## 3 Results  
### No\({}_{x}\) Reduction Potential  
While the concepts with conventional combustion chambers show no advancements in NO\({}_{x}\) and soot emissions, the advanced combustion technology shows significant reduction. At global fleet level, the NOx emissions could be reduced by 91% for the kerosene case and by 99.8% for the hydrogen concept compared with the reference D261. This strong reduction is mostly due to three features. Firstly, the combustion is operated at very lean conditions with the help of a wider stable operating range of the FLOX-based combustion technology compared to conventional swirl-stabilized combustion. Secondly, the authors assume that fully prevaporized fuel injection can be handled at an entry into service of 2040. Therefore, near stochiometric conditions around spray droplets are not present in the combustion, which helps to decrease the NOx emissions. Thirdly, due to the high momentum jets, the FLOX-based combustion achieves more homogeneous temperature profiles, reducing high temperature peaks and strong NOx sources, respectively. Assumptions on the combustion's lean blow off (LBO) limits at different input fuels were derived from atmospheric combustion experiments. Measurements of different FLOX-based combustors utilizing various gaseous fuels have shown that the global air-fuel equivalence ratio \(\lambda\) at LBO is \(\lambda_{LBO}\geq 2.8\) for relevant air preheat temperatures [9; 19; 60]. Therefore, the \(\lambda_{LBO}\) was chosen at 2.6 using prevaporized Jet A-1. Using pure hydrogen, the stable operating range is much wider. Recent unpublished experiments of a FLOX-based combustor using pure hydrogen have shown that the air-fuel equivalence ratio at LBO is \(>\)5. In this study, the \(\lambda_{LBO}\) was conservatively chosen to 3.6 using pure hydrogen. The air split S\({}_{\text{D}}\) is a free parameter in the reactor network. In order to select an optimized air split for the Jet A-1 and the hydrogen fuel case, characteristic turbo fan load points were chosen for a trade-off study. As described in Section 2.2.2 the combustion chamber inlet conditions were taken from the turbo fan performance simulations (see Section 2.3). For the trade-off study, five characteristic load points were chosen from the fuel specific performance decks: take-off, end of field, second segment, top of climb, and mid cruise. For these load points NOx emissions were traded off against combustion stability. As a marker for combustion stability, the calculated CO emissions were used. As a result of this trade-off study, the air split S\({}_{\text{d}}\) was fixed for the detailed emission study. On the basis of this study, the air split at hydrogen fuelled combustion was set to 87% and to 65% for Jet A-1 furled combustion. In the detailed emission calculations, 86 load points along the mission flight trajectory were selected from each fuel specific engine performance map (hydrogen and Jet A-1). The reactor network simulations were carried out for these load points at a fixed air split. For each of these load points, the emissions (NO\({}_{x}\), CO, H\({}_{2}\)O, and CO\({}_{2}\)) were simulated for both hydrogen and Jet A-1. The results were provided as a combustion emission map to the climate impact analysis. With the reactor network, the effect of air-fuel equivalence ratio in the combustor \(\lambda_{\text{c}}\) on the total NOx formation was investigated for the two fuel scenarios. Figure 7 shows an increase in the NOx emission indices EI with decreasing \(\lambda_{\text{c}}\) for both fuel options for a constant flight Mach number of 0.8. This trend is related to the formation of thermal NO, which is pronounced by increasing adiabatic flame temperatures with the decrease in \(\lambda_{\rm c}\). For identical \(\lambda_{\rm c}\), the adiabatic flame temperature of hydrogen flames is higher than the ones for Jet A-1. Nevertheless, due to the reactivity of hydrogen, hydrogen combustion allows a stable combustion at leaner mixing conditions compared to Jet A-1.