## 3 Results  
### Flame Structure  
Temperature profiles of the Jet A-1 and surrogate flames for three different equivalence ratios are shown in Figure 1. The temperature maximum is reached between 3.5 and 4 mm HAB and shows values between 1650 and 1750 K. After the maximum, the measured temperatures decrease slightly due to heat losses by radiation and mixing with the sheath flow. The measured temperature profiles are very similar for all flames studied, with a slight dependency on the equivalence ratio. No significant differences are found between the Jet A-1 and the surrogate. The same is observed for the profiles of the water concentration (Figure 2), which also show very similar courses for kerosene and surrogate. The maximum water concentrations are found at about 3-4.5 mm above the burner and are 12-15 vol.-%. The maximum acetylene concentrations (Figure 3) are further upstream a HAB about 4-4.5 mm and reach 1.5-1.8 vol.-%. It can be concluded that no significant differences in the flame structure and the first soot precursor are found between the Jet A-1 and surrogate flames. Figure 1: Temperature profiles measured with TDLAS at 6 cm/s inlet velocity for kerosene Jet A-1 and the surrogate. In contrast to the previous findings, the measurements of the soot volume fractions show a different trend. Figure 4 shows the profiles of the soot volume fraction. Soot is detectable from 2 mm HAB and a clear dependency on the equivalence ratio is evident, with significantly higher volume fractions for the fuel-richer blends. In addition, there are also significant differences between the Jet A-1 and the surrogate. The maximum soot concentrations in the surrogate flames can be about twice as high as the concentrations found in the kerosene flames. For all investigated flames, the volume fraction increases steadily for increasing HAB. Figure 3: Profiles of acetylene concentration measured with TDLAS at 6 cm/s inlet velocity. Figure 2: Profiles of water concentration measured with TDLAS at 6 cm/s inlet velocity. For \(\Phi\) = 2.1 and an inlet velocity of 5 cm/s, the concentration profiles of some main species and higher hydrocarbons were measured by GC in the kerosene and surrogate flames. The results are shown in Figure 5. The first part of the graph shows the profiles for hydrogen, carbon dioxide, carbon monoxide and water. As expected for fuel-rich flames, the concentrations of hydrogen and carbon monoxide are high with a maximum of just under 15 vol.-% CO. The Jet A-1 and surrogate profiles are again very similar. This was also to be expected due to the similar C/H ratio and chain length of both fuels. In the second part of Figure 5, the concentration profiles of the soot precursors benzene, toluene and naphthalene are plotted. The profiles of toluene concentrations in the Jet A-1 and surrogate flames are again very similar. More pronounced differences are seen for the other two species. In the kerosene flames, over 600 ppm naphthalene can already be measured directly at the burner inlet. This is in accordance with the composition of the kerosene used in this work. The kerosene composition analysis results shown in Table 2 give a naphthalene content in the fuel of 1.5 vol.-%, which in the mixture studied here at \(\Phi\) = 2.1 means about 500 ppm in the mixture. The naphthalene concentrations of the surrogate flames are an order of magnitude smaller. The trend of the benzene concentrations is similar for both fuels, the maximum being between 3.5 and 4 mm in each case and is rapidly consumed thereafter. However, the concentrations are consistently higher in the kerosene flames and the differences are over 200 ppm at the maximum. The lowest part of Figure 5 shows the concentrations of methane, ethylene and acetylene. The concentrations of all three species increase constantly up to a height of 3.5 mm. From this height, concentrations of methane and ethylene drop and both species are fully consumed at a height of 5 mm. At this height, the acetylene concentration also reaches its maximum, and then drops slightly.