Another try to build an engine running with diesel fuel

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Chicken

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Hi All!

Probably everyone here knows the excellent small hot bulb and diesel engines from Find Hansen.

I've already built several IC engines, but all of them running with regular gas and electronic ignition. Actually I don't like electronic ignitions as a battery is always required, and sometimes when I want to run my engines I end up with a empty battery and no fun. :(
I also made some experiments with piezo ignitions from lighters. They work ok, but are sensitive and usually fail after some few hours of operation.

Of course we all can easily build model diesel engines with regular carbs, running on diethylether fuel, but I don't like the smell of that stuff.

So here my next go to build a real diesel or hot bulb engine running on regular diesel fuel without any electronic components, similar to Find Hansens Engines and of course I want to share my experience.

I already tried to build a 2-stroke hot bulb engine with 30 cc displacement, but totally failed to get a good spray from the injector with such small diesel amounts and it ended up to be a 2-stroke gasoline engine with electronic ignition.

My new project is somehow based on a hit&miss engine I build 2 years ago. It will have a stroke of 60 mm and bore of 46 mm, which makes 100 cc displacement. I thought that a larger diesel engine should be easier to build than a small one.
I got a cast iron base, 2 large flywheels (30 cm diameter, 10 kg each :eek:), and some raw bearing supports:

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The rest of the engine is my own design. I already started last winter, but production stalled in summer as I prefer to be outside then ;)

I started of to build the crankshaft. I usually make them from several pieces. I use 2 steel blanks for the crank webs, weld them together on several small spots and drill the holes for the crank pin and crankshaft in one setup so they are exactly parallel.

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After that I machined the crank shaft and crank pin, separated the two crank webs and put everything together with some loctite just to hold everything in place. I now cross drilled the crank webs and put dowel pins through both crankshaft and crank pin like this:

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I now machined the crank webs to their final size and sawed out the piece of crankshaft between the 2 crank webs. Using this method I already prouced many good crank shafts, this one has a run out of less than 0,02 mm from end to end, which is acceptable I think.

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I continued to machine the bearing supports, the base and the cylinder angle bracket. The crankshaft runs in cast iron bushings and with good lubrication I think this should run fine. After everything was machined a test fittet everything and was happy that the crankshaft with the flywheels turns smoothly.

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Next I machined the cylinder out of some junk metal with a steel liner. The liner will be watercooled.

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I continued with the cylinder head which is also made from a junk steel blank. I pressed in bronze valve cages. I made the valves from a piece of drill rod and silver soldered a bronze head onto it. With bronze valve cages and bronze valve heads you will never have any corrosion issues due to moisture or something.

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I continued with the connecting rod, which I also make from several parts. First I made a cast iron blank for the big end bearing and drilled all holes and threads for the bearing cap. I basically made the same for the piston pin side. Both bearing blanks were now connected with a piece of steel bar. The steel bar has threads on both sides and threads into the big end and piston pin bearing. The thread is very tight and additionally secured with some loctite. Finally, I drilled the piston pin and crankshaft bearing in one setup so everythin is parallel again.
I was planning to make my own piston and rings, but found a 46 mm piston with rings and pin from an old motorcylce in my shop. As I had no other use for this piston, I decided to use it in this engine.
After putting everything together, I was happy that still everything turned nice and free.

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Next, I machined another plate which holds the rocker arms and wich has a cooling water channel at the bottom side, so the cylinder head is sufficiently cooled. I made the rocker arms from some flat steel. The camshaft runs just below the cylinder head and will be driven by a roller chain. I milled the cams similar to some I made for earlier engines. A third cam will drive the injection pump. Currently, the cams are loose on the camshaft, as I need to have the roller chain first to correctly set the valve timing. After that, I temporarly fix the cams with some loctite, then cross drill them and ad a pin.

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That's the state of the art right now. The next work will be the correct valve timing, cam for the injection pump, injection pump and injector and A hot bulb. I deciced to build a hot bulb engine, as it requires lower compression and should be better for a first go. Hot bulb engines also don't need a perfectly atomized fuel and the injection timing can be set to whatever timing and the engine should run. I want to try an injection at 180° before TDC, so the diesel fuel has enough time to evapourate.
Of course, I also need a centrifugal governor which controlls the amount of injected fuel.

I'll keep you updated, as soon as I have some more parts finished.

best regards,
Alex
 
Great project !!Thm:
Witch compression ratio you will keep?
You can fit the "hot bulb" with a glow plug
Cheers
LeZap
 
Thank you!

