Cylinder pressure analysis is widely used in the experimental investigation of combustion processes within gasoline engines. A pressure record can be processed to reveal detail of charge burning, which is a good indicator of combustion quality. The thesis describes the evaluation of an approximate technique for calculating the mass fraction of the charge that has burnt; a novel approach for determining heat loss to the block; the development of a powerful system for combustion analysis; and the investigation of the correlation between the crank angle location of the 50% mass burnt and minimum timing advance necessary to obtain the maximum engine torque. A detailed examination has been carried out into the uncertainties in the determination of the mass fraction burnt as suggested by Rassweiler and Withrow. A revised procedure has been developed which does not require a priori identification of the combustion end point, and a new approach is suggested to calculate the polytropic indices necessary for the pressure processing. This particular implementation of the analysis is able to identify late burning and misfiring cycles, and then take appropriate steps to ensure their proper analysis. The problems associated with the assumption of uniform pressure; alignment of the pressure changes to the volume changes; pressure sampling rate; clearance volume estimation; and calibrating the acquired pressure to absolute are also evaluated. A novel method is developed to ascertain, directly from the pressure history, the heat loss to the cylinder block. Both experimental and simulated data are used to support the accuracy of the suggested heat loss evaluation, and the sensitivity of the method to its inputs is examined. The conversion of procedures for combustion analysis into a format suitable for undertaking high speed analysis is described. The analysis techniques were implemented so that the engine can be considered to be on-line to the analysis system. The system was entitled Quikburn. This system can process an unlimited number of cycles at a particular running condition, updating the screen every 1.5 seconds. The analysis system has been used to study the potentially beneficial correlation between the location of the 50% mass burnt and MBT. The correlation is examined in detail, and found to be valid except under lean fueling conditions, which is seen to be caused by slow flame initiation. It is suggested that the optimum location of the 50% mass burnt can be used as a reference setting for the ignition timing, and as an indicator of combustion chamber performance. An engine simulation was employed to verify that changes in bum shape account for the small variation seen in the optimum 50% bum locations at different operating conditions of the engine. The bum shape changes also account for the range of optimum locations of the 50% mass burnt encountered in different engines.

This thesis describes research undertaken to establish the advantages and disadvantages of using high pressure common rail fuel injection systems with multiple injection capabilities. The areas covered are detailed as follows. Oscillations in the rail pressure due to the opening of the injector can affect the quantity of fuel injected in subsequent injection events. The source of these oscillations has been investigated. A method of damping or reducing the oscillations has been defined and was applied. This successfully reduced the level of unpredictability of the quantity of injected fuel in subsequent injection events. A relationship between needle lift, injection pressure and the quantity of fuel injected was established. The effects of fuel injection parameters (main injection timing, split main separation and ratio) and engine operating parameters (boost pressure and EGR level) on emissions formations and fuel economy have been investigated at five operating points. Design of Experiments techniques were applied to investigate the effect of variables on pollutant emissions and fuel consumption. The sensitivity and linearity of responses to parameter changes have been analysed to assess the extent to which linear extrapolations will describe changes in smoke number (FSN) and oxides of nitrogen (NOx); and which parameters are the least constricting when it comes to adjustments of parameter settings on the FSN-NOx map. Comparing results for split main and single injection strategies at the five operating conditions shows that split main injection can be exploited to reduce NOx or FSN values at all conditions and both NOx and FSN simultaneously at high load conditions. The influence of changing engine speed and brake mean effective pressure (BMEP) on FSN and NOx emissions with given fixed values of parameter settings has been investigated. This established how much of the operating map could be covered by discrete calibration settings. Finally the variation in parameter settings required to maintain fixed FSN and NOx values across the operating map, near the optimum trade-off on the FSN-NOx map, was analysed. Combining the information gained from the individual investigations carried out highlighted some techniques that can be used to simplify the calibration task across the operating map, while also reducing the amount of experimental testing required.

