The Effect of Fuel Injection Equipment of Water-In-Diesel Emulsions on Micro-Explosion Behaviour

The number and size distributions of the water dispersed phase have a significant effect on both the long-term stability of an emulsion, and the probability of micro-explosions inside an engine. The emulsions are subjected to intense pressure and shear flow in the fuel injection equipment resulting in changes in the number and size distributions of the dispersed phase. These changes, in turn, have significant effects on the micro-explosion behavior of the droplets. To our knowledge, these effects are not known and have not been reported previously. To uncover some of these effects we carried out a comprehensive experimental investigation on an emulsion spray of 10% water (by volume) in diesel at different injection pressures of 500, 1000 and 1500 bar. A measurement system consisting of a high-speed camera was used to visualize the droplets’ micro-explosions and a thermocouple measured the temperature. Our measurements indicated that the emulsion shear in the injector nozzle shifted the emulsion droplet size distribution towards the smaller end resulting in a delay in the onset of micro-explosion. This delay in the onset of the micro-explosion is thought to be due to the decrease in the dispersed water coalescence rate which, in turn, increases the stability of the emulsion. The results also show that this delay in the onset of micro-explosion, and the temperature required for its onset, increased with injection pressure

The effect of fuel injection equipment on the dispersed phase of water-in-diesel emulsions

Water-in-diesel emulsions are known to lead to micro-explosions when exposed to high temperatures, thereby offering a technology that could improve the mixing of fuels with the ambient gas. The number and size distributions of the dispersed phase have a significant effect on both the long-term stability of the emulsion and the probability of micro-explosion inside an engine. Although the elevated pressures, temperatures, and shear found in high-pressure pumps and common-rail injector nozzles are likely to alter the properties of emulsions, the effect of these engine components on the injected emulsion are not known. To address this issue we sampled an emulsion at several locations within the injection system, from the fuel tank to the injector nozzle, and measured the evolution of the droplet size distribution of the emulsion’s dispersed phase. We varied the water mass fraction (5, 10 and 15% by volume) of the emulsion and the injection pressure (500, 1000 and 1500 bar), imaged the samples using a high-resolution microscope and extracted the droplet size distribution using a purpose-built image processing algorithm. Our measurements reveal that the dispersed droplet sizes reduce significantly after the emulsion is compressed by the high-pressure fuel pump, and again after being injected through the nozzle’s orifices. Additionally, the dispersed droplet sizes measured from the pump’s return and injector return to the fuel tank were also smaller than the initial size, suggesting that the physical and calorific properties of the emulsion in the fuel tank can change significantly with time. Hence we propose that differences in injection equipment and engine testing duration may contribute to some of the disagreements in the literature regarding the effect of emulsified fuels on engine emissions and fuel efficiency. The engine performance and energy efficiency of vehicle fleets that use emulsified fuels will vary with engine running time, thus potentially inducing a drift in the engine performance and exhaust emissions. This investigation also suggests that, in order to be representative of actual injection conditions, fundamental studies of the micro-explosion of emulsion droplets should be performed using much smaller dispersed droplet sizes than those normally found in an unused emulsion

On the application of proper orthogonal decomposition (POD) for in-cylinder flow analysis

Proper orthogonal decomposition (POD) is a coherent structure identification technique based on either measured or computed data sets. Recently, POD has been adopted for the analysis of the in-cylinder flows inside internal combustion engines. In this study, stereoscopic particle image velocimetry (Stereo-PIV) measurements were carried out at the central vertical tumble plane inside an engine cylinder to acquire the velocity vector fields for the in-cylinder flow under different experimental conditions. Afterwards, the POD analysis were performed firstly on synthetic velocity vector fields with known characteristics in order to extract some fundamental properties of the POD technique. These data were used to reveal how the physical properties of coherent structures were captured and distributed among the POD modes, in addition to illustrate the difference between subtracting and non-subtracting the ensemble average prior to conducting POD on datasets. Moreover, two case studies for the in-cylinder flow at different valve lifts and different pressure differences across the air intake valves were presented and discussed as the effect of both valve lifts and pressure difference have not been investigated before using phase-invariant POD analysis. The results demonstrated that for repeatable flow pattern, only the first mode was sufficient to reconstruct the physical properties of the flow. Furthermore, POD analysis confirmed the negligible effect of pressure difference and subsequently the effect of engine speed on flow structures

