Concetual design of ultra-efficient cores for mid-century aircraft turbine engines

Paper in proceeding, 2019

For today’s best turbofans propulsive efficiencies are now higher than 80% whereas thermal efficiencies only reach values around 50%. The introduction of the geared engine architecture gives some hope for continued improvement in propulsive efficiency. On the other hand, for the thermal efficiency the progress pace is fairly modest despite the much larger room for improvement. Further rapid progress is primarily challenged by small turbomachinery size and efficiency, high pressure compressor exit and turbine entry temperatures and losses associated with cooling. Fundamental thermodynamics also make progress more difficult than it used to be, e.g. for the ideal Brayton cycle an increase in overall pressure ratio from 50 to 70 will only yield a 3% unit improvement.

In 2015, the EU launched a research project, the ULTIMATE project, investigating new core engine architectures. In particular, it was argued that cycle synergy could be a way forward and that the combination of several radical concepts could potentially lead to ultra-efficient cores with less technical challenges than power plants involving single radical concepts. After an initial extensive screening and down-selection, the project developed the most promising propulsion systems to TRL 2. To evaluate the environmental improvement potential the new radical propulsion systems were integrated onto advanced tube-and-wing aircraft and evaluated against the EU SRIA 2050 targets. The paper reviews key findings from the research activities, describing design choices and the architectural evolutions that the different concepts underwent. As a first, the paper also collects the top-level achievements on CO2 emissions to draw conclusions on radical core engine cycle selection.

The most notable observation on core engine down-selection is that all concepts integrating pressure rise combustion achieved very large improvements, in particular when synergies with intercooling were explored. Large cuts in CO2 emissions were retained even when compared to year 2050 reference technology.