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The effects of changes in engine geometry on the breathing and combustion processes in a spark ignition engine have been investigated. It has been shown that a survey of engine geometry can readily illustrate design limitations in three areas : Fluid dynamic, Mechanical and Thermodynamic, and so reduce the extent of investigation available to the designer. The induction performance has been analysed mathematically and comparisons made with experimental work. The results indicate that an assessment of the effect of changes of geometry can be made using empirical relationships without complex mathematics. An attempt has been made to relate the turbulent to laminar flame speed ratio to the engine's physical parameters. These results compare well with previously published work by other workers.

Spark ignition engines are a significant source of air pollution. Emissions are most severe in the period after the engine has been started from cold. This is because fuel enrichment is needed to ensure reliable combustion in the cold cylinder. The problem is compounded by the exhaust treatment catalyst not reaching operating temperature until some minutes after starting. As the majority of car usage is for short journeys, engines spend much of their time in this high emission operating regime. One route to reducing emissions is to improve mixture preparation. This is Particularly effective after a cold start as less enrichment is required to ensure combustion. The aim of this project has been to evaluate a Vortex'Amplifier as a route to improving mixture preparation. The vortex amplifier is a no moving parts fluidic control device. It regulates a large volume supply flow by imparting swirl to it with a small volume control flow. The control flow vortex creates a region of highly turbulent flow at the device outlet which possesses the potential to atomise a fuel spray. The VA has been tested experimentally. The sprays produced by the vortex amplifier were measured by a laser diffraction technique. Numerical analysis has also been undertaken to determine the motion of droplets within the vortex chamber and the potential of the flow to disrupt a fuel spray. The vortex amplifier has been found to be a highly effective atomiser. It produces sprays with a Sauter mean diameter approximately half the size of the best current technology. However the spray impacts on the walls of any pipework downstream of the VA due to the high tangential velocities in the flow exiting the VA. This problem currently precludes engine us'e, but suggestions for improving the situation are contained in the recommendations for future work.

Lean burn in spark-ignition engines offers a significant efficiency advantage compared with stoichiometric operation. The lean operation is restricted by increasing cyclic fluctuation in torque. In order to make use of the efficiency advantage and meet the mandatory emission standards the lean operation limit has to be further extended. This requires particular control of the mixing of fuel and air. To study the effect of mixture formation on cyclic variability and to provide quantitative information on the mixing of air and fuel planar laser-induced fluorescence (PLIF) was developed and applied to an operating SI engine. The method is based on imaging the fluorescence of a fluorescent marker (3-pentanone) mixed with the fuel (iso-octane). 3-pentanone was found to have similar vaporisation characteristics to those of iso-octane as well as low absorption and suitable spectral properties. The technique was applied to an one-cylinder SI engine with a cylinder head configuration based on the Honda VTEC-E lean burn system. The mixture formation process during the inlet and compression stroke could be described by measuring the average fuel concentration in four planes, between 0.7 and 15.2 mm below the spark plug, in a section of the cylinder orthogonal to the cylinder axis. The results showed that for 4-valve pent-roof cylinder head systems with swirl inlet flows, fuel impinging on the cylinder wall opposite to the inlet valves has a major influence on the mixture formation process. In order to quantify the cyclic variability in the mixture formation process and its contribution to cyclic variability in combustion the fuel concentration in a plane near the spark plug was measured on a large number of cycles. It could be shown, that the fuel concentration in a small region close to the spark plug has a dominating effect on the subsequent pressure development for lean mixtures. Variations in the mixture concentration in the vicinity of the spark plug contribute significantly to cyclic variations in combustion. In order to address the issue of no uniformity in residual gas concentration prior to ignition a laser induced fluorescence method was developed to measure nitric oxide (NO) concentrations in the unburned charge in the same one-cylinder research engine. Measurements of average and instantaneous NO concentrations revealed, that the residual gas is not homogeneously mixed with the air and that significant cyclic variations in the local residual gas concentration exist.

