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Since the inception of internal combustion engine, there has been a continual strive to improve its efficiency and refinement. Until very recently, the developments in this regard have been largely based on an experiential basis, or backed by analytical investigations, confined to particular features of the engines. This has been due to lack of computational power, and analysis tools of an integrative nature. In recent years enhanced computing power has meant that complex models, chiefly based on multi-body dynamics could be developed, and further enhanced by the inclusion of component flexibility in the form of structural modes, obtained through finite element analysis. This approach has enabled study of dynamics/vibration response of engines in a more quantitative manner than hitherto possible. Structural integrity issues, as well as noise and vibration (refinement) can then be studied in an integrated manner. However, earlier models still lack sufficient detail to include, within the same analysis, issues related to efficiency, chiefly prediction of parasitic losses due to mechanical imbalance and friction.

This work proposes to match the engine characteristics to the requirements of the Continuously Variable Transmission [CVT] powertrain. The normal process is to pair the transmission to the engine and modify its calibration without considering the full potential to modify the engine. On the one hand continuously variable transmissions offer the possibility to operate the engine closer to its best efficiency. They benefit from the high versatility of the effective speed ratio between the wheel and the engine to match a driver requested power. On the other hand, this concept demands slightly different qualities from the gasoline or diesel engine. For instance, a torque margin is necessary in most cases to allow for engine speed controllability and transients often involve speed and torque together. The necessity for an appropriate engine matching approach to the CVT powertrain is justified in this thesis and supported by a survey of the current engineering trends with particular emphasis on CVT prospects. The trends towards a more integrated powertrain control system are highlighted, as well as the requirements on the engine behaviour itself. Two separate research axes are taken to investigate low Brake Specific Fuel Consumption [BSFC] in the low speed region and torque transient respectively for a large V8 gasoline engine and a turbocharged diesel V6 engine. This work is based on suitable simulation environments established for both engines in the powertrain. The modelling exercises are aimed at supplying appropriate models that can be validated against experimental data. The simulation platforms developed then allow the investigation of CVT powertrain biased engine characteristics. The V8 engine model in particular benefited from engine and vehicle dynamometer data to validate the model behaviour and the accuracy of the prediction. It benefited from the parallel work conducted on the Electrically Assisted Infinitely Variable Transmission [EASIVT] project in Cranfield University. The EASIVT vehicle is a parallel mild hybrid aimed at demonstrating the combined fuel economy benefits of a CVT technology and hybridisation. From the CVT powertrain requirements for fuel economy, BSFC operation can be further promoted in the low speed region if Noise Vibration and Harshness [NVH] counter-measures are developed. A study of the combustion torque oscillations at the crankshaft led to the elaboration of an Active Vibration Control [AVC] strategy for the hybrid Integrated Motor Generator [IMG]. Successful implementation of the strategy in both simulation and in-vehicle helped quantify the benefits and short comings of engine operation for best fuel economy. The development in parallel of the hybrid control functions for torque assist and regenerative braking made it possible to implement the low speed AVC in the vehicle without a driveability penalty. The V6 TDI model yielded a realistic and representative simulation for the transient torque response improvement research to be undertaken. For that purpose, the model was tuned against full-load data and the air path control sub-systems were designed and calibrated similarly to a real application. The model was able to highlight the turbocharger lag issue associated with a large combined speed and torque transient inevitable in the fuel economy biased CVT powertrain. This study proposes a Manifold Air Injection [MAI] system in the intake of the engine to help breathing when the VGT operating conditions cannot be shifted rapidly enough for a manoeuvre. The system design constraints were analysed and a suitable strategy was elaborated and calibrated. A sensitivity analysis was also conducted to demonstrate the influence of the MAI design and control variables on the engine performance in the CVT powertrain In conclusion, the benefits of the engine characteristic matching were highlighted in both cases. A review of the work achieved is available in the last chapter, including prospects for further improvements and investigations. The ideal engine characteristics for gasoline and diesel engine technologies integrated in a CVT powertrain are derived from the experience gathered in the research and the results obtained from the tests in low speed operation and transient torque control respectively for the gasoline and the diesel engines. The engine characteristics can be altered toward a better match with a CVT by the use of specific hardware and control strategy. This work recommends that a direct injected, variable valve actuated gasoline engine provides the ideal starting point for low fuel consumption powertrain. When integrated within a mild hybrid CVT powertrain, the full benefits are obtained with the use of low speed operation and AVC. If no electrical machine is available to torque assist the engine, then existing supercharging concepts for a downsized engine can be applied. Diesel engines can also be downsized because of their high torque density. Increased turbocharging boost levels allow steady state torque levels to be maintained in the downsizing process. The CVT powertrain can optimise the fuel consumption and emission levels by appropriate selection of the engine steady state operating points. The torque response lag then becomes critical for the CVT to control the engine speed. This can be improved by the use of Manifold air Injection to assist the turbocharger.

