## 3 Research Results and Discussion
### Energy Indicators  
The analysis of the brake specific fuel mass consumption (BSFC_m) in the experimental research revealed that, when increasing the chicken fat concentration to 100%, the specific fuel mass consumption increased by \(\sim\)16.3% at different loads when EGR was off and by 17-19% when EGR was on (Figure 9). The results of the fuel tests revealed that the lower heating value (LHV) of F100 was \(\sim\)11.5% lower compared with the D100 (Table 2). This means that when increasing the chicken fat concentration in the fuel, the BSFC_m increased not only due to the decreased LHV, but also due to a worse thermal efficiency in the combustion process, which became even worse when EGR was on. Figure 8: Dependence of turbocharger pressure on fuel composition and engine load. Figure 7: Dependence of exhaust temperature on fuel composition and engine load. The brake specific fuel volume consumption (BSFC_v) was measured at 40 \({}^{\circ}\)C. Under these conditions, the density of the chicken fat was ~7.4% higher than the density of conventional diesel (Table 2). Therefore, the impact of chicken fat on the growth of the BSFC_v was lower compared with the growth of BSFC_m with an increasing chicken fat concentration. However, for F100, the BSFC_v remained ~8.3% higher than the D100 consumption with EGR being on and 9.0-11.0% higher with EGR off (Figure 10). Both the course of the combustion process and the degree of combustion (oxidation) of the fuel also had a significant impact on the engine's brake specific energy consumption (BSEC). The experimental research revealed that, having replaced the D100 with D70F30, the BSEC remained unchanged (Figure 11). An increase in the chicken fat concentration to 50% increased the BSEC by 0.8%, and it increased by 1.6% for D30F70. For F100, the increase in BSEC was even higher, being ~3.0% greater compared with the D100 with the engine running on different loads when EGR was off. This was due to the lower ROHR of F100 fuel in the premixed combustion phase, when a more intense combustion was postponed to a later phase. When the content of oxygen involved in combustion decreases with EGR being on, the temperature drops, also resulting in lower temperatures of fuel oxidation and, in the D100, the BSEC increased by 1.7-3.5% under different loads. When EGR was on, a gradual increase in the chicken fat concentration to 30% increased the BSEC by 2.1-3.9%, whereas for D50F50 it increased by 2.3-4.0% and for D30F70 it increased by 2.6-4.2%. When using F100, the increase in the BSEC was higher and, compared with the D100, increased by 3.7-5.5% at different loads. Figure 10: Dependence of brake specific fuel volume on fuel composition and the engine load. Figure 9: Dependence of brake specific fuel mass consumption on fuel composition and the engine load. With the increasing brake specific energy consumption of the engine, the brake thermal efficiency (BTE) decreased. At various loads and when EGR was off, the same BTE was achieved when comparing the D100 and D70F30 fuels (Figure 12), which means that the 30% chicken fat additive did not have a significant impact on the energy efficiency of the combustion process. The BTE reduced by 0.7-0.8% for the 50% chicken fat fuel, 1.5-1.6% for the 70% chicken fat fuel and 2.8-2.9% for the 100% chicken fat fuel when EGR was off. When increasing the chicken fat concentration, more heat was released to the cooling system due to a longer combustion process, and the exhaust temperature increased. When emitting more energy into the environment, the thermal efficiency of the engine decreased. Compared with EGR being off, when EGR was on, the BTE decreased by 1.7-3.4% in the D100 because gas recirculation also reduced the combustion intensity in the premix phase (Figure 3b) and increased the combustion duration. In addition, a lower oxygen content was involved in the combustion, which resulted in a worse combustion quality, increasing the smoke and decreasing the thermal efficiency.