The work described in this thesis concerns the continued development and application of a computational model to simulate the thermal behaviour of internal combustion engines. The model provides information on temperature and heat flow distributions within the engine structure, and on temperatures of oil, coolant and engine-out exhaust gas. Sub-models calculate friction levels, fuel flow rates and gas-side heat transfer, including the effects of exhaust gas recirculation (EGR), spark advance and turbocharging. The effects of auxiliary components such as a cabin heater, oil cooler, intercooler, supplementary heater and EGR cooler can also be simulated. Model developments are aligned towards improving the accessibility of the model and the scope of engine systems that can be simulated. Early versions of the model have been converted from 'C' into the current MATLAB/Simulink versions. The model structure and conversion process are described. New developments undertaken have focused on the external coolant circuit and include the modelling of the thermostat and radiator. A semi-empirical thermostat model is presented. A radiator model based on the effectiveness-NTU method is described. Simulations using the developed model, including the thermostat and radiator sub-models, investigate the effect of thermostat position on engine thermal behaviour. Positioning the thermostat on the inlet to the engine reduces thermal shock. Applications of the model to investigations of sensitivity and performance illustrate the accuracy of and confidence in model predictions. Assessments demonstrate that the model is relatively insensitive to variations of 100/0 in user inputs and is very sensitive to model assumptions if simulation conditions, implied in the model assumptions, are not matched to test conditions. A process for evaluating model performance is described. Evaluation exercises applied to three different engines demonstrate that values predicted by the model are to within 5 to 10% of experimental values. Investigations using the model of methods to improve warm-up times and fuel consumption prior to fully warm conditions show the benefits or otherwise of reduced thermal capacity, an oil cooler, a sump oil heater and an oil-exhaust gas heat exchanger. Each method is assessed over the New European Drive Cycle (NEDC) from a -10°C start. Of these methods, a combined reduction in coolant volume and engine structural mass is most beneficial for reducing coolant warm-up times. An oil-exhaust gas heat exchanger produces the greatest reduction in fuel consumption.

A systematic investigation of the effects of coolant-to-mainstream density ratio and mainstream acceleration on the heat transfer following injection through a row of holes in a flat plate into a turbulent boundary layer is described. A mass transfer technique was employed which uses a swollen polymer surface and laser holographic interferometry. The constant concentration of the test surface simulated isothermal conditions. Density ratios in excess of unity, representative of gas turbine operating conditions, were obtained using foreign gas injection into mainstream air. The experimental technique was validated for such measurements. The cooling film heat transfer coefficient was measured for a range of blowing configurations and flow conditions; the holes were spaced at three diameter intervals and inclined at 35° or 90° to the mainstream, and the ranges of the other pertinent test parameters covered were, 0.5 5 blowing rate 5 2.0, 1.0 5 density ratio S 1.52, and 0.0 S acceleration parameter S 5x 10'. However, the tests with mainstream acceleration were performed with 35° injection only. The heat transfer coefficient was found to be increased by injection, and with the blowing rate for both 35° and 90° injection. Close to the injection site, normal blowing produced higher heat transfer coefficients than angled blowing, but gave lower coefficients far downstream. There were large differences in behaviour between the two injection angles with varying density ratio. For normal injection, the heat transfer coefficient at a fixed blowing rate was insensitive to the variation of density ratio, whereas for 35° injection strong dependence was observed, an increase in the density ratio leading to a decrease in the coefficient. Similar behaviour for the inclined injection case was also found in the presence of strong favourable pressure gradient. As mainstream acceleration acts to suppress injection induced turbulence, the heat transfer coefficient under the film with and without density ratio was found to decrease in the presence of mainstream acceleration relative to that in absence of acceleration. The heat transfer coefficient was observed to relate to the acceleration parameter in an approximately linear manner, an increase in the acceleration resulting in a decrease in the coefficient. For normal injection, good scaling of the heat transfer coefficient including density ratios was achieved with the blowing parameter. For 35° injection, the coolant to mainstream velocity ratio was seen to scale the data best. Correlations for the heat transfer data using these scaling parameters. With these correlations data obtained at density ratios not representative of gas turbine practice can be adapted for design calculations. The predictions of a computational fluid dynamics general purpose program called PHOENICS were tested against the present measurements and those of others. In general, the computed results of film cooling effectiveness agreed reasonably well with available experimental data. The ability to predict the heat transfer coefficient associated with film cooling was satisfactory for normal injection, but not as satisfactory for injection through 35° holes.

