The cold start performance of automotive diesel engines is currently poor when compared to similar gasoline units. This thesis describes an experimental and theoretical investigation into the factors limiting diesel cold start behaviour. Studies have been carried out on IDI and DI designs of engine. Start behaviour has been characterised in terms of times taken to complete various stages of startup, engine speed variations and processes which affect these. Combustion and friction behaviour have been investigated in detail. Engine friction losses are dependent on temperature. During start-up these losses are relatively high compared to those when the engine is fully-warm. The work output from combustion is low at low speeds, and prone to a further deterioration at lower temperatures. Consequently, combustion output during cold cranking is initially insufficient to overcome frictional losses. The start times are extended by the need to keep the starter motor engaged until heat generated in the engine causes frictional losses to fall. Eventually, when combustion output is able to overcome friction without the aid of starter motor work, idle speed is reached. Changes to fuel injection and glowplug parameters have been used to achieve a limited improvement in low-temperature starting. Measurements of engine friction have been carried out to determine the influence of temperature and speed, and the relative contributions from each of the main component assemblies. At low temperatures, much of the friction originates in hydrodynamically lubricated components such as journal bearings, due to high oil viscosity at low temperature. Additionally, engine friction as rotation begins has been shown to be far higher than measured by conventional "steady-state" motoring tests (over twice the quasi-steady state friction at -200 e). This initially high friction transient decays towards the quasi-steady values throughout the start. For crankshaft bearings, a friction model has been developed for cold start-up through to fully warm engine conditions. The friction behaviour in the bearings is dependent on thermal conditions around the friction surfaces. Models for the starter system and blowby processes are also presented as part of a broader theoretical investigation to assess the impact of design changes on start quality.

The work described in this thesis was carried out to investigate the application of variable valve actuation (VVA) to light-duty diesel engines for use in passenger vehicles. The background to this was that there was little published on the subject and with advanced turbochargers, exhaust gas re-circulation systems and high pressure fuel injection systems reaching maturity it seemed likely that further enhancement of the air management in this type of engine, through VVA would receive greater interest. The first section of this thesis discusses the external pressures on engine manufacturers, from legislation and from the customer expectations, which could be expected to influence the adoption of VVA, while looking at the criteria on which they would assess a VVA system prior to adoption. Section two provides an overview of the effects of VVA and how they may be used to improve engine operation by highlighting the specific features of diesel engines, i.e. cold starting and compression ratio, part load fuel economy, full load torque and transient torque rise, that can be influenced by air management and what characteristics are required from the VVA system in order to provide improvements in these areas. Having identified the key features of a VVA system that would be suitable for use in light duty diesel engines section three presents a brief literature review and discusses the family of non-constant angular velocity VVA systems that were identified as having the correct characteristics and relative simplicity necessary for any system that might be made in high volume production. This section also provides a detailed analysis of one system of this type to highlight its behaviour and impact on valve train design. Software was written to model the selected mechanism and produce the valve lift characteristics for use in simulating the engine's behaviour. Section four provides an overview of engine simulation techniques and some detail of the model constructed for this investigation. It also discusses the additional code and methodologies required to model the turbine, compressor and combustion processes, which required special treatment, and presents data to compare the behaviour of the model with the baseline of known engine behaviour. Section five presents simulation results that show the following possible improvements: a) a 23% increase in torque, b) light part-load fuel economy improvements of 13% and c) transient rise to maximum torque times reduced from 2.3 seconds to 1.6 seconds. It also discusses the features of engine operation with VVA that provide the potential for these improvements in engine operation, quantifies the benefits that might be expected at a large number of operating conditions and discusses the interactions between the VVA and other systems such as the turbo-charger and EGR system. Section six presents conclusions which beside the enumeration of the potential benefits and description of the key effects of VVA, highlights the need for test data to verify the extent to which the benefits can be realised in real engines and suggests areas for future research.

Thesis (MEng)--University of South Australia, 1998

Thesis (MEng)--University of South Australia, 1998

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 1, 2008) Includes bibliographical references (p. 127-128).

Thesis (Ph. D.)--University of Michigan, 1930. / Cover title. Caption title: Motor-fuel volatility. v--Vapor pressure and vapor lock [by] E.A. Clarke, Hal B. Coats, and George Granger Brown. Reprinted from Industrial and engineering chemistry, v. 22, June, 1930. "Literature cited": p. 24.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1959. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--Rutgers University, 2008. / "Graduate Program in Mechanical and Aerospace Engineering." Includes bibliographical references (p. 78-79).

Thesis (Ph. D.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xiii, 164 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 153-164).