Author Topic: Fuel injection systems  (Read 41846 times)

Offline Roger B

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Re: Fuel injection systems
« Reply #165 on: April 21, 2018, 04:03:09 PM »
As spring has finally sprung here I thought I would give the diesel a try  ::)

I primed and tested the injection system in the workshop with alcohol and then took it outside and filled the tank with diesel. As I first trial I held  lighter in front of the injector and got some puffs of yellow flame whilst turning the engine by hand.


I then fitted the injector and gave it a try. There were a few puffs of blue smoke and then nothing. I removed the spring adjusting screw from the injector so I could remove and check the needle. Unfortunately I didn't realise how quickly it would fly out under compression pressure. Result one lost needle  :( I  hunted around with a magnet without success so I tried again with the needle from the other injector.

This time I got fairly consistent blue smoke that was controllable with the rack but no real firing  :headscratch:


Obviously the needle was not the best so I need to make a new one. I think that the compression is sufficient but I could make a compression tester although the non return valve would have to be right where the tip of the injector is to get good results. The atomisation also seems ok, but the penetration may be too much and most of the fuel is just hitting the piston crown. Lots to think about but overall not to bad. Blue smoke was more than I was expecting  :wine1:
Best regards

Roger

Offline Admiral_dk

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Re: Fuel injection systems
« Reply #166 on: April 21, 2018, 07:54:37 PM »
I really hope that this indicates that you are close to a runner on diesel  :cheers:

Offline Roger B

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Re: Fuel injection systems
« Reply #167 on: April 27, 2018, 11:09:31 AM »
I hope so too  :ThumbsUp: I have a few more things to try with this injector like a weaker spring and altering the timing. As the blast of fuel from the injector tended to blow out my lighter I think that it may be too strong.
I will make a compression tester to fit in place of the injector. It's always best to have real numbers to work with.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #168 on: May 03, 2018, 05:38:55 PM »
I decided to try and make a 'mushroom' valve injector. This is easier for petrol injection as it doesn't require a leak off and has also been used successfully in small diesels by Find Hansen.

The valve is turned from 3mm silver steel. I did wonder about upsetting the end of some 2mm silver steel but decided the heat treatment stuff was too much bother. The shaft was turned down to 2mm and the section before the valve was reduced to 1.6mm. The valve cone was turned to 15░ inclusive. The top of the shaft was threaded M2 and the valve end was hardened. This was then finish ground and polished.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #169 on: May 03, 2018, 05:42:44 PM »
The nozzle is turned from a piece of brass bar. This follows the dimensions of my existing injectors but could be made smaller. I have some 3mm AF nuts for the valve that will fit inside the 4.5mm clearance for an M5x0.5 thread.
Best regards

Roger

Online MJM460

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Re: Fuel injection systems
« Reply #170 on: May 03, 2018, 11:46:11 PM »
Incredible work Roger.  Your whole thread has been a masterclass in tiny precision work, along with great instruction on the ins and outs of injectors.  I never miss following along

MJM460
The more I learn, the more I find that I still have to learn!

Offline Roger B

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Re: Fuel injection systems
« Reply #171 on: May 06, 2018, 04:55:15 PM »
Thank you for your support  :ThumbsUp:  :ThumbsUp: I know that progress is usually slow due to work, life, etc. but I think I have made some progress. I am fairly happy with both the injection pumps and operation as manifold injection for petrol engines. Diesel injection still holds some challenges (discussed in the diesel thread).

The injector body was turned from a piece of 7mm hex brass and tapped M5 x 0.5 at both ends. the first tests were not a success  :( I did not leave enough grinding allowance on the needle so the final diameter was too small. When I tried it in spite of this there was a fuel leak between the body and the nozzle. When I tightened it some more I stripped the threads  :facepalm:

The cause of the leak was running the die right up to the end when cutting the thread in the nozzle which resulted in some score marks in the sealing face. Luckily I could salvage both parts by reducing the lengths a little and re-cutting the threads. I then made a new needle, leaving the cone larger, then grinding it down to length at the end.

