Enabling the potential of hybrid electric propulsion through lean-burn-combustion turbofans

Hybrid-electric propulsion has emerged as a promising technology to mitigate the adverse environmental impact of civil aviation. Boosting conventional gas turbines with electric power improves mission performance and operability. In this work the impact of electrification on pollutant emissions and direct operating cost of geared turbofan configurations is evaluated for an 150-passenger aircraft. A baseline two-and-a-half-shaft geared turbofan, representative of year 2035 entry-into-service technology, is employed. Parallel hybridization is implemented through coupling a battery-powered electric motor to the engine low-speed shaft. A multi-disciplinary design space exploration framework is employed comprising modelling methods for multi-point engine design, aircraft sizing, performance and pollutant emissions, mission and economic analysis. A probabilistic approach is developed considering uncertainties in the evaluation of direct operating cost. Sensitivities to electrical power system technology levels, as well as fuel price and emissions taxation are quantified at different time-frames. The benefits of lean direct injection are explored along short-, medium-, and long-range missions, demonstrating 32% NO<italic>_x</italic> savings compared to traditional rich-burn, quick-mix, lean-burn technologies in short-range operations. The impact of electrification on the enhancement of lean direct injection benefits is investigated. For hybrid-electric powerplants, the take-off-to-cruise turbine entry temperature ratio is 2.5% lower than the baseline, extending the corresponding NO<italic>_x</italic> reductions to the level of 46% in short-range missions. This work sheds light on the environmental and economic potential and limitations of a hybrid-electric propulsion concept towards a greener and sustainable civil aviation.

Optimization of Fuel Nozzle Diameter in a Novel Cross Flow Lean Direct Injection Burner

Lean Direct Injection (LDI) concept proves to be an ultra-low NOx combustion scheme for future gas turbine combustors because of its ability to operate at very lean conditions. For LDI burners, the Fuel Nozzle Diameters (FND) play a vital role in deciding a balance between the various performance criteria demanded by the gas turbine industry like efficient usage of fuel, a wide range of flame stability, uniform exit temperature distribution and very low overall emissions. This paper attempts to find the optimum FND in terms of some key combustion parameters, for a novel multi-swirl LDI burner having a cross-flow mixing between fuel jets and swirling air. At first, lean blow out limits were detected from experiments with different FND using two different fuels, methane and liquefied petroleum gas, within a range of air flow rates. It was observed that with the decrease in FND the flame extinguished at a higher equivalence-ratio. Then their performances were compared through CFD simulations with two different combustion models, namely, Eddy Dissipation and PDF Flamelet. The combined results of cold and hot flow simulations showed that with the decrease in FND the fuel jet was able to penetrate deeper into the air swirl by overcoming the air momentum, which resulted in enhanced mixing leading to more efficient utilization of fuel and also uniform exit temperature distribution resulting in lower pattern factor. Thus the findings of this research work should be resourceful in the development of modern cross-flow LDI combustors.