Дисертації з теми "Diesel fuel injector"

With increasing demands for lowering emissions from diesel engines, bio fuel has been introduced to the fuel mixture. This fuel is based on vegetable oil with a much smaller carbon footprint than fossil fuel. The chemical composition of bio fuel has lead to deposits forming inside the fuel injector in diesel engines, these deposits are usually denoted as Internal Diesel Injector Deposits (IDID). At Scania CV AB an injector test rig is designed with the goal of creating and investigating IDID. This project has made a theoretical investigation of how IDID are formed and how this affects the mechanics inside the injector. It has also analysed injector components from a worst case scenario perspective in order to find a testing method for creating IDID in the test rig. By analysing performance changes from a build-up perspective, where IDID decreases the tolerances inside the injector, as well as friction, formed when deposits cause injector mechanics to stick together, it has been found that injector performance does hardly change from build-up and that performance changes only occur when friction is introduced. From the injector component analysis it is found that the limiting factors in rig testing come from fuel system components rather than the injector itself. This is the base for a rig running test method presented.

Efforts to improve diesel fuel sprays have led to a significant increase in fuel injection pressures and a reduction in nozzle-hole diameters. Under these conditions, the likelihood for the internal nozzle flow to cavitate is increased, which potentially affects spray breakup and atomisation, but also increases the risk of causing cavitation damage to the injector. This thesis describes the study of cavitating flow phenomena in various single and multi-hole optical nozzle geometries. It includes the design and development of a high-pressure optical fuel injector test facility with which the cavitating flows were observed. Experiments were undertaken using real-scale optical diesel injector nozzles at fuel injection pressures up to 2050 bar, observing for the first time the characteristics of the internal nozzle-flow under realistic fuel injection conditions. High-speed video and high resolution photography, using laser illumination sources, were used to capture the cavitating flow in the nozzle-holes and sac volume of the optical nozzles, which contained holes ranging in size from 110 micrometers to 300 micrometers. Geometric cavitation in the nozzle-holes and string cavitation formation in the nozzle-holes and sac volume were both observed using transient and steady-state injection conditions; injecting into gaseous and liquid back pressures up to 150 bar. Results obtained have shown that cavitation strings observed at realistic fuel injection pressures exhibit the same physical characteristics as those observed at lower pressures. The formation of string cavitation was observed in the 300 micrometers multi-hole nozzle geometries, exhibiting a mutual dependence on nozzle flow-rate and the geometry of the nozzle-holes. Pressure changes, caused by localised turbulent perturbations in the sac volume and transient fuel injection characteristics, independently affected the geometric and string cavitation formation in each of the holes. String cavitation formation of was shown to occur when free-stream vapour was entrained into the low pressure core of a sufficiently intense coherent vortex. Hole diameters less than or equal to 160 micrometers were found to suppress string cavitation formation, with this effect a result of the reduced nozzle flow rate and vortex intensity. Using different hole spacing geometries, it was demonstrated that the formation of cavitation strings in a particular geometry became independent of fuel injection and back pressure once a threshold pressure drop across the nozzle had been reached.