When the diesel has had a couple of days quarantine in the garage (after the last trials) I can bring it back into the cellar for some more trials with alcohol.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #172 on: May 11, 2018, 07:30:45 PM »
The trials with the 15░ mushroom injector were not satisfactory so I decided to make a 30░ mushroom. This was much the same as before except that the clearance when grinding the tip was somewhat reduced.
I also decided to open out the normal nozzle to 0.5mm and had to make an extension holder for a 0.5mm drill. This was ok, I had a 0.5mm centre drill to start off with and running the lathe at the maximum 2000rpm all went ok.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #173 on: May 11, 2018, 07:38:21 PM »
The drill was Loctited into the extension and the nozzle was open out to 0.5mm without problems  :) I then used the Proxxon micro mill to put a couple of spanner flats on the mushroom nozzle and set it up for a try.
Turning the engine over with the drill, as in a starting trial gave quite a close spray pattern at 30 cm, maybe still to much penetration  :headscratch:  ::)  :help:


I will try the conventional injector with a 0.5mm nozzle later.
Best regards

Roger

Offline Admiral_dk

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Re: Fuel injection systems
« Reply #174 on: May 11, 2018, 08:32:40 PM »
Looking good Roger  :ThumbsUp:

Regarding the "perfect" spray pattern -- I do believe that it depends on the size and shape off the tube you spray into and the angle of doing so. It's "fairly easy" to get it to run, at lot more work to make it run good and a hell lot of work to get it perfect.
So there are a great amount of solutions for the easy, still quite a good number that will run good, but probably not that many that will run perfect.

The simplest I remember is the "carburettor" on the Velo Solex moped. There is a membrane pump on the side of the crankcase driven by the pumping pressure in the crankcase. It lifts the gasoline from the tank to the "carb" where there is a very fine nozzle that sprays the gasoline into the venture, a spring operated valve that allows the surplus to return to the tank and a throttle ... and that is it (if memory serves some 43 years after I opened one). This system isn't a bad as it sounds even though the throttle isn't very good as you get between 60 to 90 Km. on a litre gasoline.

Offline Roger B

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Re: Fuel injection systems
« Reply #175 on: May 13, 2018, 04:05:41 PM »
Thank you Per  :ThumbsUp: I have plenty of variables to play with on this before I start thinking about turbulence in the combustion chamber  :headscratch:  :headscratch:

I tried the normal injector with the nozzle increased to 0.5 mm (double the area of the original 0.35mm) I think that the penetration is reduced, but the real test will be on the engine. Until I get actual firing it's hard to know in which direction to go. I will also try the mushroom injector on the petrol engine.


Best regards

Roger

Offline Admiral_dk

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Re: Fuel injection systems
« Reply #176 on: May 13, 2018, 09:10:30 PM »
I forgot - the finer the mist, the better the mixture => less fuel needed for the same rpm.

Offline Roger B

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Re: Fuel injection systems
« Reply #177 on: May 19, 2018, 04:27:44 PM »
I fitted the mushroom injector and variable stroke pump to the horizontal engine for a petrol trial. It ran well, still showing a surprising throttle response for a fixed stroke setting on the pump. The fuel feed pump is not happy pumping into a closed system and tends to heat up and vaporise after a while. I need to add some sort of bypass or try a different style of pump.

Best regards

Roger

Offline Vixen

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Re: Fuel injection systems
« Reply #178 on: May 19, 2018, 04:35:16 PM »
Good progress Roger. The engine sounds like it is running nicely

Mike
It is the journey that matters, not the destination

Offline Art K

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Re: Fuel injection systems
« Reply #179 on: May 19, 2018, 10:59:27 PM »
Roger,
I have to admit not having followed this thread much, due to how far along it is. Curiosity got to me and I finally tuned in. Very interesting lots of very fine work. At some time in the near future I'll have to start from the beginning. Won't belong and you'll have that diesel running.
Art