Fuel injection systems

[Roger B]

The needles were polished as before and then I made some M1.4 nuts from 2mm hex stock. Amazingly none escaped 

[Admiral_dk]

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 ?

[Roger B]

Thank you Per 

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.

[Roger B]

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.

<a href="https://www.youtube.com/watch?v=9mkeQkbctW0" target="_blank">http://www.youtube.com/watch?v=9mkeQkbctW0</a>

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'

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

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

<a href="https://www.youtube.com/watch?v=qj2zM52aiLc" target="_blank">http://www.youtube.com/watch?v=qj2zM52aiLc</a>

[Vixen]

Roger, More incredible watchmaking skills on display with the newer, small injectors. 

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

Stay safe

Mike

[Roger B]

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 

<a href="https://www.youtube.com/watch?v=46-s4e_2zbk" target="_blank">http://www.youtube.com/watch?v=46-s4e_2zbk</a>

<a href="https://www.youtube.com/watch?v=MMYXSOJmW0Q" target="_blank">http://www.youtube.com/watch?v=MMYXSOJmW0Q</a>

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

[Vixen]

Hello Roger,

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

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

[Roger B]

Thank you Mike,

I am also very much a layman in this field, my qualifications are in electrical engineering     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 

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

[Roger B]

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.

[Roger B]

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  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  maybe it's scale or maybe it's some form of growth/distortion???

[Roger B]

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.

[Roger B]

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 

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.

[Roger B]

Things are going somewhat slowly at the moment. The Board of Directors has just signed off a multi million factory consolidation project. I now have to supply a new electron beam crosslinking facility from an American supplier who I cannot visit. We are trying to use Microsoft Teams etc. but it is very inefficient. In the past everyone involved would have gathered in a conference room with drawings all over the table and on the walls and in a couple of days would have produced an fairly optimised design. Now we are trying to work with multiple A0 drawings on a couple of computer screens 

Back to model engines  I cut the slot for the rack on the little Proxxon mill and it all seemed to fit together OK. I received the O rings for the element and that also seemed to fit without ripping chunks off them. The next step was the tappet mounting block. This is fixed to the end of the body with a couple of M2 bolts or studs (tbd). It was bored to 6mm in the lathe and will have a 5mm bore bronze bush to accept the existing tapped (possibly with a new bearing for those who are following the diesel thread).

[Roger B]

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[Roger B]

The tappet bush was turned from a length of bronze bar and pressed into place. The locating peg hole was drilled and tapped M2. As the body is larger than the original I can lock it with an M2 x 3 grubscrew. The fixing holes were counterbored 4mm and then taken to a depth of 3mm with an endmill. Next up is the mounting plate.