Gentlemen,
I took myself off to the London Model Engineering Exhibition today, via our lovely railways, the underground and a bus, and enjoyed the day. I bought a very nice, but expensive, book on Stirling Engines. Even though I think I know how they work I am reading up on it to clarify my thoughts, there is even some pictures in it of the Philips Generator. Can somebody explain why some engines have to be pressurised, surely this would increase friction!
Martin P
lovely railways, the underground and a bus, and
think I know how they work I am reading up on it to
would increase friction!
Hi Martin, In a Stirling engine a certain temperature change will double the pressure on the piston. If the contained pressure is doubled you will get twice the pressure changes on the piston for a given heat input. Therefore the engine is twice as efficient!
Thank you Dave, Very well put if I may say so.
Martin P
DC> Hi Martin, In a Stirling engine a certain temperature change will DC> double the pressure on the piston. If the contained pressure is DC> doubled you will get twice the pressure changes on the piston for a DC> given heat input. Therefore the engine is twice as efficient!
You might get twice the pressure swing for the same *temperature* change, but you have doubled the mass of worrking fluid so you need twice as much heat to achieve that change! Pressurising a stirling engine increases the specific power output rather than efficiency.
BUT, to get that extra heat in and out of the engine you will need more heat exchange capacity - including the regenerator if efficiency is to be maintained - which inevitably adds dead (unswept) volume to the gas circuit. This decreases the pressure swing and thus specific power. Nothing is simple with stirling engines!
Which book did you buy Martin and what else of interest was to be seen at the exhibition?
nickh=== Posted with Qusnetsoft NewsReader 2.2.0.8
Stirling and Hot Air Engines by Roy Darlington and Keith Strong Some nice steam models, my particular interest is Gauge 1 and G1MRA had there layout running with a very nice Britannia, this one was coal fired and not your usual Meths burning. Its coal shovel the owner was using was only about 3/8 ths of an inch across. Radio controlled indoor helicopters with collective pitch etc fully working, battery powered, 10 mins on a full charge. one had a propshaft driving the tail and another had a tiny variable speed motor drive the tail rotor direct £100.00 all in and working. I just could not find a good enough excuse to bring one home to the wife :-)) Usual stalls, Chronos, Warco etc.
Martin P
One of our lot had a radio controlled helicopter in the Longhall a few weeks ago. It was amazing to see the tiny thing whirring quietly in and out of the roof timbers. Only downside was the slightest gust of wind coming in the windows sent it sliding sideways, but it was too light to do itself any mischief. I think he said it was £38.00 in Tescos or something equally daft.
What wonders there are in our midst .........
Regards,
Kim Siddorn
If quizzes are quizzical, what are tests?
helicopters and the brits managed to make Lister D's all by themselves many centuries later.
With apologies to all D owners out there.
John
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