Page 24Torque, RPM & Power Comparison


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Torque is the work done by a single revolution of the engine.
We need to multiply it by the speed of the engine, the RPM, to calculate the engine power.
Power is the rate at which the engine can carry deliver work.

Using the data collected from a power measurement run, we have charted the power curve.

It is a very clear “hilltop” chart.
To get the most power out of a Stirling we must load it so that its revs are at the peak.

The torque chart is very different. See opposite.
No curve here – just a straight line. Downwards.

As mentioned before, the reason is simple.
The amount of heat energy that can be transferred into the gas per revolution, just gets less

as the engine runs faster.

This is very different from the petrol and diesel 4 stroke engine.

For each cycle of the IC engine, a fixed amount of fuel, and a fixed amount of oxygen
enters the cylinder. And each explosion produces a fixed amount of energy.

The faster the engine can be made to run, the more the power that can be generated.

More revs equals more power.

Its almost the opposite with the Stirling.

The IC engine torque chart is not flat, but it is certainly not “all downhill”.

But we can use this straight line torque chart to calculate the two values we want.
The peak power value at the top of the power curve – and the rpm rate that generates it.

Then we can set the gearing for the engine so that the engine delivers the maximum power.