Abstract
The purpose of this research has been to investigate the influence of turbulence on charge consumption and flame front propagation. There are two aspects of this work: Firstly, engine based research has been carried out in order to ascertain the turbulent structures that affect combustion. Secondly, a technique for quantifying the interaction between flame propagation and specific flow structures has been developed within a twin chamber combustion bomb. The levels of turbulence that exist within each cycle of a single cylinder DISI engine have been measured using high speed particle image velocimetry (HSPIV), then compared to engine output in terms of IMEP and the rate of charge consumption. In order to determine the range of spatial and temporal scales of turbulence that affect the burn rate and IMEP, frequency analysis was carried out upon the velocity field data. This analysis was achieved by FFT filtering the HSPIV data captured in the vicinity of the spark plug, separating the velocity fields into low frequency bulk motion and high frequency turbulence components. The data demonstrates that removing fluctuating components with a frequency below 240Hz successfully removes the variation in bulk motion from the calculation of turbulence intensity, revealing the relationship between high frequency turbulence and charge consumption. Moreover, FFT filtering of fluctuating components above 600Hz reduced the correlation between high frequency turbulence and IMEP, demonstrating the influence of these high frequency/small scale turbulent structures on flame propagation rate, and thereby rate of charge consumption and engine performance. In conjunction with the engine based analysis, research has also been carried out on the fundamental interaction between flame and flow within a twin-chamber combustion bomb. The study of the stable and repeatable flow structures produced within the bomb, which replicate known engine turbulence length scales, holds distinct advantages over the complex three-dimensional turbulent fields of the SI engine. The purpose of this data is to develop further understanding of the physical and chemical processes of turbulent flame propagation. As part of this work a new algorithm for the calculation of local burning velocity has been developed. Applying this new approach, through the use of multiple camera asynchronous PIV, has enabled the measurement of local burning velocity of a flame front as it interacts with a rotational flow.
