Master of Engineering Science
Mechanical and Materials Engineering
Fuel injection processes can contribute to combustion instability in highly energetic combustion systems. In gas turbine engine afterburners, jet-in-crossflow (JIX) injection is used. Part one of the thesis study investigates the interaction between spray droplets and turbulent flow properties of a JIX. Jet-in-counterflow (JIC) configuration was also investigated. Part two of the investigation examined the behaviour of JIX droplets around a bluff body. Droplet size and flow turbulence was characterized simultaneously using particle image velocimetry and image processing techniques. Turbulence and droplet size were correlated, particularly at momentum flux ratios ≥ 60. High speed imaging was used to identify droplet breakup mechanisms and size distribution around the bluff body. Overall, the current techniques allow for a reasonable simultaneous investigation of the coupled behaviour between JIX droplets and turbulence, and further development of the technique may have a significant impact on improved understanding of the mechanisms of JIX.
Summary for Lay Audience
In highly energetic combustion systems, such as the afterburner of a fighter jet engine, many fluid dynamic processes interact in complex ways. Proper fuel injection control is particularly important in regulating the heat in the engine and fuel flow rates may need to be adjusted depending on many flight conditions such as altitude or aircraft speed. The fuel injectors in an afterburner are very simple device which are similar to an oscillating sprinkler, except the injectors do not oscillate and the wind blows on the fuel jets at 900km/h and 1000°C. This spray injection process determines how well the afterburner is functioning. The chaotic nature of the gas and fuel mixture created by these injections is not well understood on a detailed level. Most measures of injection spray identify only the overall shape of the spray and the sizes of the droplets. To better understand this fuel injection process, this thesis investigates the movement of fluid between the spray droplets and attempts to correlated the flow behaviour with the droplet sizes in order to gain a better understanding of how the spray is mixed and distributed in an afterburner. This injection process is termed jet-in-crossflow (JIX) and it is found in many other applications such as irrigation, agricultural sprays, and numerous different combustion systems not limited to aircraft afterburners. Ultimately, a more detailed understanding of how JIX creates and distributes droplets may lead to improved control over fuel injection, therefore reducing fuel consumption. In addition, as the fight against climate change continues systems that rely on fossil fuel for combustion will need to switch to alternative fuels which need to be certified for use. Different fuels have different behaviours so understanding the fuel injection process is crucial in predicting and testing how a new fuel will behave in an existing combustion system.
Mahaffy, Matthew D., "Characterization for Spray Droplet Behaviour in Afterburner-like Flow Conditions" (2020). Electronic Thesis and Dissertation Repository. 8535.