Experimental and Computational Analysis of an Additive Manufactured Vaporization Injector for a Micro-Gas Turbine

Abstract

Vaporization injectors have been in existence for decades and are a well-proven method of preparing liquid fuels for combustion by heating them above the boiling point of their heaviest hydrocarbon ingredient. By doing so, it converts the fuels into a vapour prior to combustion. When attempting to apply this method of fuel vaporization to micro gas turbines, manufacturing difficulties arise, due to the small complex passages that are required to direct the fuel closer to the high-temperature zone in the combustion chamber and then back to a favourable injection location. This is where the use of additive manufacturing (AM) can prove advantageous due to the complex designs that can be achieved at much smaller scales and potentially at cheaper costs when compared to traditional subtractive manufacturing. The motivation behind the research is to improve the overall efficiency of micro-gas turbines, so they can be applied as range extenders in electric vehicles. Due to the increasing adoption of vehicle electrification. This paper covers the comparison of experimental results for two traditionally manufactured injectors and a third selective laser melted injector (SLM), which were tested in a swirl stabilised micro gas turbine can type combustor on the University of Baths gas stand. The operating range of the tests was 1–4 Bar and 30 to 630 °C inlet air. To the authors knowledge, this is the first such comparison to be made for a gas turbine in open literature, despite wide reports of AM being used in large gas turbines. From the tests, it was found that the 3 and 8 hole machined injectors could not produce stable combustion at the desired operating condition of 4 Bar and 630 °C. The SLM 8 hole injector, however, was able to sustain a stable and constant burn at this design point with low NOx, CO and THC emissions. It was also noticed that the flame colour changed from a yellow flame when testing the first two injectors, to a blue flame when testing the SLM injector suggesting more complete combustion was being achieved due to the lack of soot in burned products, this was assumed to be due to the fuel reaching its saturation conditions within the injector. A number of measurements were taken at various points around the combustor, which included temperatures, pressures and emissions readings. These results were then used to create and validate a non-premixed steady diffusion flamelet model in ANSYS Fluent for the AM injector case. The CFD results were found to overpredict the temperature by approximately 10% when compared to the thermocouple values. This was found to be similar to other studies with similar experimental and computational setups, so it was deemed acceptable. From the validated CFD model, the heat flux at the front surface of the injector was extracted, to be used in a simple heat balance model. Based on a conservative estimate of fuel temperature, the model found that the SLM injectors should have created very near saturation conditions in the nozzle. As this was a conservative analysis, it confirms the experimental findings that partially vaporized fuel was exciting the injector. The model also showed that the fuel in the traditionally machined, 8 hole injector would most likely exit as a liquid.

Design, simulation, and validation of additively manufactured high-temperature combustion chambers for micro gas turbines

“…On the smaller side, the Ariel Motor Company is developing the P40, an electric and micro gas turbine hybrid HIPERCAR, using a gas turbine being developed by Delta Motorsports. The initial research for its combustion chamber was conducted in the University of Bath's Institute of Advanced Automotive Propulsion Systems (IAAPS) [8].…”

Improving efficiency of micro gas turbine systems by integration of combustor and recuperator using additive manufacturing techniques

“…The results showed a fidelity problem in manufacturing when getting down to the injection surface near 0.2 mm 2 but integrating the parts and manufacturing of the burner was successful. Adamou et al [95] compared an AM injector with two other injectors manufactured using the CNC machining method. The objective was to optimise the injector design to achieve better vaporisation of fuel before injection into the CAN-type combustor of the MGT.…”

Experimental performance and emissions of additively manufactured high-temperature combustion chambers for micro-gas turbines

“…11,12 In the automotive industry the use of MGTs is not common for commercial vehicles but examples of them can be found in specialty vehicles such as the P40 hipercar developed by the Arial Motor Company which is an electric and MGT hybrid vehicle. The MGT was developed by Delta Motorsport and some initial research conducted on its combustion chamber and the use of additive manufacturing for improving the vaporization injector can be found in Adamou et al 13 Another specialty application is heavy armoured vehicles, such as the US made M1 Abrams which features a Honeywell AGT1500 gas turbine engine, 14 and the Russian made T80 which is powered by a SG-1000 gas turbine. 15 A more promising application for MGTs in the automotive industry is their use in medium-duty vehicles, such as delivery vans, buses and disposal trucks.…”