I want to go with a 10:1 compression ratio. Using this rather high compression for a hot bulb engine should reduce the required heat of the hot bulb. The hot bulb will be heatet with a small propane blow torch. A small propane tank and the blow torch will be permanently attached to the engine.
 
Looking great. Following with interest
 
Hi all,

the valve setup is mostly finished now and working great.

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The last days I started with the hot bulb system. Find Hansen says that he uses an indirect injection into some kind of vapourizer tube. My build will be different though with a direct injection into the hot bulb.

I made some kind of hotbulb holder, which threads into the cylinder head, see the following picture.

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The threaded bolt you see is actually a tube and will connect the hot bulb and injector holder to the cylinder head. It turns freely in the holder and its an allen screw. The hole opposite the bolt allows me to tighten the screw. I silver soldered a threaded sleeve into the hole. The threads inner diameter is just big enough so I can fit the allen key through there. The hole will be closed with a screw once everything is mounted. The 4 small screw holes you see will hold the actual hot bulb.
Opposite to the hot bulb end there is a thread for the injector which will hopefully inject the diesel fuel directly into the glowing bulb:

043.JPG


I will drill 2 small water channels just next to the injector thread, so the injector will also be watercooled.

I don't really have an idea yet how my injector and injection pump will look like, but I will have a first try this weekend once I've finished the hotbulb.

stay tuned and best regards,

Alex
 
Today I managed to finish the hot bulb setup, injector and injection pump.

The injector is now watercooled, so it won't overheat during operation. The hot bulb itself is just some normal steel. It's fairly thin walled, so I hope it will stay hot enough to keep the engine running without any additional heat.

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The whole assembly attached to the engine. It ended up a little cramped, but just enough space to fit in between the valves ;)

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The injector is an open style injector with a non-return valve, so the compression and combustion pressure does not push any air into the fuel system. The nozzle bore is ~ 0.1 mm. I drilled 0.3 mm, but not completely through. I then removed some material with a good mill until the hole became just visible. The nozzle is threaded into the injector body, so I can replace it just in case the spray is not good enough. If I use a syringe with some diesel and push it through the injector I get a good atomization, so I'll just give it a try with this nozzle.

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Here is a picture of the nozzle tip. The thread is 6 mm, the nozzle bore is just visible:

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The injection pump is a simple plunger type pump with a 3 mm piston. It has 2 mm ball valves. It's quite difficult to get a good tight, but still easy moving fit of the piston in the pump body. I used a good reamer and it appears to work fairly well. If I fill the pump body with diesel, I can't push the piston in by hand, so I guess the fit is OK.
in 100 cc of air about 10 µL of diesel can be burned. As the plunger is 3 mm, at maximum power it will have to move about 1,5 mm to pump this amount of diesel. At idle speed, the stroke will be much less of course. This will be controlled by a centrifugal governor, which will be the next part that needs machining.

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The injection pump in parts and fully assembled:

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best regards,
Alex
 
Chicken,
Very ambitious project. I have an old M&W 2 stroke hot bulb engine. It is low compression (~65 psi) and uses injection very early in the compression stroke. It however, injects a solid stream of fuel directed against a splatter plate adjacent to hot bulb port to atomize the fuel. The piston then pushes the fuel mist into the hot bulb. Combustion begins when ever things are right in the hot bulb which would vary greatly with load. Hence the requirement for a very low compression ratio to minimize the hazards of pre-ignition.This system had very low efficiency. It has been estimated that this design pushed about 40% of the fuel up the stack unburnt. However, the design did serve its intended purpose which was to provide an engine that burned less expensive kerosene and was safer to use than gasoline which the insurance companies liked. Later design hot bulb engines used timed injection directly into the hot bulb. With more precisely timed injection, the compression ratio's could be increased providing much higher efficiency. Using injection directly into the hot bulb starts combustion immediately upon injection so it will require injection at or just before TDC, and not at 180 degrees BTC as you suggested.

Jeff
 
Thank you for the advice. I will make the injection cam adjustable, so I can change the injection timing.
I'm copying a bit from the hot bulb design of a Lanz Bulldog, here the injection is ~ 130° before top dead center directly into the hot bulb. Pre ignition can't occur as the hot bulb is still filled with exhaust gas during injection. Combustion starts once the piston is pushing fresh air into the hot bulb. Of course the combustion is not really controlled, but still working fine. I think the same will occur in my small engine, so maybe an early injection is not that critical.
 
