When the internal pressure in
the engine is raised, there are more gas molecules to provide
more force to push the piston. Some engines won’t run
until they are pressurised.
Pressurisation is needed to
overcome the power loss caused by dead space.
make a pump to self pressurise the engine” says the
innovative Stirling engine maker.
This is an issue
where engineering enthusiasm and user requirement clash.
Stirling boat user wants to use his boat now. Not wait while the
engine self pressurises.
And it will be a long
At the very time when the engine is at its
weakest – it has yet to warm up – that is the
when fast pressurisation is needed. Because the engine
is still weak, the pump has to be
rather small. A small pump
will take an even
longer time to raise the pressure.
Philips had this
problem with their Stirling generator set. What they did was to
carrying frame into a pressure reservoir. To start
the engine they released the pressure into
the gas circuit
then started the engine. When it was warmed up, the first task was
the pump and re-pressurise the reservoir. Then the
engine was ready to generate electricity.
the answer to your engineering problem is “more”
Have a self pressurising pump and a more
complicated (and longer) startup procedure
Not a good
We need pressurisation. For £30 (in the UK)
you can buy 400 bar litres of pressurised gas.
say your engine has 1 litre of volume inside. That’s 100
charges at 4 bar.
And it takes 4 or 5 seconds to charge the
If you want engineering challenge – make
an engine that doesn’t leak.
The idea is that
once pressurised, the gas should stay in there.
The whole idea of the Stirling engine
is to heat the gas quickly and cool it quickly.
(80% nitrogen) is an insulator.
It takes time for it to
accept heat – or loose it.
We wear woollen jumpers in
winter to trap air, insulate ourselves and keep warm.
conducts heat more rapidly than nitrogen.
The gas inside the
engine heats, and cools, more quickly and the engine runs
The chart shows the extra power generated, and the
higher speed for peak power.
In the UK, 2020, a 2 litre
cylinder of helium at 200 bar costs £30
pressurise with air or nitrogen.