The effect of compression ratio on the performance of a direct injection diesel engine

This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University.This thesis considers the effect of compression ratio on the performance of a direct injection diesel engine. One aspect of engine performance is considered in great detail, namely the combustion performance at increased clearance volume. This aspect was of particular interest because variable compression ratio (VCR) systems normally operate by varying the clearance volume. The investigation relied upon results obtained both from experimental and computer simulating models. The experimental tests were carried out using a single-cylinder direct-injection diesel engine, under simulated turbocharged conditions at a reduced compression ratio. A number of one-dimensional computer models were developed; these simulate the induction and compression strokes, and the fuel spray trajectories in the presence of air swirl. The major objectives of the investigation were: to assess the benefits of VCR in terms of improvements in output power and fuel economy; to assess the effects on combustion of increased clearance volume, and investigate methods for ameliorating resulting problems; develop computational models which could aid understanding of the combustion process under varying clearance volume conditions. It was concluded that at the reduced compression ratio of 12.9:1 (compared to the standard value of 17.4:1 for the naturally-aspirated engine), brake mean effective pressure (BMEP) could be increased by more than 50%, and the brake specific fuel consumption (BSFC) could be reduced by more than 20%. These improvements were achieved without the maximum cylinder pressure or engine temperatures exceeding the highest values for the standard engine. Combustion performance deteriorated markedly, but certain modifications to the injection system proved successful in ameliorating the problems. These included: increase in the number of injector nozzle holes from 3 to 4, increase in injection rate by about 28%, advancing injection timing by about 6°CA. In addition, operation with weaker air fuel ratio, in the range of 30 to 40:1 reduced smoke emissions and improved BSFC. Use of intercooling under VCR conditions provided only modest gains in performance. The NO emission was found to be insensitive to engine operating conditions (fixed compression ratio of 12.9:1), as long as the peak cylinder pressure was maintained constant. Engine test results were used in order to assess the accuracy of four published correlations for predicting ignition delay. The best prediction of ignition delay with these correlations deviated by up to 50% from the measured values. The computer simulation models provided useful insights into the fuel distribution within the engine cylinder. It also became possible to quantify the interaction between the swirling air and the fuel sprays, using two parameters: the crosswind and impingement velocities of the fuel spray when it impinges on the piston-bowl walls. Tentative trends were identified which showed that high crosswind velocity coincided with lower smoke emissions and lower BSFC

Optimisation of pixel modules for the ATLAS inner tracker at the high-luminosity LHC

The Large Hadron Collider and its pre-accelerator complex will be upgraded in three steps to allow for the high luminosity phase. A factor of ten times more data will be collected in this period by facilitating the increased instantaneous luminosity being seven times as large as the original design value. A new inner tracker system is in preparation for the ATLAS detector in view of the high luminosity phase to start operation around 2026. This all silicon tracker relies on various innovative technologies to cope with the severe challenges arising from the increased luminosity. The pixel detector employs a new readout chip to decrease the pixel size to a fifth of the pixel size of the present generation to be able to disentangle all tracks in the high multiplicity environment close to the interaction point. Thanks to their reduced power dissipation and high charge collection efficiency after irradiation, thin planar n-in-p pixel sensors are ideally suited to cope with the expected unprecedented radiation damage. TCAD simulations are being performed to optimise the sensor layout for the new pixel cell size of 50x50um2. In this study, charge collection efficiency, electronic noise and electrical field properties are investigated both before and after irradiation. The RD53A prototype readout chip is used to build modules based on the proposed thin planar n-in-p sensors. The performance of different sensor designs is assessed by analysing data from various test-beam campaigns. The effects of storage time at room temperature for the ITk pixel detector during maintenance periods are reproduced on real modules. Pixel detector modules built with sensors of 100-150um thickness are characterised with testbeam measurements. The charge collection and hit efficiencies are compared before and after annealing at room temperature up to one year

Aircraft Noise

Noise generated by aircraft continues to be a pressing issue for society, as an increasing number of people residing in close proximity to airports make noise complaints on a regular basis. The reduction in aircraft noise is therefore a very important engineering task that would require the careful identification of different acoustic sources around the airplane, the understanding of noise source behavior and ranking along flight trajectories, sophisticated measurement techniques, and robust and accurate numerical tools aimed at predicting the generation of noise, the propagation through the atmosphere, and the resulting noise impact along approach and departure flights. For an overall assessment of the situation, it has to be assessed along entire flight trajectories rather than assessing limited operating conditions only. Furthermore, it is highly recommended to apply multiple acoustic metrics and account for different and widespread observer locations along the flight. Only then can the overall situation be adequately captured. Obviously, this is a highly multidisciplinary effort and no single discipline can address this problem. This reprint includes selected research studies with that multidisciplinary context that deal with numerical or experimental investigations that range from the investigation of specific noise sources to the assessment of noise generated by the overall aircraft in operation. Both basic and applied research studies involving the modelling and simulation of aircraft noise are included