This thesis describes an experimental investigation into ignition systems, their effects on the combustion process, and how the discharge is affected by the prevailing pressure, temperature and flow. The work is divided into four main areas, a comprehensive literature review, engine testing for ignition system suitability, non-flow rig testing (including erosion) and flow rig testing. The literature review concluded that the most practical ignition system for lean burn gas engines will continue to be based on the spark plug, but in the medium to long term, laser ignition may become viable. The measurement of the HT voltage and current is not straightforward, and appropriate methods have been identified. Capacitive and inductive ignition system types were compared in lean and diluted conditions on a single cylinder research engine of modern design at different engine loads and speeds. It was found that the most beneficial ignition system was an inductive ignition system, although that for some conditions, capacitive systems induced better engine performance with a fraction of the stored energy of the inductive alternative. Non flow tests showed that the early part of the spark discharge is sensitive to pressure and temperature effects, and as a consequence, the latter stages of the discharge are also affected. A correlation has been developed, for use with conventional nickel electrode spark plugs, to predict breakdown voltage as a function of pressure, temperature and gap. Experiments were carried out at elevated pressures in a stream of flowing air with capacitive and inductive ignition systems. Different electrode designs and orientations were also compared. It was shown that when exposed to a flow field, the discharge can be stretched which results in a shortened spark duration; in some cases the electrode can shield the discharge from flow field effects. This work showed that flow through the spark gap is a hindrance to the spark process, especially for longer duration systems. However for flame kernel growth, the literature review identified that flow is beneficial, serving to convect the kernel away from the electrodes, reducing the heat transfer from the flame. Analysis of the glow voltage history in the pressurised flow rig has been used to develop a correlation relating the voltage, current, flow velocity, pressure and time. This correlation was used to analyse the velocity records from the spark plug in a firing engine. The predicted velocities and turbulence intensity were in agreement with independent measurements.

In the first part of studies, Controlled Auto-Ignition (CAI) combustion was investigated in a Ricardo E6 single cylinder, four stroke gasoline engine. CAI combustion is achieved by employing positive valve overlap configuration in combination with various compression ratios and intake air temperature strategies. The CAI operational region is limited by engine load due to knock and partial burned boundaries. The combustion characteristics and emissions are studied in order to understand the major advantages and drawbacks of CAI combustion with positive valve overlap. The enlargement of the CAI operational region is obtained by boosting intake air and external EGR. The lean-boosted operation elevators the range of CAI combustion to the higher load region, and the use of external EGR allows the engine to operation with CAI combustion in the mid range of region between boosted and N/A CAI operational range. The results are analyzed and combustion characteristics, performance and emissions are investigated. A Ricardo Hydra single cylinder, four stroke optical gasoline engine with optical access is then experimented to investigate CAI combustion through negative valve overlap configuration and an intake heater. The effects of direct fuel injection timings spark timings and air/fuel ratio are studied by means of simultaneous incylinder heat release study and direct visualization, chemiluminescence techniques which uses full, OH radical and CHO species. Both heat release analysis and chemiluminescence results have identified the pressure of minor combustion during the NVO period. Both the charge cooling and local air/fuel ratio effects are also investigated by varying the quantity of direct air injection.

This thesis is about modelling of the combustion and emissions of dual fuel HCCI engines for design of “engine combustion system”. For modelling the combustion first the laminar flamelet model and a hybrid Lagrangian / Eulerian method are developed and implemented to provide a framework for incorporating detailed chemical kinetics. This model can be applied to an engine for the validation of the chemical kinetic mechanism. The chemical kinetics, reaction rates and their equations lead to a certain formula for which the coefficients can be obtained from different sources, such as NASA polynomials [1]. This is followed by study of the simulation results and significant findings. Finally, for investigation of the knock phenomenon some characteristics such as compression ratio, fuel equivalence ratio, spark timing and their effects on the performance of an engine are examined and discussed. The OH radical concentration (which is the main factor for production of knock) is evaluated with regard to adjustment of the above mentioned characteristic parameters. In the second part of this work the specification of the sample engine is given and the results obtained from simulation are compared with experimental results for this sample engine, in order to validate the method applied in AVL Fire software. This method is used to investigate and optimize the effects of parameters such as inlet temperature, fuels ratio, diesel fuel injection timing, engine RPM and EGR on combustion in a dual fuel HCCI engine. For modelling the dual fuel HCCI engine AVL FIRE software is applied to simulate the combustion and study the optimization of a combustion chamber design. The findings for the dual fuel HCCI engine show that the mixture of methane and diesel fuel has a great influence on an engine's power and emissions. Inlet air temperature has also a significant role in the start of combustion so that inlet temperature is a factor in auto-ignition. With an increase of methane fuel, the burning process will be more rapid and oxidation becomes more complete. As a result, the amounts of CO and HC emissions decrease remarkably. With an increase of premixed ratio beyond a certain amount, NOX emissions decrease. With pressure increases markedly and at high RPM, knock phenomenon is observed in HCCI combustion.

