## 3 Research Results and Discussion
### Combustion Indicators
The ROHR and rise in temperature trends were similar. The maximum rise in temperature value was reached using conventional diesel (EGR Off \(\sim\)57\({}^{\circ}\) K/CAD, EGR On \(\sim\)47\({}^{\circ}\) K/CAD (decreased by \(\sim\)18%) at 9 CAD ATDC) (Figure 3). The maximum temperature rises of the D70F30 fuel mixture declined by \(\sim\)9% with EGR off and \(\sim\)12% with EGR on, in D50F50 by \(\sim\)15% and \(\sim\)14%, respectively, in D30F70 by \(\sim\)21% and \(\sim\)17%, respectively, and in F100 by \(\sim\)28% and \(\sim\)20%, respectively. It was observed that when increasing the chicken fat concentration in fuel, the rise in temperature decreases in the premix phase and increases in the diffusion phase, which confirms the fact that combustion starts at a later stage and lasts longer. Figure 2: The in-cylinder rate of heat release depending on fuel composition with (a) exhaust gas recirculation (EGR) off and (b) EGR on. The in-cylinder temperature graph (Figure 4) also confirms the fact that increasing the chicken fat concentration led to a longer combustion process. It was observed that, having increased the chicken fat concentration in the fuel to 100%, the in-cylinder temperature increased during the diffusion combustion phase from 1420 K to 1438 K with EGR off and from 1367 K to 1384 K with EGR on. This improved soot combustion, but more energy was evolved with exhaust gas. Gas of a higher temperature stayed in the cylinder, increasing the turbocharger pressure; therefore, the temperature at the end of the compression stroke was higher. This improved the ignition of the fuels that contained chicken fat additive. The highest pressure rise in the premix combustion phase was achieved using pure diesel (\(\sim\)0.12 MPa/CAD with EGR off and \(\sim\)0.08 MPa/CAD with EGR on) (Figure 5). For D7/0F30, the pressure rise in the premix phase decreased \(\sim\)17% with EGR off and \(\sim\)27% with EGR on, declining \(\sim\)30% and \(\sim\)35% for D50F50, \(\sim\)46% and \(\sim\)43% for D30F70 and \(\sim\)62% and \(\sim\)60% for F100, respectively. With EGR off and on, the maximum temperature rise was achieved at 8 CAD ATDC for all fuel mixtures. When increasing the chicken fat concentration in the fuels, the pressure rise declined in the premix phase and moving to the diffusion phase, which reduced the load on the engine parts and the evolved noise. Figure 4: In-cylinder temperature, depending on fuel composition with (**a**) EGR off and (**b**) EGR on. Figure 3: The in-cylinder rise in temperature, depending on fuel composition when (**a**) EGR is off and (**b**) EGR is on. When EGR was off and the engine ran on conventional diesel, the maximum combustion pressure in the cylinder was \(\sim\)6.14 MPa and, when EGR was on, it was \(\sim\)5.5 MPa (\(\sim\)10% lower) (Figure 6). When using pure chicken fat and its mixtures with diesel, the maximum combustion pressure declined to \(\sim\)6.0 MPa and \(\sim\)5.4 MPa, respectively, even though the pressure of the end of compression increased. It was observed that when using diesel and its mixtures with chicken fat, the maximum combustion pressure was reached at \(\sim\)11 CAD ATDC, and when using chicken fat, it was reached 2 CAD earlier. This was due to a later heat release, where the piston came down and the pressure did not rise. The exhaust flue temperature (Figure 7) and turbocharger pressure (Figure 8) measured during the experimental research confirmed the results of the numerical analysis of the combustion process. The exhaust temperature was observed to have a tendency to increase (1-2%) both with EGR off and EGR on for all engine loads (BMEP = 0.3 MPa, 0.4 MPa and 0.6 MPa) when increasing the chicken fat concentration in the fuel from 50% to 100%. The flue gas temperature graph correlates with \(\sim\)1% turbocharger pressure. A higher exhaust energy volume was due to a later combustion of the chicken fat. Figure 5: Pressure rise in-cylinder depending on the fuel composition with (**a**) EGR off and (**b**) EGR on.