## 5 LBV of Key Hydrocarbon Components in Aviation Fuel
### LBV of Iso-Alkanes in Aviation Fuel  
The experimental conditions, testing methods, and publication years of LBV tests for iso-alkanes are summarized in Table 5. For C4 alkanes, [PERSON] et al. highlighted in their study of n-butane and isobutane that with an increase in the number of branches in saturated alkanes of the same carbon number, the LBV gradually decreases [67]. Studies by [PERSON] et al. and [PERSON] et al. on butane also support this observation. Under conditions of 1 atm and 298 K, with an equivalence ratio near 1.1, the LBV\({}_{\text{max}}\) for isobutane is 33.7 cm/s, while that for n-butane reaches 37.1 cm/s [90; 91]. Similarly, [PERSON] et al. obtained an LBV of 37.3 cm/s for n-butane under the same conditions [92], and [PERSON] et al. summarized the LBV for n-butane in the range of 35-40 cm/s [22]. Isobutane does not exist in aviation kerosene, but research on this iso-alkane with the lowest carbon number clearly shows that the LBV of iso-alkanes is lower than that of n-alkanes with the same carbon number. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Iso-Alkanes**} & \multicolumn{2}{c}{**Experimental Conditions**} & \multirow{2}{*}{**LBV Measurement Methods**} & \multirow{2}{*}{**Year**} & \multirow{2}{*}{**Ref.**} \\ \cline{2-2} \cline{5-5}  & **P (atm)** & & & & \\ \hline Isobutane & 1, 2, 5, 10 & 298 & Spherical flame method & 2018 & [91] \\ Isobutane & 1 & 298–398 & Flat flame burner, spherical flame method & 2016 & [90] \\
2,2,4-Trimethylpentane & 1 & 298, 400, 470 & Stagnation flame method & 2010 & [93] \\
2,2,4-Trimethylpentane & 1 & 298, 358, 398 & Heat flux & 2013 & [87] \\
2,2,4-Trimethylpentane & 1 & 353 & Stagnation flame method & 2012 & [94] \\
2-Methylheptane & 1 & 353 & Stagnation flame method & 2012 & [94] \\
3-Methylheptane & 1 & 353 & Stagnation flame method & 2012 & [94] \\
2,5-Dimethylhexane & 1 & 353 & Stagnation flame method & 2012 & [94] \\
2,2,4,6,6-Pentamethyl-heptan & 1, 3 & 473 & Bunsen burner & 2023 & [95] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Summary of LBV test information for different iso-alkanes. Figure 7: Summary of LBV data for n-alkanes at 1 atm and various temperatures. The double-dotted line, solid line, dashed line, and dotted line represent LBV measurements at 353/373 K, around 400 K, around 423 K, and 443 K, respectively. The data were obtained via multiple methods: H = heat flux method, S = spherical flame method, C = counterflow configuration. Data sources: n-C5 [85], n-C6 [86], n-C7 [87], n-C8 [88], n-C9 [89], n-C10 [79], n-C12 [24], n-C14 [18], n-C16 [14]. For C8 alkanes, [PERSON] et al. measured the LBV_max values at approximately 51.8 cm/s, 47.7 cm/s, 47.6 cm/s, 45.4 cm/s, and 45.0 cm/s for n-octane, 2-methylheptane, 3-methylheptane, 2,5-dimethylhexane, and iso-octane (2,2,4-trimethylpentane), respectively, under conditions of 353 K and 1 atm, with an equivalence ratio near 1.04 [94]. Through the analysis of combustion mechanisms, they attributed the decrease in LBV to the generation of non-reactive resonance-stabilized intermediates such as propene, isopropyl, and isobutene. In a study by [PERSON] et al. on the impact of ethanol addition to commercial fuels and iso-octane on LBV, it was found that ethanol content below 15 vol% had no significant effect on the measured fuel LBV [87]. [PERSON] et al. measured the LBV of iso-octane at multiple temperatures, and after extrapolating the values to 353 K [93], they were found to be consistent with the results from [PERSON] et al. and [PERSON] et al. For C12 alkanes, [PERSON] et al. extended the testing results of ATJ fuel to 473 K under 1 atm conditions, revealing an LBV_max of 78.3 cm/s near an equivalence ratio of 1.1 [95]. The ATJ fuel, composed of 90%, is confirmed to be iso-dodecane (2,2,4,6,6-pentamethylheptane). [PERSON] et al. measured the LBV_max of n-dodecane at 79.7 cm/s under conditions of 473 K and 1 atm [24]. Thus, for hydrocarbon fuels with a carbon number of 12, the presence of branching still leads to a decrease in LBV.