Decades of research on compression ignition engines have led to a highly efficient combustion cycle in contemporary diesel engines. Nonetheless, the combustion process is being studied perpetually to meet both current and future emission regulations. One of the most influential parameters that impacts the combustion quality, is the fuel spray evolution during injection, and subsequent fuel-air mixture formation inside the engine cylinder. The spray evolution has been investigated to a high level of detail, and the highly complex processes of mixture formation and combustion are well-documented for diesel engines. Most of these investigations are limited to studying either research-grade injectors, or brand new production injectors. Injectors in real-world diesel engines, i.e. normal passenger cars and trucks that are used on a daily basis, are however subject to deposit formation at the tip of the injector nozzle. These deposits have the potential of altering the internal nozzle flow and fuel spray pattern, which in turn degrades combustion quality and increases engine emissions. In the work presented in this thesis the spray evolution of production injectors has been studied over a wide range of injector conditions. Common rail light-duty injectors with a usage history of up to 90 000 miles were acquired from the UK commuter car parc, and several brand new injectors were studied for comparison purposes. It is shown that the spray pattern of the injected fuel changes over the lifetime of the injector. For used injectors a reduced penetration rate was observed in the transient regime of fuel injection, during needle lift. The reduced penetration rate was often accompanied by anomalous radial expansions. Although the magnitude of the effects varied from injector to injector, the highest mileage injectors tended to produce the strongest spray deviations. For several high-mileage injectors the end of injection appeared retarded with respect to new injectors. Expulsions of liquid ligaments and droplets after the end of injection were observed from all injectors, irrespective of the mileage of the injector.

Increased availability of natural gas has boosted research and development efforts to further increase gas turbine performance. Performance has been increased remarkably and unit cost reduced due to achievements gained in improving thermodynamic cycles and cooling technologies. However, increased complexity in power industry regulations and fluctuations in fuel price have indicated that all the aforementioned improvements in gas turbine performance could not cope with the increased competition in the gas turbine industrial market. Innovation within the aero-derivative concept has enabled further significant improvement in the performance of industrial gas turbines. It allows a more beneficial approach than developing new designs of industrial gas turbines owing to reduced designing time and cost. Objectives in this project focus on developing a methodology of design and assessing aeroderivative gas turbine engines derived from a 130-seat aircraft engine. Developed methodology includes techno-economic and environmental assessment, conducted through further developments of models based on Techno-economic and Environmental Risk Assessment (TERA) philosophy, to be applied in further industrial applications. Tools used in this investigation include a significant literature research on the development of aero-derivative gas turbine technologies, including thermodynamic cycles and its land-based applications. Turbomatch is a homebased code developed in Cranfield University, used in calculating design point and predicting off-design performance of parent aero-engine and the aeroderivative engines developed. Excel and FORTRAN code are also used in calculating engine’s design parameters, and creating a model of life estimation Creep. Moreover, FORTRAN code is used for building emission and economic models for power generation and combined heat and power applications. Finally, MATLAP code is used in creating a small model for generating performance TXT files, and running marine integrated models platform. All models needed to develop the methodology have been created, and calculations of an engine’s performance and assessment were conducted based on this developed methodology. Sensible results are generated from the investigated methodology and they show acceptable designs of aero-derivative engines on different thermodynamic cycles. Based on the acceptable level of technology and material thermal barriers, all design and off-design performance limitations of new developed aero-derivative engines have been determined for a wide range of ambient conditions. Techno-economic and environmental assessment performed through implementing the developed aero-derivative engines on power generation and marine applications under different operating scenarios. Results of operating the engines on power generation and marine applications have been investigated and compared. It is observed that engines respond differently when operating under different environmental profiles, depending on the number of units engaged and their thermodynamic cycle as well as mechanical configurations. Also, the selected specific gas turbine engine can be the best economical choice for operating on determined scenario, while it cannot be when operating in different scenarios. Assessment of developed engines on the investigated application shows how the lowest specific cost (small engine size) can constitute important criteria in engine selection.

