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Our earlier experimental study has shown that exhaust unburnt hydrocarbon emissions from spark-ignition engines can be reduced effectively by using in-cylinder catalysts on the surface of the piston top-land crevice. In order to improve the understanding of the process and mechanism by means of which unburnt hydrocarbon emissions are reduced, a phenomenological mathematical model was developed for catalytic oxidation processes in the piston-ring-pack crevice. This paper describes in details the modelling of the processes of the gas flow, mass diffusion and reaction kinetics in the crevices. The flow in the crevices is assumed to be isothermal and at the temperature of the piston crown surface. The overall rate of reaction is calculated using expressions for mass diffusion for laminar flows in channels and a first-order Arrhenius-type expression for catalytic reaction kinetics of hydrocarbon oxidation over platinum.

The work was concerned with experimental study of the turbulent flame development process of ethanol fuels in an optically accessed spark ignition research engine. The fuels were evaluated in a single cylinder engine equipped with full-bore overhead optical access and operated at typical stoichiometric part-load conditions. High-speed natural light (or chemiluminescence) imaging and simultaneous in-cylinder pressure data measurement and analysis were used to understand the fundamental influence of both low and high ethanol content on turbulent flame propagation and subsequent mass burning. Causes for the difference in cyclic variations were evaluated in detail, with comparisons made to existing burning velocity correlations where available.

A program is described here that analyzes the behaviour of roller-follower valve gear. The motion is computed from a kinematic analysis; the instantaneous radius of curvature and the pressure angle are determined, so that the contact force and stresses can be evaluated at the cam/follower interface. The validation of the software is discussed. Also analyzed, is the hydrodynamic lubrication of the roller-follower journal bearing. A case study is described in which journal and bearing wear are attributed to inappropriately sited oil feed holes. It is shown that there is a region where no hydrodynamic pressure develops, thus providing an appropriate location for the oil feed holes. The assumptions in the hydrodynamic analysis are discussed.

Tumble and swirl motions in the cylinder of a four-valve SI engine with production type cylinder head were investigated using a cross-correlation digital Particle Image Velocimetry (PIV). Tumble motion was measured on the vertical symmetric plane of the combustion chamber. Swirl motion was measured on a plane parallel to the piston crown with one of intake ports blocked. Large-scale flow behaviours and their cyclic variations were analysed from the measured two-dimensional velocity data. Results show that swirl motion is generated at the end of the intake stroke and persists to the end of the compression stroke. Tumble vortex is produced in the early stage of the compression stroke and distorted in the late stage of the stroke. The cyclic variation of swirl motion is noticeable. The cyclic variation in tumble dominated flow field is much greater.

Biobutanol, i.e. n-butanol, as a second generation bio-derived alternative fuel of internal combustion engines, can facilitate the energy diversification in transportation and reduce carbon dioxide (CO2) emissions from engines and vehicles. However, the majority of research was conducted on spark-ignition engines fuelled with n-butanol and its blend with gasoline. A few investigations were focused on the combustion and exhaust emission characteristics of homogeneous charge compression ignition (HCCI) engines fuelled with n-butanol-gasoline blends. In this study, experiments were conducted in a single cylinder four stroke port fuel injection HCCI engine with fully variable valve lift and timing mechanisms on both the intake and exhaust valves. HCCI combustion was achieved by employing the negative valve overlap (NVO) strategy while being fueled with gasoline (Bu0), n-butanol (Bu100) and their blends containing 30% n-butanol by volume (Bu30).

The goal of this research was to study and quantify the effect of exhaust valve timing and residual gas dilution on in-cylinder flow patterns, flame propagation and heat release characteristics in a spark ignition engine. Experiments were carried out in a recently developed single cylinder optical engine. Particle image velocimetry (PIV) was applied to measuring and evaluating the in-cylinder flow field. Detailed analysis of flame images combined with heat release data was presented for several engine operating conditions, giving insight into the combustion process in terms of visible flame area and flame expansion speed. Results from PIV measurement indicates that the limited alteration of the in-cylinder bulk flow could be observed with the variation of exhaust valve timing. The in-cylinder fluctuating kinetic energies and their Coefficient of Variations (COVs) decrease with the advance of the exhaust valve timing.

In recent years, in order to develop more efficient and cleaner gasoline engines, a number of new engine operating strategies have been proposed and many have been studied on different engines but there is a lack of comparison between various operating strategies and alternative fuels at different SI modes. In this research, a single cylinder direct injection gasoline engine equipped with an electro-hydraulic valve train system has been commissioned and used to study and compare different engine operation modes. In this work, the fuel consumption, gaseous and particulate emissions of gasoline and its mixture with ethanol (E15 and E85) were measured and analysed when the engine was operated at the same load but with different load control methods by an intake throttle, reduced intake valve duration, and positive overlap.

