## 3 Results
### Comparison of the Combinations of Cooling Systems Studied
Even though a small amount of cooled coolant is able to flow back into the cooler inlet pipe, there is coolant in the pipe at the operating temperature limit. In order for the coolant of the long cooling circuit to be ready to be re-injected by the water pump after the thermostat has released the hot coolant, it is necessary to cool the coolant located in the inlet and outlet pipes but primarily in the heat exchange surface of the cooler. Figure 10 evaluates the inlet temperatures during the cooling process for the best nozzle spacing from the heat exchange surface with the shortest cooling time compared to the fan. Figure 9: Comparison of the outlet cooler temperatures \(T_{out}\) for the most effective spacing for inline and staggered arrangement of the nozzles: (**a**) Nozzle inline spacing 160 mm and mutual combination nozzle inline spacing 160 mm and fan compared to the fan; (**b**) Nozzle staggered spacing 160 mm and mutual combination nozzle staggered spacing 140 mm and fan compared to the fan. Figure 10a shows that the most effective cooling in the inlet pipe was observed for nozzles arranged inline at a spacing of \(s\) = 90 mm (nozzles alone) and \(s\) = 60 mm (combination of inline nozzles and fan). For the nozzle in staggered arrangement (Figure 10b), the fastest cooling was observed at \(s\) = 170 mm (nozzle alone) and \(s\) = 60 mm (combination of staggered nozzles and fan). After a lapse of 30 s at a time of 46 min, the temperature at the inlet of the cooler with the fan running was \(T_{in}\) = 80.39 \({}^{\circ}\)C. Hence, the thermostatic valve remained open and the coolant was not cooled below the required operating temperature, which reduced the efficiency of engine operation. Cooling by the air nozzle system at a spacing of 90 mm (inline arrangement) at a time of 46 min achieved a value of \(T_{in}\) = 79.54 \({}^{\circ}\)C, an improvement of 0.85 \({}^{\circ}\)C compared to the fan (Figure 10a). In this case, the thermostatic valve was fully closed and the coolant circulated only in a short cooling circuit, ensuring optimum engine operation. Cooling by the combination of nozzle (inline) and fan at a spacing of 60 mm at the same time achieved a value of \(T_{in}\) = 79.18 \({}^{\circ}\)C, an improvement of 1.29 \({}^{\circ}\)C compared with the fan. For the nozzle staggered arrangement at a distance of 170 mm, the lowest value of \(T_{in}\) = 79.43 \({}^{\circ}\)C was recorded at a time of 46 min, an improvement of 0.96 \({}^{\circ}\)C compared to the fan and 0.11 \({}^{\circ}\)C compared to the nozzles at a distance of 90 mm (inline). For the combination of nozzle (\(s\) = 60 mm, staggered) and fan, a value of \(T_{in}\) = 78.93 \({}^{\circ}\)C was recorded, which represents a decrease and thus an improvement of 1.46 \({}^{\circ}\)C compared to the fan and 0.25 \({}^{\circ}\)C compared to the nozzle (\(s\) = 60 mm, inline) and fan. Figure 11 represents the temperature differences of the coolant between the inlet and outlet tubes of the cooler when cooling with an air nozzle system (Figure 11a) and when cooling with a mutual combination of air nozzles and a fan (Figure 11b). The values are also compared with cooling using only the fan. From Figure 11a, it can be seen that the temperature difference increases with the spacing of the nozzles from the heat exchange surface of the cooler (\(s\) = 60 mm and \(s\) = 160 mm). As the distance of the nozzles from the cooler increases, complete coverage of the heat exchange surface by the air flow is ensured, which leads to a reduction in the cooling time of the coolant and an increase in the temperature difference. Figure 10: Comparison of the inlet cooler temperatures \(T_{in}\) for the most effective spacing for inline and staggered arrangement of the nozzles: (**a**) Nozzle inline spacing 90 mm and mutual combination nozzle inline spacing 60 mm and fan compared to the fan; (**b**) Nozzle staggered spacing 170 mm and mutual combination nozzle staggered spacing 60 mm and fan compared to the fan.