Chicken,
The Lanz tractor is a 2 stroke engine with compression at about 5:1. That is similar to the M&W engines which used early injection. The 2 stroke FM Y engines used a 10:1C/R and used timed injection near TDC. I am not sure what other differences there might be between those two designs. With your engine design being a 4 stroke, it could allow enough air scavenging within the bulb to allow combustion on injection. Anyway, I think allowance in your design for injection timing variation is prudent. Good luck with your project. I will be watching your progress.
Jeff
 
Dear Jeff,

thank you for your fine comments, maybe you are right. I have 2 Lanz Bulldogs, one with a 10,5 liter hot bulb engine (45 hp), the other with a 7,5 liter (60 hp) "Lanz Diesel", which is some kind of hybrid between hot bulb and real diesel engine (direct injecting 2-stroke, but uncooled cylinder head. It's started with a diesel/gas mixture and electric spark and turned to pure diesel after a few minutes of operation, the spark is then turned off). the 10,5 liter hot bulb has a 7:1 compression ratio and injection is 130 ° before TDC, the other is 11:1 and 20° before TDC. Of course, both lanz engines are 2-stroke.
I have no idea how my small 4-stroke engine will behave, so I think the best idea is to make the injection cam adjustable and then find the best timing by trial and error.

best regards,
Alex
 
Hi!

Today I had some time to start with the centrifugal governor and machined the 2 pivots holding the governor weights.
My governor will be similar to a bosch type diesel governor:

centrifugal-governor.jpg


my governor will run directly on the camshaft and change the stroke of the injection pump.
In the meantime I have also recived a roller chain and some chain wheels, so the whole cam setup can also be finished now.

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best regards,
Alex
 
Hi!

The centrifugal governor is now fully assembled. I had to make quite heavy weights, as it runs directly on the camshaft. I want to have the engine running at 400 rpm idle, so the governor needs to work properly at ~200 rpm. Tried it out on my lathe and from 150 rpm onwards it works ok.
In the meantime I have also bored the chain wheels to match my design. After adjusting the cam layout I've pinned them onto the camshaft. The injector cam has a set screw now so I can change the injection timing.

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This weekend I could also mostly finish the injection setup. The centrifugal goveror moves a conical bar which then limits the injection pump stroke.
In the following picture you can see the setup with Injection pump, injection pump plunger that is operated by the camshaft, camshaft bearings and conical bar (the cone is in the inside of the plunger housing). The governor will regulate the injection pump stroke between 0 and 1,6 mm.

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best regards,
Alex
 
this is a very cool build. too bad find hansen wont share how he crated true diesel engines.
 
Hi!

Today I ran into a problem. I finished the governor setup and tested everything on my lathe. It does actually work, but due to the low rpm on the camshaft, the governor response is very slow. Probably way too slow to have the engine running nicely. I'll see how I can change this over the weekend...

best regards,
Alex
 
Hi!

Things like that seem to happen when building an engine without any plans ;)

anyway I have found a solution for my problem. I've made a second shaft just parallel to the camshaft which will hold the centrifugal governor. It will be gear driven from the camshaft with a 1:3 gear ratio. This should solve the governor lag problems.
Now I just need to cut 2 small gears...

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Hi ,

Just a few thoughts :

(1) A true diesel is unlikely to function at all with a compression ratio less
than about 9:1 .

(2) A true diesel engine which is hot requires a lower compression ratio to
keep going than a cold engine does to start up . For this reason
various methods have been devised to make engines start
more easily .

(3) The two most common methods are :

Preheating cylinder head and inlet manifold .

Using a temporary supply of more ignition friendly fuel such as
petrol .

(4) Various high and low tech methods have been devised over the years
to make diesel engines run at lower compression ratios . Some of
these are :

Preheating diesel in hot injector to be quite near ignition temperature .

Flame injection and flame pocket ignition helpers .

Catalytic ignition .

(5) Just a bit of personal history :

I come originally from a country district of South Wales - then an
active farming area . Not long after the war and there were many
and varied diesel/tvo tractors in use - mostly worn out wrecks .

Starting any of these on a winters day was difficult indeed . I
remember seeing one of the more obstinate ones being started by
means of setting the c/o valve to petrol , wrapping petrol soaked rags
about the inlet manifold , setting fire to the rags and then the farmer
cranking the engine the engine like a madman . Took a few goes but
started in the end . Very dangerous and Not recommended !

Regards ,

Michael WilliamS .
 

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