Controlled auto-ignition (CAI) combustion – also described as homogeneous charge compression ignition (HCCI) combustion – was investigated. The primary experiments concerned a direct-injection single-cylinder gasoline engine equipped with a poppet valve combustion system. This engine was operated with both the two-stroke working cycle and the four-stroke cycle. The engine experiments were used to establish combustion characteristics and the envelope of operation for CAI combustion, and to investigate the influence of a number of engine parameters including engine speed and load, air-fuel ratio, intake-air heating and exhaust-port throttling. Results from one-dimensional fluid-dynamic calculations were used to support the main data set and to develop hypotheses concerning CAI combustion in practical gasoline engines. Images from parallel investigations using an equivalent optical-access engine, and three-dimensional fluid-dynamic calculations, were used to supplement the results generated by the author and to further develop and test understanding of gasoline CAI processes. Finally practical implementation of CAI combustion in passenger vehicles was considered, including possible routes to series production of CAI engines.

The development and combusting behaviour of a diesel spray were investigated to provide a deeper understanding of the formation of nitric oxide (NO) in diesel engines. To characterise the spray, the nozzle flow was measured by the rate tube technique. The sensitivity of the flow to injection pressure was shown to follow the theoretical behaviour. Penetrations of the liquid spray were measured by means of high speed video imaging. The innovative measurements of the liquid penetration during the combustion allowed combustion phases and liquid jet lengths to be associated. Hydroxyl (OH) radicals were acquired by planar laser-induced fluorescence (PLIF). Combined with high speed videos of the flame natural luminosity, they were used to identify precisely the evolution of combustion in time and space. The measured OH distributions compared favourably with results from simulations using the KIVA code. The OH radicals were shown to be present mainly in the mixing controlled phase, distributed in a thin layer around the vapour fuel in the jet, within the diffusion flame location. OH radicals could be seen as early as 0.4 ms before the pre-mixed heat-release spike and until the end of apparent heat release. In the conditions studied, the diffusion flame, therefore, spanned most of the combustion process, starting very soon after autoignition. Finally distributions of NO were acquired by LIF and compared with the evolution of combustion. NO was found to appear 0.5 to 1 ms after the development of the diffusion flame, on the lean side of the flame front, outside the region with a high density of OH radicals but also later on, downstream the spray, on the outskirts of the zone with high soot density. The formation rate of NO was found almost constant during the mixing controlled combustion, with a small increase at the end of injection, when the flame collapsed on the fuel spray. The observed increase was linked to a rapid cooling of the flame plume and the associated freezing of the thermal-NO mechanism. Varying injection pressures did not significantly affect the overall formation rate although peak NO densities were seen to gradually move downstream the flame plume with increased injection pressure. NO formation increased with the in-cylinder pressure in accordance with a higher density of air and higher local temperatures.

The last few years have seen a rapid growth in the number of cars equipped with air-conditioning systems. The space available to fit the system is limited and the under bonnet environment is hostile. Moreover, the depletion of the stratospheric ozone has led to legislation on the phasing out of the chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs ). These substances are used as refrigerants in most refrigeration, heat pump and air-conditioning systems in service today. The aim of this research project was to study existing air-conditioning systems used in automotive applications to develop a model that simulates the components of these systems. This provides a better understanding of the effect of using different refrigerants in the system and its performance. Experimental studies of the performance of the different heat exchanger geometries used provided inputs to the model developed. Automotive air-conditioning condensers and evaporators simulation models were developed and used to compare the performance of these heat exchangers using CFC and HCFC refrigerants and the non-ozone depleting replacements. Thermodynamic properties of the new refrigerants were derived from the equation of state. The evaporator was simulated taking into consideration the mass transfe r associated with the heat transfer in humid conditions. Two types of compact heat exchangers were modelled, round tube with plane fin and plate tube with corrugated fin. These cover most automotive, domestic and industrial applications. The basic performance data of various geometries were determined experimentally. An existing thermal wind tunnel was re-instrumented and modified to improve accuracy at the low air velocities was used in this study. A new data logger linked to a personal computer was used with newly written software to collect and analyse the test data. The results for all geometries tested were correlated and presented in non-dimensional form. The test data were used to determine the effect of various geometrical parameters on the performance for an optimisation of condenser and evaporator designs. The model developed is being used by industrial collaborators for the design of heat exchangers in automotive air-conditioning systems.

No description available.

