Jet fuel spray characterisation using optical methods: an experimental study of high speed fuel injection systems in small rotary engines

This thesis was initiated by the need to develop a stable low vibration engine with a high power to weight ratio. A new rotary (Wankel) engine was chosen to meet these requirements. A further operating criterion was that the engine was required to use JP8 (aviation fuel). The difficulty created by the use of JP8 is that its combustion temperature is higher than other conventional fuels, and preheating is necessary, especially in the case of cold start. Thus, the question posed was, could a more appropriate and efficient method of fuel delivery be devised? This thesis presents the design and construction of a fluid spray visualisation system for investigating the macroscopic and microscopic characteristics of fuel sprays using low injection pressure up to 10 bar (1 MPa). Laser imaging techniques have been used for data acquisition. The thesis has been divided into several aspects. Firstly, a background study of fluid sprays and fuel injection strategies was carried out. This has centred on the relationship between droplet size and the combustion process. It further investigated what differentiated the fuel delivery approach to Wankle from that to other engines. Secondly, two families of fuel injector were tested and evaluated within the optical engineering laboratory using deionised water (DI) water for safety reasons. The first family involved conventional gasoline injectors with several nozzle arrangements. The second family involved medical nebulisers with several nozzle diameters. The evaluation of the fuel injectors required developing a fluid delivery circuit, and a specific ECU (Electronic Control Unit) for controlling pulse delivery and imaging instrument. The company associated with the project then set up a test cell for performing experiments on JP8 fuel. The initial global visualisation of the jet spray was made using a conventional digital camera. This gave a measurement of the spray angle and penetration length. However, as the study moved to the more precise determination of the fuel spray particulate size, a specialised Nd:YAG laser based diagnostic was created combined with a long range diffraction limited microscope. Microscopic characterisation of the fuel sprays was carried out using a backlight shadowgraph method. The microscopic shadowgraphy method was applied successfully to resolve droplets larger than 4 microns in diameter. The spray development process during an individual fuel injection cycle was investigated, presenting the frequency response effect of electronic fuel injectors (EFI) on the spray characteristics when operating at high injection frequencies (0.25 -­‐ 3.3 kHz). The velocity distribution during the different stages of an injection cycle was investigated using PIV. The influence of the injection pressure on the spray pattern and droplet size was also presented. Novel fluid atomisation systems were investigated for the capability of generating an optimum particulate distribution under low pressure. Finally, it was found that a new electronic medical nebuliser (micro-­‐dispenser) could be used to deliver the fuel supply with the relevant particle size distribution at low flow rate and high injection frequency. However, as yet it has not been possible to apply this approach to the engine; it is hoped that it will yield a more efficient method of cold starting the engine. The characteristics of this atomiser can be applied to provide a controllable fuel supply approach for all rotary engines to improve their fuel efficiency. The second part of this research discusses the droplets-­‐light interaction using Mie scattering for fluid droplets smaller than the microscope visualisation limit (4 microns). Mie scattering theory was implemented into Three-­‐Components Particle Image Velocimetry (3C-­‐ PIV) tests to address a number of problems associated with flow seeding using oil smoke. Mie curves were used to generate the scattering profile of the oil sub-­‐micron droplets, and therefore the scattering efficiency can be calculated at different angles of observation. The results were used in jet flow PIV system for the determination of the optimum position of the two cameras to generate balanced brightness between the images pairs. The brightness balance between images is important for improving the correlation quality in the PIV calculations. The scattering efficiency and the correlation quality were investigated for different seeding materials and using different interrogation window sizes

Analisi di spray: Tecnica tomografica per il rilevamento meccanico della quantità di moto ed elaborazione di immagini digitali mediante trasformata di Lòeve-Karhunen

L'abstract è presente nell'allegato / the abstract is in the attachmen

Diesel fuel and Diesel fuel with Water Emulsions Spray and Combustion Characterization

The legislative demand to simultaneously reduce nitrogen oxide(s) emissions and particulate matter emissions from compression ignition engines is proving difficult to achieve in the real world. One promising strategy is the use of Diesel fuel emulsified with water. There is little work concerning the e↵ect of emulsification on fuel injection sprays. This work details an experimental campaign to characterize non-vaporizing sprays of Diesel fuel and Diesel emulsions, with 10% and 20% water by mass. Characterization of the fuel sprays has been done using: high speed photography, applying focused shadowgraphy and a di↵used back-lighting technique and; hydraulically using a force transducer placed 0.5mm from the injector nozzle to measure spray momentum flux. All measurements have been made in an optically accessible high pressure chamber filled with nitrogen, resulting in an ambient gas density of 22.6 kg/m3 and 34.5 kg/m3, with injection pressures of 500, 700 and 1000bar used. The images collected have been used to determine the spray cone angle, the tip penetration and the tip velocity. The signal from the force transducer has been used to determine spray momentum flux, instantaneous mass flow rate, dimensionless nozzle coefficients and injection velocity. The injection pressure had no discernible influence on the spray cone angle for the Diesel fuel sprays but did for the emulsified fuels. Increasing the ambient density resulted in an increase in the spray cone angle for Diesel fuel, this was not always the case for the emulsified fuel sprays. The spray tip emerged from the nozzle and accelerated for a very short period after the start of injection until a maximum velocity was reached. The momentum flux for each fuel was almost the same for corresponding conditions. Increasing the chamber gas density reduced the measured spray momentum. The total mass of fuel injected for Diesel fuel was larger than for the emulsions for the equivalent conditions and duration, although emulsions had a larger density and viscosity. The emulsions had a higher injection velocity. The nozzle discharge coefficient for Diesel was higher than for the emulsions. The velocities measured hydraulically are much higher than the maximum tip velocities measured optically. The study has been completed by some preliminary combustion studies of the fuels in an optically accessible combustion chamber. The emulsion tested exhibited much lower natural flame luminosity, used to determine the spatially integrated natural luminosity of the flame which may be useful as a soot indicator. There was no evidence that the microexplosion phenomenon was present in these tests.Advanced Engine Research (A.E.R, Basildon, Essex, UK

Digital Imaging Based Measurement of Diesel Spray Characteristics

This paper presents a direct photographic imaging and image processing system for the analysis and characterization of diesel sprays. A high-resolution CCD camera with a flash light source is used to capture the spray images through an optically accessible, constant volume chamber. A set of macroscopic characteristic parameters of the sprays including tip penetration, near and far field angles, spray tip velocity and average fuel area density are derived from the images. Experimental work was undertaken on a common rail fuel injection rig. The relationships between the spray characteristics and corresponding injection conditions are presented and discussed

Digital-Imaging-Based Measurement of Diesel Spray Characteristics

This paper presents the application of a direct photographic imaging and image processing system in the quantitative characterization of diesel sprays. A high-resolution charge-coupled device (CCD) camera with a flashlight source is use to capture images of sprays in an optically accessible constant-volume chamber. A set of macroscopic characteristic parameters of the sprays, including tip penetration, near- and far-field angles, spray-tip velocity, and average fuel area density, is derived from the images. Experimental work was undertaken on a common rail fuel injection rig. The relationships between the spray characteristics and the corresponding injection conditions are presented and discussed