## 3 Properties of the Mixture of Jet A-1 Aviation Kerosene and FAME Biofuel
#### 4.1.5 The Course of Changes in SJE-20 Parameters When Using a Mixture of 60% Jet A-1 and 40% FAME
The reliable launch of the SJE-20 was possible with a cold engine at temperatures of the surrounding atmosphere of t\({}_{\rm{H}}\) = 20 \({}^{\circ}\)C only up to 40% of FAME biofuel mixed with Jet A-1 aviation kerosene. At higher concentrations of FAME biofuel in the mixture (45% and 50%), the SJE-20 was successfully started only if the engine was warmed up after the previous operation when radiant heat from heated engine parts was used for faster evaporation of the given fuel mixture. Figure 8: Graphic course of changes in SJE-20 parameters when using a mixture of 60% Jet A-1 aviation kerosene and 40% FAME biofuel at an engine temperature of 70.1 \({}^{\circ}\)C.  
The Influence of Different Concentrations of Jet A-1 Aviation Kerosene and FAME Biofuel on Individual Parameters of SJE-20  
Based on the measured courses of the basic parameters of the SJE-20 experimental engine, it was possible to analyze the specific influence of the composition of Jet A-1 aviation kerosene and FAME biofuel on selected parameters in steady modes as well as in transient modes of engine operation. The next part of this chapter will gradually analyze the influence of the addition of FAME biofuel in the range from 0% to 40% to Jet A-1 aviation kerosene on the total air pressure behind the compressor p2U, the total air temperature behind the compressor t2U, the engine revolutions speed n and the total gas temperature in front of the gas turbine t3U, the total gas temperature behind the gas turbine t4U, fuel mass flow rate Qfuel, and engine thrust F2T. 2.1 The Effect of Different Concentrations of Jet A-1 Aviation Kerosene and FAME Biofuel Mixture on the Total Air Pressure behind the Compressor p2U  
The change in the composition of Jet A-1 aviation kerosene and FAME biofuel in the stable modes of operation of the experimental SJE-20 does not fundamentally affect the value of the total air pressure behind the compressor p2U (see Figure 9 and Table 11). During start-up, there is a time shift (prolongation) in the start-up process. At a concentration of 20% FAME biofuel addition to Jet A-1 aviation kerosene, the start-up process was extended by 5 s due to the delayed ignition of the mixture (Figure 9). \begin{table}
\begin{tabular}{c c c c c c} \hline Fuel Mixture Composition & **20 th Second** & **25 th Second** & **30 th Second** & **35 th Second** & **40 th Second** \\ \hline
**100\%** Jet A-1 + 0\% FAME & 263,645.8 & 261,216.0 & 262,923.1 & 260,976.4 & 260,784.9 \\
**90\% Jet A-1 + 10\% FAME** & 271,898.8 & 268,193.9 & 266,424.3 & 267,459.8 & 265,237.7 \\
**80\% Jet A-1 + 20\% FAME** & 260,738.0 & 273,515.4 & 269,633.5 & 268,204.3 & 269,522.1 \\
**70\% Jet A-1 + 30\% FAME** & 273,594.7 & 263,637.8 & 264,797.7 & 258,757.8 & 259,291.2 \\
**60\% Jet A-1 + 40\% FAME** & 264,152.6 & 262,794.3 & 260,099.0 & 259,086.4 & 258,769.7 \\ \hline \end{tabular}
\end{table} 
Table 11: Change in total air pressure behind compressor p2U [Pa] SJE-20 with different concentrations of Jet A-1 aviation kerosene and FAME biofuel. Figure 9: Graphical course of the change in the total air pressure behind the SJE-20 p2U compressor [Bar] when using different mixtures of Jet A-1 aviation kerosene and FAME biofuel. Due to the fact that the SJE-20 is a single-mode experimental engine which has a control system set to maintain a constant operating speed, the value of the total air pressure behind the compressor will also correspond to this speed since the dependence p\({}_{2t}\) = f(n) applies. 2.2 The Effect of Different Concentrations of Jet A-1 Aviation Kerosene and FAME Biofuel Mixture on the Total Temperature of the Air behind the Compressor t\({}_{2t}\)  
The graphic course of the change in the total temperature of the air behind the compressor t\({}_{2t}\) depending on the change in the composition of the mixtures of aviation kerosene Jet A-1 and FAME biofuel (Figure 10) indicates the tendency of this temperature to increase depending on the time of engine operation in stable modes. This tendency was most pronounced in the case of pure aviation kerosene.