# How to measure the power output of a stirling engine

I'm doing a project for thermodynamics where I have to measure the power (work over time) of a Stirling engine for varying temperature differences. I don't necessarily need an exact answer (as in: ... Watt), but a "relative" measurement would also work (i.e. when the temperature difference between the hot end and the cold end is doubled, the work increases by a factor of ...).

I've thought of filming the engine run in slow-mo, and then using the RPM of the Stirling engine to calculate power, but I could not quite work out how to do this.

Any suggestions? Thanks in advance!

• I could start to brainstorm, but what have you researched so far? I guess if you read papers on stirling engines that measure power output, you'll find sdescriptions of their power output!. p.s. also measure thermal power input, not only temps, to get meaningful data!
– mart
Commented Mar 22, 2020 at 19:48
• Also please give an order of magnitude of how much mechanical power you expect (mW, W ...). Is the sitling engine of the free piston type, or does it turn a shaft?
– mart
Commented Mar 23, 2020 at 13:49

## 1 Answer

You need a load to calculate power. Meaning you need to move something or generate something.

Traditional steam and internal combustion engines used brakes to calculate torque, which was then converted to power. Modern automobile dynomometers uses either a load cell to measure the torque, or measure the speed of the dyno cylinder and calculate the power it takes to accelerate the mass of the cylinder. My guess is that unless you build or buy a large Stirling engine, any load you out on it will make it stop. The typical demonstration devices you can buy to run on top of your coffee mug will not work well enough for this.

I think that powering a generator is your best bet. You will need a large enough engine to generate a measurable amount electricity.

• Thanks for your reply. I have been reading some papers, and I have found a lot of useful information regarding calculating the theoretical power output. However, I would like to contrast the theoretical output with the real output (with friction, drag etc.). I have not found a source that explains how to measure that. As for the thermal input, the hot end of the stirling engine will be kept at a constant temperature (by placing it on a heated bed of a 3D printer). Since the output relies on the temperatures of the hot and the cold end, I figured measuring those would be enough for this experim Commented Mar 22, 2020 at 23:50