## 3 Results and Discussions
### Engine Performance Estimation  
In predicting the turbofan engine's performance running on liquid hydrogen as against kerosene, key indicators such as specific fuel consumption, turbine entry temperature and fuel flow rate are used in the results. Tables 2 and 3 show the engine's gas path characteristics for jet fuel and \(\text{LH}_{2}\), respectively. Table 5 is a performance comparison of both fuels at take-off and cruise conditions, with net thrust retained.  
Compared to jet fuel, \(\text{LH}_{2}\) combustion has a lower mass flow rate, due to the higher LHV of the fuel, to achieve the same net thrust. This also reflects an increase in the enthalpy drop and changes in the gas composition through the turbine. The LHV influences the gas speed in the expander, hence, the impact on the compressor's pressure ratio. The result shows a 64% decrease in the flow rate, which could also affect the thrust due to reduced exhaust mass flow rate, as described by [PERSON] and [PERSON] [8]. However, the reduction in thrust is partly offset by changes in the specific heat constant \(\text{C}_{\text{p}}\), which shows a slight increase due to the combustion product of \(\text{LH}_{2}\). The slight decrease in TET would imply favorable cooling options for the turbine hot section, and reduces NOx formation [5; 25]. The result also shows a decrease in the specific fuel consumption, due to a decrease in the fuel flow rate of \(\text{LH}_{2}\). The resulting discussion comparing hydrogen with jet fuel is consistent with a similar assessment done for the EU CRYOPLANE project, in collaboration with Cranfield University and Universidad Politecnica, Madrid [15], although their work also considered the effect of the fuel temperature of the cycle performance, which shows that fuel temperature above the liquefaction temperature will raise the TET by 2 \({}^{\circ}\)C to 3 \({}^{\circ}\)C to achieve the same thrust, hence it is important to vaporize the hydrogen fuel efficiently.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Description**} & \multicolumn{2}{c}{**Hydrogen (\(\text{LH}_{2}\))**} & \multicolumn{2}{c}{**Jet-A (Kerosene)**} \\ \cline{2-5}  & **Take-Off** & **Cruise** & **Take-Off** & **Cruise** \\ \hline Net thrust (kN) & 123 & 89.54 & 123 & 89.54 \\ Mass flow (kg/s) & 385 & 269 & 385 & 269 \\ Altitude (m) & 0 & 10,000 & 0 & 10,000 \\ Fuel flow rate (kg/s) & 0.58 & 0.45 & 1.61 & 1.27 \\ Specific fuel consumption (kg/kNs) & 17.1 & 19.23 & 46.96 & 51.1 \\ Turbine entry temperature (\({}^{\circ}\)C) & 1119 & 891 & 1125 & 900 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Turbofan performance comparison of \(\text{LH}_{2}\) and jet fuel.  
The most important change contributing to the variation of performance for LH\({}_{2}\) compared to jet fuel is the specific heat capacity. Despite LH\({}_{2}\) having a low fuel rate, its low density could still pose a potential drag that reduces flight efficiency. The CRYOPLANE study results suggest that fuel tank drag could lead to between 9% to 14% more energy for the LH\({}_{2}\) subsonic application than jet fuel [15; 38]. Although this is not discussed extensively in this study, one area of consideration if the turbo component of an existing conventional aero engine is used for this assessment will be the matching of the turbo set and the combustor and control system modification to accommodate fuel changes. Lower NOx can be achieved with a micromix LH\({}_{2}\) combustor, compared to using a conventional combustor.