Free Piston Diesel Engine

[Diesel Dave]

I've been doing a bit of digging around experimental diesel engines (funding applications are the best source)

I came across this little nugget, I don't have any drawings but I'll try to describe ot the best I can.

Imagine a bore with a cylinder head at each end, inside is a double headed piston. The centre section of the piston is the magnetic part of a linear alternator and outside the bore is the magnetic coils part.

So no crank, conrod or any motion output - all electrical from the linear alternator.

The piston bounces from end to end in the bore generating an electrical output from the alternator - all very compact indeed.

Of necessity the design is a 2 stroke with a supercharger pump to improve scavange and there are technical challenges over lubrication and starting but such a design will be very compact for the power output.

It would make a diesel electric bike a very real possibility.

Regards
Dave

[Stuart]

Hi Dave,
I wonder how much current that could put out? I know the little torches you can buy http://tinyurl.com/akmwk work on the same priciple.
(Faraday I think) but they need to charge a capacitor before the light will work proper.
I'm just recalling my days at Enduro Race meetings where I saw large capacity two strokes such as the KTM 495 and Maico's. Those bikes had engines that could really rev like crazy and if the coil technology was applied to big engines like that I'm sure they'd pump out a fair bit of voltage. Whether it would be enough to run a bike I'm not sure.
but a floating piston arrangment would certainly be different. Setting the timing would be interesting

[andrewaust]

Hi Dave


Yeah what a great idea - here's a link I've got regarding the use of such an engine in a hybrid car http://www.greencarcongress.com/2006/11 ... _twos.html
Surely something like this could be adapted for a Motorcycle - only time will tell hay


Cheers

Andrew

[Byrdman]

Kind of reminds me of the Fairbanks Morse opposed piston engines.

Well, it's really nothing like it except that the pistons run in the same bore.

[Stuart]

I emailed the original picture about at work and it caused a fair bit of interest. Some concluded it would be started by energuising the coils with DC to shoot the pistons along and other's wondered how you'd stop the thing and if the heat might have a detremental effect on the magnets.
Interesting stuff though.
There is a website dedicated to a bike with six stroke engine if I could only find it. Stroke 5 & 6 having nothing to do with the piston but instead bringing the roof of the cyclinder down and up to increase compression. Now that took some doing

[tappy]

I'm very sceptical about the longevity of a magnet's properties if it's in a piston being exposed to massive vibration / acceleration and high temperatures.
The best way to use a free piston engine is as pressure rise combustion within a gas-turbine cycle - i.e. take power out using a turbine driven by the exhaust gases, with a smaller turbine pumping the air in.

[smokyjoe]

An interesting but somewhat unrelated? Diesel engine was used in the air compressors on the WW2 German U-Boats. It had a big piston that when one end was fired would shoot across the bore to the other side compressing air as it went. If I remember right it was a 2 "cylinder" affair and before the piston bottomed out the other side would fire. The compressor put out about 3,000 PSI and was used to fill the tanks used to purge the water from the ballast tanks. I am sure there is a better explanation with pictures and nice drawings somewhere on the web. I would love to have one of these! (I love weird engines, that's why my bike is sporting an engine whose cam turns at 1/4 crankshaft speed .)

That German compressor must have sounded pretty cool, but I am sure that those poor sailors in their tin can coffins hated it with a passion.

I saw it at the Chicago Museum of Science and Industry where they have one of the subs used in filming Das Boot, along with a "dismounted" engine. There are also a couple more at the Deutsch Museum in Munich.

[Diesel Dave]

This any good:

http://www.jsme.or.jp/tsd/ICBTT/confere ... AHARA.html

[smokyjoe]

Really good find Dave! Thanks. I've bookmarked it and will read it later. I'd love to someday build one of these, but for now the bike is enough I've got a garage and little barn full of unfinished projects and am in the process of weeding out what is not important any more.

[Sphere]

Joe, you should build one and supersize this baby: http://www.dumpert.nl/mediabase/658441/ ... kanon.html

[smokyjoe]

That's a cool pumpkin shooter! There are many pumpkin farms around me and this is the "pumpkin season" with Halloween and today's "American" Thanksgiving. As a side note, the Turkey almost became the "American National Bird" instead of the Bald Eagle. We have many native wild turkeys around here, although most people prefer the farm-raised domesticated type for their Thanksgiving dinner.

A few of the locals near me have built catapult type pumpkin chuckers (trebuchets?), there was a contest last year but I didn't see it, unfortunately. A friend went to it, and someone had a compressed air pumpkin cannon. It used 250 gallon oil tanks for air storage, but I don't know the pressure. They had a boring old construction-type compressor to fill the tank. One of those U-boat Diesel compressors would have been a spectacle in itself, let alone the pumpkin cannon!

Around the time of the Spanish-American War (1898?) the US had a battleship that fired dynamite projectiles with compressed air. I think it had 16" barrels and used about 1,000 PSI and had a range of many miles. It was used briefly, but better and more stable explosives came into being making it obsolete. But one of those cannons would have made one heck of a pumpkin chucker. Unfortunately there has to be a point of diminishing returns where the acceleration and velocity gets high enough that the pumpkin is sprayed rather than "projected"! It would make for some very instant pumpkin pie filling.

Well, I'm off to stuff my belly with turkey, bread stuffing, hubbard squash and pumpkin pie! Happy Thanksgiving to all.