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Reported in the current paper is a study of the effects of Nitric Oxide (NO) within a simulated Exhaust Gas Residual (sEGR) on Spark Ignition (SI) engine end gas autoignition. A modified version of the single cylinder Leeds University Ported Optical Engine Version 2 (LUPOE-2) engine was designed to completely eliminate retained residual gas and so allow unambiguous definition of the composition of the in-cylinder charge. The engine was alternately operated on stoichiometric mixtures of iso-octane, two Primary Reference Fuels (PRF), a Toluene Reference Fuel (TRF), and a commercially available Unleaded Gasoline (ULG) and air. These mixtures were diluted with sEGR (products of the complete stoichiometric combustion of the given fuel/air mixture) in mass fractions ranging from 0-15%; with and without 5000ppm NO (0.52% by mass) within that sEGR.

The paper is concerned with the effects of cyclic variation in turbulence (expressed in terms of rms turbulent velocity) on the burn rate and subsequent cyclic variation in in-cylinder pressure derived parameters. The task has been addressed by applying a thermodynamic engine modelling approach for simulations of two very different engines; a single cylinder research engine in which sources of cyclic variation other than turbulence had been minimised and a multi-cylinder production engine. The cyclic variability in the two engines had a number of similar features; the effects of turbulence variation cycle-to-cycle proved dominant in the production engine, mixture strength secondary and prior-cycle residual concentration feedback marginal.

This work is concerned with the analysis of different charge dilution strategies employed with the intention of inhibiting knock in a high output turbocharged gasoline engine. The dilution approaches considered include excess fuel, excess air and cooled external exhaust gas re-circulation (stoichiometric fuelling). Analysis was performed using a quasi-dimensional combustion model which was implemented in GT-Power as a user-defined routine. This model has been developed to provide a means of correctly predicting trends in engine performance over a range of operating conditions and providing insight into the combustion phenomena controlling these trends. From the modelling and experimental data presented, it would appear that the use of cooled externally re-circulated exhaust gases allowed fuel savings near to those achieved via excess air, but with improved combustion stability and combustion phasing closer to the optimum position.

Modern engine developments result in very different gas pressure-temperature histories to those in RON/MON determination tests and strain the usefulness of those knock scales and their applicability in SI engine knock and HCCI autoignition onset models. In practice, autoignition times are complex functions of fuel chemistry and burning velocity (which affects pressure-temperature history), residual gas concentration and content of species such as NO. As a result, autoignition expressions prove inadequate for engine conditions straying far from those under which they were derived. The currently reported study was designed to separate some of these effects. Experimental pressure crank-angle histories were derived for an engine operated in skip-fire mode to eliminate residuals. The unburned temperature history was derived for each cycle and was used with a number of autoignition/knock models.

There is worldwide interest in developing Homogeneous Charge Compression Ignition concepts for lean burn/heavily diluted, low emissions, combustion engines. Although there has been much work and considerable progress relating to autoignition onset in such engines, there has been relatively little study of the reasons for the knock which limits their operation at high power. Building on earlier work on end gas autoignition development and knock in spark ignition engines, it is suggested that the problem is rooted in the mode of autoignition. The conditions supporting the most violent “developing detonation” mode, with increasing charge dilution, bulk unburned gas temperature level and local temperature gradient are explored in relation to HCCI engines.

A novel dual seeding method has been developed to obtain full bore cyclically resolved simultaneous flame images and associated velocity fields in an optically accessed single cylinder research spark ignition engine. The technique has been used to study interaction between the propagating flame and in-cylinder gas motion. Light generated by a fast repetition rate copper vapour laser was formed into a thin light sheet, which passed horizontally through the disc shaped combustion space of a spark ignition engine having complete overhead optical access. Mie scattered light from relatively sparse and large particles (∼65μm) at successive intervals allowed flow definition by particle tracking velocimetry. Simultaneous scattering from dense small seed (∼0.22μm) was used to generate flame front images, which were digitised and analysed to quantify turbulent flame structure and development. The flame was shown to have significant effect on local unburned gas motion as well as vice versa.

Laminar and turbulent burning velocity are important parameters of a combustible mixture. Each is used in mathematical models of spark ignition engine combustion. However, reported data are inconsistent and sparse at elevated pressure and temperature. The present paper presents precise definitions and results of fundamental experiments at Leeds on both laminar and turbulent burning velocities. Reasons for the considerable differences in reported values are put forward and the often neglected effects of flame stretch rate and instabilities on burning velocities are discussed. Relevance is discussed in relation to observations of turbulent flame propagation in a research engine.