Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

The investigation reported in this thesis is concerned with the topic of soot formation and soot particle motion in the cylinder of a light duty automotive diesel engine. CFD has been employed to simulate in-cylinder conditions and to investigate the source of particles which are transferred to the oil. The accumulation of soot in the lubricating oil of diesel engines is one of the factors limiting the interval between oil changes and hence service interval. Soot particles can be transferred to oil film on the cylinder wall layers through the complex motion of the fluid flow in the cylinder. The paths of soot particles from specific in-cylinder locations and crank angle instants have been explored using the results for cylinder charge motion predicted by the Kiva-3v CFD code. Using the velocity fields from the simulation data, massless tracking of the in-cylinder soot particles in space and time is carried out employing a particle tracking with trilinear interpolation technique. From this investigation, new computational codes for the prediction of soot particle paths and soot particle size change along a specific path in a diesel engine have been developed. This investigation is the first numerical study into soot particle trajectories within an engine and thus opens up a novel branch of research of soot formation within internal combustion engines. Computed soot paths from the investigation show that soot particles formed just below the fuel spray axis inside the middle bowl area during early injection period are more likely sources of soot particles on the cylinder wall layers than those formed later. Soot particles that are formed above the fuel axis have less tendency to be transported to the cylinder wall layers thus are not likely to be the main source of soot at the cylinder walls. Soot particles that are from the bowl rim area are found to be another source of soot transfer to the boundary layer, as they are directly exposed to reverse squish motion during the expansion stroke. Soot particles that are formed near the cylinder jet axis during fuel injection tend to move into the bowl. These soot particles are found to be from the relatively less concentrated area. In contrast, particles from the most concentrated areas tend to be moving into the bowl and pose least risk of contaminating oil films on the liner. Sensitivity studies of soot particle paths to swirl show that engine operating with low swirl ratios are more vulnerable to soot in oil problem as low swirls cause the bulk fluid flow to be moving closer to the cylinder walls due to fuel jet velocity and reverse squish motions. Decreasing the spray angle lessens the possibilities of soot particles from being transported close the cylinder wall layers while increasing the spray angle increases the possibilities of soot from the bowl region to be transported close to the cylinder wall layers. The temporal and spatial evolution of soot particle size can be predicted by using the history of temperature, pressure and gas species along the paths. An explorative investigation has been carried out to determine the most suitable method to tackle this soot particle evolution. With proper multipliers, all approaches perform quite satisfactorily in terms of predicting the trend of size change. Soot particles that are likely to be transferred to the cylinder wall layers are predicted to change in size parallel to the average mass profile in the whole cylinder where they quickly peak to maximum at around 18° CA ATDC, and gradually decrease in size through EVO.

No description available.

The crankshaft is a complex component, and as such, the influence of its geometric parameters on stresses seen under service loads is not well understood. The objectives of this work are to investigate the effects of a wide range of geometric parameters on stresses in overlapped crankshafts, to find correlation between results and to formulate simple methods of predicting peak stress levels: It is intended to achieve this by use of the Finite Element (FE) and Boundary Element (BE) methods. Individual crankthrows are loaded under the important load cases of bending and torsion. Stress concentration factors are determined by normalising peak stresses with respect to the nominal stress occurring in the most appropriate section in the neck between the fillets. Analyses are carried out in 2D and 3D, making use of symmetry as far as possible. Many of the governing dimensions of the crankthrow are included in the analyses; crankpin and journal diameters, crankpin and journal overlap, and web thickness. Variations in SCF are plotted over a wide range for each of these parameters. Additionally, features such as fillet size and shape, bore-holes, dimples, cut-back webs and oil holes are investigated. It is found that the effects on stress of individual parameter changes can be superimposed to accurately predict the effect of combining various parameter changes in one model. The crankpin and journal fillet radii and the length of the minimum section between the fillets are shown to be the critical parameters in determining the peak stress levels in the crankshaft. SCFs obtained from the range of analyses performed show good agreement with the classical theory of SCFs in notched bars. Bore-holes and dimples are found to offer significant benefits in terms of peak stress reduction, in addition to their common usage of reducing the out of balance crankpin mass. The FE and BE methods give accurate results for stress analysis of crankshafts and offer several advantages over traditional experimental techniques; they are ideally suited to parametric analyses, can be carried out relatively quickly, results are repeatable because boundary conditions can be exactly defined, and the cost of analysis is significantly reduced.

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.