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.

The work presented herein describes thesis research in an on-going camshaft grinding evaluation study, initially under the sole sponsorship of Ford Motor Company, and subsequently under the auspices of the National Science Foundation, with industrial participation from American Stress Technologies, Ford Motor Company, G.E. Superabrasives and Litton Automotive Services. Six mechanically assembled camshafts were ground with each of their eight induction hardened lobes receiving a different depth of cut per pass. X-ray residual stress measurements made with depth identified significant near-surface tensile residual stresses in abusively ground regions of the lobes. Acid etching at the time of grinding and subsequent microhardness measurements were employed to verify the x-ray depth results. The grinding operation was further characterized with use of profile and roughness measurements. Burn (defined as a localized tempering of the cam lobe as a result of the grinding operation) appeared in those lobes that received the larger depth of cut, and was concentrated along the ramps and base circle. Several non-destructive examination techniques were then compared with each other to discover which best detected burn. Intercomparison involved evaluating the strength and consistency of the measurement signal. Background noise occurred in all cases due to the measurement technique, instrument error, and human error. Measurement of grinding forces and x-ray diffraction line width analysis were found to be suitable for rapidly and reliably detecting grinding burn in the induction-hardened carbon steel cam lobes. In this regard, it may now be possible to have reliable, quantitative, and non-destructive cam lobe examination in place of the traditional acid etching. / Master of Science

The 3/4-race cam and dual carburetors tested in this investigation provided moderate increases in maximum power output at speeds above 3000 rpm, The fuel consumption was reduced by the use of the racing type cam and increased with the use of two standard carburetors. However in the latter case it is possible that the economy would have been improved had the proper carburetor jets been installed. The maximum power afforded by the dual carburetors occurred at about the same speed as that for the stock engine whereas the maximum power afforded by the 3/4-race cam occurred at 250 rpm higher than that of the stock engine. Large increases in maximum power output and increase in the speed for maximum power were provided by a combination of a 3/4-race cam and dual carburetors. However the gain in speed and power was obtained at the expense of fuel consumption. The above modifications in engine equipment were beneficial for high speed operation, the only advantage at low speeds being an increase in the accelerating ability of the engine. / Master of Science