The effects of in-cylinder and injection pressures on the formation and autoignition of diesel sprays at realistic automotive in-cylinder conditions was investigated. A two-stroke diesel Proteus engine has been modified to allow optical access for visualisation of in-cylinder combustion processes. Various optical techniques were used to investigate the combustion processes. These include high-speed video recording of the liquid phase, high-speed schlieren video recording of the vapour phase and laser-induced incandescence for soot imaging. The spray cone angle and penetration with time data extracted from photographic and high-speed video studies are presented. The effects of droplet evaporation, breakup and air entrainment at the initial stage of spray penetration were studied theoretically using three models. It was found that the predictions of the model combining bag breakup and air entrainment are in good agreement with the experimental measurements. Spray autoignition was investigated using video, in-cylinder pressure, and schlieren recordings. Pseudo three-dimensional visualisation of the autoignition was achieved by simultaneous use of two high-speed video cameras at right angles to each other. The effects of elevated injection and in-cylinder pressures on the ignition delay and ignition sites have been investigated. Laser-induced incandescence was performed to obtain maps of soot concentration for a range of engine conditions. The influence of in-cylinder and injection pressures on soot formation sites and relative soot concentration has been studied. The work has been mainly focused on the specificities of soot formation under extreme in-cylinder conditions.

The results of a comparative analysis of liquid and gas phase models for fuel droplets heating and evaporation, suitable for implementation into computational fluid dynamics (CFD) codes, are presented. Among liquid phase models, the analysis is focused on the model based on the assumption that the liquid thermal conductivity is infinitely large, and the so called effective thermal conductivity model. Seven gas phase models are compared. These are six semi-theoretical models, based on various assumptions, and a model based solely on the approximation to experimental data. It is pointed out that the gas phase model, taking into account the finite thickness of the thermal boundary layer around the droplet, predicts the evaporation time closest to the one based on the approximation to experimental data. The values of the absorption coefficients of gasoline fuel (BP Pump Grade 95 RON ULG), 2,2,4-trimethylpentane (CH3)2CHCH2C(CH3)3 (iso-octane) and 3-pentanone CH3CH2COCH2(CH3)3 have been measured experimentally in the range of wavelengths between 0.2 μm and 4 μm. The values of the average absorption efficiency factor for all fuels have been approximated by a power function aRdb, where Rd is the droplet radius. a and b in turn have been approximated by piecewise quadratic functions of the radiation temperature, with the coefficients calculated separately in the ranges 2 - 5 μm, 5 - 50 μm, 50 - 100 μm and 100 - 200 μm for all fuels. This new approximation is shown to be more accurate compared with the case when a and b are approximated by quadratic functions or fourth power polynomials of the radiation temperature, with the coefficients calculated in the full range of 2 - 200 μm. Results of experimental studies of heating and evaporation of monodisperse ethanol and acetone droplets in two regimes are compared with the results of modelling. It is pointed out that for relatively small droplets the experimentally measured droplet temperatures are close to the predicted average droplet temperatures, while for larger droplets the experimentally measured droplet temperatures are close to the temperatures predicted at the centre of droplets. All the developed models have been implemented into the KIVA-2 CFD code and validated against available in-house experimental data referring to spray penetration and ignition delay in Diesel engines.

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.