This thesis considers the effect of compression ratio on the performance of a direct injection diesel engine. One aspect of engine performance is considered in great detail, namely the combustion performance at increased clearance volume. This aspect was of particular interest because variable compression ratio (VCR) systems normally operate by varying the clearance volume. The investigation relied upon results obtained both from experimental and computer simulating models. The experimental tests were carried out using a single-cylinder direct-injection diesel engine, under simulated turbocharged conditions at a reduced compression ratio. A number of one-dimensional computer models were developed; these simulate the induction and compression strokes, and the fuel spray trajectories in the presence of air swirl. The major objectives of the investigation were: to assess the benefits of VCR in terms of improvements in output power and fuel economy; to assess the effects on combustion of increased clearance volume, and investigate methods for ameliorating resulting problems; develop computational models which could aid understanding of the combustion process under varying clearance volume conditions. It was concluded that at the reduced compression ratio of 12.9:1 (compared to the standard value of 17.4:1 for the naturally-aspirated engine), brake mean effective pressure (BMEP) could be increased by more than 50%, and the brake specific fuel consumption (BSFC) could be reduced by more than 20%. These improvements were achieved without the maximum cylinder pressure or engine temperatures exceeding the highest values for the standard engine. Combustion performance deteriorated markedly, but certain modifications to the injection system proved successful in ameliorating the problems. These included: increase in the number of injector nozzle holes from 3 to 4, increase in injection rate by about 28%, advancing injection timing by about 6°CA. In addition, operation with weaker air fuel ratio, in the range of 30 to 40:1 reduced smoke emissions and improved BSFC. Use of intercooling under VCR conditions provided only modest gains in performance. The NO emission was found to be insensitive to engine operating conditions (fixed compression ratio of 12.9:1), as long as the peak cylinder pressure was maintained constant. Engine test results were used in order to assess the accuracy of four published correlations for predicting ignition delay. The best prediction of ignition delay with these correlations deviated by up to 50% from the measured values. The computer simulation models provided useful insights into the fuel distribution within the engine cylinder. It also became possible to quantify the interaction between the swirling air and the fuel sprays, using two parameters: the crosswind and impingement velocities of the fuel spray when it impinges on the piston-bowl walls. Tentative trends were identified which showed that high crosswind velocity coincided with lower smoke emissions and lower BSFC.

This study was concerned with the performance of biofuels in diesel engines. Generally, the basic combustion and emission characteristics of Rapeseed Oil (RSO) and Soya Oil (SO) result in a lower in-cylinder pressure peak than diesel. This led to the reduction of Nitrogen Oxides (NOx) emissions and to relatively high soot emissions. Further measurements of RSO were done in order to investigate the influence of injection pressure, injection timing and Exhaust Gas Recirculation (EGR) on combustion and emission characteristics. A high soot emission from RSO was reduced by increased injection pressure. Moreover, injection timing also had to be varied in order to reduce the soot emissions from RSO. The retarded injection timing (3 deg bTDC) and increased injection pressure (1200 bar) for the blend of 30% RSO resulted in a reduction of soot emission to the same level as from diesel fuel. Further investigation regarding the soot emissions was done for Rapeseed Methyl Ester (RME) under turbocharged engine operation. The application of the boost pressure resulted in stable engine operation at a late injection timing of 5 deg aTDC. A simultaneous reduction of soot and NOx emissions has been achieved for RME at an injection timing of TDC and high EGR percentage (40 – 50 %). The soot particles size distribution under different engine operating conditions for RME and diesel has also been investigated. Moreover, the characteristic of Electrostatic Mobility Spectrometer (EMS) and the design of primary dilution system have been provided in order to understand the influence of the dilution process and to obtain more real results. Generally, RME showed less particles concentration in the nucleation mode when compared to diesel. Moreover, high EGR caused a shift of the particles from the nucleation mode by agglomeration into the accumulation mode for both fuels. The effect of injection pressure could only be seen in the accumulation mode, where high injection pressure slightly reduced the concentration number. The soot emission was effectively reduced by the usage of the diesel particulate filter (DPF). For this purpose, the soot particles size distributions before and after the DPF have been measured at different engine speeds and loads. At low engine torque, the soot was effectively filtered while the operation under high engine loads resulted in low soot particle concentration especially in the nucleation mode, after the DPF.

