## 2 Experimental Setup  
### Premixed Kerosene Flat Flame  
A flat flame burner (McKenna burner) was used to produce laminar one-dimensional flames. This burner stabilizes a flame over a tempered porous plate. The plate of the burner is made of sintered bronze particles and has a diameter of 60 mm. Integrated into the plate is a copper tube coil through which thermal oil was passed to temper the plate to a predetermined temperature. Around the burner plate, there is another annular sintering plate through which inert gas (always nitrogen in this work) flows to shield the flame from the ambient air, thus avoiding reactions and hence changes in the soot and temperature field at the edge of the flame. Flames stabilized on this burner are quasi-one-dimensional near the burner plate, so that quantities such as temperature and soot volume fraction depend only on the distance from the burner plate. In a first step, the liquid fuel (kerosene or surrogate) was vaporized in a carrier gas vaporizer (Bronkhorst CEM). This was necessary because the vaporization temperature of kerosene is up to 300 \({}^{\circ}\)C, but thermal decomposition can occur at lower temperatures. For example, initial reactions with the atmospheric oxygen dissolved in the fuel can start at 150 \({}^{\circ}\)C [11]. Furthermore, the auto-ignition temperature of kerosene is 220 \({}^{\circ}\)C and this temperature should not be exceeded in this premixed system. Mixing with a carrier gas lowered the partial pressure of the kerosene and thus the temperature required for complete evaporation, so that the vaporizer could be operated at 150 \({}^{\circ}\)C.  
Kerosene was filled in a piston accumulator and the piston was pressurized to about 5 bar using nitrogen. The kerosene was fed through a coriolis mass flow meter (Bronkhorst High-Tec) into the evaporator, where it was mixed with argon and evaporated. From there, the mixture was transported to the burner via heated lines. Near the burner, oxygen was mixed into the stream. Thermal oil with a temperature of 150 \({}^{\circ}\)C was pumped through the burner plate. In addition, the burner as well as the supply line of the oil was heated with electric heating cords and the entire structure was insulated in order to minimize heat losses and to ensure a homogeneous temperature distribution across the burner. To monitor the boundary conditions, the temperature of the thermal oil was measured immediately before it entered the burner. The temperature of the incoming kerosene mixture was measured by a thermocouple positioned in the plenum of the burner. Four different flames were investigated for each fuel. For the first three cases, the cold gas exit velocity (v) was kept constant at v = 6 cm/s and the equivalence ratio (\(\Phi\)) was varied between 2.1 and 2.3. For the fourth case, the equivalence ratio was set to \(\Phi\) = 2.1 and the cold gas outlet velocity was reduced to v = 5 cm/s. In all cases, the volumetric oxygen to argon ratio was set at 21/79. An overview of all investigated operating points can be found in Table 1. All operating points were investigated using TDLAS and laser extinction but only the last point was investigated in greater detail using the GC system. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\Phi\) & **C/O** & **v (cm/s)** & **Jet A-1 (g/h)** & **O\({}_{2}\) (slpm)** & **Ar (slpm)** \\ \hline
2.1 & 0.7 & 6 & 76.29 & 1.45 & 5.47 \\
2.2 & 0.73 & 6 & 79.81 & 1.45 & 5.46 \\
2.3 & 0.77 & 6 & 83.32 & 1.45 & 5.45 \\
2.1 & 0.7 & 5 & 64.93 & 1.21 & 4.56 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Overview of the investigated operating points. The fuel in this study was either a typical jet fuel kerosene (Jet A-1) or a surrogate mixture. Important properties of the kerosene fuel were measured by an external lab and are reported in Table 2. The surrogate mixture comprised of 80 m% n-decane and 20 m% 1,2,4 trimethylbenzene. This surrogate mixture has already been studied by several groups (e.g., [12; 13; 14; 15]).