It is appreciated that the deposition of liquid gasoline on the wall of the cylinder liner is known to be detrimental to the life of an SI engine. Liquid fuel on the combustion chamber and cylinder liner surfaces may lead to an increase in hydrocarbon emissions, particularly during cold-start operation. In addition, liquid fuel on the cylinder bore may wash the protective oil film from the surface liner, making it vulnerable to increased wear and chemical attack by the corrosive combustion chamber products (the latter particularly true when the liner surface is still cold, promoting the condensation of acids). Finally, liquid fuel on the cylinder wall may pass the piston rings, particularly when clearances are at their largest, causing high rates of 'lost fuel' to the crankcase and dilution of the crankcase oil. In 1997 BMW admitted they had a problem with their small capacity 6-cylinder engines. BMW was forced to retrofit customer cars with new engines after relatively low mileage and change the design of the engine from Nikasil coated aluminium liners to a more durable cast iron liner. Nikasil coated liners are particularly vulnerable due to the fact that the nickel coating is relatively thin. If wear of the cylinder wall exceeds the 80-micron coating thickness, then the softer aluminium backing material is exposed and wear is accelerated. The Jaguar AJV8 engine employs Nikasil liners similar to those used by BMW. There has been no published information suggesting that there is a bore wear concern with the Jaguar AJV8. However, being able to evaluate the deposition of liquid fuel of the cylinder wall of an engine during the development process would be extremely valuable. This thesis details the instrumentation, tools and techniques which can be used for such analysis. The results obtained provide an insight into the wall wetting characteristics of a number of four-valve cylinder head designs. There is an absence of such information in the scientific literature. This research suggests that the engine geometries tested in this work should not suffer from any durability concerns related to bore wetting.

This work focuses on aspects of combustion in a spark ignition engine. A pent-roof research engine was used to generate an experimental data set which was combined with a preexisting data set from a disc-chamber research engine. The combined dataset was used to refine a thermodynamic spark ignition engine combustion code which could operate in either a three-zone entrainment and bum up, or a two-zone direct combustion, configuration. The pent-roof engine was skip-fired to ensure residual gases were purged and care was taken to ensure that the thermodynamic state and chemical composition of the intake mixture were well defined. The combustion chamber, which featured near complete optical access, was illuminated using a sheet of laser light. Mie scattered laser light from fine seed particles was recorded allowing the position of the flame front to be tracked. These images were then ensemble averaged and combined to give a three-dimensional reconstruction of the mean combustion progress variable field for three different engine speeds. As the flame approached the combustion chamber walls it was found to decelerate. A relationship between the burning velocity of an unconstrained flame and a flame approaching a wall was derived which agreed well with the experimental results. This relationship was incorporated into the engine simulation code and found to improve greatly the predictions of the two-zone combustion model. New flame acceleration and laminar burning velocity submodels reported in the literature were added to the engine simulation code. The suitability of these models for simulating spark ignition engine combustion was evaluated using the disc and pent roof experimental data sets and model constants adjusted to optimise the performance of each submodel. Although there were substantial differences between the individual submodels, over the range of operating conditions for which experimental data was available changes to the submodel used had a negligible effect on the combustion model predictions. The work concludes with an evaluation of the performance of the three-zone combustion model for simulating a pent-roof engine. The model was modified for the pent-roof engine to include suitable assumptions for turbulence and the position of the centre of the flame. Using constants which were chosen to fit data recorded in the disc chamber engine, the model predictions for the pentroof engine were comparable in accuracy to predictions for the disc roof engine. The model was incorporated in a commercially available manifold gas dynamics simulation software to allow the predictive simulation of complete engine cycles.

Gasoline Direct Injection (GDI) engines work with stratified charge at part load and burn with lean mixtures in order to save fuel, whilst at full load, the fuel and air mix homogeneously for maximum power output. The higher compression ratio and the absence of throttling are two of the most significant benefits of GDI engines. The key issues facing GDI combustion include in-cylinder mixture preparation and post-combustion soot formation. This work was intended to investigate these aspects and was undertaken on a dedicated Jaguar single-cylinder optical GDI engine with a spray-guided combustion system. The spray-guided concept does not rely as much on charge motion or piston design, and can avoid wall-wetting effects so as to reduce engine emissions. Relevant engine control hardware and data acquisition equipment were commissioned. Data/image processing software was also developed to suit the measurements. A data-processing case study with data from a small two-stroke glow ignition engine has been conducted to develop a method to combine the burn rate and heat release analyses in the study of engines with premixed charge but compression ignition. Difficulties such as unknown ignition timing and polytropic index have been addressed. Results for all operating conditions have shown good correlations between the two methods. The technique of quantitative planar laser-induced fluorescence is useful for measuring 2-D fuel distribution in GDI engines. The relevant physics and literature were reviewed in depth. A multi-component fuel was designed to give reasonable co-evaporation characteristics with tracers matching different fuel fractions. The absorption and fluorescence features of each fuel component and tracer were characterised. Optimisation of hardware and signal-to-noise ratio was performed. A recirculating loop was set up for the calibration of the technique. The technique of colour-ratio pyrometry (CRP) for estimating the temperature and loading of soot was applied on the GDI engine. Critical features of the candidate CCD colour camera including its spectral response and noise behaviours were fully studied. Validation tests with reference sources together with an error analysis suggested an accuracy of ±50K within the combustion temperature range. Engine combustion images were then taken under various operating conditions. Temperature estimates were shown to be insensitive to the concentration of soot. Simulation with a thermodynamic modelling package, ISIS, was introduced for comparison with the experimental data. With careful tuning, ISIS gave outputs comparable to the CRP and proved to be a cost-effective tool to study GDI engines. High-speed combustion imaging was carried out using a CMOS camera, allowing the study of flame properties as well as crank-angle resolved CRP. By using a lens in the piston crown to give full bore optical access and appropriate image processing, the flame front could be detected reliably throughout the main combustion process.