The cold start performance of automotive diesel engines is currently poor when compared to similar gasoline units. This thesis describes an experimental and theoretical investigation into the factors limiting diesel cold start behaviour. Studies have been carried out on IDI and DI designs of engine. Start behaviour has been characterised in terms of times taken to complete various stages of startup, engine speed variations and processes which affect these. Combustion and friction behaviour have been investigated in detail. Engine friction losses are dependent on temperature. During start-up these losses are relatively high compared to those when the engine is fully-warm. The work output from combustion is low at low speeds, and prone to a further deterioration at lower temperatures. Consequently, combustion output during cold cranking is initially insufficient to overcome frictional losses. The start times are extended by the need to keep the starter motor engaged until heat generated in the engine causes frictional losses to fall. Eventually, when combustion output is able to overcome friction without the aid of starter motor work, idle speed is reached. Changes to fuel injection and glowplug parameters have been used to achieve a limited improvement in low-temperature starting. Measurements of engine friction have been carried out to determine the influence of temperature and speed, and the relative contributions from each of the main component assemblies. At low temperatures, much of the friction originates in hydrodynamically lubricated components such as journal bearings, due to high oil viscosity at low temperature. Additionally, engine friction as rotation begins has been shown to be far higher than measured by conventional "steady-state" motoring tests (over twice the quasi-steady state friction at -200 e). This initially high friction transient decays towards the quasi-steady values throughout the start. For crankshaft bearings, a friction model has been developed for cold start-up through to fully warm engine conditions. The friction behaviour in the bearings is dependent on thermal conditions around the friction surfaces. Models for the starter system and blowby processes are also presented as part of a broader theoretical investigation to assess the impact of design changes on start quality.

The successful design of a long-lived and efficient gas turbine engine requires a good knowledge of the thermal and aerodynamic performances of the components of the turbine. Of particular importance, is the heat transfer rate from the hot gases to the cooled turbine blades, since this limits the maximum turbine entry temperatures which can be obtained. Much gas turbine research is concentrated on experimental modelling and measurements to assist in the development of improved theoretical prediction techniques. The difficulties of instrumenting fully rotational rigs, which are necessary for a full understanding of the complex three dimensional flow in the turbine, have, however, to a large extent, limited most experimental research to stationary facilities. A technique is described which will allow heat transfer rate measurements to be made on fully rotating test facilities using mutlilayered model turbine blades comprising an electrical insulator on a metal base. An accurate and computationally efficient method for determining the surface heat flux to a multi-layered model turbine blade is developed theoretically, together with a method for calibrating the thermal properties of the multi-layered system. This method allows the existing successful heat flux measurement technique, which utilises electronic analogue circuitry in conjunction with thin film surface thermometers on a model made from a thermal insulator, to be extended for application to multi-layered models. The production of test models by the application of a vitreous enamel (as an electrical insulator), to a mild steel, is identified as the most suitable coating technique for experimental application. Radiant and wind tunnel testing of multi-layered cylindrical models are described, which confirm that the method is both practical and accurate.

The work described in this thesis was carried out to investigate the application of variable valve actuation (VVA) to light-duty diesel engines for use in passenger vehicles. The background to this was that there was little published on the subject and with advanced turbochargers, exhaust gas re-circulation systems and high pressure fuel injection systems reaching maturity it seemed likely that further enhancement of the air management in this type of engine, through VVA would receive greater interest. The first section of this thesis discusses the external pressures on engine manufacturers, from legislation and from the customer expectations, which could be expected to influence the adoption of VVA, while looking at the criteria on which they would assess a VVA system prior to adoption. Section two provides an overview of the effects of VVA and how they may be used to improve engine operation by highlighting the specific features of diesel engines, i.e. cold starting and compression ratio, part load fuel economy, full load torque and transient torque rise, that can be influenced by air management and what characteristics are required from the VVA system in order to provide improvements in these areas. Having identified the key features of a VVA system that would be suitable for use in light duty diesel engines section three presents a brief literature review and discusses the family of non-constant angular velocity VVA systems that were identified as having the correct characteristics and relative simplicity necessary for any system that might be made in high volume production. This section also provides a detailed analysis of one system of this type to highlight its behaviour and impact on valve train design. Software was written to model the selected mechanism and produce the valve lift characteristics for use in simulating the engine's behaviour. Section four provides an overview of engine simulation techniques and some detail of the model constructed for this investigation. It also discusses the additional code and methodologies required to model the turbine, compressor and combustion processes, which required special treatment, and presents data to compare the behaviour of the model with the baseline of known engine behaviour. Section five presents simulation results that show the following possible improvements: a) a 23% increase in torque, b) light part-load fuel economy improvements of 13% and c) transient rise to maximum torque times reduced from 2.3 seconds to 1.6 seconds. It also discusses the features of engine operation with VVA that provide the potential for these improvements in engine operation, quantifies the benefits that might be expected at a large number of operating conditions and discusses the interactions between the VVA and other systems such as the turbo-charger and EGR system. Section six presents conclusions which beside the enumeration of the potential benefits and description of the key effects of VVA, highlights the need for test data to verify the extent to which the benefits can be realised in real engines and suggests areas for future research.