Carbonaceous engine deposits tend to accumulate on most of the inner surfaces of the car engine. The presence of these deposits leads to a deteriorated efficiency of the engine and a number of adverse effects, such as higher propensity of the engine to knock. It has been proposed that selective adsorption of some of the fuel components in the porous deposits (and changing composition of the pre-combustion fuel) could be a contributing mechanism of the diminished efficiency of the engine. This, as well as other mechanisms of the deposits action, crucially depend on the porous structure of the material. Therefore, the aim of this investigation is to develop a method, which is able to accurately characterize the internal porous structure of the engine deposits and predict their adsorption properties at different conditions. This should allow us to assess whether the selective adsorption of fuel components is indeed a plausible contributing mechanism to the diminished performance of the engine. Accurate characterization of the engine deposits faces several difficulties due to their complex porous structure and chemical composition. A widely adopted approach in the characterization of activated carbons, which combines molecular simulation, specifically grand canonical Monte Carlo (GCMC) in slit pores, and experimental adsorption isotherms, is the starting point for the method suggested in this work. In this thesis, we will demonstrate that, by systematic modification of the solid-fluid interaction in the molecular simulation, we are able to correctly account for the chemical structural heterogeneity of the samples used. The new parameters of solid-fluid interaction allow us to extract representative pore size distributions and investigate the adsorption properties under different conditions of temperature and pressure, based on the obtained pore size distribution. Specifically, using the experimental data from a single ethane isotherm at 278K we accurately predict ethane adsorption at other temperatures and in different samples. Additionally, the proposed method is able to predict the adsorption of more complex hydrocarbons, i.e. n-butane and isobutane. The performance of the method is assessed by comparing the simulations results with the experimental adsorption measurements data on the engine deposits samples. Another important capability of the method is that it enables us to generate adsorption predictions of two key components commonly used to represent the combustion properties of the fuel, n-heptane and isooctane. We explore the equilibrium adsorption properties of these components based on the determined pore size distributions of the deposit samples. The results presented in the thesis highlight the importance of the adsorption in the internal porous structure of the engine deposits. The present study reinforces the value of molecular simulation combined with a limited number of experimental measurements, to accurately characterize heterogeneous carbonaceous materials and to make predictions at different conditions with sufficient precision.

