<p> Natural gas/diesel dual fuel engines offer a path towards meeting current and future emissions standards with lower fuel cost. However, numerous technical challenges remain that require a greater understanding of the in-cylinder combustion physics. For example, due to the high compression ratio of diesel engines, substitution of natural gas for diesel fuel at high load is often limited by engine knock and pre-ignition. Additionally, increasing the natural gas percentage in a dual fuel engine often results in decreasing maximum load. These problems limit the substitution percentage of natural gas in high compression ratio diesel engines and therefore reduce the fuel cost savings. Furthermore, when operating at part load dual fuel engines can suffer from excessive emissions of unburned natural gas. Computational fluid dynamics (CFD) is a multi-dimensional modeling tool that can provide new information about the in-cylinder combustion processes causing these issues. </p><p> In this work a multi-dimensional CFD model has been developed for dual fuel natural gas/diesel combustion and validated across a wide range of engine loads, natural gas substitution percentages, and natural gas compositions. The model utilizes reduced chemical kinetics and a RANS based turbulence model. A new reduced chemical kinetic mechanism consisting of 141 species and 709 reactions was generated from multiple detailed mechanisms, and has been validated against ignition delay, laminar flame speed, diesel spray experiments, and dual fuel engine experiments using two different natural gas compositions. Engine experiments were conducted using a GM 1.9 liter turbocharged 4-cylinder common rail diesel engine, which was modified to accommodate port injection of natural gas and propane. A combination of experiments and simulations were used to explore the performance limitations of the light duty dual fuel engine including natural gas substitution percentage limits due to fast combustion or engine knock, pre-ignition, emissions, and maximum load. In particular, comparisons between detailed computations and experimental engine data resulted in an explanation of combustion phenomena leading to engine knock in dual fuel engines. </p><p> In addition to conventional dual fuel operation, a low temperature combustion strategy known as reactivity controlled compression ignition (RCCI) was explored using experiments and computations. RCCI uses early diesel injection to create a reactivity gradient leading to staged auto-ignition from the highest reactivity region to the lowest. Natural gas/diesel RCCI has proven to yield high efficiency and low emissions at moderate load, but has not been realized at the high loads possible in conventional diesel engines. Previous attempts to model natural gas/diesel RCCI using a RANS based turbulence model and a single component diesel fuel surrogate have shown much larger combustion rates than seen in experimental heat release rate profiles, because the reactivity gradient of real diesel fuel is not well captured. To obtain better agreement with experiments, a reduced dual fuel mechanism was constructed using a two component diesel surrogate. A sensitivity study was then performed on various model parameters resulting in improved agreement with experimental pressure and heat release rate.</p>

Thesis (M.S.)--Boston University / The purpose or the automotive technical publication is to simplify distinct technical principles. In reality, however, just the opposite is taking place within the automotive industry. Complexity of language, poorly organized illustrations, and misleading installation instructions are continually handed the reader. The aim of this study is to simplify and clarify the. three major typesof automotive technical publications: the parts catalog, the technical bulletin, and the promotional brochure.

The development of the quality of gasoline and diesel fuel has never been static. It is no longer newsworthy to say that the world of energy and chemical technology is changing fast. However, these changes are so fast that changes in related technology have to advance at the same speed. Consequently it has been a challenging time for analytical chemists in different types of laboratories involved in the analysis of automotive fuel, such as in the analysis of oxygenates in gasoline, to keep up with all the developments. Since gasoline testing is moving into the stage which requires more advanced technology, laboratories need to be equipped to utilise a range of different techniques in order to suit the peculiarities of the different nature of the samples. During the last few years, the volume of gasoline testing by different bodies such as the independent petroleum laboratories has increased. In practice, laboratories are under considerable pressure to implement the designated analytical regulatory methods, and to constantly improve analytical quality. To help resolve these issues, laboratories sometimes turn to instrument vendors for advice on methodological advances in this type of work. The author has been involved directly with the challenges of this work and has experienced the practical limitations of current methods. Therefore the author has aimed to evaluate various analytical approaches in the study of the characterisation of fuel blending additives and, in particular, oxygenates. This work starts out with an introduction about the development of automobile fuel technology and the use of anti-knock additives throughout the period from the early days to the present. Thereafter further chapters review the current methods applied for the characterisation of these type of fuel additives in gasoline, in particular high performance fuels as used in the motor racing industry. The main aim of this work is to evaluate the strengths and limitations of these methods. The thesis then includes a detailed discussion of different analytical approaches encompassing initially micro-elemental analysis for the direct determination of oxygen content. Then follows the most popular method, gas chromatography, which continues to be the key instrumental technique for the measurement of the main parameters of gasoline. Thereafter follows a study of the GC-MS technique. The next chapter discusses the combustion technique using a Laminar burner to investigate the effect of oxygenates on the reduction of the sooting tendency in diesel. The final method under discussion is the estimation of oxygenates using Nuclear Magnetic Resonance Spectroscopy. Each of the above methods has been used on similar types of samples in different categories. Thus the results may be compared and interpreted using the relevant tables, and correlated against each other. The final part of this work has therefore concentrated on the conclusion of the comparative advantages of each method and its reliability. The main samples used throughout this research work have been actual commercial conventional gasolines and specialised fuels. These have been evaluated against a set of reference standards.

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.

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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.