In many practical combustion devices, including those used in gas turbine engines for aircraft and power generation, a high energy spark kernel is necessary to reliably ignite the turbulently flowing flammable gases. Complicating matters, the spark kernel is sometimes generated in a region where a non-flammable mixture is present, or where there is no fuel at all. This requires the spark kernel to travel to a flammable region before rapid combustion can begin in non-premixed or stratified flows. This transit time allows for chemical reactions to take place within the kernel as well as mixing with surrounding gases. Despite these demanding conditions, the majority of research in ignition has been for low energy sparks and premixed conditions, not resembling those found in many combustion devices. Similarly, there is little work addressing this issue of spark kernel evolution in the non-premixed flowing environment, and none available that control the time allowed for transit. The goal of this thesis is to understand the development of a spark kernel issued into a non-premixed flow and the sensitivities of the ignition process. To this effect, a stratified flow facility for ignition experiments has been fabricated utilizing a high speed schlieren and emission imaging system for visualizing the kernel motion and ignition success. Additionally, OH chemiluminescence and CH PLIF were used to track chemical species during the ignition process. This facility is also used to control the important variables regarding the flow and spark kernel interaction to quantify the influence on ignition probability. A reduced order model employing a perfectly stirred reactor (PSR) has also been developed based on experimental observations of the entrainment of fluid into the evolving kernel. The simulations provide additional insight to the chemical development in the kernel under different input conditions. This model was enhanced by introducing random perturbations to the input variables, mimicking a practical situation. A computationally efficient support vector machine was trained to replicate the numerical model outputs and predict ignition probabilities for nominal input conditions, providing comparison to experimental results. Experimental and numerical results show that initial mixing with non-flammable fluid quickly reduces the ability for the kernel to ignite the flammable flow, resulting in a strong influence of the inlet temperature and the kernel transit time on the probability of ignition. Once the kernel reaches the flammable mixture, entrainment of this flow occurs, which requires on the order of a vortex turn-over time before chemistry can begin. Initial chemical reactions include endothermic fuel decomposition, further reducing the kernel temperature prior to heat release, creating a competition between the cooling effect of additional mass entrainment and the delayed heat release reactions. CH PLIF results show that flame chemistry is initially confined to a thin region that corresponds to the interface layer where the flammable gases mix with the hot kernel fluid from the vortex entrainment of ambient gas. The dependence of the ignition probability to variations in flow conditions is captured reasonably well by the reduced order model, validating the PSR approach and the probability prediction tool. The development of this reduced order model is a major contribution of this work with the ability to predict the effects of the important physical ignition processes, which can be used when considering an ignition system's feasibility. This work will provide knowledge to guide the use and design practices in industry, as well as a simple model to test ignition feasibility based on mixing, entrainment, and chemical reactions. Furthermore, the flow facility is well characterized, and a database has been developed that can provide validation points for future computational simulations. Future modeling will be important to further understand fluid dynamic effects that are difficult to measure experimentally, and study a broader range of conditions.

No description available.

Particle Image Velocimetry (PIV) is now emerging as a powerful tool for the investigation of unsteady fluid mechanics. At the same time, the study and optimisation of in-cylinder flow processes in automotive Internal Combustion (IC) engines is of increasing importance in the design of improved combustion systems with lower emissions and favourable power and efficiency characteristics. This thesis describes the development and application of PIV as a routine diagnostic tool for the investigation of in-cylinder flows in a production geometry single cylinder research engine exhibiting "barrel swirl" or "tumbling" in-cylinder fluid motion. The work has involved the design and installation of a complete PIV engine facility, based around a four-valve, four-stroke Rover research engine equipped with piston crown optical access and a glass cylinder liner. Novel techniques for the on-line monitoring of important experimental parameters have been developed which permit the reliable acquisition of high spatial resolution PIV data from both horizontal and vertical measurement planes within the engine cylinder. A novel optical correction technique has been developed to control the severe particle image degradation which was experienced when imaging vertical planes within the glass cylinder. A simple means for selection of an appropriate corrective lens for this application is described, together with an experimental evaluation of the lens performance. A representative set of PIV images and data from both horizontal and vertical planes are then presented. These have been selected from a comprehensive set of flow mapping experiments in the motored engine. The data are discussed with reference to the work of others in engines of similar geometry and have shed new light on the detailed processes involved in the formation and breakdown of barrel swirl. Initial PIV measurements ahead of a flame under part load, skip fired conditions have also been made in the engine. This has demonstrated the possibility of investigating incylinder flow behaviour under conditions approaching those in a fully firing, production geometry optical engine. Finally, limitations in the PIV technique employed in this work and methods of overcoming them are described and the prospects for further work are discussed.