**5. Results and Discussions**

The testing procedure is the following:

	- setting the temperature to 450–500 ◦C;
	- positioning of the type-K thermocouple for the primary exchanger of the Stirling engine;
	- propane supply by opening the 26 L cylinder tap;
	- ignition of the burner;
	- adjustment of air flow through the mixing chamber;

Following the functioning tests, the automation and control installation has achieved stable operation under secure conditions.

The experimental data derived from the acquired and monitored parameters are further presented in the form of graphs using the trend and process analyst functions of the Citect Scada application.

In the graph presenting the variation of temperatures monitored by the automation (Figure 17), it can be clearly observed that the temperatures collected by the sensors located on the primary exchanger of the Stirling engine have a fast stabilization towards the working temperature, according to thermal power provided by the heat source. Each iteration is done at 330 ms.

**Figure 17.** Heat exchanger temperature diagram.

Similarly, in the engine rotations/minute graph (Figure 18), the speed of the engine quickly reaches the synchronization speed of 1475 rot/min, keeping it constant.

These observations lead to the conclusion that the automation system performs the control of the operating processes of the Stirling engine.

The presentation of pressure monitoring on the Stirling BP3 engine and of the Helium cylinder pressure BP4 is shown in Figure 19.

By realizing the automation of the power generation unit using a Stirling engine, we performed the first stage for starting up the main module.

Another main stage is the implementation of the automation and control of the solar concentrator positioning. The supply of the sun position was made by a Solys2 installation (Figure 20) manufactured by Kipp & Zonen in order to determine the sun's position. It uses two pyranometers, one for global radiation measurement and the other for diffused radiation, as well as a pyrheliometer with temperature sensor for direct solar radiation measurement.

**Figure 18.** Generator rotation diagram.

**Figure 19.** Helium Stirling engine and bottle pressure diagram.

**Figure 20.** Solys2 solar detection station.

The acquisition system transmits data to the control unit of the solar concentrator director that will position the axis of the concentrator in the direction of the sun through the two motors that control the rotations for elevation (vertical plane) and azimuth (horizontal plane), in order to obtain the maximum radiation.

According to [40], a computational analysis was completed using Ansys Fluent software, creating a model on which some simulations were performed for the exposure to thermal radiation around 1000 W/m2, a model validated by the experimental results.

Regarding the use of the engine with the realized automation and other energy sources, the tests performed confirmed the operation in the following cases:


The Stirling engine has worked with different heat sources, with stable and repeatable operation under safe conditions.
