## 5 Conclusions  
The measurements confirmed that due to the small differences in calorific value between Jet A-1 aviation kerosene and FAME biofuel, individual concentrations of the mixture affect the measured parameters of the SJE-20 experimental engine only to a small extent.  
Small differences in some measured parameters (speed n, fuel flow rate Q\({}_{\rm f}\), engine thrust F\({}_{\rm T.T}\)), depending on the composition of the mixture of Jet A-1 aviation kerosene and FAME biofuel, were influenced by the engine regulation law in the working mode, which ensures the maintenance of a constant speed n\({}_{\rm max.}=\) const.  
The composition of the mixture of Jet A-1 aviation kerosene and FAME biofuel had a significant effect on the course of launching the SJE-20. As the addition of FAME biofuel to Jet A-1 aviation kerosene increased, the time to reach the working mode increased. When reaching 40% concentration of FAME biofuel mixed with Jet A-1 aviation kerosene, the start-up process was unsuccessful with a cold SJE-20 engine. The unsuccessful ignition of the mixture with the given composition was insufficient evaporation of the mixture due to insufficient atomization of the fuel mixture with the fuel nozzle, which was intended for the atomization of Jet A-1 aviation kerosene. The igniters used, which ignited the mixture of fuel and air only by the electrical discharge of the spark plug, were insufficient to ignite a mixture with a different composition than pure Jet A-1 aviation kerosene. Re-starting a heated SJE-20 engine after its previous operation was also successful with a mixture of 60% Jet A-1 aviation kerosene and 40% FAME biofuel. Radiant heat from the heated parts of the SJE-20 was used to evaporate this mixture.  
Also atypical was the delayed start of the SJE-20 engine when using a mixture of 80% Jet A-1 aviation kerosene and 20% FAME biofuel. The most significant deviations were measured when using this mixture.  
Figure 16: The graphical course of SJE-20 thrust F\({}_{\rm T.T}\) [N] changes when using different mixtures of Jet A-1 aviation kerosene and FAME biofuel.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \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** & 448.7 & 444.9 & 451.3 & 451.3 & 444.9 \\
**90\% Jet A-1 + 10\% FAME** & 441.3 & 440.5 & 444.8 & 438.9 & 438.8 \\
**80\% Jet A-1 + 20\% FAME** & 418.7 & 460.9 & 460.8 & 454.7 & 456.4 \\
**70\% Jet A-1 + 30\% FAME** & 456.2 & 448.9 & 448.8 & 448.9 & 442.8 \\
**60\% Jet A-1 + 40\% FAME** & 450.1 & 446.1 & 441.9 & 439.9 & 439.9 \\ \hline \hline \end{tabular}
\end{table}
Table 21: Change in thrust F\({}_{\rm T.T}\) [N] with different concentrations of Jet A-1 aviation kerosene and FAME biofuel.  
From the analysis of the influence of individual mixtures of Jet A-1 aviation kerosene and FAME biofuel on the measured parameters, it can be concluded that these mixtures caused the most significant deviations in the total air temperature behind the compressor t\({}_{2\text{t}}\). Future work in alternative aviation fuels will focus on researching other possible impacts that the blends of FAME biofuel and Jet A-1 aviation kerosene could have on the various aircraft components.  
Conceptualization, M.H. and S.A.-R.; methodology, M.H. and S.A.-R.; software, M.H.; validation, M.H., S.A.-R. and M.K.; formal analysis, S.A.-R. and M.K.; investigation, S.A.-R. and M.K.; resources, M.H.; data curation, M.H.; writing--original draft preparation, M.H., S.A.-R. and M.K.; visualization, S.A.-R.; supervision, M.H. and S.A.-R. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.