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An experimental study of the mixture response performance of novel, port-fuel injection strategies upon combustion stability in a gasoline engine was undertaken at low engine load and speed conditions in the range of 1.0 bar to 1.8 bar GIMEP and 1000 rpm to 1800 rpm. The aim was to improve the thermal efficiency of the engine, by extending the lean limit of combustion stability, through promotion of stable charge stratification. The investigation was carried out using a modified 4-valve single-cylinder head, derived from a 4-cylinder, pent-roof, production, gasoline engine. The cylinder head was modified by dividing the intake tract into two, separate and isolated passages; each incorporating a production fuel injector. The fuel injection timing and duration were controlled independently for each injector.

The results of recent developments of analytical vortex ring models and the applications of these models to interpretation of the experimentally observed dynamics of vortex ring-like structures in gasoline sprays, under non-evaporating conditions, are summarized. Analytical formulae in the limit of small Reynolds numbers (Re), are compared with numerical solutions. Particular attention is focused on the generalized vortex ring model in which the time evolution of the thickness of the vortex ring core L is approximated as atb, where a and b are constants (1 ≤ b ≤ 1/2). This model incorporates both the laminar model for b=1/2 and fully turbulent model for b=1/4. The values of velocities in the region of maximal vorticity, predicted by the generalized vortex ring model, are compared with the results of experimental studies of fuel droplets distributed in vortex ring-like structures in two gasoline injectors, under cold-start, engine-like conditions.

The results of an experimental study of the low speed and low load operation of an optical research engine are presented for spark-ignition (SI) and spark-assisted, controlled auto-ignition (SA-CAI). A direct injection gasoline engine was modified for optical access into the combustion chamber. At 1000 rpm and 3 bar NIMEP, stable SA-CAI combustion was achieved with predicted EGR rates in excess of 45%. The coefficient of variation (CoV) in NIMEP was 4.8% compared to 6.5% recorded in the SI case, with no EGR. Particle image velocimetry measurements of the airflow showed lower mean and turbulent velocities in the SA-CAI case at the end of the compression stroke. Planar Laser Induced Fluorescence (PLIF) measurements of the fuel vapour signal in the air-fuel-residual distribution were significantly lower than in the SI case. Indicating analysis showed that the main combustion burn duration was considerably greater in the SA-CAI case.

Recently developed liquid and gas phase models for fuel droplet heating and evaporation, suitable for implementation into computational fluid dynamics (CFD) codes, are reviewed. The analysis is focused on the liquid phase model based on the assumption that the liquid thermal conductivity is infinitely large (infinite thermal conductivity (ITC) model), and the so called effective thermal conductivity (ETC) model. Seven gas phase models are compared. It is pointed out that the gas phase model, taking into account the finite thickness of the thermal boundary layer around the droplet predicts the evaporation time closest to the one based on the approximation of experimental data. In most cases, the droplet evaporation time depends strongly on the choice of the gas phase model. The dependence of this time on the choice of the liquid phase model, however, is weak if the droplet break-up processes are not taken into account.

The effects of injection pressure, in-cylinder pressure and in-cylinder temperature at the start of injection on diesel spray penetration were studied experimentally and numerically. The study also considered injection delay, hesitation period and the effect of the number of nozzle holes. The experiments were conducted in a rapid compression machine based on a single cylinder Ricardo Proteus test engine installed at University of Brighton. The numerical studies were carried out using the recently developed multidimensional engine combustion computer code KIVA 3V rel2. Results using single hole, 3-hole and 5-hole nozzles were compared. The injection pressure was varied between 60 and 160 MPa whilst the in-cylinder pressure varied from 2 MPa to 6 MPa. Two in-cylinder temperatures were investigated; ‘cold air intake’ at 576° K and ‘hot air intake’ at 721° K.

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.

As part of an ongoing investigation, the influence of In Cylinder Pressure (ICP) and fuel injection pressure on the soot formation processes in a diesel fuel spray were studied. The work was performed using a rapid compression machine at ambient conditions representative of a modern High Speed Direct Injection diesel engine, and with fuel injection more representative of full load. Future tests will aim to consider the effects of pilot injections and EGR rates. The qualitative soot concentration was determined using the Laser Induced Incandescence (LII) technique both spatially and temporally at a range of test conditions. Peak soot concentration values were determined, from which a good correlation between soot concentration and injection pressure was observed. The peak soot concentration was found to correlate well with the velocity of the injected fuel jet.

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.

As part of an ongoing investigation, the influence of in-cylinder charge density, and injector nozzle geometry on the behaviour of diesel sprays were examined using high-speed imaging. Both liquid and vapour penetration profiles were investigated in operating conditions representative of a modern turbocharged after-cooled HSDI diesel engine. These conditions were achieved in an optical rapid compression machine fitted with a common rail fuel injection system. Differences in spray liquid and vapour penetrations were observed for different nozzle geometries and in-cylinder conditions over a range of injection fuelling representative of those in a typical engine map. Investigation into the differences in spray structure formed by multi-hole and single-hole injections were also undertaken.

In an investigation to gain a deeper understanding of the relationships between port geometry and performance characteristics, a parametric inlet port design tool has been developed using statistical design-of-experiments (DoE) techniques. A strong emphasis has been placed on achieving realistic, production-feasible port geometry that may be used directly during concept design projects. A modular approach has been developed using flexible, interchangeable, generic inlet port models. Constraints are used to represent additional features in the cylinder head and external packaging requirements. A thorough assessment of performance was made possible by using rapid-prototype models and reliable experimental methods. The in-cylinder flows were successfully validated by comparing predicted results with new test data.

The influences of injector nozzle geometry, injection pressure and ambient air conditions on a diesel fuel spray were examined using back-lighting techniques. Both stills and high speed imaging techniques were used. Operating conditions representative of a modern turbocharged aftercooled HSDI diesel engine were achieved in an optical rapid compression machine fitted with a common rail fuel injector. Qualitative differences in spray structure were observed between tests performed with short and long injection periods. Changes in the flow structure within the nozzle could be the source of this effect. The temporal liquid penetration lengths were derived from the high-speed images. Comparisons were made between different nozzle geometries and different injection pressures. Differences were observed between VCO (Valve Covers Orifice) and mini-sac nozzles, with the mini-sac nozzles showing a higher rate of penetration under the same conditions.

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.

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.