This thesis describes work undertaken at the University of Brighton on a rapid compression machine based on a two-stroke diesel engine (Proteus) with an optical head to allow observation of the fuel spray. A long-tube, rate of injection rig was used to measure the injection rate of the fuel injection system. Quantification of cyclic variation and rate of injection were carried out for single and multiple-injection strategy. For multiple-injections, it was found that the injected mass of the first of the split was approximately 19% less than that of the single injection strategy for the same injection duration. The second split reduction was less than 4% in comparison to the single injection strategy. The transient response of the fuel injection equipment was characterised and compared with steady-state behaviour. The characteristics of the Proteus rig in terms of trapped air mass and transient incylinder temperature were investigated and quantified. The effect of in-cylinder temperature, density and pressure, as well as injection pressure on the characteristics of spray formation, for single and multi-hole nozzles were investigated using high speed video cameras. Cycle-to-cycle and hole-to-hole variations for multi-hole nozzles were investigated and attributed to uneven fuel pressure distribution round the needle seat, and subsequent cavitation phenomena. Simultaneous Planar Laser Induced Fluorescence (PLIF) and Mie scattering techniques were used to investigate spray formation and vapour propagation for multihole nozzles for single and multiple-injection strategy. The multiple injection work focused on the effect of dwell period between each injection. Two different modes of flow were identified. These are described as 'wake impingement' and 'cavity mode wake effect', resulting in increased tip velocity of the second split spray. The increase in tip velocity depended on dwell period and distance downstream of the nozzle exit. The maximum increase was calculated at 17 m/s. A spray pattern growth for the second of the split injections, the 'exceed type' was identified, resulting from an increase in tip penetration due to air entrainment of the first split and propagation into the cooler vapour phase from the first split. The effect of liquid core length near the nozzle exit was investigated using modified empirical correlations and the evolution of the discharge coefficient obtained from rate of injection measurements. The results showed increased injection pressure and increased in-cylinder gas pressure reduce both break-up length and break-up time. Penetration was modelled using conservation of mass and momentum of the injected fuel mass. The input to the numerical model was the measured transient rate of injection. The model traced the centre-of-mass of the spray and was validated against PLIF data for centre-of-mass. Overall, the same value of modelling parameters gave good agreement for single and split injection strategy.

A high-speed video camera was used to obtain photographs of a transient spray. The spray images were analysed to provide spray characteristics which include the spray tip penetration length, initial spray hesitation, nozzle opening time delay, hole-to-hole spray variation and spray structure. Both single and multi-hole nozzles were used to study these parameters. Fuel droplet characteristics within dense Diesel sprays were studied using Phase Doppler Anemometry (PDA) in an optical rapid compression machine. A comprehensive study of the PDA operating parameters was conducted. Additionally, the effects of injection pressure and in-cylinder pressure and temperature upon spray properties were studied. PDA has proved to be a valuable technique in providing an understanding of the structure and characteristics of sprays. However, the application of PDA to dense sprays is difficult. The results obtained are not always reliable and the accuracy of the results is often questionable. Phase Doppler Anemometers are not immune to errors and by carefully identifying these errors, the accuracy of the technique can be significantly improved. The effects of the PDA system parameters on the measurement accuracy have been studied. It was found that a thorough study of the operating parameters was required to tailor the system to the measurements of dense sprays. The photomultipliers voltages, the laser beam power and the size of the measurement volume all show significant effects on measured droplet diameters. Spray produced from a common-rail injection system proved to be a challenging environment for the PDA. Following the calibration of the PDA, investigations were conducted to study the effects of various parameters on spray characteristics including injection pressure, in-cylinder pressure and temperature. Results are presented for incylinder pressures ranging from 1.6 to 6 MPa and injection pressures from 60 to 160 MPa. The highest injection pressure produced faster droplets and improved the spray atomisation.

The results of numerical study of heating and evaporation of monodisperse fuel droplets in an ambient air of fixed temperature and atmospheric pressure are reported and compared to experimental data from the literature. The numerical model is based on the Effective Thermal Conductivity (ETC) model and the analytical solution to the heat conduction equation inside droplets. It is pointed out that the interactions between droplets lead to noticeable reduction of their heating in the case of ethanol, 3-pentanone, n-heptane, n-decane and n-dodecane droplets, and reduction of their cooling in the case of acetone. A simplified model for bi- component droplet heating and evaporation is developed. The predicted time evolution of the average temperatures is shown to be reasonably close to the measured one (ethanol/acetone mixture). The above-mentioned simplified model is generalised to take into account the coupling between droplets and the ambient gas. The model is applied to the analysis of the experimentally observed heating and evaporation of a monodispersed n-decane/3-pentanone mixture of droplets at atmospheric pressure. It is pointed out that the number of terms in the series in the expressions for droplet temperature and species mass fractions can be reduced to as few as three, with possible errors less than about 0.5%. In this case, the model can be recommended for implementation into CFD codes. The simplified model for bi- component droplet heating and evaporation, based on the analytical solutions to the heat transfer and species diffusion equations, is generalised to take into account the effect of the moving boundary and its predictions are compared with those of the model based on the numerical solutions to the heat transfer and species diffusion equations for both moving and stationary boundary conditions. A new model for heating and evaporation of complex multi-component hydrocarbons fuel droplets is developed and applied to Diesel and gasoline fuels. In contrast to all previous models for multi-component fuel droplets with large number of components, the new model takes into account the effects of thermal diffusion and diffusion of components within the droplets.

