Author Topic: Fuel injection systems  (Read 58444 times)

Offline Roger B

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Re: Fuel injection systems
« Reply #270 on: May 26, 2020, 06:37:08 PM »
The needles were polished as before and then I made some M1.4 nuts from 2mm hex stock. Amazingly none escaped  :wine1:
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Roger

Offline Admiral_dk

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Re: Fuel injection systems
« Reply #271 on: May 26, 2020, 08:57:06 PM »
This are very small parts and you need a very good finish too .... but it looks like you have achived it - does the small lathe make it any easier to do those sizes ?

Offline Roger B

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Re: Fuel injection systems
« Reply #272 on: May 27, 2020, 08:17:11 AM »
Thank you Per  :ThumbsUp:

The small lathe certainly makes it easier to see what is going on. If I was using an ER32 chuck and 10mm tooling the parts would be almost completely hidden and it would be difficult to get a micrometer in to measure. It is certainly a different process to using the big lathe (well big to me). I will be running at 2000rpm plus with depth of cut less than 0.2 mm often down to 0.05mm or less but the feed is as fast as I can turn the handle.
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Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #273 on: May 29, 2020, 05:34:59 PM »
The other benefit of the small lathe (and mill) is that to clean them down you hold them over the waste bin and shake them  :)

I put the 10░ nozzle together and gave it a try with the test pump. As expected it was just scattered droplets.



I then lapped the seating with 2.5 micron diamond paste for a few minutes. I allowed the valve to swing in the hope of making a slightly less sensitive bell shaped seating. With the spring screwed down quite tightly, it would just open with a 1.2kg weight on the end, I got a good pattern and the characteristic 'squeak'



Finally I reduced the spring pressure a bit (not calibrated) and still got a fairly good result:










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Roger

Online Vixen

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Re: Fuel injection systems
« Reply #274 on: May 29, 2020, 05:40:20 PM »
Roger, More incredible watchmaking skills on display with the newer, small injectors.  :ThumbsUp: :ThumbsUp:

The spray pattern looks neat and compact. but I still prefer the flame thrower test.

Stay safe

Mike
It is the journey that matters, not the destination

Offline Roger B

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Re: Fuel injection systems
« Reply #275 on: May 30, 2020, 06:02:03 PM »
Thank you Mike  :)

The 'flame thrower' test takes a little preparation but I tried it on the new 10░ and 15░ needles. There is a significant difference but I am not sure if it is the design or due to  construction tolerances. The spray patterns are also different so I think I will have to make another 10░ injector and see if I get similar results  :headscratch:






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Roger

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Re: Fuel injection systems
« Reply #276 on: May 30, 2020, 07:06:23 PM »
Hello Roger,

I am not sure of the scientific value of the flame thrower test but they do look a lot more spectacular. :ThumbsUp: :ThumbsUp:

To me, as a layman, the 15 degree cone appears to reach complete combustion in a shorter distance and time compared to the 10 degree injector. I guess it's because the wider jet entrains more air and so burns quicker.  Any thoughts?

Stay in and stay safe

Mike
It is the journey that matters, not the destination

Offline Roger B

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Re: Fuel injection systems
« Reply #277 on: June 01, 2020, 06:52:42 PM »
Thank you Mike,

I am also very much a layman in this field, my qualifications are in electrical engineering   :zap:  The bit I am struggling with at the moment is the difference between what I see in free air and what is happening at 30 Bar  :thinking: :headscratch:

The needle type injector is trying to keep closed against compression pressure but the mushroom type is trying to open against compression pressure  :thinking:
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Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #278 on: June 06, 2020, 04:28:24 PM »
As mentioned in the diesel thread the helix pump had worn to a level that it would not prime. Wear problems in the mild steel body had always been at the back of my mind and I had started a new pump design using a round element made from silver steel in an aluminium body. This would also allow multi element pumps for future developments. I have some concerns about distortion when hardening as I just have a 'Camping Gaz' blowtorch for heating but we will see what happens.
The pump element is generally made as before but has a couple of O rings to seal the inlet side to the pump body and a locating flat to ensure that the inlet port will line up with the one in the body. I was in two minds as to cut the locating step and then the flat or cut the flat and then the step which left more to hold the element with until the final operation.
After reaming the 1.96mm pin gauge would pass through but the 1.97 would barely enter, much as before.
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Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #279 on: June 06, 2020, 06:37:12 PM »
The element was then moved to the vice for drilling the inlet port and milling the locating flat before moving back to the lathe to turn the locating step. It may have been better to turn the step first  :headscratch: but the finished surface was below the interrupted cut. The element was then heated to middle red and dunked into cold water. The file test suggests that the surface is hardened, I have no idea about the bore  ::) Interestingly I can't even get the 1.95mm pin gauge to enter  :thinking: maybe it's scale or maybe it's some form of growth/distortion???
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Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #280 on: June 08, 2020, 07:08:45 PM »
Next up is the body. This is from the same DIY store 15.5mm aluminium I used for the carburettor project. A the inlet side must be flat to make the seal I had to slightly asymmetrically mill this down to 15mm. The bores are not central to give a space for the control rack so this was set up in the 4 jaw independent chuck. The steps were drilled undersize, reamed and then finished to depth with appropriately sized end mills. The slot for the rack was milled on the Proxxon mill so I didn't have to change the Hobbymat back to milling mode.
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Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #281 on: June 14, 2020, 08:16:02 AM »
After the rack slot was finished I drilled and tapped the inlet port and the retaining grub screw holes. The element was lapped to fit the helix plunger. If it is too worn I can make a new plunger and lap out the bore to suit. The parts were all cleaned in the ultrasonic bath and assembled.
Problem  :( I didn't allow for the effective PCD of the rack so it barely engages with the gear  :toilet_claw:

Having received a 1.99 and a 2.00mm pin gauge I cut the old body in half and carefully deburred the bore. The 1.99mm pin gauge would not go in so the wear was less than 0.01mm. I also noted that that body was one were I had silver soldered a replacement thread in the inlet port so the bore may have been damaged even though it was lapped to 1.98mm.

I could have milled the rack slot deeper and used a shim behind the rack but having received some 15mm square aluminium (rather than the DIY Store 15.5mm with grooves) I decided to make a new body.
« Last Edit: June 14, 2020, 03:17:38 PM by Roger B »
Best regards

Roger