Thesis (Ph. D.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xxiii, 284 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 227-235).

Pressure data measurements have been made in a single-cylinder, spark-ignition engine over 100 consecutive cycles. The engine was operated on natural gas at a wide range of engine speed and equivalence ratios. The effects of spark electrode geometry, combustion chamber geometry, spark gap and throttling have also been examined. From these pressure measurements standard deviations in burning times in mass-fraction-burned values were determined. Because of the existing evidence that the origin of cyclic variations is in the early combustion period, the standard deviations of cyclic variation in time required for a small (almost zero) mass-fraction-burned is estimated by extrapolation. These extrapolated values of standard deviation are compared with the implication of a hypothesis that cyclic variations in combustion in spark-ignition engines originate in the small-scale structure of turbulence (after ignition). The nature of turbulence structure during combustion is deduced from existing knowledge of mixture motion within the combustion chamber of the engine. This research determines the turbulent parameters, such as turbulence intensity, turbulent length scales and laminar burning velocity. The standard deviation in burning times in the early stages of combustion is estimated, within experimental uncertainty, by the parameter ⋋/4uℓ where ⋋ is the Taylor microscale and uℓ is the laminar burning velocity of the unburned mixture. This parameter is the consequence of the Tennekes model of small-scale structure of turbulence and Chomiak's explanation of the high flame propagation rate in regions of concentrated vorticity and the assumption that theignition behaves as though it were from a point source. The general conclusion reached is that the standard deviation in the burning time for small mass-fraction-burned is associated with the early stages of burning-predictable from the knowledge of the Taylor microscale and the laminar burning velocity. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

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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.

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No description available.

Gasoline Direct Injection (GDI) engines work with stratified charge at part load and burn with lean mixtures in order to save fuel, whilst at full load, the fuel and air mix homogeneously for maximum power output. The higher compression ratio and the absence of throttling are two of the most significant benefits of GDI engines. The key issues facing GDI combustion include in-cylinder mixture preparation and post-combustion soot formation. This work was intended to investigate these aspects and was undertaken on a dedicated Jaguar single-cylinder optical GDI engine with a spray-guided combustion system. The spray-guided concept does not rely as much on charge motion or piston design, and can avoid wall-wetting effects so as to reduce engine emissions. Relevant engine control hardware and data acquisition equipment were commissioned. Data/image processing software was also developed to suit the measurements. A data-processing case study with data from a small two-stroke glow ignition engine has been conducted to develop a method to combine the burn rate and heat release analyses in the study of engines with premixed charge but compression ignition. Difficulties such as unknown ignition timing and polytropic index have been addressed. Results for all operating conditions have shown good correlations between the two methods. The technique of quantitative planar laser-induced fluorescence is useful for measuring 2-D fuel distribution in GDI engines. The relevant physics and literature were reviewed in depth. A multi-component fuel was designed to give reasonable co-evaporation characteristics with tracers matching different fuel fractions. The absorption and fluorescence features of each fuel component and tracer were characterised. Optimisation of hardware and signal-to-noise ratio was performed. A recirculating loop was set up for the calibration of the technique. The technique of colour-ratio pyrometry (CRP) for estimating the temperature and loading of soot was applied on the GDI engine. Critical features of the candidate CCD colour camera including its spectral response and noise behaviours were fully studied. Validation tests with reference sources together with an error analysis suggested an accuracy of ±50K within the combustion temperature range. Engine combustion images were then taken under various operating conditions. Temperature estimates were shown to be insensitive to the concentration of soot. Simulation with a thermodynamic modelling package, ISIS, was introduced for comparison with the experimental data. With careful tuning, ISIS gave outputs comparable to the CRP and proved to be a cost-effective tool to study GDI engines. High-speed combustion imaging was carried out using a CMOS camera, allowing the study of flame properties as well as crank-angle resolved CRP. By using a lens in the piston crown to give full bore optical access and appropriate image processing, the flame front could be detected reliably throughout the main combustion process.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 246-257).

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Supervisor: Ronald D. Matthews. Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xiii, 160 p.; also includes graphics (some col.). Includes bibliographical references (p. 156-160). Available online via OhioLINK's ETD Center