Sustainable and energy efficient aviation relies strongly on the substitution of fossil energy sources via renewable energies. Due to the very high power and energy density requirements of aircraft, combustion-based propulsion systems based on liquid energy carriers plays an indispensable role. The application of e-fuels fulfils both requirements for high energy density fuel and carbon-neutral aviation. Additionally, the non-CO2 emissions have to be reduced. For that, the research vision of the very clean lean prevaporized premixed (LPP) combustion concept is seen, being not applicable for current fuels like kerosene. Within ICA-C3.3 therefore other fuels are searched for, which will allow the premixing of the fuel and the compressed heated combustion air without the danger of self-ignition or flashback.
The research to find such alternative sustainable aviation fuels has been started within the first research period with an atmospheric test rig for flashback studies at ITV and on the rapid compression machine and shock tube at PTB for pure fuels with focus on the class of low-chained alcohols and furans. Based on the experimental and numerical investigation the propanol and butanol isomers have been identified from the alcohols as so far most fitting LPP-fuels, if single component fuels are regarded.
Progressing into the second funding period, PTB Braunschweig is focussing on exploring realistic boundary conditions of aviation engines during cruise flights and investigating ignition properties of blended sustainable e-fuels, considering both liquid-liquid and liquid-gaseous fuel mixtures according to the results from 1st funding phase. Adding to this, the development of chemical kinetics mechanisms, enriched with machine learning applications, along with robust modelling and simulations, will further augment the research scope, particularly under varied operating conditions and using different fuel blends.
The experimental investigation of the flame behaviour is being carried out at the ITV Hannover. The primary objective is the evaluation of the selected e-fuels and fuel blends with regard to their tendency to flashback. Firstly, the well-established multi-fuel burner will be rebuilt, including the installation of a new heater and additional insulation to investigate the processes of prevaporization, premixing, pre-ignition and flashback at elevated temperatures. Furthermore, the multi-fuel burner will be modified to study e-fuel blends consisting of liquid-liquid as well as mixtures of liquid and gaseous fuels. Also a new testing facility is under construction to consider the elevated pressures within the engine. This will be used to carry out tests at high temperatures and pressures of up to 850 K and 9 bar at the combustor inlet, replicating cruise flight scenarios.
The properties of these fuels are pivotal for various design aspects, including determining combustion air amounts, compressor layouts, tank system infrastructure, and overall aerodynamic and aircraft design (referenced as ICA B, ICA-B5, and A4). Additionally, the fuel mixtures are instrumental in gauging the economic and environmental implications of such innovations, contributing to the 2050 sustainable aviation visions outlined in ICA-A1.