The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. Under normal operation the engine was operated under port fuel injection with a stoichiometric airfuel mixture. Multiple centred auto-ignition events were regularly observed, with knock intensities of up to ~30bar. Additional excess fuel was then introduced directly into the end-gas in short transient bursts. As the mass of excess fuel was progressively increased a trade-off was apparent, with knock intensity first increasing by up to 65% before lower unburned gas temperatures suppressed knock under extremely rich conditions. This trade-off is not usually observed during conventional low intensity knock suppression via over-fuelling and has been associated with the competing effects of reducing auto-ignition delay time and charge cooling/ratio of specific heats.Overall, the results demonstrate the risks in employing excess fuel to suppress knock deep within a heavy knocking combustion regime (potentially including a Super-Knock regime).

The aim of this experimental work was to improve understanding of the influence of hydrous ethanol on combustion in an engine demonstrating a tendency for biased flame migration towards the hotter exhaust walls as often reported for typical modern pent roof design IC engines. The work aimed to uncover the degree of residual water content that can be reasonably tolerated in terms of combustion characteristics in future ethanol SI engines (with the energy required to reduce water levels then potentially reduced).The experiments were performed in a single cylinder optical research engine equipped with a modern central direct injection combustion chamber and Bowditch type optical piston. Results were obtained under part-load engine operating conditions (selected to represent typical highway cruising conditions) with hydrous ethanol at 5%, 12% and 20% volume water. Baseline results were obtained using pure isooctane. High-speed cross-correlated particle image velocimetry was undertaken at 1500rpm under motoring conditions with the intake plenum pressure set to 0.5 bar absolute. The horizontal imaging plane was fixed 10mm below the combustion chamber "fire face". Comparisons were made to CFD computations of the in-cylinder flow. Complimentary flame images were obtained via the "natural light" (chemiluminescence) technique over multiple engine cycles. The flame images revealed the tendency of an iso-octane fueled flame to migrate towards the exhaust side of the combustion chamber, with no complimentary bulk air motion apparent in this area in the horizontal imaging plane. The faster-burning ethanol offset this tendency of the flame to migrate towards the hotter exhaust walls. The fastest combustion rate occurred with pure ethanol, with higher water content (>5%) generally slowing down the flame speed rate to 10.64 m/s from 10.92 of ethanol and offsetting the flame speed/migration benefit (in good agreement with recent laminar burning velocity correlations for hydrous ethanol). When adding 20% water to ethanol the combustion rate was significantly slower (8.2 m/s) with a considerable increase in flame shape distortion as quantified by flame image shape factor values. The results demonstrate how the added water increases flame distortion and leads to higher flame centre displacement. Such flame centre displacement could potentially be offset in the future with a spark plug location biased further towards the intake side of the chamber (albeit sometimes practically constrained by the priorities given to intake valve sizing and local cooling jacket design). The results indicate that ethanol fuels offset such bias flame growth and allow residual water to be tolerated for an equivalent degree of biased flame migration. The implication is reduced fuel production energy and cost required to produce usable ethanol fuels.

No abstract

No abstract

The work was concerned with improving understanding of the interaction of the bulk in-cylinder flow with turbulent premixed flame propagation when using varied fuels including iso-octane, ethanol or butanol. The experiments were performed in a single cylinder research engine equipped with a modern central direct injection combustion chamber and Bowditch style optical piston.Results were obtained under typical part-load engine operating conditions. High speed cross-correlated particle image velocimetry was undertaken at 1500rpm under motoring conditions with the plenum pressure set to 0.5 bar absolute, with the horizontal imaging plane fixed 10mm below the combustion chamber "fireface". Comparisons were made to CFD computations of the flow.Complementary flame images were then obtained via natural light (chemiluminescence) over multiple engine cycles. The flame images revealed the tendency of the flame to migrate towards the hotter exhaust side of the combustion chamber, with no complementary bulk air motion apparent in this area in the imaging plane. In terms of fuel effects, the addition of 16% butanol to iso-octane resulted in marginally faster combustion. Fastest combustion was observed with ethanol, in good agreement with laminar burning velocity correlations within the literature. The ethanol could be seen to offset the tendency of migration of the flame toward the exhaust walls under the fixed spark timing conditions. This exhaust migration phenomenon has been noted previously by others in optical pent-roofed engines but without both flow and flame imaging data being available. The results may imply that the spark plug should ideally be biased further towards the intake side of the chamber if the flame is to approach the intake and exhaust walls at similar times resulting in symmetrical flame propagation, reduced premature wall quenching and hence increase combustion stability and thermal efficiency. Such a layout is typically not preferred due to the priority given to the central fuel injector (and associated cooling jacket) location and maximizing the size of the inlet valves for improved volumetric efficiency.