Fuel Injection Systems Part 2

[Admiral_dk]

I see that you turn to KISS - 'Keep It Simple Stupid' ....
.... and it has saved my bacon on a number of times, too ...! 

Come to think about it - your new aproch might work even better with an 'Indirect Injection System' .... if you got the room for it .... 

Per       

[steamer]

Not much special about the body, the bore was reamed 2mm and the ball seating was lapped with a 3mm diamond ball lap.

The injection seems to be more of a squirt than an atomisation with the hand test pump:

<a href="https://www.youtube.com/watch?v=S9XOfphk89w" target="_blank">http://www.youtube.com/watch?v=S9XOfphk89w</a>

<a href="https://www.youtube.com/watch?v=fS5owr5DIJQ" target="_blank">http://www.youtube.com/watch?v=fS5owr5DIJQ</a>

A mushroom injector appears better:

<a href="https://www.youtube.com/watch?v=9D-_l4zTTv0" target="_blank">http://www.youtube.com/watch?v=9D-_l4zTTv0</a>

As does the latest needle injector:

<a href="https://www.youtube.com/watch?v=V5M0mXQIXQ8" target="_blank">http://www.youtube.com/watch?v=V5M0mXQIXQ8</a>

Hopefully I can do some running trials in the next couple of weeks 

Hey Roger,
Just an observation, the nozzle in your test video is hanging at the end of a copper tube....and I'm noticing it's vibrating.     That vibration is going to have a fairly significant effect on you paper spray pattern.    If you're counting on that....just sayin....
Dave

[Roger B]

Thank you both 

Per, I have thought about indirect injection, it makes the injection theoretically easier but increases the heat loss due to a larger surface area combustion chamber. The current four stroke diesel combustion chamber is about as small as it can be. There's a poster on HMEM i am following who is looking at building an indirect injection diesel.

Dave, I'm not too worried about the actual pattern at the moment, just the atomisation. Previously while I was trying to work out how to keep everything concentric it was important and someone (possibly Per?) pointed out the vibration of the pipe. The spray from the needle and mushroom injectors lights easily, the jet from the open nozzle just makes my lighter oily. With a much faster pressure rise in an engine turning at 2000 rpm rather that me pushing the handle on the test pump things may be different     

[Admiral_dk]

I can only agree on the heat loss - was just thinking out loud ....

Best wishes     

Per

[Roger B]

I had a quick trial with these injectors today. The workshop I use has been reorganised so the area I can use has a parquet floor rather than concrete so my 'workmate' is rather more lively.

A cold start with the needle injector was as good as last time, supporting the airlock theory.

<a href="https://www.youtube.com/watch?v=nHYDfQaNw98" target="_blank">http://www.youtube.com/watch?v=nHYDfQaNw98</a>

The open injector would not fire properly at all, there was some light blue smoke and a few pops but nothing useful. Most of the fuel came straight out of the exhaust 

<a href="https://www.youtube.com/watch?v=f6O0ms1kg7c" target="_blank">http://www.youtube.com/watch?v=f6O0ms1kg7c</a>

As a confirmation I refitted the needle injector which performed as before.

<a href="https://www.youtube.com/watch?v=nynKOU7mE0E" target="_blank">http://www.youtube.com/watch?v=nynKOU7mE0E</a>

If you look carefully you can see the fuel leaking past the needle coming out of the hole in the spring adjusting screw. Maybe I need to add a return pipe.

[Admiral_dk]

Easy starting with the old model Injectors 

If you look carefully you can see the fuel leaking past the needle coming out of the hole in the spring adjusting screw. Maybe I need to add a return pipe.

Considering that this engine isn't using much fuel (or most likely not doing so) - it is certainly a percentage lost that way. It appears to contain some polutants too - so if you decide to do so, run it through a filter ...

I guess that you already have a seal where it leaks .... 

Per     

[Roger B]

I have been discussing fuel injection with another member on here and started thinking about my last diesel trials.

The engine ran with the injection needle jammed open so I assumed that the fuel was being atomised via the 0.2mm orifice. I made an open nozzle with a 0.2mm orifice and tried that without any success. I now think that the needle jammed partially open and the atomisation was due to the small opening, but how small?

I decided to try and measure the needle lift for both the needle and mushroom injectors. The test pump was set up and primed with lamp oil (like diesel but not so smelly) and I set up a DTI to attempt to measure the lift. There was nothing measurable  Any movement of the indicator needle seemed due to the lack of rigidity of the simple set up. This suggests that the lift is just a few microns and the fuel is atomised by this gap. Lots more to think about 

<a href="https://www.youtube.com/watch?v=4ylfLu_BJJY" target="_blank">http://www.youtube.com/watch?v=4ylfLu_BJJY</a>

<a href="https://www.youtube.com/watch?v=x84gqNyPM6w" target="_blank">http://www.youtube.com/watch?v=x84gqNyPM6w</a>

[Brendon M]

Hello Roger,

Could you instead make a "micrometer" style setup where you can gradually decrease the gap to the point where it starts running?

