Created new blog just for Open Stirling Engines

Having my personal stuff mixed in with the Stirling engine project was awkward, so I created a new blog just for the engines. It is https://openstirlingengine.blogspot.com/ and I will start to post my prototype status reports there. Please make comments on that site, rather the this one. Also please visit the official Open Stirling Engine project site

Thanks

Upgraded HP/Compaq TC1100 hard disk problems

I just finished updating my old 40 gig drive with a 120 gig Fujitsu drive.

After trying several approaches to transfer the OS and files to the new drive and make it bootable, the solution was a freeware version of HDClone. I tried using Microsoft backup to copy the system and data to the new drive, but the disk was not bootable. Then I tried GPartEd, but it gave me errors and failed.

HDClone also reported errors in reading the data from my original disk, but gave the option to continue. After rebooting with the new drive, XP detected a hardware change and wanted to reboot again.

After that my system was back to "normal". The reason for the quotes is that Windows Explorer hangs when I try to get the properties of a disk drive. I would have to kill it using the task manager to restart it. I think I have bad sectors, but can't figure out how run Check Disk without bring up the properties for it.

Well at least I have a bunch of new space to download podcasts using Miro and room to add a Ruby on Rails development environment. I was at 97% and had to clean up all the time. Now I can wait a while before having to watch the Diggnation podcasts. Maybe download a movie or two.

Proposed new site for Open Stirling Engine project

I have created a google site for the project. It seems to have the features I need. It is at http://sites.google.com/site/openstirlingengine/Home check it out and give me feedback. Thanks.

Tom

4 cylinder Alpha Stirling engine almost complete

After working all weekend to build another half of the engine. It is almost complete. Unfortunately the first 2 cylinders have lost pressure, so I will have to track that down before I begin pressure testing. The 2 new ones seem to hold air well Got to go to my real job now.

Alpha Stirling engine protoype half done

I got 2 cylinders with push rods and cam assembled in a case. I changed the cam to a smaller one, cut from 1- 3/4" dia rod, so it is as smooth as glass. Pistons can now spin the shaft, now I need to add a flywheel to see if I can get it running. I have to be careful because it is still using polyethylene bags, so I have to limit the temperature.

Here is a picture of the partially completed prototype, but with the old cam.

Since I am using low pressure air as the working gas, the stresses on the push rods is not too bad. But I will need to add the cam follower guides so prevent the rods from bending when the press down on a inclined section of the cam with higher pressures.

I found a 7" flywheel pulley on my old vacuum pump. It had a 5/8" hole for the shaft, but I had a 1/2" bearing that had a 5/8" OD to adapt it. There is still not enough inertia to make on rev, so rather then getting a bigger flywheel, I've decided to complete the other 2 cylinders to balance the forces. Since they were always in the plan, might as well build them and test the entire unit. I will complicate matters having to apply heat and cold to 2 sets of cylinders. The other option would be to buy a larger flywheel from Grainger for $50. I guess I want to see it running before pouring more money into the project. I'll post a new picture soon of the assembled 2 cylinder version.

Sketchup model of 4 Cylinder section of alpha config

I finally got something I can show. This the Stirling engine design I would like to do as an open source project. It is modified alpha configuration that uses a cam instead of crank to drive the shaft. The horizontal cylinders are the hot ones and the vertical are the cold. There are still some pieces missing, in particular the push rods need a guide, otherwise they bend and bind in the hole through the case cover. There is also corner gussets in the case to hold the guides and to screw the end pieces to.

This is a 4 cylinder section. These sections are designed to stack along the shaft. The heads would just be extended to cover all the cylinders for each quadrants. The cam case pieces can just be extend too.

I am still learning Google Sketchup and had trouble making all the holes go through the head. I didn't finish added the head bolts and only installed one, it isn't even tightened. The head is suppose to be counter sank the the flat head bolts. The diagonal pipes are intended to be regenerators, that is why they are so wide. I am just going to use pressure hose for now. I still have to get the 3" wide 1/4" aluminum extrusion for the head. It can also be used for the case, since it is 3" deep, if you don't stack them. The case is intended to be sealed. A fly wheel will also be needed.

I am hoping to have the prototype to run with the cylinders pressurized to around 100 psi. The pistons are 2" diameter so the force pushing down on the push rod is over 300 lbs. That is one reason to have a sealed case. It could have back pressure to reduce the forces on the cam.

Now I can finish making the clear plastic prototype. It is made using mostly 3/8" thick sheet material. I am working on a spread sheet that would calculate the sized of the component based on other thicknesses.

Diagam of sealed piston with pictures

Here is a diagram of the sealed piston that I am planning to use for the Stirling engine. I have exaggerated the gap to make drawing the bag easier. The kink in it on top of the piston is suppose to be the heat sealed end of the bag. A metal cap will be fitted over the cavity of the piston to hold it in place with a screw.


























The area will be pressured with a working gas, most likely methane, so the bag will be tightly pressed against the cylinder and piston, so in those areas it will not feel the pressure. Only where the bag makes the U turn, will it have to support the pressure of the gas in the cylinder. With a small gap, the force on membrane will be on the order of 1/10th the tensile strength of the material.

Here are some pictures of my tests on the sealed piston.

Piston at bottom of cylinder. The plastic bag is tucked into the top of the piston, but not completely. Then it goes down 1/3 of the length and goes back up to the top of the cylinder.
It is under ~10 psi pressure.


As the piston is pushed into the cylinder, the bag's U-turn moves further down the piston.

Piston at top of cylinder. Note: bag should not extend past the end of the piston.