Effect of Injection Strategy and Fuel Pressure on Diesel Spray Penetration: Application to HCCI Engines

ABSTRACT Direct injection strategies play an important role in modern Diesel engines and high-pressure common rail injection systems made easier to achieve better engine performances and lower fuel consumption. It is generally recognized that the design of the fuel injection strategy and in particular the performance of the injection system represent the key factor in meeting the increasing demand for improvement of engine performance and reduced exhaust emissions. The recent introduction of the homogeneous charge compression ignition (HCCI) combustion concept, as an attractive alternative for future IC engines, poses an increased demand for better fuel injection strategies and improvement of the mixture formation process. The HCCI concept requires early fuel injection in a gas environment at lower pressure and density, compared to the conventional Diesel engines, and thus the injection strategy needs modification to assure sufficient mixing and to match evaporation and ignition requirements, while avoiding fuel impingement on the combustion chamber surfaces. This paper describes spray penetration characteristics of a common-rail piezo-type injector operated at medium-high pressures. Optical diagnostics and CCD camera photography are currently applied to generate an extensive data base which is intended for validation of CFD simulations of HCCI engines. The preliminary results show that a proper selection of the injection strategy together with high injection pressures can fulfil the main requirements of HCCI engine conditions, still avoiding impingement of the spray on the wall. However, poor mixture formation is achieved and intense gas motion may be necessary inside the engine cylinder.