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This paper describes a two-year programme of research conducted by the authors investigating HCCI in direct injection gasoline engines. Poppet-valved two-stroke cycle operation has been investigated experimentally, using conventional gasoline compression ratios and fuel, and ambient temperature intake air. Extensive combustion and emissions data was gathered from the experimental engine. Computational Fluid Dynamics (CFD) has been used to model HCCI combustion, and the CFD tool validated using experimental data. Based on experience with the two-stroke engine and modelling techniques, a four-stroke engine has been designed and tested. Using this range of tools, practical options for gasoline HCCI engines are evaluated, and a scenario for the market introduction of HCCI is presented.

A system for stratifying recycled exhaust gas (EGR) to substantially increase dilution tolerance has been applied to a port injected four-valve gasoline engine. This system, known as Combustion Control through Vortex Stratification (CCVS), has shown greatly improved fuel consumption at a stoichiometric air/fuel ratio. Both burnrate (10-90% burn angle) and HC emissions are almost completely insensitive to EGR up to best economy EGR rate. Cycle to cycle combustion variation is also excellent with a coefficient of variation of IMEP of less than 2% at best economy EGR rate. This paper describes a research programme aimed at gaining a better understanding of the in-cylinder processes in this combustion system.

The paper describes a water analogy rig and its associated instrumentation and data acquisition system, developed to make particle image velocimetry (PIV) measurements of in-cylinder flow during the intake stroke. Methods of producing parameters to describe the flow characteristics of four valve engines with tumbling air motion are evaluated and correlation with combustion performance is examined for two different engines with a total of seven different inlet port designs. Each inlet port configuration was also evaluated by conventional steady flow methods. The results show that the dynamic water flow rig gave improved correlation with combustion data than that obtained with conventional steady flow methods of characterising in-cylinder flow patterns.

The pursuit of flexibility is a recurring theme in engine design and development. Engines that are able to switch between the two-stroke operating cycle and four-stroke operation promise a great leap in flexibility. Such 2S-4S engines could then continuously select the optimum operating mode - including HCCI/CAI combustion - for fuel efficiency, emissions or specific output. With recent developments in valvetrain technology, advanced boosting devices, direct fuel injection and engine control, the 2S-4S engine is an increasingly real prospect. The authors have undertaken a comprehensive feasibility study for 2S-4S gasoline engines. This study has encompassed concept and detailed design, design analysis, one-dimensional gas dynamics simulation, three-dimensional computational fluid dynamics, and vehicle simulation. The resulting 2/4SIGHT concept engine is a 1.04 l in-line three-cylinder engine producing 230 Nm and 85 kW.

Two experimental techniques, Particle Image Velocimetry (PIV) using a water-analogy Dynamic Flow Visualisation Rig (DFVR) and Laser Doppler Anemometry (LDA) in a motored research engine, were used to investigate the flow pattern generated within the combustion chamber of a gasoline direct injection (G-DI) engine. The in-cylinder flow was also modelled for the two cases using the Computational Fluid Dynamics (CFD) code VECTIS; that is, models were created using first water and then air as the working fluid. The experimental and computational results were converted into the same format and hence compared qualitatively and quantitatively. All results showed good agreement and were used to validate the different techniques. The correlation between the CFD air simulation results and the LDA results demonstrates that the CFD code can be used to predict reliably the air motion created in the combustion chamber of a G-DI engine.