Hot Bulb Engine, here we go...

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cfellows

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Meager beginnings. I started with the injector pump. Find had an exploded view of (most) of the parts on his pump. He also supplied a couple of dimensions, so I took it from there. My ball check valves will be 3/32" compared to his 1mm. Also, my plunger rod will also be 3/32" compared to his 2mm. The rest of the dimensions are approximations with the square part being .25" and the round part 3/16". I'm hoping there is nothing other than close tolerances required to make this work. And I don't see how it could be more frustrating than my experience thus far with carburetors!

The injector also looks pretty straight forward and I think I have the hot bulb figured out. I don't know what materials he used for the hot bulb. I'm guessing stainless steel would be best but I may have to settle for mild pr silver steel for starters.

This will likely be a slow process since I have a number of other domestic projects that I can't seem to avoid, try as I might. I also will probably use more conventional gearing than Find's very nice helical gearing. Would love to make helical gears but that sounds like a project for another time (maybe another lifetime!).

So, drift in and out from time to time and we'll see how it goes.

Chuck



InjectorPump.JPG
 
How do you plan to make the injector?
 
Chuck

Looks an interesting build. Are the plans available anywhere so we can see where your going or are you going to keep us in suspense?

Pete
 
No plans or drawings. All I have to go on are some pictures and a few descriptsions at Find Handsen's website:

http://www.findsminimodelhotbulbengines.dk/

I'm not going to attempt to build any of his engines, but rather come up with my own.

Chuck
 
Chuck

OK now you really do have me interested.

And we'll get some plans at the end..................?



Pete
 
IIRC there's also some useful information mixed into the original hot-bulb patents (linked off the Wikipedia page)

Unlike a diesel, the injector just has to get some fuel inside the cylinder and onto something hot, not actually vaporize it during the injection process (that's what the hot-bulb is for)
 
I looked at that fellow's engines, Chuck. They look wonderfully complex. This should be a great
build thread. The newly made parts look nice.

Dean
 
shred said:
IIRC there's also some useful information mixed into the original hot-bulb patents (linked off the Wikipedia page)

Unlike a diesel, the injector just has to get some fuel inside the cylinder and onto something hot, not actually vaporize it during the injection process (that's what the hot-bulb is for)

Yeah, I had kind of figured that the injector only needed to get the fuel into the engine and onto a hot surface. I have to also think that timing is pretty critical. Find Hansen indicates that you also need a 7:1 or better compression ratio to help keep the hot bulb hot.

Chuck
 
Deanofid said:
I looked at that fellow's engines, Chuck. They look wonderfully complex. This should be a great
build thread. The newly made parts look nice.

Dean

Thanks, Dean. Find's engines are pretty amazing, comprised of all the things that really pique my interest. I especially like the helical gears. I'm not anticipating building anything quite as complex as his engines, at least not at first. I've actually contemplated converting my Plumbing Parts engine over to hot bulb operation.

Chuck
 
Hot bulb engines are described in a SAE paper 2002-01-0115 Olaf Erlandson from Lund in Sweden.
I worked on the last factory that made this kind of engines in the world in 1977 in Hundested,Denmark.
The final versions were crankcase scavenged two strokes of one or two cylinders.From memory the biggest single cylinder was 420 mm bore and 450 mm stroke.This was for fishing vessels and gave 150 horsepower directly to a two bladed screw that changed pitch to go astern.Timing of injection in the full size engines was not very critical and this was their main argument against real diesel engines.
Try Youtube Hundested hot bulb
 
Looking forward to this build Chuck. Your parts look good.

Neil your comments above bring back memories of a canal boat holiday I did a few years back when we passed a Bollenger powered working boat going the other way through the Braunston tunnel, that wonderful sounding engine coming towards us out of the darkness was just magic.

Nick
 
Cheers Neils,

Yep that's the sound, lovely, possibly the same boat. Sorry I got the spelling wrong, unfortunately, nothing new there then - note to self: it's Bolinder not Bollinger, close but no cigar :)

Chuck I hope your engine makes a similarly distinctive sound too.

Nick
 
I'm really bummed about the hot bulb engine project. I had originally thought that the fuel was injected at or near TDC and that's what controlled the ignition timing. Now I find out that the fuel is injected into the hot bulb chamber during the air intake stroke and that ignition timing is controlled by when the air reaches the fuel vapor and the hot bulb. Sounds dicey at best and it could be very time and labor intensive to get this thing running. Aarggghhhhh!

Chuck
 
Chuck,
Injection during the intake stroke doesn't quite sound right. Where did you get this information? The 2 stroke hot bulb engines used injection at mid compression stroke. I would think the 4 strokes would be similar.

Jeff
 
The patents also speak to injecting fuel during the intake stroke. They intake air separately from fuel-- fuel goes into the hot-bulb for vaporization, air into the cylinder. They don't mix until the compression stroke. At least one of the patents suggests timing is done by the ratio of the volumes and compression ratio-- get enough air into the hot bulb and you get ignition.

http://www.google.com/patents?id=3n...=gbs_selected_pages&cad=1#v=onepage&q&f=false
http://www.google.com/patents?id=oe...=gbs_selected_pages&cad=1#v=onepage&q&f=false
http://www.google.com/patents?id=05...=gbs_selected_pages&cad=1#v=onepage&q&f=false

The engines seem so simple it doesn't seem like it would be that hard to get one going, but there might be a whole lot of trial-and-error tribal knowledge that's gone by the wayside. They do seem to have a pretty generous unswept cylinder volume, so you could install blocks and such to vary the compression ratio. I'm guessing the fuel-air mixture ratios needed to support combustion are fairly well known, but what other devils are hiding in the details, lord only knows.




 
Shred, to your point of generous unswept cylinder volume, I've noticed this and wonder how they manage to get the compression ratio high enough to generate additional heat.

Chuck
 
Chuck,
I checked the web and my book shelf and hot bulb engines have several names. They are also called oil engines and semi-diesel engines. Lyle Cummins Jr. devoted a chapter to them in "Internal Fire". I glanced through the chapter and it is good information. This book is going for around $25 or less on Amazon.

I also found a cross section drawing of a Mietz and Weiss hot bulb engine in "Elements of Diesel Engineering" Adams 1936.

I should have looked sooner as I could have made the Austin Machinist Club meeting and brought the books for a discussion topic.

Here is a thread on a full size Mietz and Weiss engine:
http://gasengine.farmcollector.com/gas-engines/Start-Your-Engines.aspx

Dan

 

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