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A variable compression ratio concept that can give a different expansion ratio to the compression ratio has been evaluated by means of a simulation of a turbocharged diesel engine. The VR/LE mechanism kinematics have been defined and described, and the compression ratio and expansion ratio have been presented as a function of the eccentric phase angle (αo). A zero-dimensional engine simulation that has been the subject of comprehensive validation, has been used as the basis of the VR/LE study. The effect of the compression ratio on the engine performance at fixed loads is presented. The principal benefits are a reduction in fuel consumption at part load of about 2%, and a reduction in ignition delay that leads to an estimated 6 dB reduction in combustion noise. The study has been conducted within the assumption of a maximum cylinder pressure of 160 bar.

The piston bowl design is one of the most important factors that affect the air/fuel mixing and the subsequent combustion and pollutant formation processes in a direct injection diesel engine. The bowl geometry and dimensions, such as pip region, bowl lip area, and torus radius are all known to have an effect on the in-cylinder mixing and combustion process. In order to understand better the effect of torus radius, three piston bowls with different torus radius and lip shapes designs but with the same lip area and pip inclination were investigated using Computational Fluid Dynamics (CFD) engine modelling. KIVA3V with improved sub-models was used to model the in-cylinder flows and combustion process, and it was validated on a High-Speed Direct Injection (HSDI) engine with a 2nd generation common rail fuel injection system.

A programme of work is being undertaken to improve the performance of a spark-ignited natural gas engine, that has been converted from a diesel engine. The aim of this work is to reduce the fuel consumption and NOx emissions. All experimental data and predictions refer to full throttle operation at 1500 rpm. The work to be reported here will include baseline tests that have been used to calibrate a two-zone combustion model. Particularly important are the predictions of the NOx emissions. The simulation has then been used to predict the effects of using: a higher compression ratio, and a faster burn combustion system. The design philosophy of the resulting fast burn combustion system is discussed, and some preliminary results are presented. There will be a discussion of the ignition parameters that affect the lean burn operation, and the effect of the spark plug gap position is discussed in the context of results from a phenomenological model of turbulent combustion.

The influence of swirl on combustion in diesel and spark ignition engines is reviewed briefly, and this leads to a resumé of the swirl measuring techniques. The numerous ways of analysing swirl data are summarised and the relations between the different swirl parameters are presented. Experimental results are presented from a diesel engine in which the flow has been measured by a hot wire anemometer, a paddle wheel and a swirl torquemeter. The performance of the different measurement techniques is compared. Further results are presented (from a spark ignition engine) which illustrate the influence of the inlet port, manifold and entry conditions on the swirl measurements. Integration techniques are reviewed for producing a single swirl parameter to characterise the combined performance of the inlet port, valve and camshaft. Finally, the difficulty in standardising measurements of barrel swirl are discussed.

Reductions in fuel consumption, noise level, and pollutant emissions such as, Nitrogen Oxide (NOX) and Particulate Matter (PM), from direct-injection (DI) diesel engines are important issues in engine research. To achieve these reductions, many technologies such as high injection pressure, multiple injection, retarded injection timing, EGR, and high swirl ratio have been used in high-efficiency DI diesel engines in order to achieve combustion and emission control. However, each technology has its own advantages and disadvantages, and there is a very strong interaction between these methods when they are simultaneously used in the engine. This study presents a computational study of both the individual effect and their interactions of injection timing, EGR and swirl ratio separately and their interaction in a HSDI common rail diesel engine using the KIVA-3V code.

This is a first of a series of papers describing how the replacement of some of the inlet air with EGR modifies the diesel combustion process and thereby affects the exhaust emissions. This paper deals with only the reduction of oxygen in the inlet charge to the engine (dilution effect). The oxygen in the inlet charge to a direct injection diesel engine was progressively replaced by inert gases, whilst the engine speed, fuelling rate, injection timing, total mass and the specific heat capacity of the inlet charge were kept constant. The use of inert gases for oxygen replacement, rather than carbon dioxide (CO2) or water vapour normally found in EGR, ensured that the effects on combustion of dissociation of these species were excluded. In addition, the effects of oxygen replacement on ignition delay were isolated and quantified.

This is the second of a series of papers on how exhaust gas recirculation (EGR) affects diesel engine combustion and emissions. It concentrates on the effects of carbon dioxide (CO2) which is a principal constituent of EGR. Results are presented from a number of tests during which the nitrogen or oxygen in the engine inlet air was progressively replaced by CO2 and/or inert gases, whilst the engine speed, fuelling rate, injection timing, inlet charge total mass rate and inlet charge temperature were kept constant. In one set of tests, some of the nitrogen in the inlet air was progressively replaced by a carefully controlled mixture of CO2 and argon. This ensured that the added gas mixture had equal specific heat capacity to that of the nitrogen being replaced. Thus, the effects of dissociated CO2 on combustion and emissions could be isolated and quantified (chemical effect).

The extraction of small quantities of gas and particulates from diesel engine cylinders allows time-resolved gas and particulate analysis to be performed outside the engine during a short window of a few degrees crank angle at any stage of the engine cycle. The paper describes the design features and operation of a high-speed, intermittent sampling valve for extracting in-cylinder gases and particulates from diesel engines at any selected instant of the combustion process. Various sampling valve configurations are outlined. Detailed analysis of gas flow through the valve and the performance of the electromagnetic actuator and plunger are given in order to facilitate the design of the sampling valve. Finally, examples of the uses of the sampling valve in a direct-injection diesel engine are provided. These demonstrate how gaseous emissions such as NOx, uHC, CO2, and particulate emissions can be sampled at any part of the combustion process and analysed.

Water vapour is a main constituent of exhaust gas recirculation (EGR) in diesel engines and its influence on combustion and emissions were investigated. The following effects of the water vapour were examined experimentally: the effect of replacing part of the inlet charge oxygen (dilution effect), the effect of the higher specific heat capacity of water vapour in comparison with that of oxygen it replaces (thermal effect), the effect of dissociation of water vapour (chemical effect), as well as the overall effect of water vapour on combustion and emissions. Water vapour was introduced into the inlet charge, progressively, so that up to 3 percent of the inlet charge mass was displaced. This was equivalent to the amount of water vapour contained in 52 percent by mass of EGR for the engine operating condition tested in this work.