[Roger B]

Hello Brendon,

Technically yes, but I would run out of hands holding the drill, adjusting the fuel rack and adjusting the injector. Maybe it would be easier when I fit a governor the look after the fuel rack I also suspect the gap may be speed dependant so adjusting the spring may be more practical

As I have said many times I am making this up as I go along, all thoughts and ideas are most welcome     

[Roger B]

Find Hansen, one of the successful small diesel engine makers, recently made a couple of videos showing how he improved a commercial Chinese model diesel engine.

I watched both videos to look for helpful tips and seem to have addressed most of his points. The things to look at are a bigger flywheel and possibly lower compression which are being addressed in the engine thread:

https://www.modelenginemaker.com/index.php/topic,12249.0.html

and a smaller injector with a floating needle which I will post on here.

The mushroom/poppet style injectors I have been using are based on a 1.4mm bore. I have an M1 die and taps so I will try and scale the current design down to 1mm bore. I started out using floating needles but some of my trials seemed more successful with a guided needle so I have used that design since then. A floating needle is potentially easier to make.

I started out as before centre drilling a length of 1.5mm silver steel with a 0.5mm centre drill. The first section was turned down to 1mm to be threaded M1. This is where the problems started, the die was very hard to start and needed quite a force to turn resulting in the rod breaking off     This was a brand-new Volkel die      Luckily the broken piece still had the 0.5mm centre hole so I was able to drill out the broken piece and try again. Same result   
 
I was not sure if the die was faulty or I was just expecting too much so I tried again with an M1.2 die that I got from work when they amalgamated the apprentice workshops. This thread cut with almost no resistance     

Next, I turned up a brass guide bush to support the needle for turning the next sections, first the rest of the shank to 1.2mm.

[Roger B]

The section before the cone was then turned down to 1mm to allow the fuel to flow and finally the cone was turned with a 10° full angle. This angle is another area for experimentation, if it is too acute the needle locks in place. The needle was then parted off and is ready for hardening and polishing the cone.

Finally, I made a few M1.2 nuts.

I am now awaiting a 1.2mm reamer for this injector and a replacement M1 die to continue with the 1mm injector.

[Admiral_dk]

Smaller and smaller again - but as you mention - Find Hansens Injectors are Really small + working well > worth amming for.

Almost a shame that you cant start with a Ø1mm. precision ground pin and grow one end a bit in diameter to get the cone.
Like a 'Die' with a precise 1mm hole and a cone in the top ('negative off the valve') - heat the pin to Red-Hot in one end, drop it into the 'Die' and give it a Wack with a hammer => now only missing the thread in the opposite end ....

Still following and wishing for your succes     

Per       

[pirmin]

the M1 Threads can be realy tricky on this part. i found a good way to hold the needle while turning the Die very very very carefully half a turn and then back off ....since the needle is so long it will start to twist and the Die cant apply the corect force ( thats what i believe ). so i found those fine jewelery hand vises for small drills and needles, it is basically like a collet in Pen format, this allowed me to let only the end that needs threading to stick out of the hand grip and the rest was secured, no twisting could occur. about the m1 Die, i had to drill mine out several times, also a Völkel . with a 0,5mm drill it works out just perfect

[Vixen]

Hello Roger,

Definitely into watch and clock making territory. Trying to thread a 1mm tube ain't going to be easy
I admire your tenacity

Mike   

[Roger B]

Thank you all   

While waiting for the reamer, dies and springs for the smaller injectors I decided to review/check my existing injectors and make sure I could repeat the previous test runs of the 4-stroke diesel.

I have four mushroom pattern injectors and one needle design which I believe have run in the past. The first step was to dismantle the mushroom injectors, check if they were guided or floating needle and measure the cone angle. All were guided with cone angles between 8° and 12°. I then set them all to open with a load of 12N on the needle. The spanners in the pictures are 2mm AF.

Next I fitted the needle injector to the diesel and made a couple of output trials to compare to the previous results. I only did the 500 rpm tests with the battery drill as these should show up most problems. The results were fairly close   

I then set up the test pump to check the mushroom injectors. The first one gave a satisfactory ‘buzz’ and a fairly good spray pattern although there were still a few big droplets.

<a href="https://www.youtube.com/watch?v=1-zZxH6jCcM" target="_blank">http://www.youtube.com/watch?v=1-zZxH6jCcM</a>