Another try to build an engine running with diesel fuel

[Chicken]

Hi!

A spring loaded injector is a real challenge. It's quite difficult to machine a needle with little taper that is perfectly round and furthermore drill a tapered hole that holds the needle. All things must be 100 % tight and the injector must make a squeaking sound when pumping fuel through it.
My first attempt is not too bad, but I call it a failure as the spray is one sided, so either needle or tapered hole are not 100 % perfectly round.
I will try again tomorrow...

best regards,
Alex

 

[Chicken]

Hi!

It looks like I'm failing again. No matter what I try, I never get a useable spray from any injector. It doesn't matter if they are open injectors, or spring loaded injectors. Either they are just dripping or the spray is very irregular.

The frustrating thing: If I close the pressure hose by hand and push on really tight, I get the most beautiful spray one could imagine

slowly running out of ideas now

br,
Alex

 

[Mechanicboy]

Dripping injector is not good. Lap the valve against valve seat with Autosol chrome paste to be sure the valve is tight against pressure before opening pressure is beginning. With other word, the pressure is build up in the injector before opening pressure to make a fine atomized fuel out of injector.

 

[digiex-chris]

following along because I'm on the edge of my seat watching you troubleshoot. I have a feeling you're very close!

 

[Chicken]

Hi!

There is some progress, but minor. I managed to get a sort of useable injector, but the spray is still too bad. I had the engine running for a minute or so. but excess soot forced my to stop it quickly. after this short time, the hot bulb built up quite some soot deposits. I tried a lighter fuel (kerosene), but that didn't make much difference.
I think the only way to solve this is to get a perfect injector which atomizes the fuel into the finest possible dust.

best regards,
Alex

 

[Niels Abildgaard]

Find Hansen is using turpentine.Maybe easier for troubleshooting.

[ame]https://www.youtube.com/watch?v=UGksYSwFucI[/ame]

 

[Chicken]

Hi!

long time no update, was very busy recently with other work.
I have a new injector now which sprays far more reliable than all my previous ones. It's also spring loaded with a fine needle, but 8 mm piston. The piston has an O-ring seal and the spring tension is adjustable. I'll see if there will be another start attempt in the next days.

best regards,
Alex

 

[bigrigbri]

Nice prototyping there Alex.
Inspires me in my diesel build with this sticky area.

 

[Mechanicboy]

Well done with injector. Hope your engine is running with the new injector. Add film while the engine is running in this forum..

 

[Ripcrow]

Can I make stupid suggestion. Build your cam with four lobes. One for intake one exhaust one for driving injector and one that holds injector closed until firing. The lobe will work opposite to most cam lobes but ensures no leakage until up resource is right and allowed to open. Instead of a extended lobe the lobe just has a indent. Not sure how the governor or throttle works in as it puts a lit of pressure on opening and pumping setups

 

[Mechanicboy]

Can I make stupid suggestion. Build your cam with four lobes. One for intake one exhaust one for driving injector and one that holds injector closed until firing. The lobe will work opposite to most cam lobes but ensures no leakage until up resource is right and allowed to open. Instead of a extended lobe the lobe just has a indent. Not sure how the governor or throttle works in as it puts a lit of pressure on opening and pumping setups

Same principle as the first diesel engine in 1897 with cam operated injector + airpressure to atomize the fuel into combustion camber. Unuseful in model engine.

 

[Ripcrow]

Not quite. While the injector is still operating on pressure created by the cam driven pump the forth cam operates the opening. This way fuel is under pressure before the injector is allows to open instead of relying on a ball valve to hold pressure to a point before opening. This way fuel is under maximum pressure which should help with atomisation

 

[Mechanicboy]

I discovered in your picture of injector, where is the return pipe from injector? The O-ring is not allways tight and can have leakage where return pipe wil lead the rest of fuel back to fuel tank under use.

 

[Chicken]

Ripcrow, interesting idea, although maybe a little bit hard to regulate, as the pressure will decrease significantly with decreasing fuel amounts under no load conditions.

Jens, currently there is no return pipe. Currently there are no leaks past the O-ring yet, but for further testing I need to find a stronger spring to increase the injection pressure. Maybe I can improve the spray pattern a little more. But now I'm very close to a running engine. Some new start attempts and hopefully also a video will come within the next few days

best regards,
Alex

 

[Mechanicboy]

Ri

Jens, currently there is no return pipe. Currently there are no leaks past the O-ring yet, but for further testing I need to find a stronger spring to increase the injection pressure. Maybe I can improve the spray pattern a little more. But now I'm very close to a running engine. Some new start attempts and hopefully also a video will come within the next few days

best regards,
Alex

A correct adjusted injector will give a growling sound (sound as rrr-rrr-rrr) when pumping fast with a test pumping set (i am car mechanic). Maybe or no maybe in the model injector can make a growling sound when pumping fast under test, the importand is well atomized fuel out of nozzle.

 

[Ripcrow]

Is your injector a unit injector or a pump separate to injector

 

[Chicken]

Hi!

Today I tried to start it again, but sadly failed again

I get a nice spray from the injector, engine compression is very good, I also get ignitions, but it just refuses to run.

As fuel, I again tried diesel fuel and a light kerosene, the result is quite comparable, the engine won't start on either, although kerosene produces less soot.

I don't know what else I should try. Maybe my combustion chamber geometry is bad.

Or maybe speed it up with a good power drill. Right now I always tried to hand start it.

Ripcrow: there is a separate injection pump.

best regards,
Alex

 

[Ripcrow]

My thoughts are on a model engine a separate pump and injector won't be successful or at least take a lot of work to get it right

 

[Stefan-K]

Hi chicken

Maybe the amount of fuel that is injected is still too much. Try to reduce the stroke of the injection pump. As a guide line look at the injection pump that Hansen uses. It's very very small. And that has a reason.
Where are you from?
Stefan

 

[Stefan-K]

One more thought!
The differential pressure between the combustion chamber and the fuel pressure must be very high. Otherwise you won't get any spray inside the combustion chamber. I. E. If your compression pressure inside the engine is let's say 20 bar and your fuel pressure is 25 bar, the difference is only 5 bar. That's not enough to form any spray inside the engine. The fuel will just form drops inside. You must at least have the same difference in pressure that you have when you test your injector at normal room pressure. You can achieve this by adjusting the spring pressure of the injector needle. The bigger the difference the better it is.
Hope I could explain what I mean.

Stefan