Death of Fo Mi Chin
Posted: Thu Sep 08, 2005 3:40 pm
The Fo Mi Chin II engine is now nothing more than an artifact of Third Millenium pulsejet technology.
After a couple of successful runs yesterday afternoon, I decided I needed to get one more photo of the engine running hot in semi-darkness, to try to show the intake flame, chamber heating pattern, etc. So I got the shot metered, got the camera into position and fired her up. Started nicely and I got it running just right and was just about to circle around to the camera to snap the shutter, when suddenly the pulsation pitch went up about two full steps! I knew something was very wrong. After two or three seconds running like this, the engine quit running, with yellow flame billowing from the exhaust port and some point on the chamber opposite my position (naturally!) so I quickly shut down the propane.
The hole opened up low on the right side of the chamber. It is a roughly crescent-shaped, rough-edged hole almost an inch (25mm) end-to-end. The hole is centered perhaps 4 cm aft of the front welded seam (where the dome is welded on). The metal remaining at the edge is basically tissue paper thin, and the edges appear quite sharp, not melted back. Here are some interesting things to think about regarding this engine and its ultimate failure:
- This is the lightest and most compact valveless engine I have ever gotten to run well: 2.6 inches max diameter (67 mm), 22.5 inches length (ignoring spark plug) (572 mm) and 15 ounces total weight (including plug)
- Due to the thin material, this was one of the most difficult welding projects ever - but, it was ultimately doable
- Intake flame visible during the final run was straight out, parallel to the tailpipe surface
- This kind of ultimate failure was expected sooner or later, because of the very thin steel can used for the chamber
- The engine continued to run after the hole opened up, but at a higher frequency, presumably due to the creation of an additional pressure node
- Since the hole was on the opposite side where I couldn't see it, I can only speculate that it started small, then enlarged, killing pulsation
- The steel material was NOT blown out - it was sucked INTO the chamber (I shook it out after the engine cooled); the material consisted of a variety of tissue-paper-thin flakes, rough and grey in appearance
- The hole is the result of brittle fracturing, not melting
There is absolutely no point I can see in trying to repair this engine. All the metal around the breach is probably thinned out to the point that it will be virtually impossible to weld to it. This wasn't a very 'serious' project anyway, just something to try to see how well it would work. As is, it makes a nice artifact of the modern valveless pulsejet era. It would be possible (even fairly easy) to re-use the intake/tailpipe assembly to make a prototype Reynstodyne (TM) FMC II engine, with a custom-built chamber of reasonable weight material; I don't know if I want to tear it up for that, though. Maybe it would just be better to mount it on a nice piece of oiled walnut and use it as a wall hanging.
This is where I'll post the final photos of Fo Mi Chin as a memorial, when I get them.
L Cottrill
After a couple of successful runs yesterday afternoon, I decided I needed to get one more photo of the engine running hot in semi-darkness, to try to show the intake flame, chamber heating pattern, etc. So I got the shot metered, got the camera into position and fired her up. Started nicely and I got it running just right and was just about to circle around to the camera to snap the shutter, when suddenly the pulsation pitch went up about two full steps! I knew something was very wrong. After two or three seconds running like this, the engine quit running, with yellow flame billowing from the exhaust port and some point on the chamber opposite my position (naturally!) so I quickly shut down the propane.
The hole opened up low on the right side of the chamber. It is a roughly crescent-shaped, rough-edged hole almost an inch (25mm) end-to-end. The hole is centered perhaps 4 cm aft of the front welded seam (where the dome is welded on). The metal remaining at the edge is basically tissue paper thin, and the edges appear quite sharp, not melted back. Here are some interesting things to think about regarding this engine and its ultimate failure:
- This is the lightest and most compact valveless engine I have ever gotten to run well: 2.6 inches max diameter (67 mm), 22.5 inches length (ignoring spark plug) (572 mm) and 15 ounces total weight (including plug)
- Due to the thin material, this was one of the most difficult welding projects ever - but, it was ultimately doable
- Intake flame visible during the final run was straight out, parallel to the tailpipe surface
- This kind of ultimate failure was expected sooner or later, because of the very thin steel can used for the chamber
- The engine continued to run after the hole opened up, but at a higher frequency, presumably due to the creation of an additional pressure node
- Since the hole was on the opposite side where I couldn't see it, I can only speculate that it started small, then enlarged, killing pulsation
- The steel material was NOT blown out - it was sucked INTO the chamber (I shook it out after the engine cooled); the material consisted of a variety of tissue-paper-thin flakes, rough and grey in appearance
- The hole is the result of brittle fracturing, not melting
There is absolutely no point I can see in trying to repair this engine. All the metal around the breach is probably thinned out to the point that it will be virtually impossible to weld to it. This wasn't a very 'serious' project anyway, just something to try to see how well it would work. As is, it makes a nice artifact of the modern valveless pulsejet era. It would be possible (even fairly easy) to re-use the intake/tailpipe assembly to make a prototype Reynstodyne (TM) FMC II engine, with a custom-built chamber of reasonable weight material; I don't know if I want to tear it up for that, though. Maybe it would just be better to mount it on a nice piece of oiled walnut and use it as a wall hanging.
This is where I'll post the final photos of Fo Mi Chin as a memorial, when I get them.
L Cottrill