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Over the past few decades, Homogeneous Charge Compression Ignition (HCCI) or Controlled Auto-Ignition (CAI) if it is fuelled with gasoline type of fuels has shown its potential to overcome the limitations and environmental issue concerns of the Spark Ignition (SI) and Compression Ignition (CI) engines. However, controlling the ignition timing of a CAI engine over a wide range of speeds and loads is challenging. Combustion in CAI is affected by a number of factors; the local temperature, the local composition of the air/fuel mixture, time and to a lesser degree the pressure. The in-cylinder engine charge flow fields have significant influences on these factors, especially the local gas properties, which leads to the influences towards the CAI combustion. In this study, such influences were investigated using a Computational Fluid Dynamics (CFD) engine simulation package fitted with a real optical research engine geometry.

Valve timing strategies aimed at producing internal exhaust gas re-circulation in a conventional spark ignition, SI, engine have recently demonstrated the ability to initiate controlled auto-ignition, CAI. Essentially the exhaust valves close early, to trap a quantity of hot exhaust gases in-cylinder, and the fresh air-fuel charge is induced late into the cylinder and then mixing takes place. As a logical first step to understanding the fluid mechanics, the effects of the standard and modified valve timings on the in-cylinder flow fields under motored conditions were investigated. Laser Doppler anemometry has been applied to an optical engine that replicates the engine geometry and different valve cam timings. The cycle averaged time history mean and RMS velocity profiles for the axial and radial velocity components in three axial planes were measured throughout the inlet and compression stroke.

The Otto cycle delivers theoretical maximum thermal efficiency. The traditional design of internal combustion engines using a simple slide-crank mechanism gives no time for a constant volume combustion which significantly reduces the cycle efficiency. In this study, using a high torque, high bandwidth, permanent magnet electric drive system attached to the crankshaft, variable angular velocities of the engine crankshaft were implemented. The system enabled reductions in piston velocity around the top dead centre region to a fraction of its value at constant crankshaft angular velocity typical in conventional engines. A quasi-constant volume combustion has thus been successfully achieved, leading to improvements in engine fuel consumption and power output which are discussed in detail.