[EN] The injection system is one of the topics that has been paid most attention to by researchers in the field of direct injection diesel engines, due to its key role on fuel atomization, vaporization and air-fuel mixing process, which directly affect fuel consumption, noise irradiation and pollutant emissions. The increasing injection pressures in modern engines have propitiated the need of studying phenomena such as cavitation, compressible flow or the effect of changes in the fuel properties along the process, whose relative importance was lower in early stages of the reciprocating engines development. The small dimensions of the injector ducts, the high velocities achieved through them and the transient nature of the process hinder the direct observation of these facts. Computational tools have then provided invaluable help in the field. The objective of the present thesis is to analyse the influence of the thermal effects on the performance of a diesel injector. To this end, the fuel temperature variation through the injector restrictions must be estimated. The influence of these changes on the fuel thermophyisical properties relevant for the injection system also needs to be assessed, due to its impact on injector dynamics and the injection rate shape. In order to give answer to the previous objectives, both experimental and computational techniques have been employed. A dimensional and a hydraulic experimental characterization of a solenoid-actuated Bosch CRI 2.20 injector has been carried out, including rate of injection measurements at a wide range of operating conditions, with special attention to the fuel temperature control. A 1D computational model of the injector has been implemented in order to confirm and further extend the findings from the experiments. Local variations of fuel temperature and pressure are considered by the model thanks to the assumption of adiabatic flow, for which the experimental characterization of the fuel properties at high pressure also had to be performed. The limits of the validity of this assumption have been carefully assessed in the study. Results show a significant influence of the fuel temperature at the injector inlet on injection rate and duration, attributed to the effect of the variation of the fuel properties and to the fact that the injector remains in ballistic operation for most of its real operating conditions. Fuel temperature changes along the injector control orifices are able to importantly modify its dynamic behaviour. In addition, if the fuel at the injector inlet is at room temperature or above, the temperature at the nozzle outlet has not been proved to importantly change once steady-state conditions are achieved. However, a significant heating may take place for fuel temperatures at the injector inlet typical of cold-start conditions.
[ES] El sistema de inyección es uno de los elementos que más interés ha despertado en la investigación en el campo de los motores diésel de inyección directa, debido a su papel clave en la atomización y vaporización del combustible así como en el proceso de mezcla, que afectan directamente al consumo y la generación de ruido y emisiones contaminantes. Las crecientes presiones de inyección en motores modernos han propiciado la necesidad de estudiar fenómenos como la cavitación, flujo compresible o el efecto de los cambios de las propiedades del combustible a lo largo del proceso, cuya importancia relativa era menor en etapas tempranas del desarrollo de los motores alternativos. Las pequeñas dimensiones de los conductos del inyector, las altas velocidades a través de los mismos y la naturaleza transitoria del proceso dificultan la observación directa en estas cuestiones. Por ello, las herramientas computacionales han proporcionado una ayuda inestimable en el campo. El objetivo de la presente tesis es analizar la influencia de los efectos térmicos en el funcionamiento de un inyector diésel. Para tal fin, se debe estimar la variación de la temperatura del combustible a lo largo de las restricciones internas del inyector. La influencia de estos cambios en las propiedades termofísicas del combustible más relevantes en el sistema de inyección también debe ser evaluada, debido a su impacto en la dinámica del inyector y en la forma de la tasa de inyección. Para dar respuesta a estos objetivos, se han utilizado técnicas experimentales y computacionales. Se ha llevado a cabo una caracterización dimensional e hidráulica de un inyector Bosch CRI 2.20 actuado mediante solenoide, incluyendo medidas de tasa de inyección en un amplio rango de condiciones de operación, para lo que se ha prestado especial atención al control de la temperatura del combustible. Se ha implementado un modelo 1D del inyector para confirmar y extender las observaciones extra\'idas de los experimentos. El modelo considera variaciones locales de presión y temperatura del combustible gracias a la hipótesis de flujo adiabático, para lo cual también se ha tenido que llevar a cabo una caracterización experimental de las propiedades del combustible a alta presión. Los límites de la validez de esta hipótesis se han analizado cuidadosamente en el estudio. Los resultados muestran una influencia significativa de la temperatura del combustible a la entrada del inyector en la tasa y duración de inyección, atribuida al efecto de la variación de las propiedades del combustible y al hecho de que el inyector permanece en operación balística para la mayoría de sus condiciones de funcionamiento. Los cambios en temperatura del combustible a lo largo de los orificios de control del inyector son capaces de modificar su dinámica considerablemente. Además, si el combustible a la entrada del inyector se encuentra a temperatura ambiente o por encima, se ha observado que la temperatura a la salida de la tobera no varía de manera importante una vez se alcanzan condiciones estacionarias. No obstante, un calentamiento significativo puede tener lugar para temperaturas de entrada típicas de las condiciones de arranque en frío.
[CAT] El sistema d'injecció és un dels elements que més interés ha despertat en la investigació en el camp dels motors dièsel d'injecció directa, degut al seu paper clau en l'atomització i vaporització del combustible, així com en el procés de mescla, que afecten directament el consum i la generació de soroll i emissions contaminants. Les creixents pressions d'injecció en motors moderns han propiciat la necessitat d'estudiar fenòmens com la cavitació, flux compressible o l'efecte dels canvis de les propietats del combustible al llarg del procés, la importància relativa dels quals era menor en les primeres etapes del desenvolupament dels motors alternatius. Les menudes dimensions dels conductes de l'injector, les altes velocitats a través dels mateixos i la natura transitòria del procés dificulten l'observació directa en estes qüestions. Per això, les ferramentes computacionals han proporcionat una ajuda inestimable en el camp. L'objectiu de la present tesi és analitzar la influència dels efectes tèrmics en el funcionament d'un injector dièsel. Per a tal fi, es deu estimar la variació de la temperatura del combustible al llarg de les restriccions internes de l'injector. La influència d'estos canvis en les propietats termofísiques del combustible més relevants en el sistema d'injecció també ha de ser avaluada, degut al seu impacte en la dinàmica de l'injector i en la forma de la tasa d'injecció. Per tal de donar resposta a estos objectius, s'han utilitzat tècniques experimentals i computacionals. S'ha dut a terme una caracterització dimensional i hidràulica d'un injector Bosch CRI 2.20 actuat mitjançant solenoide, incloent mesures de tasa d'injecció en un ampli rang de condicions d'operació, per al que s'ha prestat especial atenció al control de la temperatura del combustible. S'ha implementat un model 1D de l'injector per tal de confirmar i estendre les observacions extretes dels experiments. El model considera variacions locals de pressió i temperatura del combustible gràcies a la hipòtesi de flux adiabàtic, per la qual cosa també s'ha hagut de dur a terme una caracterització experimental de les propietats del combustible a alta pressió. Els límits de la validesa d'esta hipòtesi s'han analitzat acuradament en l'estudi. Els resultats mostren una influència significativa de la temperatura del combustible a l'entrada de l'injector en la tasa i duració d'injecció, atribuïda a l'efecte de la variació de les propietats del combustible i al fet que l'injector roman en operació balística per a la majoria de les seues condicions de funcionament. Els canvis en temperatura del combustible al llarg dels orificis de control de l'injector són capaços de modificar la seua dinàmica considerablement. A més, si el combustible a l'entrada de l'injector es troba a temperatura ambient o per damunt, s'ha observat que la temperatura a l'eixida de la tobera no varia de manera important una vegada s'han assolit condicions estacionàries. No obstant això, un escalfament significatiu pot tenir lloc per a temperatures d'entrada típiques de les condicions d'arrancada en fred.
Carreres Talens, M. (2016). Thermal effects influence on the Diesel injector performance through a combined 1D modelling and experimental approach [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/73066
TESIS

Current fuel injection systems should provide more and more reliable performance in management and control of the injection event, to improve the efficiency of the fuel combustion process and thus meet both environmental and consumer demands. Small fuel quantities are usually injected before the main injection to reduce the combustion noise. Whereas, small injections following the main shot are employed to optimize the combustion development and to reduce pollutant emissions. Since the number of shots in multiple injections has increased over the years, the injected amount of fuel for each shot has become smaller, given a fix total amount of fuel. The control of injected fuel quantities is therefore a demanding task and any failure causes a worse combustion process and higher pollutant emissions. This study is focused on the modelling of Common Rail (CR) fuel injection systems for diesel applications and the implementation of specific mathematical techniques to examine phenomena pertaining to the fuel injection dynamics. New methodologies for detecting key events of the injection process and to estimate the injected fuel quantity have been developed for control purposes. A 1D numerical model of a solenoid-actuated injector equipped with a pressure-balanced pilot-valve has internally been developed to evaluate the main hydraulic and mechanical quantities. The impact of a pressure-balanced and a standard pilot-valve layout has been investigated, and the performance of a standard CR system has been compared to that of a novel injection system concept, i.e., the Common Feeding (CF). A sensitivity analysis of the main design parameters of the pressure-balanced pilot-valve layout has been carried out, with the purpose of improving the general performance of the system. A dedicated lumped parameter model of the high-pressure hydraulic circuit of the CR system has been used to calculate the natural frequencies and modes of vibration. It has been found that the direction and the magnitude of the fuel flow rates along each pipe of the apparatus can be derived from the first three modes (and the corresponding eigenvectors). The main objective is to identify which components could primarily be stressed for the main modes of vibration. Finally, external forcing terms acting on the system have been investigated to determine possible causes of hydraulic resonance. The identification of specific events that characterize the injection process, such as pilot-valve and injector nozzle opening and closure phases, might play a significant role for diagnostics and control of the system in on-board and real-life applications. To this end, time-frequency analysis techniques have been used to detect key events of the injection process. The method has then been applied to several working conditions to test its robustness. Specifically, the pressure time-history acquired along the rail-to-injector pipe has been transformed from the time domain into the joint time-frequency domain, so that changes within the new signal would highlight the events to be detected. Even though the diagnostics of injection events is an important topic, one of the main issues for injection systems is the absence of a closed-loop real-time control. The control unit should be able to evaluate the amount of fuel injected into the combustion chamber and eventually to correct it, based on the comparison with the target quantity stored in the engine maps. In this perspective, a quadratic correlation between the fuel amount that enters the injector and the injected fuel quantity has been found. The presented algorithm, which is specific for small injections, converts the pressure time-history acquired along the rail-to-injector pipe into an instantaneous fuel flow rate, calculates the fuel amount at the injector inlet by integration and the actual injected fuel quantity by means of the quadratic correlation. The entire process can be executed in real-time.