A novel approach was proposed and investigated to reduce unburned hydrocarbon emissions from spark-ignition engines using in-cylinder catalysts. The unburned hydrocarbons in spark-ignition engines arise primarily from sources near the combustion chamber walls, such as flame quenching at the entrance of crevice volumes and at the combustion chamber wall, and the absorption and desorption of fuel vapour into oil layers on the cylinder wall. The proximity of these sources of unburned hydrocarbons to the wall means that they can be reduced significantly by simply using in-cylinder catalysts on the combustion chamber walls, in particular on the surfaces of the crevice volumes. A platinum-rhodium coating was deposited on the top and side surfaces of the piston crown, and its effects on the engine combustion and emission characteristics were examined in this experimental investigation.

Over the last decade, the diesel engine has made dramatic progress in its performance and market penetration. However, in order to meet future emissions legislations, Nitrogen Oxides (NOx) and particulate matters' (PM) emissions will need to be reduced simultaneously. Nowadays researchers are focused on different combustion modes which can have a great potential for both low soot and low NOx. In order to achieve this, different injection strategies have been investigated. This study investigates the effects of split injection strategies with high levels of Exhaust Gas Recirculation (EGR) on combustion performance and emissions in a single-cylinder direct injection optical diesel engine. The investigation is focused on the effects of injection timing of split injection strategies. A Ricardo Hydra single-cylinder optical engine was used in which conventional experimental methods like cylinder pressure data, heat release analysis and exhaust emissions analysis were applied.

This work was concerned with study of lubricant introduced directly into the combustion chamber and its effect on pre-ignition and combustion in an optically accessed single-cylinder spark ignition engine. The research engine had been designed to incorporate full bore overhead optical access capable of withstanding peak in-cylinder pressures of up to 150bar. An experiment was designed where a fully formulated synthetic lubricant was deliberately introduced through a specially modified direct fuel injector to target the exhaust area of the bore. Optical imaging was performed via natural light emission, with the events recorded at 6000 frames per second. Two port injected fuels were evaluated including a baseline commercial grade gasoline and low octane gasoline/n-heptane blend. The images revealed the location of deflagration sites consistently initiating from the lubricant itself.

A programme of work is being undertaken to improve the performance of a spark-ignited natural gas engine, that has been converted from a diesel engine. The aim of this work is to reduce the fuel consumption and NOx emissions. All experimental data and predictions refer to full throttle operation at 1500 rpm. The work to be reported here will include baseline tests that have been used to calibrate a two-zone combustion model. Particularly important are the predictions of the NOx emissions. The simulation has then been used to predict the effects of using: a higher compression ratio, and a faster burn combustion system. The design philosophy of the resulting fast burn combustion system is discussed, and some preliminary results are presented. There will be a discussion of the ignition parameters that affect the lean burn operation, and the effect of the spark plug gap position is discussed in the context of results from a phenomenological model of turbulent combustion.

A numerical study was performed to elucidate the link between cyclic combustion variations in spark-ignition engines and instabilities in the non-linear processes occurring during the combustion. The instabilities in combustion were investigated by examining the response of a two-zone phenomenological combustion models to small deviations of mixture and flow conditions in the cylinder, such as the turbulence intensity at ignition, the overall equivalent ratio and the local equivalent ratio around the ignition site. The predicted combustion characteristics were validated and in good agreement with experimental data obtained from a single-cylinder research engine. The study suggested that the main deficiency of combustion in spark-ignition engines is the point-source ignition: it gives rise to slow development of initial flame; variations of the intermittent combustion process can occur when initial conditions at the ignition site are not repeatable from cycle to cycle.

A novel experimental technique was used to investigate the in-cylinder air-fuel ratio excursions of a port-injected spark-ignition engine during load and fuel transients. This involved sampling directly from the engine cylinder using a fast flame ionisation detector (FID) system throughout an engine transient test. All tests were conducted with the coolant at the normal operating temperature of 90°C. The research engine used was a 1.6ltr four-cylinder multi-point fuel injection spark-ignition (SI) engine with four-valves-per-cylinder, with sequential injection and an electronic management system. The engine transient involved a rapid throttle opening within about 15msec. Various load steps were investigated at 2000rev/min along with the effect of altering the type of fuel injector.

