## 4 Engine Operation and Testing Procedure  
The engine was installed into the test bench, connected to a transmission box, and through the transmission box the free power turbine, two hydraulic dynamometers HS2600 were installed through which the engine was operated. A single dynamometer [14], can perform a maximum power of 2.6 \(\mathrm{[MW]}\), with a maximum torque of 1356 \(\mathrm{[Nm]}\) at a maximum speed of \(24,000\)\(\mathrm{[rpm]}\), with a water consumption of 24.5 \(\mathrm{[L/Kwh]}\) at optimum water pressure of 3.5 \(\mathrm{[bar]}\). The engine testing involved following an engine operation and testing procedure which described the stages of the engine experimentation, beginning  
Figure 4: TV2-117A engine instrumentation lines. Figure 3: TV2-117A engine stations and instrumented parameters. with a start-up procedure and ending with an engine operation method to obtain different working regimes. The start-up procedure represented the sequence of the starting process by presenting the phases of the start-up sequence in the correct order, in order to control the engine by executing the starting process [15]. Figure 5 presents, in diagram form, the scheme of the hot start-up procedure for the TV2-117A engine, which was equipped with an electrical starter-generator. So, to execute an engine starting, the fuel pump FP must be turned on, the fuel shut-off valve FSHV must be opened and the start lever SLV must be put into the idle position and after that, the starter must be turned on. The starter increases the engine gas generator speed \(N_{\text{CG}}\), and when speed reaches \(\approx\)10 [%] the ignition is turned on, and at \(\approx\)20 [%] the starting fuel valves FSV are opened to allow the mix of air and fuel to light-up. After the light-up, the engine accelerates and when the speed reaches \(\approx\)55 [%], the ignition is turned off the ignition, as are the fuel starting valves and starter while the engine is still in acceleration. When the speed reaches \(\approx\)65 [%] the engine is on an idle (a) regime. Until a certain regime, the engine was operated through the starting system, by the start-up fuel lever SLV, and through the engine fuel pump regulator EFPR, by the throttle lever \(\alpha_{TLV}\) through which the fuel flow was metered to ensure the engine increase in high operating regimes. From this regime, the engine was operated only through the dynamometer by varying the load on the free power turbine. In Figure 6, the mode of engine adjustment and the mode of loading the free turbine with various torque values [13], to test the engine on the test bench are presented. Figure 5: TV2-177A engine start-up diagram. Figure 6: Engine fuel control and engine operation law scheme. So, the engine is on idle (a) mode, with gas generator speed at \(\approx\)65 [%] and free turbine speed at \(\approx\)45 [% ]. Because the engine is working with the free turbine constant speed, the throttle lever \(\alpha_{TLV}\) into 100 [%] is moved to reach the free turbine speed at 98 \(\div\) 100 [%], and in this way the functionality of free turbine speed regulator FTSP is checked and the engine is ready to be operated to higher regimes. When a higher value of torque is set, the free turbine speed decreases, so the free turbine speed regulator in correlation with the engine fuel pump regulator EFPR adjusts to increase the fuel flow to the combustor chamber to maintain the free turbine speed at same working speed of 98 \(\div\) 100 [%]. To obtain different regimes from the dynamometer operator higher values of load are set, which corresponds to higher values of torque [15]. Figure 7 presents the dynamometer operating system (Texcel VX100, software version 1.21, Froude Limited, Worcester, England) with user interface through which manages the dynamometer by torque demand to operate and control the engine [16]. To test the engine according to the engine manual it is necessary to determine the working torque domain of the free power turbine by calculating the minimum and the maximum value of torque.