## 2 Aviation Fuel Emissions
### Comprehensive Comparison of Emissions Performance between SAFs and Conventional Aviation Fuels
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ref.** & **Fuel** & **Method/Burning Platform** & **UHC Emissions** \\ \hline [PERSON] et al. (2022) [68] & 18 different ratios of HEFA and Jet & GTCR95 aircraft APU & With the increase in HEFA proportion, there is no clear trend of change; the UHC emissions of HEFA-blended fuel slightly decrease. \\  & A-1 blend fuels & & HEFA-blended fuel slightly decrease. \\ \hline [PERSON] et al. (2023) [148] & RP-3 & ZFR50 jet engine & The impact of HCFI doping on the EI-UHC of RP-3 shows no clear trend. \\  & 5\% and 10\% HCFI blend fuels & & RP-3 shows no clear trend. \\ \hline [PERSON] et al. (2014) [149] & Jet-A & & GTL fuel \textgreater{}1-A \textgreater{} 30\% JME blend fuel \\  & 30\% JME blend fuel & & (50,000–60,000 rpm). \\ \hline [PERSON] et al. (2019) [77] & Jet A-1 & & EI-UHC decreases with the increase of Camelina or \\  & Biofuel (Camelina) & High enthalpy rig with combustor & the decrease of Jatroph in the fuel mixture. \\  & & & \\ \hline [PERSON] et al. (2017) [150] & Jet A-1 & & 50\% CTME blend fuel and 50\% CRME blend fuel & \\  & 50\% CRME blend fuel & Olympus E-start HP turbojet engine & 50\% CTME blend fuel and 50\% CRME blend fuel \\  & 50\% CRME blend fuel & & respectively reduced EI-UHC by 36.5\% and 30.8\%. \\ \hline [PERSON] et al. (2011) [151] & Diesel & & \\  & 15\% Jatropha biodiesel & IS/60 Rovers gas turbine & Diesel \textgreater{} 15\% Jatropha biodiesel \\  & 25\% Jatropha biodiesel & & \textgreater{} 25\% Jatropha biodiesel \\ \hline GE [152] & Conventional aviation fuel & & GE engine & The emissions of UHC increase by 20–45\%. \\  & Bio-SPK & & \\ \hline Rolls Royce [152] & JP-8 & & \\  & FT fuel & Annular rig & Not much difference. \\ \hline Pratt and Whitney [152] & Jet A-1 & & \\  & Neste oil & a Pratt and Whitney Canada small & \\  & 50\% Neste oil blend fuel & turbdan engine & Not much difference. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Information regarding the investigated SAF and fuels and for burning platforms and changes for UHC emissions in literature. tests control power output, maintaining similar combustion temperatures. Hence, the difference in NO\({}_{\rm x}\) emissions between SAFs and traditional aviation fuels is minimal. Similarly, under identical conditions, SAFs and traditional aviation fuels exhibit minor differences in CO emissions, with variations in EI-CO among different fuels possibly stemming from viscosity, carbon content, SMD, and final boiling point. EI-UHC is influenced by both engine operating conditions and fuel properties. When the composition and properties of SAFs are similar to conventional aviation fuels, the difference in EI-UHC is minimal. SAFs with lower aromatic hydrocarbon content, and lower distillation points are advantageous for reducing UHC emissions. However, if some properties of the SAFs, such as viscosity, density, residence time, etc., do not align with the design of the engine's atomization and combustion systems, then incomplete fuel combustion result, with a concomitant tendency for increased UHC emissions.