Numerical Investigation of Ignition Performance of a Lean Burn Combustor at Sub-Atmospheric Conditions

Stringent environmental requirements are pushing the current development of aero gas turbine combustors towards lean combustion concepts with relatively small combustor volume. This approach has a detrimental effect on the high altitude relight capability of an aeronautical engine. But the ability to light up at a specific altitude is one of the certification requirements that an engine has to fulfil. To ensure the relight capability, extensive testing for new combustor developments is needed. These test set-ups are expensive as they have to be conducted at sub-atmospheric conditions. Thus, the use of a simple tool to evaluate the ignition tendency of a combustor at an early development stage is advantageous. The code SPINTHIR, developed by Cambridge University, is capable of calculating the ignition performance in turbulent spray flames in a simplified approach. It has been previously validated for different types of flames and applications. In order to adjust the code for lean burn combustors, a new function for a better resemblance of the turbulent spray dispersion has been introduced and the high sensitivity towards cell sizes has been balanced by modifying the ignition criteria. Finally, the results of the code have been compared in this work with recently obtained ignition test performed by Rolls-Royce. Thereby, the influence of varying combustor geometries on the lean ignition limit has been tested. In comparison with these tests, the code’s results show very good matches which verify the conducted changes and give further credence to the model.