![Figure 1. Thermodynamic principles of a Stirling engine. [1]](https://s3-us-west-2.amazonaws.com/secure.notion-static.com/618d268a-9c11-4ac3-a7f8-b74a113ab663/Untitled.png)
Welcome to the Stirling Engine Lab! This segment attempts to integrate concepts from different modules you will undertake during your following years to contextualise the real-world usefulness of the theory you will learn. You may be coming across some of these concepts for the first time, but fret not, much following are meant as a surface level introduction and are not examined (yet…). So take this as a gentle romp in the wonderful world of engineering, ask lots of questions, and most importantly, have fun!
Figure 1. Thermodynamic principles of a Stirling engine. [1]
A Stirling Engine is a heat engine that converts thermal energy to mechanical energy in the form of the rotating motion of the flywheel. The thermal energy comes from a heat source $T_2$ placed under the cylinder, and is driven by the temperature differential with a heat sink $T_1$ on top of the cylinder (in this case atmospheric air). It operates on a closed cycle, meaning the working fluid remains contained in the cylinder throughout the entire thermodynamic cycle. We can monitor the effect of the temperature differential on the efficiency of the engine by measuring the RPM of the flywheel. This is achieved by taking measurements from transducers, or sensors as the engine is running.
The sensors used in this setup are: 2 x TMP36 temperature sensors to measure temperature at the top and bottom plates of the cylinder, and 1 infrared (IR) beam sensor.
The temperature sensor is made of a resistive element whose resistance is a function of temperature: it is connected in a potential divider circuit and the voltage output is measured. A conversion is required to change this to a temperature reading.
The IR sensor consists of an IR emitter and receiver. The receiver normally receives IR light from the emitter, but when something passes between them (like spoke on the flywheel), the beam is broken and this can be registered on a computer as a signal.
![Figure 2. TMP36 sensor and IR beam break sensor consisting of receiver (left) and emitter (right) [2] [3]](https://s3-us-west-2.amazonaws.com/secure.notion-static.com/c3630320-4993-4cb9-9ee0-951b95de3946/Untitled.png)
Figure 2. TMP36 sensor and IR beam break sensor consisting of receiver (left) and emitter (right) [2] [3]
The sensors are connected to an Arduino Uno, which is known as a microcontroller and acts as the ‘brains’ of the operation. It provides input/output (I/O) connections for these sensors so that your personal computer can read/write data to the sensors, and is effectively a mini-computer itself.
Arduinos are widely used in hobby control systems, such as remote control (RC) cars and drones, and data acquisition systems, etc. (here are some cool projects you can build with Arduinos). Arduinos make building robotic systems economical and easily accessible for hobbyists possessing basic coding and electronics knowledge.
The Arduino queries the sensors and notes down the values they read multiple times within a fixed period of time. This is the concept of sampling, and the rate at which this is done is known as sampling frequency.