There is a growing interest in alternative transport fuels. There are two underlying reasons for this interest; the desire to decrease the environmental impact of transports and the need to compensate for the declining availability of petroleum. In the light of both these factors the Diesel Dual Fuel, DDF, engine is an attractive concept. The primary fuel of the DDF engine is methane, which can be derived both from renewables and from fossil sources. Methane from organic waste; commonly referred to as biomethane, can provide a reduction in greenhouse gases unmatched by any other fuel. The DDF engine is from a combustion point of view a hybrid between the diesel and the otto engine and it shares characteristics with both. This work identifies the main challenges of DDF operation and suggests methods to overcome them. Injector tip temperature and pre-ignitions have been found to limit performance in addition to the restrictions known from literature such as knock and emissions of NOx and HC. HC emissions are especially challenging at light load where throttling is required to promote flame propagation. For this reason it is desired to increase the lean limit in the light load range in order to reduce pumping losses and increase efficiency. It is shown that the best results in this area are achieved by using early diesel injection to achieve HCCI/RCCI combustion where combustion phasing is controlled by the ratio between diesel and methane. However, even without committing to HCCI/RCCI combustion and the difficult control issues associated with it, substantial gains are accomplished by splitting the diesel injection into two and allocating most of the diesel fuel to the early injection. HCCI/RCCI and PPCI combustion can be used with great effect to reduce the emissions of unburned hydrocarbons at light load. At high load, the challenges that need to be overcome are mostly related to heat. Injector tip temperatures need to be observed since the cooling effect of diesel flow through the nozzle is largely removed. Through investigation and modeling it is shown that the cooling effect of the diesel fuel occurs as the fuel resides injector between injections and not during the actual injection event. For this reason; fuel residing close to the tip absorbs more heat and as a result the dependence of tip temperature on diesel substitution rate is highly non-linear. The problem can be reduced greatly by improved cooling around the diesel injector. Knock and preignitions are limiting the performance of the engine and the behavior of each and how they are affected by gas quality needs to be determined. Based on experiences from this project where pure methane has been used as fuel; preignitions impose a stricter limit on engine operation than knock.
QC 20120626
Diesel Dual Fuel

A diesel fuel injector has been modified to allow rotationaround its axis, driven by an electric motor. Injections at upto 6000 rpm from the rotating injector have been investigatedunder the influence of air swirl on one optical research engineand one optically accessible heavy-duty diesel engine.

The experiments show that changing from a normal, staticinjection to a sweeping injection has profound effects on sprayformation, dispersion and penetration. This influences thefuel/air-mixing, autoignition, combustion rate and emissionsformation. The spray propagation is stronger influenced byinjector rotation than by air swirl.

The air entrainment into the spray increases forcounter-swirl rotation of the injector and this speeds up thevaporization and decreases the formation of soot. In addition,the oxidation of soot is enhanced since the counter-swirlinjection forces the intense fuel-rich and soot containingspray core to penetrate into fresh air instead of replenishingthe rich regions in the head of the spray. Fuel accumulationalong the piston bowl wall decreases as an effect of thereduced penetration with counter-swirl injection. Altogether,this decreases the smoke emissions for low and intermediateengine loads.

For the combustion system studied, counter-swirl rotation ofthe injector cannot decrease the smoke emissions at high engineload since the reduced spray penetration impairs the airutilization. Fast and efficient combustion at high loadrequires spray induced flame spread out into the squish region.Spray induced flow of cool fresh air from the bottom of thepiston bowl in towards the injector is also important for lowsoot formation rates.

Co-swirl rotation of the injector reduces the airentrainment into the spray and increases the soot formation.The increased smoke and CO emissions with co-swirl injectionare also attributed to the excessively large fuel-rich regionsbuilt up against the piston bowl wall.

Increased air swirl generally reduces smoke and COemissions. This is mainly an effect of enhanced burnout due tomore intense mixing after the end of fuel injection.

Changes in smoke as an effect of injector rotation aregenerally accompanied with opposite, but relatively small,changes in NO. Fast and efficient burnout is important for lowsmoke emissions and this raises both the temperature andproduction of NO. NO production is strongly influenced by thein-cylinder conditions during the latter part of themixing-controlled combustion and in the beginning of theburnout.

Keywords:diesel spray combustion, rotating injector,air swirl, air/fuel-mixing, soot, NO, CO, flame visualization,Chemkin modeling, soot deposition

Thesis (M.S.)--West Virginia University, 1999.
Title from document title page. Document formatted into pages; contains x, 96 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 61-62).

