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In this thesis various aspects of the diesel engine fuel injection, combustion and emission formation processes have been evaluated. Several types of evaluation tools and methods have been applied. Fuel spray momentum was used to characterize injection rate and hole-to-hole variations in fuel injectors. Using both instantaneous fuel impulse rates and instantaneous mass flow measurements, spray velocity and nozzle flow parameters were evaluated. Several other hole-to-hole resolved injector characterization methods were used to characterize a set of fuel injectors subjected to long term testing. Fuel injector nozzle hole-to-hole variations were found to have a large influence on engine efficiency and emissions. The degree of hole-to-hole variations for an injector has been shown to correlate well with the performance deterioration of that injector. The formation and atomization of fuel sprays, ignition onset and the development of diffusion flames were studied using an optical engine. Flame temperature evaluations have been made using two different methods. NO-formation depends strongly on flame temperature. By applying a NO-formation evaluation method based on both heat release rate and flame and gas temperature it was possible to achieve a reasonable degree of correlation with measured exhaust emissions for very varying operating conditions. The prediction capability of the NO-formation evaluation method was utilized to evaluate spatially and temporally resolved NO-formation from flame temperature distributions. This made it possible to pinpoint areas with a high degree of NO-formation. It was found that small hot zones in the flames can be responsible for a large part of the total amount of NO that is produced, especially in combustion cases where no EGR is used to lower the flame temperature. By applying optical diagnostics methods the combustion and emission formation phenomena encountered during production engine transients were evaluated. The transient strategy of the engine involved reducing the EGR-rate to zero during the initial parts of the transient. Increased general flame temperature and the occurrence of small hot zones were found to explain the increase in NO-emissions during these transients. / QC 20110530

This thesis describes the application of microprocessor engine management techniques to the control of the hydrogen/petrol engine. A discussion of the world's fuel resources and the need for energy conservation is followed by a review of the literature related to the use of hydrogen as a fuel. The concept of hydrogen supplementation is introduced and then the work of other researchers in this field is studied in some detail in order to establish the control requirements for hydrogen/petrol operation. A survey of the literature relating to engine management techniques precedes a description of the microprocessor-based controller which was developed for this work. Following this is a description of the engine calibration process which involves the use of specially developed surface-fitting and contour-tracing software. Steady-state operation in the hydrogen/petrol mode resulted in significant energy savings but poor driveability was obtained when the control system was fitted into a Ford Transit Crew Bus. Transient operation during the ECE-15.04 test resulted in a small fuel economy gain but the exhaust emissions exceeded the legislative limits. It was concluded that, although the steady-state performance showed promise, further development of the control system was required to meet the demands of transient operation.

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This study was concerned with improvement and validation of a thermodynamic spark ignition engine simulation code developed in Leeds. Experimental validation data were generated using a central ignition, disc-shaped combustion chamber variant of a ported single-cylinder research engine with full-bore overhead optical access. These data included simultaneous measurement of cylinder pressure and flame position at different operating conditions. The engine was skip fired (fired once every five cycles), to remove residuals and ensure well defined in-cylinder fuel-air mixture for simulation. Flames were imaged using a digital camera capturing the light emitted from the flame ("natural light"). New methods were developed to process the pressure and film data. Flame pictures were processed to determine enflamed area, mean flame radius and flame centroid. Parameters were also developed to describe flame "circularity" ("shape factor") and to describe asymmetry of flame approach to the cylinder walls ("active perimeter fraction", APF). Time-base crank angle records allowed evaluation of engine speed variation within a cycle and mean engine speed for a cycle. Although generated principally for model validation, the experimental results proved interesting in their own right. Middle, slow and fast cycles were defined for each condition. Analysis of these cycles suggested that there was no correlation between the initial flame centroid displacement, its locus over the flame propagation period or the flame "shape factor" and the speed of combustion and pressure development. As the flame approached the wall, the active perimeter fraction fell in a similar manner for all the middle cycles. Substantial modifications were made to a pre-existing thermodynamic engine cycle code. Deficiencies in the blowby, heat transfer and thermodynamic aspects were corrected. An additional ("Zimont") turbulent burning velocity sub-model and a new routine for the influence of engine speed variation within a cycle were incorporated into the code. The active perimeter fraction parameter function determined in the experiments was encoded to allow for the effects of flame-wall contact on entrainment rate during the late flame propagation. A radial stratified charge model was also developed. Burned gas expansion over the flame propagation period was shown to significantly change the unburned gas charge stratification from the initial variation. Two types of initial stratification (linear and parabolic distributions, rich of the centre and lean close to the wall) were imposed. Faster combustion development was observed in both cases, c. f that for equivalent homogeneous charge. Good agreement was observed between experimental results and "Zimont model" predictions at different equivalence ratios and engine speeds. Other computations using the pre-existing Leeds K and KLe correlations gave reasonable predictions at the various engine speeds and at rich conditions; however, they yielded slower results than experimentally observed for lean conditions.