Philips stirling on ebay

It looks like one I used to own about 15 years ago. I bought it to pass it on to a Swedish friend but kept it long enough to try to start it for a few months. I never succeeded. I still have the origional handbook for it if anyone needs a photocopy. (25 pages) The frame of the set is sealed & acts as a pressure vessel to store air for starting.

-- Dave Croft Warrington England

Map Map

Seen one running at Kew Bridge stirling bash, so they do work!

I think the stirling engines are fascinating.....the most fascinating thing about them is that they are claimed to be ultra efficient compared with 4 stroke IC engines, and yet, there seems to be nothing more than a few toys based on the principle. It amazes me that there arent more commercial units - and it is great to see something that almost resembles a production piece of kit. However, from the figures given on ebay (180w x 8 hours produced from 3.3litres of fuel) I can only conclude that this engine is little more than 2-3%efficicient. Well our friend the 4stroke normally manages 25%.....even for little engined generators. Any comments?

The other thing I would be interested to know is what they sound like. I assume that they are almost silent in operation, revolve at much lower speeds....is that right?

Cheers

Adrenalin!

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ISTR we had a brief bash at this one a month or so ago. I think the size of the unit is quite telling, one would expect at least 1KVA from that sort of package with an IC engine. So specific power output is not one of the Stirling engines strong points.

As for efficiency, the stirling engine has the theoretical potential to approach the limiting, carnot, figure for any heat engine, but in the real world maybe 50% of this would be a realistic aim.

Nearest current equivalent to the MP1002C I could find data on is the

0.7KVA/600w Honda EX7 which, at 1/4 load, gives a run time of 4.5 hours from its 2.3 litre tank, ie 3.4 litres/KWh. Quoted figures for MP1002C give 2.3 litres/KWh. Though I would treat the figures for both sets with some caution, this certainly does not substantiate the 25% / 2-3% difference you refer to (25% overall efficiency for a small IC genset doesn't sound right to me, power stations manage about 40% I believe!).

Noise wise, there is a gentle blowlampy sort of noise from the burner and slight mechanical rattle from the engine.

Our 2.2kva Honda 160cc based genny runs from 10.30 ish in the morning until

4pm ish in the afternoon (5 plus hours) on 2.5 litres of unleaded. It is never loaded to more than 1 kva during PA duties, but grunts quite loudly when running power tools. The latter is a lot more intermittent, but the run time is about the same.

So this does bear out the data that Nick found from real life experience.

Regards,

Kim Siddorn,

Looks reasonable

In practice it's far more limited by the hot end materials than a conventional ic engine (with the exception of a gas turbine which is able to entrain extra cooling mass flow)

In practice our 3cylinder lister 10kVA set averages only 2kW and averages only 20% thermal energy to electricity conversion. I think we might push on to 30% at around 7kW. A 100kW caterpillar is rated at

34% at 70% rated load and the big ship's engine which was posted here a while back had figures of over 40%. Integrated gas fired dual cycle turbines in the 10MW class have exceeded 50% now.

Fuel cost is not necessarily the biggest consideration though, stirlings have run under solar power and I think thermo nuclear waste heat. It's their ability to deliver power for long periods with no lubrication that interest me, if indeed they can.

AJH

I wonder how many actual kWhrs are used, if 1kW is never exceeded can we assume an average of 500W? I think a litre of petrol will be about

10% less than diesel which IIRC is 10.75kWhrs(t), say 9.5kWhrs(t). With 5 hours at 500W being 2.5kWhrs(e) and using about 24kWhrs(t) of fuel this looks like a conversion of ~10%, about the same we get from the lucas apu at 40kW.

AJH

wrote (snip):-

Philips set was designed to operate between 873K and 333K giving a theoretical efficiency of about 62%. So 30% is probably achievable for the motor itself, clearly burner and generator losses would subtract something from that.

Have a look at the whispergen website, ISTR their claim for time between overhauls is pretty impressive. Mind you as a sealed system there is no reason why a stirling engine should be any less reliable than say a refrigeration compressor.

wrote (snip):-

Leaving a handy 400K or so temperature drop to exploit with your stirling engine!

As I'm sure you know, theoretical efficiency of air standard Otto cycle is determined solely by compression ratio and, though it can be expressed in terms of temperature at the beginning and end of compression stroke (assuming adiabatic conditions of course), combustion temperature does not enter into it. Mind you ISTR that Otto efficiency at 10:1 CR is about 60%, so, again assuming that around half this is a realistic figure, the advantage of a stirling engine is by no means clear cut in terms of efficiency alone.

If an engine were able to expliot the full potential of that 2200K down to a

393K ambient, potential efficiency would be some 82%.

This illustrates my point, a stoichiometric petrol burn will be about

2200K with the waste dumped to atmosphere at 700K so even though it is inherently less efficient it has advantages.

Yes this was the point (my fridge is over 20 years old and still ok) made to me by another devotee of stirlings, which is what set me wondering what engine wear was all about.

AJH

Or steam engine. Actually I see now caterpillar are investigating a small permanent magnet alternator built into the turbocharger for all the engine electrical needs.

I was aware that power was directly proportional, though not 1:1, to cr and as the fuel:air mix is stoichiometric in a si engine this would be directly related to efficiency. However I thought the burn at constant volume then expansion was just a limit on the otto cycle, within the Carnot limit set by heat in minus heat out. Still it's many years since A level physics when I learned the little I think I know.

Again I was trying to illustrate the point that though the stirling has enticed designers by its inherent higher theoretical efficiency for many years when it comes to it the reciprocating ic engine's ability to absorb high temperature, discrete burns means it out performs the stirling despite it's theoretical disadvantages.

AJH

Here is a similar product made locally

wrote (snip):-

Probably time to draw this thread to a close then lest the lurking multitudes find our half remembered thermo risible (over twenty years now since I used any of that stuff in anger!).

rec.engine.stationary bods will have ignored the thread, they like grime not theory :-).

36 years since physics lessons and you don't need much knowledge of thermo dynamics to chop trees down, even so HSE say I need re training for that ;-).

AJH