The study presents a one-dimensional, transient and compressible flow models of a commercial Common Rail Injector (CRI) and a prototype of a single-fuel Hydraulically actuated Electrically controlled Unit Injector (HEUI) developed at the University of New South Wales (UNSW) in conjunction with local industry. The unique feature of the UNSW HEUI is the fact that it uses diesel fuel as the driver for pressure amplification within the unit injector. The work undertaken is part of a wider study aimed at optimization of the design of diesel injectors for dual-fuel systems to reduce green house gas emissions. The contribution of this thesis is the development of the model of the UNSW HEUI injector, which can be used to investigate possible modifications of the injector for its use in dual-fuel injection systems. The developed models include electrical, mechanical and hydraulic subsystems present in the injectors. They are based on Kirchhoff??s laws, on the mass and momentum conservation equations and on the equilibrium of forces. The models were implemented in MATLAB/SIMULINK graphical software environment, which provides a high degree of flexibility and allows simulation of both linear and nonlinear elements. The models were used to perform sensitivity analysis of both injectors. The sensitivity analysis has revealed that the temperature of the solenoid coil is one of the critical parameters affecting the timing and the quantity of the fuel injection of both injectors. Additional critical parameters were found to be the dimensions of the piston of the CRI, the stiffness of the needle spring of the HEUI and the dimensions of the intensifier of the HEUI. The models also revealed that in the case of pilot injections the speed of the solenoid is the major limiting factor of the performance. The developed models provide better understanding of the issues and limitations of the injectors. They give detailed insight into their working principles. The investigations of the models permit making quantitative analysis of the timing of the HEUI solenoid and to evaluate the proposed change of the direction of the pressure acting on the HEUI solenoid plunger.

The purpose of this investigation was to determine whether hydrogen injected into a diesel internal combustion engine has the potential to reduce overall fuel consumption. The most economical means of performing the required tasks was used whenever possible in an attempt to mimic a small off-grid application. The genset was a small 4kW compression ignition diesel. The electrolyzer was an off-the-shelf model designed for automotive applications. It combines hydrogen and oxygen output and is currently found from many manufacturers over the internet. It was found that the H2/02 mixture actually did help conserve fuel by about 18% in a low load case but generally, savings were under 5%. At a higher proportion of generator rated load, fuel consumption was shown to increase with H2/02 injection by up to 5%, thus the H2/02 output must be optimized to achieve any savings. Reasons for this phenomenon are discussed and recommendations for further research are included.

Recent imaging studies have provided a new conceptual model of the internal structure of direct injection diesel fuel jets as well as empirical correlations predicting jet development and structure. This information was used to create a diesel cycle simulation model using C language including compression, fuel injection and combustion, and expansion processes. Empirical relationships were used to create a new mixing-limited zero-dimensional model of the diesel combustion process. During fuel injection five zones were created to model the reacting fuel jet: 1) liquid phase fuel 2) vapor phase fuel 3) rich premixed products 4) diffusion flame sheath 5) surrounding bulk gas. Temperature and composition in each zone is calculated. Composition in combusting zones was calculated using an equilibrium model that includes 21 species. Sub models for ignition delay, premixed burn duration, heat release rate, and heat transfer were also included. Apparent heat release rate results of the model were compared with data from a constant volume combustion vessel and two single-cylinder direct injection diesel engines. The modeled heat release results included all basic features of diesel combustion. Expected trends were seen in the ignition delay and premixed burn model studies, but the model is not predictive. The rise in heat release rate due to the diffusion burn is over-predicted in all cases. The shape of the heat release rate for the constant volume chamber is well characterized by the model, as is the peak heat release rate. The shape produced for the diffusion burn in the engine cases is not correct. The injector in the combustion vessel has a single nozzle and greater distance to the wall reducing or eliminating wall effects and jet interaction effects. Interactions between jets and the use of a spray penetration correlation developed for non-reacting jets contribute to inaccuracies in the model.

The recent advances in Fuel Injection Equipment (FIE) have led to the identification of deposits found in the fuel filters and injector equipment. The work carried out here identifies the effects of cavitating flows on the physical and chemical properties of diesel fuel in order to try to evaluate the mechanism for deposit formation in FIE equipment using optical techniques to characterise the cavitating flows. Two sets of experiments have been carried out in order to understand the impact of cavitating flow on diesel fuels. The first experiment investigated the effects of sustained cavitating flow using a fuel recirculation rig. Samples of commercial diesel were subjected to forty hours of intense cavitating flow across a diesel injector in a specially designed high-pressure recirculation flow rig. Changes to the optical absorption and scattering properties of the diesel over time were identified by the continuous measurement of spectral attenuation coefficients at 405 nm by means of a simple optical arrangement. Identical diesel samples ~ere maintained at 70°C for forty hours in a heated water bath, in order to distinguish the effects of hydrodynamic cavitation and the regulated temperature on the cavitated diesel samples. The commercial diesel samples subjected to high pressure cavitating flow and heat tests revealed a response to the flow and temperature history that was identified by an increase in the optical attenuation coefficients of the cavitated and heated samples. The contribution of cavitating flow and temperature to the variation in spectral attenuation coefficient was identified. It was hypothesised that the increases observed in the spectral attenuation coefficients of the cavitated commercial diesels were caused by the cavitation affecting the aromatics in the commercial diesel . samples. The fuels were sent for a GC x GC and particle count analysis and results show significant increase in particle number count in the fuels as a result of cavitating flow. An increase in particle count to such high magnitudes was not observed for the heat test samples. Qualitative chemical modelling results of the pyrolysis of fuel vapour cavities during collapse at high pressures and temperatures have shown possible pathways leading to the formation of particulates. The presence of aromatics in diesel fuel was considered to be key species to the formulation of soot particles, however at extreme pressures and temperature paraffins may also have the propensity to breakdown into aromatics and further on to the formation of soot particles as observed by the pathway analysis in the modelling in the appendix. The second study undertaken involved the analysis of the near nozzle external spray dropsizing and atomisation characteristics of fuels with different distillation profiles using LIF-MIE image ratios. The LIF -Mie image ratios were simultaneously captured synchronously with the internal nozzle hole cavitating flow. Internal nozzle flow and sac observations after needle return have led to the conclusions that flow angular momentum is sustained in the sac flow after needle return. This flow was observed to have a high angular momentum which reduced over time. During the end of needle return, bubbles were observed in the sac hole forming as a result of needle cavitation. These bubbles retained the angular momentum of the flow post injection (after needle seal). The vortical motion in the sac lead to regions of high and low pressures in the sac volume and thus resulted in suction and discharge of bubble in the nozzle holes. The bubbles may have a high propensity of containing a mixture of fuel and air vapour whereas the suction and discharge offers a pathway to external gases entering the nozzle holes and sac volume. For operating engine conditions this would be post-combustion exhaust gases re-entering the nozzle holes. The combination of the bubble formation, its vOI1Ical motion due to the angular momentum of the liquid flow, its composition and high temperature, may form ideal conditions for pyrolysis like reactions which may lead to the formation of soot particles and deposits in the nozzle hole, sac and needle. Fuels with different distillation profiles were investigated to observe their external drop sizing distributions at 350 bar injection pressure. Results showed that fuels with lighter fractional compositions which also had lower viscosity produced lower Sauter Mean Diameter (SMD) distributions than fuels with higher distillation fractions and higher viscosity. Whether this is as a consequence of the distillation profile alone and is not influenced by the viscosity differences has not been investigated yet and would form the basis of further investigations and publications.

