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Compared to conventional homogeneous direct injection or port-fuel injected engines, the second generation, spray guided, direct injection engine (SGDI) has the potential for significantly improved fuel economy during part load stratified charge operation. Multiple fuel injection strategies can be utilised to increase the unthrottled operating range, leading to further improvements in fuel economy. However, careful optimisation of these strategies is essential to ensure that benefits are maintained whilst further minimising emissions within combustion stability limits and consumer driveability demands. The effects of multiple injection strategies upon fuel consumption, emissions and combustion stability were investigated in a single cylinder Ricardo Hydra engine with a spray guided combustion system. An outwardly opening piezoelectric actuated injector was employed. The fuel injection strategy utilised up to five injections per engine cycle.

The 2/4SIGHT engine concept is based on a novel design of combustion system, which makes use of an electric-hydraulic valvetrain and advanced control technologies, enabling automatically controlled dynamic switching of the engine between two- and four-stroke operations. This concept has the potential to improve fuel consumption by up to 30% compared to a conventional gasoline engine. A 3 cylinder GDI engine with two stage boosting system and electro-hydraulic valvetrain is the main application for this project, with 6 cylinder application being studied in simulation. The design of a Control System poses several challenges due to the simultaneous introduction of several innovations such as advanced boost system, electro-hydraulic valvetrain system and two/four stroke operating mode. In order to develop and optimise the design of the control system, an integrated simulation environment has been developed.

Reducing engine swept volume (so-called ‘downsizing’) offers the potential to meet future tighter CAFÉ standards and reduced CO2 vehicle emissions in Europe. In downsizing the gasoline engine, a key challenge is controlling octane requirement without sacrificing fuel economy. The authors have investigated five alternative approaches on a turbocharged DI gasoline engine: Conventional stoichiometric operation, with reduced compression ratio (CR) Lean Boost DI (LBDI) with lean operation at full-load to control octane requirement while maintaining a high CR EGR Boost with cooled EGR dilution rather than excess air to control octane requirement Miller cycle concept, where valve-timing strategies are employed to reduce the effective compression ratio at high load Dual injection strategies to control octane requirement Each approach has been investigated using engine performance and vehicle simulation codes.

The performance of a direct injection gasoline engine (G-DI) is highly dependent on the quality of the air-fuel mixture preparation. This is of particular importance when operating at a stratified charge condition, where the ideal mixture distribution would be a stoichiometric region around the spark plug, surrounded by air. To achieve this ideal situation over a wide range of speeds and loads is extremely difficult, requiring an understanding of the fuel spray, the in-cylinder air motion and their interactions. This paper presents the results of Phase Doppler Anemometry (PDA) and Laser Induced Fluorescence (LIF) measurements made both within an optically accessed direct injection gasoline engine and under atmospheric conditions. The experimental results are compared with those of a VECTIS Computational Fluid Dynamics (CFD) simulation of the same engine.

A single cylinder research engine has been used to study a range of gasoline combustion chamber designs which have been divided into three categories open, compact and four valve. Measurements of fuel consumption and exhaust emissions are presented at full load and part load conditions, and a comparison is made of the best chamber from each category. At full load the performances of the three chambers were very similar at low speeds but at high speeds the superiority of the four-valve was clearly shown. At part load there were significant differences in the burn rate when operating at lean mixtures with the compact design showing the highest level and hence the most extended lean limit. The relationship between part load fuel consumption and full load octane requirement is presented as a method of comparing the relative performance of a range of combustion chamber designs.