spray angle) and a significant higher swirl level, a stratified charge engine behavior could also be realized. The minimum fuel consumption is reached with the 120° hollow cone nozzle.