Computational fluid dynamics methodologies have been achieving in the last decades remarkable progresses in predicting the complex physical process in internal combustion engines, which need to be continuously optimised to get the best compromise between fuel economy, emissions and power output/drivability. Among the variety of computational tools developed by researchers to investigate the multi-Phase flow development from high-pressure fuel injection systems for modem diesel and gasoline direct injection engines, the Eulerian-Lagrangian stochastic methodology, which models the air/vapour mixture as continuous phase and the liquid droplets as the dispersed one, has become standard among the developers of commercial or in-house university CFD codes due to its intuitive assumptions and simple implementation. It is generally recognised that this method is specifically suitable for dilute sprays, but it has shortcomings with respect to modelling of the dense sprays present in the crucial region close to the nozzle exit of fuel injection systems. Moreover, the mathematical formulation of the Eulerian-Lagrangian models is intrinsically related to critical numerical issues, like the difficulty of correctly estimating the initial conditions at the nozzle hole exit required by spray modelling calculations and, furthermore, the dependency of the results on the spatial and temporal discretisation schemes used to solve the governing flow equations. To overcome some of these difficulties, a modified Lagrangian methodology has been developed in this study. The interaction between the Eulerian and the Lagrangian phases is not treated on the cell-to-parcel basis, but using spatial distribution functions, which allow for distribution of the spray source terms on a number of cells located within a distance from the droplet centre. The end result is a numerical methodology which can handle numerical grids irrespective of the volume of the Lagrangian phase introduced. These improvements have been found to offer significant advances on Lagrangian spray calculations without the need to switch to Eulerian models in the near nozzle region. Besides these fundamental numerical issues, the present study offers some new insights on the physical processes involved in evaporating sprays under a wide range of operating conditions typical of advanced diesel and gasoline direct injection engines. Attention hag been directed on the topic of liquid droplet vaporisation modelling, which has been addressed by implementing and discussing different models published in the literature. Topics of particular emphasis include phase equilibrium, quasi-steadiness assumption, fuel composition, physical properties correlation, droplet shape and energy and mass transfer in the liquid and gas phases. The models have been implemented and validated against an extensive data base of experimental results for single and multi-component droplets vaporising under suband super-critical surrounding conditions and then implemented in the in-house GFS code, the multi-phase CFD solver developed within the research group over the last decade. A variety of physical sub-models have been assessed against comprehensive experimental data, which include the effect of thermodynamic, operating and physical parameters on the liquid and vapour penetration of diesel sprays. In particular, the effect of liquid atomisation, evaporation, aerodynamic drag, droplet secondary break-up and fuel physical properties has been thoroughly tested. The sensitivity of the predictions on the numerical treatment of the multi-phase interaction has been investigated by identifying and properly modelling the numerical parameters playing the most crucial role in the simulations. Finally the validated code has been used to investigate the flow processes from three high-pressure injection systems for direct injection spark-ignition engines. These have included the pressure swirl atomiser, the multi-hole injector and the outward-opening pintle nozzle. These investigations have enlightened the crucial role of the accurate modelling of the link between the internal nozzle flow prediction and the characteristics of the forming sprays in term of the successive multi-phase flow interaction, as function of the design of the fuel injection system used.

To meet stringent control and emissions requirements, diesel fuel injectors need to be characterised accurately in terms of timing and rate of change of mass flow rate. Such characterisation is carried out with various rate metering devices which overwhelmingly utilise a liquid into liquid injection process. These devices have historically been hampered by unwanted 'noise' in the measurement signal whose source was poorly understood and mitigation relied on post processing filtering techniques. A model of a constant volume metering device with optical access was constructed and a hybrid schlieren laser imaging technique applied to the flow field external to the nozzle with simultaneous chamber pressure measurement. This technique is sensitive to the second derivative of density and so directly able to visualise pressure waves within the domain. LES simulations were also performed to extract relationships not available through experimental data. The experimental results show cloud cavitation in the shear layer of the jet whose vapour bubbles begin collapsing shortly after injection begins and persist more than 500 microseconds after the end of injection. Compression waves due to the collapse of cavitation bubbles are visualised directly and parameters such as their spatial origin and time are calculated. Compression wave diffraction, reflections and interaction between individual jets are demonstrated. The 'noise' in a constant volume chamber is therefore shown to actually be an accurate representation of the pressure field arising from the superposition of complex flow phenomena in the near field of the injector nozzle due to an interaction of pressure waves and cavitation. The novel use of a hybrid schlieren technique demonstrates the utility of this arrangement to fully three dimensional problems. Cavitation and its associated processes are shown to be the dominating force in liquid to liquid injection processes for the flows encountered in fuel injection metering.

