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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.

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.

Due to its potential for simultaneous improvement in fuel consumption and exhaust emissions, controlled autoignition (CAI) combustion has been subject to continuous research in the last several years. At the same time, there has been a lot of interest in the use of alternative fuels in order to reduce reliance on conventional fossil fuels. Therefore, this experimental study has been carried out to investigate the effect of alcohol fuels on the CAI combustion process and on the resulting engine performance. The experimental work was conducted on an optical single cylinder engine with an air-assisted injector. To achieve controlled autoignition, residual gas was trapped in the cylinder by using negative valve overlap and an intake air heater was used to ensure stable CAI combustion in the optical engine. Methanol, ethanol and blended fuels were tested and compared with the results of gasoline.

Controlled Auto-Ignition (CAI) combustion, also known as HCCI or PCCI, has recently emerged as a viable alternative combustion process to the conventional spark ignition (SI) or compression ignition (CI) process for internal combustion (IC) engines, owing to its potential for high efficiency and extremely low emissions. One of the most effective and practical means of achieving CAI combustion in an engine is to retain or recycle the burnt gases. In order to understand better the effects of recycled burnt gases on CAI combustion, detailed analytical and experimental studies have been carried out. The analytical studies were performed using an engine simulation model with detailed chemical kinetics. The five effects of the recycled burned gases studied include: (1.) Charge heating effect: higher intake charge temperature due to hot burned gases; (2.) Dilution effect: the reduction of oxygen due to the presence of the burned gases; (3.)

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.

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.

This paper presents results from an experimental programme researching the in-cylinder conditions necessary to obtain homogenous CAI (or HCCI) combustion in a 4-stroke engine. The fuels under investigation include three blends of Unleaded Gasoline, a 95 RON Primary Reference Fuel, Methanol, and Ethanol. This work concentrates on establishing the CAI operating range with regard to Air/Fuel ratio and Exhaust Gas Re-circulation and their effect on the ignition timing, combustion rate and variability, Indicated thermal efficiency, and engine-out emissions such as NOx. Detailed maps are presented, defining how each of the measured variables changes over the entire CAI region. Results indicate that the alcohols have significantly higher tolerance to dilution than the hydrocarbon fuels tested. Also, variations in Gasoline blend have little effect on any of the combustion parameters measured.

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.

Chemical reaction kinetics plays an important role in homogeneous charge compression ignition (HCCI) combustion. In order to control the combustion process, the underlying mechanism of auto-ignition must be explored, especially for the HCCI combustion using negative valve overlap (NVO) strategy, in which the residual gas affects the auto-ignition of next cycle remarkably. In this research, experimental research was carried out in a single cylinder gasoline engine equipped with an in-cylinder sampling system which mainly consists of a special spark plug, a sampling tube and a high-speed electromagnetic valve. In-cylinder charge was sampled at compression stroke and analyzed by FTIR with two types of fuel injection strategy, such as port fuel injection (PFI) solely and port fuel injection combined with injection during negative valve overlap (PFI & NVO-Injection).

Homogeneous charge compression ignition (HCCI) technology is promising to reduce engine exhaust emissions and fuel consumption. However, it is still confronted with the problem of its narrow operation range that covers only the light and medium loads. Therefore, to expand the operation range of HCCI, mode switching between HCCI combustion and transition SI combustion is necessary, which may bring additional problems to be resolved, including load fluctuation and increasing the complexity of control strategy, etc. In this paper, a continuously adjustable load strategy is proposed for gasoline engines. With the application of the strategy, engine load can be adjusted continuously by the in-cylinder residual gas fraction in the whole operation range. In this research, hybrid combustion is employed to bridge the gaps between HCCI and traditional SI and thus realize smooth transition between different load points.

This paper is concerned with the performance of the sensors and associated instrumentation used for the standard cetane tests for diesel fuels according to the ASTM D-613 procedure. The two primary sensors are replaced by modern units, and the analogue monitoring system is replaced by a digital one; the changes in the performance of the instrumentation system are then assessed. It is shown that the main source of inaccuracy in the measurement of ignition delay (on which the cetane test is based) is cyclic instability in the start of combustion, and that the current instrumentation and monitoring methods do not cope well with this instability. Although some of the cyclic variation can be ascribed to the instrumentation system, a large part is contributed by variability in the fuel ignition and injection processes. Improvements to the instrumentation and monitoring systems are presented and assessed.

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.

The paper first describes three linked computational models which allow the estimation of: swirl generated during the induction process; the modification of swirl with bowl-in-piston combustion chambers during compression as the piston approaches top dead centre; the interaction of the fuel sprays with swirl including relative crosswind velocities between the air and the fuel sprays and spray impingement velocities. The paper then presents experimental results from a single-cylinder direct injection diesel engine, during which both the fuel spray and swirl parameters were changed systematically. Finally, the predicted spray impingement and crosswind velocities for this engine are correlated with the engine performance obtained experimentally, in particular, with fuel economy and smoke emission.

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.

Comparisons have been made between the ignition delay and combustion performance of sunflower oil and diesel fuel. The experimental results have been obtained in a naturally aspirated direct injection diesel engine, and particular attention has been given to the heat release analysis, ignition delay, combustion noise and lubricant degradation. The anomalous behaviour of sunflower oil is explained by reference to its physical properties and ignition quality, as reported in the literature from bomb tests. It is concluded that the power output and brake efficiency are largely unaffected by the use of the sunflower oil, and that lubricant degradation is not likely to be significant. However, the build up of combustion deposits already widely reported in the literature was observed. Suggestions are made as to how this might be ameliorated through modifications to the injection system.

Fast throttle opening in port-injected gasoline engines often results in a lean air-fuel ratio excursion lasting several engine cycles. Even when the engine is equipped with a three-way catalyst this lean excursion can lead to high tailpipe emissions. This paper will describe an in-cylinder method of measuring these air-fuel ratio excursions, using a fast flame ionisation detector. Examples will be given of air-fuel ratio excursions obtained on a four-valve-per-cylinder sequentially-injected gasoline engine equipped with a lambda sensor. The air-fuel ratio excursions together with measurements of the engine air flow are used to estimate me build up of the fuel film on the inlet manifold walls. Whilst air-fuel ratio excursions have been recorded previously by other investigators, their results were obtained from exhaust gas analysis using fast oxygen sensors.

The measurement of the instantaneous flame temperature and soot concentration in the combustion chamber of a running diesel engine can provide useful information relating to the formation of two important exhaust pollutants, NOx and particulates. The two-colour method is based on optical pyrometry and it can provide estimates of the instantaneous flame temperature and soot concentration. The theoretical basis of the method is outlined in a companion paper. This paper deals with the practical problems involved in the construction of a working system, including suitable calibration techniques. The accuracy of the measurements of flame temperature and soot concentration is also discussed using results from a various sources.

The two-colour method is based on optical pyrometry and can readily be implemented at a modest cost for the measurement of the instantaneous flame temperature and soot concentration in the cylinders of diesel engines. With appropriate modification, this method can be applied to other continuous and intermittent combustion systems, such as those for gas turbine and boiler burners. This paper outlines the theoretical basis of the method, with particular attention being paid to the assumptions relating to the evaluation of the flame temperature and soot concentration. A companion paper deals with the practical problems involved in constructing a working system, including suitable calibration techniques, and assessment of the method accuracy.

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.

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.