## 4 Conclusions  
The following conclusions were made, having conducted the experimental research of a compression ignition engine running on pure conventional diesel (D100) fuel and pure chicken fat (F100), as well as mixtures of these fuels (D70F30, D50F50 and D30F70) at various engine loads with EGR on and off, as well as numerical analysis of the combustion process:  
1. When using fuel which contains chicken fat, the fuel was heated to ~50 \({}^{\circ}\)C in order to reduce the high viscosity and fuel filter plugging. The comparison of the F100 and D100 fuels revealed that the chicken fat lubricity properties were no worse, the  
Figure 17: Dependence of hydrocarbon (HC) emissions on fuel composition and the engine load. Figure 18: Dependence of nitrogen oxide (NO\({}_{\text{x}}\)) emissions on fuel composition and the engine load. density was -7.4% higher, the LHV was ~11.5% lower and the C/H ratio was ~2.7% higher, while oxygen accounted for ~ 11% of the chicken fat mass;
2. When increasing the concentration of the chicken fat in the fuel mixtures, the intensity of the fuel injection, evaporation and combustion changed due to the changed fuel properties. Having replaced the D100 with F100 fuel, the start of ignition timing was determined to change slightly, but the maximum ROHR decreased by ~27% in the premixed combustion phase when EGR was on and by ~22% when EGR was off, and combustion in the diffusion phase was more intense. The turbocharger boost pressure, which depends on the kinetic energy of the exhaust gas, increases, which in turn increases the volumetric efficiency of the engine. The specific fuel mass consumption (BSFC_m) of the F100 fuel increased by ~16% when EGR was off and by ~18% when EGR was on, due to a lower chicken fat LHV and a lower combustion thermal efficiency. It was found that, with the engine running at different loads when EGR was off, an increase of the chicken fat concentration to 30% left the engine's BTE unchanged, but increasing the fat concentration to 100% decreased the efficiency by 2.8-2.9% due to a longer combustion process. When EGR was on, the combustion process was even longer, and the engine's BTE decreased by 3.5-5.1% when using F100 duel, compared with D100, when EGR was off;
3. An increase in the engine's CO2 emissions when increasing the concentration of the chicken fat was due to a higher C/H ratio of the F100 fuel, increasing fuel consumption and the specifics of combustion of the chicken fat containing O2. However, the fact that the F100 fuel is a renewable fuel allows for stating that the CO2 emissions of this fuel during the life cycle are much lower compared with D100;
4. When increasing the chicken fat concentration, CO emissions also increased as the C/H ratio increased and larger droplets of higher fuel density burned harder. EGR further increased CO emissions as the combustion temperature and the amount of oxygen involved in oxidation decreased. HC emissions decreased slightly when increasing the chicken fat concentration to 50%, but when the fat concentration increased to 100%, the HC emissions increased due to worse combustion;
5. Although a higher C/H ratio in the F100 fuel and the increasing fuel consumption when increasing the chicken fat concentration should theoretically increase the amount of smoke, the smoke decreased by 57-70% when EGR was off. This was due to a slower combustion in the premixed combustion phase, more intense combustion in the diffusion phase and the oxygen contained in the fuel;
6. Decreasing the chicken fat ROHR in the premix combustion phase resulted in a lower NOx formation intensity. When EGR was off, the 100% chicken fat fuel reduced NOx emissions at various loads by 13-22%, and when EGR was on, the combined effects of EGR and the chicken fat reached 48-52%. Conceptualization, A.R. and J.M. ; methodology, A.R., T.V. and D.K. ; software, A.R. and S.S.; formal analysis, A.R. and J.M. ; validation, A.R. and S.S.; writing--original draft preparation, T.V., A.R. and S.S.; writing--review and editing, J.M. and A.R.