Engine manufacturers have acknowledged that in order to meet future strict emission regulations, greater optimisation of the combustion process is necessary. They are also aware that in a direct injection diesel engine, the Fuel Injection Equipment (FIE) plays the most critical role in the combustion efficiency and the formation of exhaust pollutants. In fact, the engine torque curve, fuel consumption, smoke, noise and exhaust emissions are all determined by the quantity and manner in which the fuel is injected into the engine cylinder. In modern high speed diesel engine applications, it is the inwardly-opening needle valve which fulfils this purpose. Its location, being situated within the tip of a fuel injector nozzle, ensures that the needle valve is the ultimate link between the FIE and the combustion process. This arguably makes this valve the single most important component within the whole fuel injection system, or in other words, the most important piece of the puzzle. This thesis details a series of experimental projects which were carried out to study the internal flow inside some common types of valves found within diesel FIE. Although primarily focusing on the needle valve design, both ball and cone check valves were also considered. The typical approach of visualising the internal flow structure involved the use of enlarged transparent models and a refractive index matched working fluid. Laser Light sheet illumination and Particle Image Velocimetry techniques were adopted to provide qualitative and quantitative analysis of the internal flow structure within the aforementioned types of valves. In the case of the needle valve, two reported flow phenomena, the ‘flow transition’ and the ‘flow overshoot’ were confirmed to occur within the nozzle sac, whilst a third previously unknown flow structure, the ‘reverse overshoot’ was exposed. PIV analysis has quantified flow structures within the injection holes and these have been associated with vortical structures known to exist within the emerging spray plumes. Additional observations were made of the growth of the separated region and the influence of hole entry cavitation on the bulk flow within the injection hole. In the case of an un-sprung ball check valve, a novel design of lift stop was put forward and found during steady-state flow to improve the operational performance and neutralise some undesirable behaviour. This effect was especially apparent at the full lift condition. It is anticipated that knowledge gained and described within this thesis will have commercial value to assist with design optimisation of future FIE components and for the validation of simulation data, in particular with regard analysis of the flow within the injection hole.

The temporal and spatial distribution of fuel in cylinders is a key factor affecting the combustion characteristics and emission generation of a DI diesel engine. The airfuel mixing quality is critical for controlling ignition timing and combustion duration. Avoiding fuel-rich areas within the cylinder can significantly reduce soot formation as well as high local temperatures resulting in low NOx formation. The present investigation is focused on the effects of advanced fuel injections and air path strategies as well as the effects of piston geometry and fuel spray angle on air-fuel homogeneity, combustion process and their impacts on the performance and emission of the engine. A Ricardo Hydra single-cylinder engine in combination with AVL Fire CFD software was used in this investigation. An experimental analysis was conducted to assess the combustion characteristics and emissions formation of the engine under various injection strategies such as different injection timing, quantity, ratio, dwell angles between injections with various exhaust valve opening times and exhaust back pressures. A quan- titative factor named Homogeneity Factor (HF) was employed in the CFD code in order to quantify the air-fuel mixing and understand how the air-fuel homogeneity within the cylinder can influence the combustion and emissions of the engine. The investigation concludes that multiple injection strategies have the potential to reduce diesel emissions while maintaining meaningful fuel economy. Split injection can be used to improve the air-fuel mixture locally and control temperature generation during the start of combustion. Increased air-fuel homogeneity results in fewer fuel-rich areas within the cylinder and contributes to the reduction of soot emission. Extending the pre-mixed combustion phase has a direct effect on the reduction of soot formation while NOx generation is highly dependent on the scale of the primary fuel injection event.

The fuel pressure is one of the central control variables of a modern common-rail injection system. It influences the generation of nitrous oxide and particulate matter emissions, the brake specific fuel consumption of the engine and the power consumption of the fuel pump. Accurate control of the fuel pressure and reliable diagnostics of the fuel system are therefore crucial components of the engine management system. In order to develop for example control or diagnostics algorithms and aid in the understanding of how hardware changes affect the system, a simulation model of the system is desirable.  A Simulink model of the XPI (Xtra high Pressure Injection) system developed by Scania and Cummins is developed. Unlike the previous models of the system available, the new model is geared towards fast simulations by modelling only the mean flow and pressure characteristics of the system, instead of the momentary flow and pressure variations as the engine rotates. The model is built using a modular approach where each module represents a physical component of the system. The modules themselves are based to a large extent on the physical properties of the components involved, making the model of the system adaptable to different hardware configurations whilst also being easy to understand and modify.
Bränsletrycket är en av de centrala styrvariablerna i ett modernt common-rail insprutningssystem. Det påverkar utsläppen av kväveoxider och partiklar, motorns specifika bränsleförbrukning och bränslepumpens effektförbrukning. Nogrann reglering och tillförlitliga diagnoser av bränslesystemet är därför mycket viktiga funktioner i motorstyrsystemet. Som ett hjälpmedel vid utveckling av dessa algoritmer samt för att öka förståelsen för hur hårdvaruförändringar påverkar systemet är det önskvärt med en simuleringsmodel av bränslesystemet.  En Simulink modell av XPI (Xtra high Pressure Injection) systemet som utvecklats av Scania och Cummins har utvecklats. Till skillnad från de redan tillgängliga modellerna av systemet fokuserar denna modell på snabba simuleringsförlopp genom att enbart modellera medeltryck och medelflöden istället för de momentana trycken och flödena i systemet när motorn roterar. Modellen är uppbyggd av moduler som var och en representerar en fysisk komponent i systemet. Modulerna är mestadels uppbyggda kring de fysikaliska egenskaperna hos komponenten de försöker modellera vilket gör modellen av systemet anpassningsbar till olika hårdvarukonfigurationer och samtidigt lätt att förstå.