The last stage of a deflagration-to-detonation transition (DDT) process involves the propagation and acceleration of a fast flame. This process is currently poorly understood. The difficulties lie in its complex structure, which is turbulent and involves multi-dimensional gasdynamic phenomena. Previous experimental studies have established these fast flames from the interaction of a detonation wave with a row of obstacles or porous plate. Two main questions remain unsolved: 1) What is the propagation speed of the fast flame obtained in these configurations and 2), Which factors dominate the occurrence of the DDT phenomenon? To answer these questions, two models have been constructed in the present work. Firstly, a quasi-1D gasdynamic model is proposed for estimating the transmitted reaction front speed and the strength of the transmitted shock. By alternately assuming a Chapman-Jouguet (CJ) deflagration or an inert shock, the model estimated the transmitted shock speeds. The comparison with extensive experimental data for a range of hydrocarbon fast flames revealed that the burning velocity required for transition to detonation was the CJ value. Secondly, a numerical shock-induced ignition model, which can impose mechanical fluctuations from a driven piston, was established in order to investigate the ignition and acceleration process, thereby clarifying the other question of interest. The results from the simulations indicated that the mechanical fluctuations can play an important role in triggering DDT by means of promoting the local ignition and amplification of the reaction front stemming from such ignition. It was also found that the maximum amplification effects occur with a fluctuation period between the non-fluctuated ignition delay and the time scale of chemical energy deposition. The inert simulation results show that two types of gasdynamic effects from the fluctuations were vital to the hot-spot formation. These hot spots make significant contribution to the detonation initiation.

The experimental and theoretical investigation of the effect of swirl on the fuel-air mixing process in direct-injection diesel engines is described. The experimental work involved the further development of an existing hydraulic analogue technique which enables excellent flow visualisation. This was followed by the design and construction of a novel high-swirl combustion bomb which reproduces engine conditions under fine control. This experimental apparatus includes facilities for high-speed cine photography and a micro-computer based data acquisition and control system providing flexible software control of the fuel injection equipment and data sampling rates of up to 70 kHz. Typical non-combusting and combusting results are presented. Theoretical models of fuel-air mixing are reviewed. The phenomenological jet-mixing model developed and presented is based on an existing continuum mechanics approach and is solved by an integral method. The model includes momentum, heat and mass transfer and simulates jet cross-section distortion and the non-similarity of property profiles. It is intended that this model will form the basis of a proposed multi-zone combustion model.

Increases in demand, lower emission standards, and reduced fuel supplies have fueled the recent effort to find new and better fuels to power the necessary equipment for society’s needs. Often, the fuels chosen for research are renewable fuels derived from biomass. Current research at Texas A&M University is focused on the effectiveness of using cattle manure biomass as a fuel source in conjunction with coal burning utilities. The scope of this project includes fuel property analysis, pyrolysis and ignition behavior characteristics, combustion modeling, emissions modeling, small scale combustion experiments, pilot scale commercial combustion experiments, and cost analysis of the fuel usage for both feedlot biomass and dairy biomass. This paper focuses on fuel property analysis and pyrolysis and ignition characteristics of feedlot biomass. Deliverables include a proximate and ultimate analysis, pyrolysis kinetics values, and ignition temperatures of four types of feedlot biomass (low ash raw manure [LARM], low ash partially composted manure [LAPC], high ash raw manure [HARM], and high ash partially composted manure [HAPC]) as well as blends of each biomass with Texas lignite coal (TXL). Activation energy results for pure samples of each fuel using the single reaction model rigorous solution were as follows: 45 kJ/mol (LARM), 43 kJ/mol (LAPC), 38 kJ/mol (HARM), 36 kJ/mol (HAPC), and 22 kJ/mol (TXL). Using the distributed activation energy model the activation energies were 169 kJ/mol (LARM), 175 kJ/mol (LAPC), 172 kJ/mol (HARM), 173 kJ/mol (HAPC), and 225 kJ/mol (TXL). Ignition temperature results for pure samples of each of the fuels were as follows: 734 K (LARM), 745 K (LAPC), 727 (HARM), 744 K (HAPC), and 592 K (TXL). There was little difference observed between the ignition temperatures of the 50% blends of coal with biomass and the pure samples of coal as observed by the following results: 606 K (LARM), 571 K (LAPC), 595 K (HARM), and 582 K (HAPC).

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