A typical long-haul heavy duty Diesel engine currently rejects up to 50% of the total fuel energy in the form of heat. Due to increasing CO2 emissions and fuel costs, there is a growing interest in techniques that can even partially utilise this wasted resource to improve the overall system efficiency. Fluid Bottoming Cycles (FBC) including Rankine and organic Rankine cycles offer one means towards converting waste heat into usable power. This thesis investigates the potential of FBCs to improve the net power of two computationally modelled (Ricardo WAVE V8.1) 10 litre engine platforms operating at Euro 6 emission levels.

abstract: Over the past decade, proton exchange membrane fuel cells have gained much momentum due to their environmental advantages and commutability over internal combustion engines. To carefully study the dynamic behavior of the fuel cells, a dynamic test stand to validate their performance is necessary. Much attention has been given to HiL (Hardware-in-loop) testing of the fuel cells, where the simulated FC model is replaced by a real hardware. This thesis presents an economical approach for closed loop HiL testing of PEM fuel cell. After evaluating the performance of the standalone fuel cell system, a fuel cell hybrid electric vehicle model was developed by incorporating a battery system. The FCHEV was tested with two different control strategies, viz. load following and thermostatic. The study was done to determine the dynamic behavior of the FC when exposed to real-world drive cycles. Different parameters associated with the efficiency of the fuel cell were monitored. An electronic DC load was used to draw current from the FC. The DC load was controlled in real time with a NI PXIe-1071 controller chassis incorporated with NI PXI-6722 and NI PXIe-6341 controllers. The closed loop feedback was obtained with the temperatures from two surface mount thermocouples on the FC. The temperature of these thermocouples follows the curve of the FC core temperature, which is measured with a thermocouple located inside the fuel cell system. This indicates successful implementation of the closed loop feedback. The results show that the FC was able to satisfy the required power when continuous shifting load was present, but there was a discrepancy between the power requirements at times of peak acceleration and also at constant loads when ran for a longer time. It has also been found that further research is required to fully understand the transient behavior of the fuel cell temperature distribution in relation to their use in automotive industry. In the experimental runs involving the FCHEV model with different control strategies, it was noticed that the fuel cell response to transient loads improved and the hydrogen consumption of the fuel cell drastically decreased. / Dissertation/Thesis / Masters Thesis Engineering 2014

The battery in an EV is designed according to a power to energy ratio and is a trade-off in the design of the pack. It also suffers from effects such as rate capacity effect, ripple effects and inefficiency under charging. These effects result in losses through which the capacity and life span of the batteries are compromised affecting range and drivability. In this thesis a novel development path resulting in a novel Power and Energy Management Strategy (PEMS) is presented. The effects of (dis)charging a battery are researched and converted to an energy optimisation formula and result in reduced power demand for the converter which reduces weight. The resulting Power Management Strategy (PMS) aims to recover energy more efficiently into UC while responding fast to a change in demand. The effects of converters on the battery current ripple are researched and discussed, resulting in an optimal topology layout, improved battery life and reduced losses. Through the use of Markov Chain analysis and a newly derived Bias function a predictive Energy Management Strategy (EMS) is developed which is practical to use in EVs. This resulted in a PEMS which because of the fast PMS results in a fast response time. The use of Markov Chain results in predictive EMS and improves the efficiency of the energy sources and allows the design to be reduced in size. Through the design methodology used the parallel topology (the battery converter parallel to the UC Module) was rated preferred choice over battery only and battery with UC Module. The rating was based on capacity, ripple control, weight, 10 year cost, potential for motor controller efficiency improvement, range and efficiency. v The combination of method and PEMS resulted in an improved life expectancy of the pack to over 10 year (up from 7) while increasing range and without sacrificing drivability.