Search found 127 matches

by Bumpkin
Fri Aug 03, 2018 6:02 pm
Forum: Stirling and "Hot Air" Engine Forum
Topic: Gamma type cylinder and displacer
Replies: 24
Views: 1303

Re: Gamma type cylinder and displacer

Looks like it's been worked out, but if we would say SWEPT volume for the ratio of displacer to power, it might save some confusion.
:smile:
Bumpkin
by Bumpkin
Sun Jun 10, 2018 11:02 am
Forum: Stirling and "Hot Air" Engine Forum
Topic: the volume ratio between displacer cylinder and power cylinder
Replies: 4
Views: 457

Re: the volume ratio between displacer cylinder and power cylinder

Hi Oscarmike. Here's a link to something about the math stuff. The relevant stuff is towards the top.

http://www.spragueriver.com/index.php/bumpkin-tech

Bumpkin
by Bumpkin
Wed Mar 21, 2018 11:27 am
Forum: Stirling and "Hot Air" Engine Forum
Topic: Large LTD Diaphragm Gamma Stirling Questions
Replies: 19
Views: 2035

Re: Large LTD Diaphragm Gamma Stirling Questions

Hi playludesc Development of these engines is more important to me than the modeling, so know I mean this respectfully. You can always copy other engines, but for unique circumstances and applications you should learn the basic science behind the ratios. You could Google the Ideal gas law or Boyle's...
by Bumpkin
Fri Dec 29, 2017 11:24 pm
Forum: Stirling and "Hot Air" Engine Forum
Topic: small wood gassifier generator
Replies: 11
Views: 1676

Re: small wood gassifier generator

Hey Ian, I always wondered how a prony brake could be consistent enough to get a good reading. Now I see the springs and it's clear. Thanks. Alfista, I watched the video. I would think it might be easier to test your engine's power by finding the biggest load (light bulbs?) it will run up to voltage...
by Bumpkin
Sun Dec 17, 2017 10:33 am
Forum: Stirling and "Hot Air" Engine Forum
Topic: small wood gassifier generator
Replies: 11
Views: 1676

Re: small wood gassifier generator

The trouble, as I see it, with small scale wood gasification is it tends to take a lot more tending than just a basic wood stove. Also if it's done inside a living space there's always some degree of danger from carbon monoxide - stuff happens. There are off-grid folks who use wood-gas to run a more...
by Bumpkin
Tue Nov 21, 2017 9:56 pm
Forum: Stirling and "Hot Air" Engine Forum
Topic: Double-acting solar Gamma, twin rotary displacers
Replies: 4
Views: 1156

Re: Double-acting solar Gamma, twin rotary displacers

Nearly 40 years off-grid here myself, and a big Stirling fan, but it's hard to compete with modern P.V. system prices, even including batteries wires controllers and inverters. A solar Stirling combination with a VAWT is intriguing. The big problem with Stirling rotary displacers is that they move a...
by Bumpkin
Fri Mar 10, 2017 11:21 pm
Forum: Stirling and "Hot Air" Engine Forum
Topic: Heater & Regenerator Design
Replies: 60
Views: 15681

Re: Heater & Regenerator Design

I like your crankshaft design. It always seems funny when people turn the crank back to the main center before swinging it back out 90 degrees, even without the purpose of providing another main bearing. That said; is there a key or something to register the clamping of the second throw for accurate...
by Bumpkin
Mon Feb 27, 2017 12:16 pm
Forum: Stirling and "Hot Air" Engine Forum
Topic: Low temperature differential (LTD) alpha designs?
Replies: 4
Views: 2195

Re: Low temperature differential (LTD) alpha designs?

I'm not a fan of Alphas except for high temp versions, and even then they generally use heat sources that might be better and more efficiently spent elsewhere. But that said; you can lower the peak volume ratio to where it works with lower temps, with variable volume. The weight of a few inches of w...
by Bumpkin
Mon Feb 20, 2017 10:41 am
Forum: Stirling and "Hot Air" Engine Forum
Topic: Pressurization
Replies: 20
Views: 6206

Re: Pressurization

Aviator, I forgot to mention another problem with a pressure imbalance above and below the piston. (beyond the normal power pulses) There is a greatly increased rod and main bearing load. I bumped into that while trying to think up a pressurized diaphragm type engine. A set of two opposed and linked...
by Bumpkin
Sun Feb 19, 2017 12:31 pm
Forum: Stirling and "Hot Air" Engine Forum
Topic: Pressurization
Replies: 20
Views: 6206

Re: Pressurization

Hi Pete. Neat that you saw the Jim Dandy six operating. 15 or 20 minute feeding intervals wouldn't be too bad if you were right there working in the shop anyway. Burning home-made fuel beats buying pellets any day. Aviator, you are probably a better machinist than me, but I'd still bet an open-crank...
by Bumpkin
Sat Feb 18, 2017 8:44 am
Forum: Stirling and "Hot Air" Engine Forum
Topic: Heater & Regenerator Design
Replies: 60
Views: 15681

Re: Heater & Regenerator Design

"Looking to run at 15bar fairly quickly but then maybe more." - You probably already know, but remember not to mix air and oil at high pressures/temperatures. From wikipedia - "At high temperatures and pressures, the oxygen in air-pressurized crankcases, or in the working gas of hot air engines, can...
by Bumpkin
Thu Feb 16, 2017 11:51 am
Forum: Stirling and "Hot Air" Engine Forum
Topic: Disappointing
Replies: 34
Views: 9656

Re: Disappointing

Back to the thread premise; I pretty much agree with this paper:
http://file.scirp.org/pdf/ENG_2015121717392471.pdf
Bumpkin
by Bumpkin
Mon Feb 06, 2017 10:26 pm
Forum: Stirling and "Hot Air" Engine Forum
Topic: Pressurization
Replies: 20
Views: 6206

Re: Pressurization

I don't know how to interpret the text, but looking at the videos I can only imagine the extra pressure is in the interest of fun or science. As it is, the bores must leak enough that maintaining pressure probably takes more power than is produced. It probably wouldn't be very difficult to make a pr...
by Bumpkin
Mon Feb 06, 2017 12:03 pm
Forum: Stirling and "Hot Air" Engine Forum
Topic: Pressurization
Replies: 20
Views: 6206

Re: Pressurization

Pressurized Siemens-type Alphas or double-acting Gammas don't need sealed cases, but rod seal leaks may require constant replacement pressure. Diaphragm/roll-sock designs solve that problem but have their own limitations. Just my opinion, but I'm not a fan of very high pressure. I don't see a Stirli...
by Bumpkin
Sat Jan 07, 2017 3:14 pm
Forum: Stirling and "Hot Air" Engine Forum
Topic: Heater & Regenerator Design
Replies: 60
Views: 15681

Re: Heater & Regenerator Design

Hey Aviator. It sounds like Rich is venting the displacer to the crankcase, where it wouldn't affect the working volume dead space.
Bumpkin