The continuous update of challenging emission legislations has renewed the interest for the use of alternative fuels. The low carbon content, the knocking resistance, and the abundance reserves, have classified natural gas as one of the most promising alternative fuels. The major constituent of natural gas is methane. Historically, the slow burning velocity of methane has been a major concern for its utilisation in energy efficient combustion applications. As emphasized in a limited body of experimental literature, a binary blend of methane and gasoline has the potential to accelerate the combustion process in an SI engine, resulting in a faster combustion even to that of gasoline. The mechanism of such effects remains unclear. This is partially owned to the inadequate prior scientific understanding of the fundamental combustion parameters, laminar burning velocity (Su0) and Markstein length (Lb), of a gasoline-natural gas Dual Fuel (DF) blend. The value of Lb characterises the sensitivity of the flame to stretch. The flame stretch is induced by aerodynamic straining and/or flame curvature. The current research study has therefore being concerned on understanding the combustion mechanism of premixed gasoline - natural gas DF blends both on a fundamental as well as practical SI engine level. The understanding on the contribution of Su0 and Lb to the velocity of a stretched laminar propagating flame has been extended through numerical analysis. A conceptual analysis of the laminar as compared to the SI engine combustion allowed further insights on the effect of turbulence to the mass burning rate of the base fuels. On a fundamental level, the research contribution is made through the quantification of the response of Su0 and Lb with the ratio of methane to PRF95 (95%volliq iso-octane and 5%volliq n-heptane) in a DF blend. Methane has been used as a surrogate for natural gas and PRF95 as a surrogate for gasoline. Constant volume laminar combustion experiments have been conducted in a cylindrical vessel at equivalence ratios of 0.8, 1, 1.2, initial pressures of 2.5, 5, 10 Bar, and a constant temperature of 373 K. Methane was added to PRF95 in three different energy ratios 25%, 50% and 75%. Spherically expanding flames visualised through schlieren photography were used to derive the values of Lb and Su0. It has been concluded that for pressures relevant to SI engine operation ( > 5bar) and stoichiometric to lean Air Fuel Ratios (AFRs), there is a positive synergy for blending methane to PRF95 due to the convergence of Lb of the blended fuel towards that of pure gas and Su0 towards that of pure liquid. In an SI engine environment, the research contribution is made through the characterisation and scientific understanding of the mechanism of DF combustion, and the importance of flame-stretch interactions at various engine operating conditions. Optical diagnostics have been integrated with in-cylinder pressure analysis to investigate the mechanism of flame velocity and stability with the addition of natural gas to gasoline in a DF blend, under a sweep of engine load (Manifold Absolute Pressure = 0.44, 0.51. 0.61 Bar), speed (1250, 2000, 2750 RPM) and equivalence ratio (0.8, 0.83, 1, 1.25). Consisted with the constant volume experiments, natural gas was added to gasoline in energy ratios of 25%, 50% and 75%. It has been concluded that within the flamelet combustion regime the effect of Lb is dominating the lean burn combustion process both from a flame stability and velocity prospective. The effect of Su0 on the combustion process gradually increases as the AFR shifts from stoichiometric to fuel rich values. For stoichiometric to fuel lean mixtures, the effect of turbulence on the increase of the mass burning rate is on average 13% higher for natural gas as compared to gasoline. The higher turbulence sensitivity of natural gas is attributed to its lower Lb value.

Particulate number (PN) standards in current and future emissions legislation pose a challenge for designers and calibrators during the warm-up phases of cold direct injection spark ignition (DISI) engines. To achieve catalyst light-off conditions in the shortest time, engine strategies are often employed that inherently use more fuel to attain higher exhaust temperatures. These can lead to the generation of locally fuel-rich regions within the combustion chamber and hence the formation and emission of particulates. To meet these emissions requirements, further understanding of the DISI in-cylinder processes during cold-start are required. This thesis investigates the effect of cooling an optical research engine to temperatures as low as -7°C, one of the legislative test conditions. A high-speed 9 kHz optical investigation of the in-cylinder combustion and fuel spray along with in-cylinder pressure measurements was completed with the engine motored and fired at 1500 rpm during combustion conditions that were essentially homogeneous and stoichiometric. Results showed significant differences between the flame growth structures at various operating temperature conditions with the notable presence of fuel-rich regions, which are understood to be prominent areas of particulate formation. Measured engine performance parameters such as indicated mean effective pressure (IMEP) and mass fraction burned (MFB) times correlated with the observed differences in combustion characteristics and flame growth speed. It was shown that flash boiling of the fuel spray was present in the fully heated engine case and significantly reduced the penetration of the spray plume and the likelihood of piston crown and cylinder liner impingement. The flow and combustion processes of a transient production cold start-up strategy were analysed using high-speed particle image velocimetry (HSPIV). Results highlighted a broad range of flame structures and contrasting flame stoichiometry occurring at different times in the start-up process. Turbulent flow structures were identified that have an effect on the fuel spray development and combustion process as well as providing a path for cold-start emissions reduction. PN and transient hydrocarbon (HC) emissions were measured at cold conditions to further elucidate the effect of operating temperature and correlate emissions data with in-cylinder measurements. A clear link between the quantity and size range of particulate and HC emissions and operating temperature was shown and the precise in-cylinder location of HC emissions, caused by fuel impingement, was inferred from the HC emissions data.