Author Topic: Fuel Injection Systems Part 2  (Read 2019 times)

Offline Roger B

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Fuel Injection Systems Part 2
« on: November 14, 2021, 08:36:12 AM »
My first fuel injection thread was getting a bit unwieldy so with some new thoughts I decided to start a new thread. The original is here https://www.modelenginemaker.com/index.php/topic,4906.0.html

The first piece will be a new, smaller, helix controlled injection pump. The last run of the 2 stroke diesel showed significant damage due to overtravel/overshoot of the cam follower so I decided to reduce the size and weight of the various components. The first step was a Mod 0.4 rack and pinion in place of the earlier Mod 0.5 one. The rack is wide enough that the sliding motion can take place there so I can reduce the width (and weight) of the pinion.

The pump element is made much as before, the guide for the pinion is reduced from 5 to 4mm. The cylinder was drilled 1.85mm and reamed 1.95mm using a floating reamer holder. A 1.97mm pin gauge would just enter the start of the bore. The delivery valve seating is finished with a 4.5mm end mill rather than a 4mm one. This makes it easier to cut the M5 x 0.5 thread for the delivery valve body.
Best regards

Roger

Offline Admiral_dk

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Re: Fuel Injection Systems Part 2
« Reply #1 on: November 14, 2021, 11:46:18 AM »
Well I will still be following your progress, as I'm sure will a lot more here  :cheers:

Per
« Last Edit: November 14, 2021, 09:04:16 PM by Admiral_dk »

Offline Don1966

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Re: Fuel Injection Systems Part 2
« Reply #2 on: November 14, 2021, 08:37:55 PM »
I will be with you also Roger!


Don

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Re: Fuel Injection Systems Part 2
« Reply #3 on: November 14, 2021, 11:25:59 PM »
Watching along!!!    Hope you have a 12 plunger unit coming along!   8)
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline 90LX_Notch

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Re: Fuel Injection Systems Part 2
« Reply #4 on: November 15, 2021, 10:51:37 AM »
I will still be following along Roger.  This is great stuff.

-Bob
Proud Member of MEM

My Engine Videos on YouTube-
http://www.youtube.com/user/Notch90usa/videos

Offline Roger B

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Re: Fuel Injection Systems Part 2
« Reply #5 on: November 21, 2021, 06:50:03 PM »
Thank you all for your support and interest  :) This is, as I have said before, a long term project but I hope to be able to offer some solutions. A 12 cylinder version is just a lot of single cylinder versions  :) The Porsche 917 pump was actually quite interesting. It had two rows of pumps with the rack down the middle so you needed plungers with left and right hand helixes.

Having finished the pinion and the end of the pump element I tried it with the return spring. A 1.2kg mass compressed the spring around halfway. Is that too much or too little  :thinking: no idea, it will have to wait for some running trials. Next up I drilled the inlet port in the pump element and milled the locating flat. I did this using my home made fine feed for the little Proxxon drill. I could also have moved the vice over to the Proxxon mill which would also have kept the alignment.

The pump body is again made much as before using the 4 jaw independent chuck to give the offset. The final stage was a quick sanity check that the recess to locate the element was of the correct depth.
Best regards

Roger

Offline Dave Otto

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Re: Fuel Injection Systems Part 2
« Reply #6 on: November 22, 2021, 01:08:59 AM »
Still following along!  :ThumbsUp:

Dave

Offline Roger B

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Re: Fuel Injection Systems Part 2
« Reply #7 on: November 27, 2021, 05:09:26 PM »
Thank you Dave  :)

Next up I moved to the small Proxxon tools and milled the cavity in the pinion for the tappet. The inlet hole in the body was finished with a 4.5mm endmill to give a flat bottom and the most threads for the inlet union. I used the small Proxxon drill to tap the M2 threads to attach the flange to the body and then moved onto the tappet. This is made from a short piece of 3mm keysteel so it can be hardened. The ends were shaped by filling rather than some complicated mill set up with rounding cutters and the centre was spotted from the pinion using a 4mm diameter centre drill.