Large eddy simulation of spray combustion in an HSDI engine is carried out in this thesis. The implementation of the code was performed in logical steps that allowed both assessment of the performance of the existing KIVA-LES and later development. The analysis of the liquid annular jet confirmed existence of typical, annular jet exclusive structures like head vortices, stagnation point and recirculation in the inner zone. The influence of the swirl in the ambient domain was found to have profound impact on the development, penetration and radial spreading of the jet. Detailed results were reported in Jagus et al. (2008). The code was further validated by performing an extensive study of large eddy simulation of diesel fuel mixing in an engine environment. The reaction models were switched off in order to isolate the effects of both swirl and the different numerical treatment of LES. Reference RANS simulation was performed and significant differences were found. LES was found to capture much better the influence of the swirl on the liquid and vapour jets, a feature essentially absent in RANS results. Moreover, the predicted penetration of the liquid was much higher for the LES case and more in accordance with experimental measurements. Liquid penetration and subsequent evaporation are very important for prediction of heat release rates and encouraging results formed a good basis to performing a full simulation with models for ignition and combustion employed. The findings were analyzed in the paper by Jagus et al. (2009). Further modifications were introduced into the LES code, among them changes to the combustion model that was originally developed for RANS and calculation of the filter width. A new way of estimating the turbulent timescale (eddy turnover time) assured that the incompatibilities in the numerical treatment were eliminated and benefits of LES maximized. The new combustion model proved to give a very good agreement with experimental data, especially with regard to pressure and accumulated heat release rates. Both qualitative and quantitative results presented a significant improvement with respect to RANS results and old LES formulation. The new LES model was proved to give a very good performance on a spectrum of mesh resolutions. Encouraging results were obtained on a coarse mesh sets therefore proving that the new LES code is able to give good prediction even on mesh sizes more suitable for RANS. Overall, LES was found to be a worthy alternative to the well established RANS methods, surpassing it in many areas, such as liquid penetration prediction, temperature-turbulence coupling and prediction of volume-averaged data. It was also discovered that the improved LES code is capable of producing very good results on under-resolved mesh resolutions, a feature that is especially important in industrial applications and on serial code structure.

Approved for public release; distribution is unlimited
In support of the Navy’s Green Fleet Initiative, this thesis researched the ignition characteristics for diesel replacement fuels used with Navy-relevant fuel injectors. A constant-volume combustion chamber was used to simulate Top-Dead-Center conditions of a diesel engine using an ethylene-air preburn with appropriate make-up oxygen. The injection conditions ranged from temperatures of 1,000 K to 1,300 K and densities has high as 14.8 kg/m3. Hydrotreated renewable diesel (HRD) and direct sugar-to-hydrocarbon (DSH) fuels were injected into the combustion chamber using a Sturman research injector, a Yanmar injector, and an Electro Motive Diesel (EMD) injector. The primary means of data collection was optical emission imaging of laser induced fluorescence of the fuel and broadband emission of the combustion event. The ignition delay was determined using high speed imaging at 50 kHz to determine the time delay between start of injection and start of combustion. The results of the study show that the ignition delay characteristics for the F-76/HRD 50/50 blend are compatible with those of conventional F-76 diesel fuel for both the Yanmar and EMD injectors at the conditions tested. The ignition delay characteristics of the F-76/DSH 50/50 blend fuel for the Yanmar injector were also compatible with those of F-76.

Includes bibliographical references (leaves 78-81).
Reducing the pollution of new vehicles has become a priority to vehicle manufacturers, particularly given the fact that emissions requirements that must be achieved by diesel vehicles are becoming more stringent. Modem fuel injectors on common-rail diesel vehicles use very high rail pressures to aid atomisation and increase combustion efficiency. However, associated with the high injections pressures is the issue of nozzle cavitation. Cavitation leads to pockets of diesel vapour forming in the nozzle and it is hypothesised that this causes the formation of deposits in the nozzle. It is also suggested that the collapse of the cavitation vapour space results in extremely high temperatures within the nozzle, resulting in thermal cracking of the fuel and eventually the formation of carbon deposits. A two-dimensional axisymmetric CFD model with dimensions representative of an injector nozzle was constructed using a fully structured grid.

The overall objective of this thesis was to develop field deployable instrumentation for the selective, sensitive determination of additives in diesel fuels using flow injection with chemiluminescence detection. The target analytes were the detergent dodecylamine and the lubricity additive P655. Chapter One describes the types of additives that are used in fully formulated diesel fuels in order to improve performance and outlines the need for robust analytical methods to be able to detect their presence / absences in fuels at the point of distribution, i.e. at the petrol pump. Flow injection (FI), and chemiluminescence (CL) are described as suitable techniques for sample preparation and detection respectively. The application of FI-CL for the quantitative determination of various analytes is reviewed, with the focus on real sample matrices. Finally the technique of solid phase extraction is discussed as a means of selective analyte preconcentration / matrix removal prior to FI-CL detection Chapter Two describes the development and optimisation (both univariate and simplex) of an FI-CL method for the determination of dodecylamine in acetonitrile / water mixtures using the catalytic effect of amines on the peroxyoxalate / sulphorhodamine 101 CL reaction. The linear range for dodecylamine was 0 - 50 mg Lˉ¹ with a detection limit of 190 µg Lˉ¹ and RSDs typically < 4 %. The effect of indigenous diesel compounds on the CL response is also investigated. Chapter Three investigates the applicability of the method developed in Chapter Two to determine dodecylamine in diesel fuels. Solid phase extraction was needed prior to analysis by FI-CL. The development of a solid phase extraction that is compatible with the FI-CL system is detailed. GC-NPD and GC-MS analysis are used in order to validate the solid phase extraction procedure. A range of diesel fuels have been spiked with an additive package containing dodecylamine and have been analysed off-line using FI-CL. Recoveries for all diesel fuels analysed were < 72 % and all fuels could by identified from the corresponding base fuel. Chapter Four describes the design and construction of a fully automated on-line solid phase extraction flow injection chemiluminescence analyser for the determination of dodecylamine in diesel fuel. Details of the automation and programming using LabVIEW are described. Results obtained using the automated on-line system are compared with results obtained using off-line SPE with FI-CL detection from Chapter Three. Recoveries for all fuels except SNV were < 71 %, and all fuels except SNV could be positively identified from the corresponding base fuels. No significant differences were found between the on-line and off-line results (within 95 % confidence limits). Chapter Five investigates the feasibility of determining the lubricity additive P655 in diesel fuel using FI-CL. The optimisation and development of a method using the competing reactions of periodate with alcohols and periodate with the CL oxidation reaction with pyrogallol is discussed, and the development of a solid phase extraction procedure for the extraction of P655 from an organic matrix is described. The limit of detection for P655 using SPE without preconcentration was 860 mg Lˉ¹ and was linear in the range 0 - 10000 mg Lˉ¹ (R² = 0.9965).