Investigation of puffing and micro-explosion of water-in-diesel emulsion spray using shadow imaging

Water-in-diesel emulsions potentially favor the occurrence of micro-explosions when exposed to elevated temperatures, thereby improving the mixing of fuels with the ambient gas. The distributions and sizes of both spray and dispersed water droplets have a significant effect on puffing and micro-explosion behavior. Although the injection pressure is likely to alter the properties of emulsions, this effect on the spray flow puffing and micro-explosion has not been reported. To investigate this, we injected a fuel spray using a microsyringe needle into a high-temperature environment to investigate the droplets’ behavior. Injection pressures were varied at 10% v/v water content, the samples were imaged using a digital microscope, and the dispersed droplet size distributions were extracted using a purpose-built image processing algorithm. A high-speed camera coupled with a long-distance microscope objective was then used to capture the emulsion spray droplets. Our measurements indicated that the secondary atomization was significantly affected by the injection pressure which reduced the dispersed droplet size and hence caused a delay in puffing. At high injection pressure (500, 1000, and 1500 bar), the water was evaporated during the spray and although there was not enough droplet residence time, puffing and micro-explosion were clearly observed. This study suggests that high injection pressures have a detrimental effect on the secondary atomization of water-in-diesel emulsions

Unveiling the status of emulsified water-in-diesel and nanoparticles on diesel engine attributes

Due to the obvious increase in the environmental and human health concerns produced by diesel engines, there has been a lot of interest in ecologically friendly diesel fuels. Current research and development efforts are focused on water-in-diesel emulsion (WiDE) fuels, which have the potential to reduce nitrogen oxide (NOx) and particulate matter (PM) emissions while enhancing performance and allowing for more efficient energy development in a cleaner environment using existing diesel engines. The current topic is concerned with the WiDE fuel principle, emulsification stability, physio-chemical attributes, latest trends in emulsion fuel, the impact of WiDE fuel on engine attributes and the barriers to commercialization of emulsified fuel. Furthermore, the importance of nanoparticle additives in WiDE, nano-fuel formulation, and their impact on engine attributes are explored

Experimental study of Gas-To-Liquid (GTL) and diesel fuel blends evaporation behaviour and droplet lifetime through Leidenfrost effect

Gas to Liquid (GTL) fuel is considered a clean alternative fuel and has been given much attention to replacing conventional fuel. Evaporation behaviour and droplet lifetime are critical aspects that need to be determined as these aspects can affect the fuel spray properties and improve the combustion process. In this study, a set of GTL–diesel fuel blends are prepared, which are G20, G50, G80, and G100 (the number represents the GTL percentage fuel ratio in the fuel blends). Subsequently, using a single droplet drop test on the hot plate (Leidenfrost effect), the GTL fuel blends droplet lifetime and evaporation behaviour are visualised using a high-speed camera connected to long-distance microscopy. An image processing system and a MatLab were used to measure and analyse the droplet evaporation data. Comparing the fuel characterisation of the GTL fuel and conventional diesel fuel, the GTL fuel shows a lower value in all properties tested except for the calorific value, cetane number, and vapour pressure. The qualitative results through the Leidenfrost effect have shown that increasing the GTL fuel ratio (20% to 100%) decreases the heating phase duration (37.3 % to 14.4 %) and evaporation rate (1.29 mm 2/s to 1.10 mm 2/s) while increasing their steady evaporation phase duration and droplet lifetime. The shorter period to achieve steady evaporation is beneficial as the spray inside the chamber has a limited time to evaporate for combustion