Controlled Auto-Ignition (CAI) combustion was realised in a production type 4-stroke 4-cylinder gasoline engine without intake charge heating or increasing compression ratio. The CAI engine operation was achieved using substantially standard components modified only in camshafts to restrict the gas exchange process The engine could be operated with CAI combustion within a range of load (0.5 to 4 bar BMEP) and speed (1000 to 3500 rpm). Significant reductions in both specific fuel consumption and CO emissions were found. The reduction in NOx emission was more than 93% across the whole CAI range. Though unburned hydrocarbons were higher under the CAI engine operation. In order to evaluate the potential of the CAI combustion technology, the European NEDC driving cycle vehicle simulation was carried out for two identical vehicles powered by a SI engine and a CAI/SI hybrid engine, respectively.

Controlled Auto-Ignition (CAI) combustion has been achieved in a production type 4-stroke multi-cylinder gasoline engine. The engine was based on a Ford 1.7L Zetec-SE 16V engine with a compression ratio of 10.3, using substantially standard components modified only in design dimensions to control the gas exchange process in order to significantly increase the trapped residuals. The engine was also equipped with Variable Cam Timing (VCT) on both the intake and exhaust camshafts. It was found that the largely increased trapped residuals alone were sufficient to achieve CAI in this engine and with VCT, a range of loads between 0.5 and 4 bar BMEP and engine speeds between 1000 and 3500 rpm were mapped for CAI fuel consumption and exhaust emissions. The measured CAI results were compared with those of Spark Ignition (SI) combustion in the same engine but with standard camshafts at the same speeds and loads.

This is a first of a series of papers describing how the replacement of some of the inlet air with EGR modifies the diesel combustion process and thereby affects the exhaust emissions. This paper deals with only the reduction of oxygen in the inlet charge to the engine (dilution effect). The oxygen in the inlet charge to a direct injection diesel engine was progressively replaced by inert gases, whilst the engine speed, fuelling rate, injection timing, total mass and the specific heat capacity of the inlet charge were kept constant. The use of inert gases for oxygen replacement, rather than carbon dioxide (CO2) or water vapour normally found in EGR, ensured that the effects on combustion of dissociation of these species were excluded. In addition, the effects of oxygen replacement on ignition delay were isolated and quantified.

A number of tests were conducted on a 2.5 litre, high-speed, direct-injection diesel engine running at various loads and speeds. The aim of the tests was to gain understanding which would lead to more effective use of exhaust gas recirculation (EGR) for controlling exhaust NOx. In addition to exhaust emission measurements, extensive in-cylinder sampling of combustion gases was carried out using a fast-acting, snatch-sampling valve. The results showed that the effectiveness of EGR in suppressing NOx was enhanced considerably by intercooling the inlet charge and by cooling the EGR. A companion paper (SAE 960841) deals with the effects of EGR on soot formation and emission [1].

This paper presents the development of an engine simulation program for SI engines and its application to a two-stage expansion cycle. The two-stage expansion analysis is performed using the engine simulation, where a sudden expansion much faster than the normal expansion takes place during the expansion stroke. The changes in NO emissions and knock tolerance of the resulting new engine cycle are investigated for the same compression ratio. The changes in NO emissions and specific fuel consumption through increasing the compression ratio in order to return to the same amount of work done within the cycle are also studied.

The work was concerned with visualisation of the charge homogeneity and cyclic variations within the planar fuel field near the spark plug in an optical spark ignition engine fitted with an outwardly opening central direct fuel injector. Specifically, the project examined the effects of fuel type and injection settings, with the overall view to understanding some of the key mechanisms previously identified as leading to particulate formation in such engines. The three fuels studied included a baseline iso-octane, which was directly compared to two gasoline fuels containing 10% and 85% volume of ethanol respectively. The engine was a bespoke single cylinder with Bowditch style optical access through a flat piston crown. Charge stratification was studied over a wide spectrum of injection timings using the Planar Laser Induced Fluorescence (PLIF) technique, with additional variation in charge temperature due to injection also estimated when viable using a two-line PLIF approach.

The influence of swirl on combustion in diesel and spark ignition engines is reviewed briefly, and this leads to a resumé of the swirl measuring techniques. The numerous ways of analysing swirl data are summarised and the relations between the different swirl parameters are presented. Experimental results are presented from a diesel engine in which the flow has been measured by a hot wire anemometer, a paddle wheel and a swirl torquemeter. The performance of the different measurement techniques is compared. Further results are presented (from a spark ignition engine) which illustrate the influence of the inlet port, manifold and entry conditions on the swirl measurements. Integration techniques are reviewed for producing a single swirl parameter to characterise the combined performance of the inlet port, valve and camshaft. Finally, the difficulty in standardising measurements of barrel swirl are discussed.