This thesis describes research undertaken to establish the advantages and disadvantages of using high pressure common rail fuel injection systems with multiple injection capabilities. The areas covered are detailed as follows. Oscillations in the rail pressure due to the opening of the injector can affect the quantity of fuel injected in subsequent injection events. The source of these oscillations has been investigated. A method of damping or reducing the oscillations has been defined and was applied. This successfully reduced the level of unpredictability of the quantity of injected fuel in subsequent injection events. A relationship between needle lift, injection pressure and the quantity of fuel injected was established. The effects of fuel injection parameters (main injection timing, split main separation and ratio) and engine operating parameters (boost pressure and EGR level) on emissions formations and fuel economy have been investigated at five operating points. Design of Experiments techniques were applied to investigate the effect of variables on pollutant emissions and fuel consumption. The sensitivity and linearity of responses to parameter changes have been analysed to assess the extent to which linear extrapolations will describe changes in smoke number (FSN) and oxides of nitrogen (NOx); and which parameters are the least constricting when it comes to adjustments of parameter settings on the FSN-NOx map. Comparing results for split main and single injection strategies at the five operating conditions shows that split main injection can be exploited to reduce NOx or FSN values at all conditions and both NOx and FSN simultaneously at high load conditions. The influence of changing engine speed and brake mean effective pressure (BMEP) on FSN and NOx emissions with given fixed values of parameter settings has been investigated. This established how much of the operating map could be covered by discrete calibration settings. Finally the variation in parameter settings required to maintain fixed FSN and NOx values across the operating map, near the optimum trade-off on the FSN-NOx map, was analysed. Combining the information gained from the individual investigations carried out highlighted some techniques that can be used to simplify the calibration task across the operating map, while also reducing the amount of experimental testing required.

Includes abstract.
This study set out to investigate the effects of diesel fuel properties on the behaviour of a common rail fuel injection system, with particular emphasis on the injection rate shape characteristics. The investigation included the design and commissioning of experimental equipment for the measurement of fuel properties at typical common rail pressures, as well as the measurement of instantaneous fuel flow rate by a modified Bosch Indicator method. Data was then collected for two different diesel fuels, operating in two different fuel injector designs. The two fuels were EN590 (a European reference fuel) and GTL (a fuel derived from natural gas). The two injectors were a Bosch solenoid type injector, and a Bosch piezo type injector.

The introduction of alternative fuels such as natural gas is likely to occur at an increasing rate. The dual-fuel concept allows these low cetane number fuels to be used in compression-ignition (CI, diesel) type engines. Most CI engine conversions have pre-mixed the alternative fuel with air in the intake manifold while retaining diesel injection into the cylinder for ignition. The advantage is that it is simple for practical adaptation; the disadvantage is that good substitution levels are only obtained at midload. A better solution is to inject both the alternative and diesel fuels directly into the cylinder. Here, the fuel in the end-zone is limited and the diesel, injected before the alternative, has only a conventional ignition delay. This improves the high-end performance. Modern, very high pressure diesel injectors have good turndown characteristics as well as better controllability. This improves low-end performance and hence offers an ideal platform for a dual-fuel system. Several systems already exist, mainly for large marine engines but also a few for smaller, truck-sized engines. For the latter, the key is to produce a combined injector to handle both fuels which has the smallest diameter possible so that installation is readily achieved. There exists the potential for much improvement. A combined gas/diesel injection system based on small, high pressure common-rail injectors has been tested for fluid characteristics. Spray properties have been examined experimentally in a test rig and modelled using CFD. The CFD package Fluent was used to model the direct-injection of natural gas and diesel oil simultaneously into an engine. These models were initially calibrated using high-speed photographic visualisation of the jets. Both shadowgraph and schlieren techniques were employed to identify the gas jet itself as well as mixing regions within the flow. Different orientations and staging of the jets with respect to each other were simulated. Salient features of the two fuel jets were studied to optimise the design of a dual-fuel injector for CI engines. Analysis of the fuel-air mixture strength during the injection allowed the ignition delay to be estimated and thus the best staging of the jets to be determined.

With the slow but ineluctable depletion of fossil fuels, several avenues are currently being explored in order to define the strategic boundaries for a clean and sustainable energetic future, while accounting for the specificities of each sectors involved. In regard to transport applications, alternative fuels may represent a promising solution, at least at short or middle term, such as the International Energy Agency foresees that their share could account for 9% of the road transport fuel needs by 2030 and 27 % by 2050, with the potential resources to reach 48% beyond. If they have already been included in significant blending proportions with conventional fossil fuel in most of the occidental countries, their introduction also coincides with a long-time established program of continuously more drastic standards for engine emissions of NOX and PM, now even further demanding by the seek for combustion efficiency aiming at reducing CO2 emissions. While several works discuss the alternative fuels effect on exhaust emissions when used directly in production Diesel engines, results and analysis are sometimes contradictory, depending sometimes on the conditions in which they were obtained, and the causes of these results remain unclear. Therefore, in order to better understand their effect on the combustion processes, and thus extract the maximum benefits from these fuels in the optimization of engine design and calibration, a detailed comprehension of their spray and combustion characteristics is essential. The approach of this study is mostly experimental and based on an incremental methodology of tests aiming at isolating injection and combustion processes with the objective to identify and quantify the role of both fuel physical and chemical properties at some key stages of the Diesel combustion process. After obtaining a detailed characterization of their properties, five fuels have been injected in an optical engine enabling a sharp control of the thermodynamic e
Nerva, J. (2013). An Assessment of fuel physical and chemical properties in the combustion of a Diesel spray [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29767
Palancia

L'objectif de ce travail a été d'étudier les possibilités de visualisation (avec une camera CCD intensifiée) du spray de fuel dans un moteur Diesel à injection directe par fluorescence induite par les trois harmoniques (soit 532 nm, ou 355 nm, ou 266 nm) d'un laser YAG pulsé. Un fuel Diesel standard (commercial) a été utilise de façon à se trouver dans des conditions de fonctionnement moteur réalistes. Les spectres d'absorption et de fluorescence du fuel Diesel Shell standard et de ses 4 fractions distillées (0-25%, t<207°C ; 25-50%, 207°C