The next steps are to harden and lap the element and to grind the helix in the plunger.
Best regards

Roger

Offline Roger B

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Re: Fuel Injection Systems Part 2
« Reply #8 on: December 05, 2021, 08:05:24 AM »
Next up is the pump mounting flange. There were several possible ways to make this however I decided to do most of the work in the lathe. It is fixed to the body with M2 countersunk screws. The final operations will be completed the next time I'm in milling mode.
Best regards

Roger

Offline Roger B

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Re: Fuel Injection Systems Part 2
« Reply #9 on: December 11, 2021, 04:28:45 PM »
The flange was milled to width and then profiled with some filing buttons. Next the slot for the control rack was milled with a 5mm endmill and then opened up to 6mm to be a closed fit on the rack.

A 30mm piece of the rack was cut to approximate size with a hacksaw and finished by milling.
Best regards

Roger

Offline Roger B

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Re: Fuel Injection Systems Part 2
« Reply #10 on: December 12, 2021, 04:31:32 PM »
The rack is held in place with a small 2mm thick brass plate. This was cut to size with the Proxxon table saw so didn't need any finishing. It's held in place with 2 M2 capheads.

Due to various design changes the spigot on the flange was 3mm instead of 4mm. The was a suitable piece of aluminium with the right diameters in the odds and ends box so I just parted off a 1mm slice.

The pump element was hardened by heating to red for a few minutes and then quenching in water. When it was made the 1.96mm pin gauge would pass straight through. After hardening a 1.95mm pin gauge would not enter. The bore was lapped using Acro needle laps starting with 5 micron diamond paste, finishing from 1.96mm to 1.97mm with 1 micron paste.

The first needle lap is already worn after maybe 6 pumps. That's why the are sold in packs of 10 I guess.
Best regards

Roger

Offline Admiral_dk

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Re: Fuel Injection Systems Part 2
« Reply #11 on: December 13, 2021, 01:09:55 AM »
Still crossing all my fingers etc. and praying that you succeed and may it not take too many more tries before you are happy with the result.

 :popcorn:    :cheers:

Offline Roger B

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Re: Fuel Injection Systems Part 2
« Reply #12 on: December 26, 2021, 01:39:53 PM »
A little bit more on this one.
The delivery valve seating was lapped with a 3mm diamond charged ball as before and then I needed to cut the metering helix in the plunger.
This is another thing that tests my lathe's abilities. I have worked out a change gear set up that gives the required 4mm pitch. As the cutting is controlled by the leadscrew handle at low speed I can set the gears with zero clearance to reduce the backlash. The original Hobbymat milling angle plate was modified to allow me to set the Proxxon hand drill/grinder at the required 32. The cut was made with a grey Proxxon disc at 20 000rpm with an infeed of 0.05mm and a slow drive from the leadscrew handle. The slide was withdrawn after each cut to further reduce the backlash effects.
As this set up takes some time I cut a second helix on the other end of the piece of 1.97mm pin gauge. After a light deburr with a fine diamond one the plunger passed smoothly through the pump element.
Best regards

Roger

Offline Roger B

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Re: Fuel Injection Systems Part 2
« Reply #13 on: March 09, 2022, 11:16:05 AM »
I fitted the new smaller helix pump onto my two cylinder engine, the details are here:

https://www.modelenginemaker.com/index.php/topic,7883.msg248312/topicseen.html

There were various problems with this design:

1) The O ring seal between the pump element and pump body requires close control of tolerances and careful smoothing of almost hidden edges to avoid damaging the O rings.

I conceived this design to allow for hardened pump elements and a modular system to make a multi cylinder pump. Im now not so sure that this is an optimal solution, maybe a simple hardened sleeve shrunk/Loctited into an aluminium body might be better  :thinking: Care would be needed to ensure that the inlet port in the sleeve lined up with the port in the  body, easy with Loctite, harder with a shrink fit.

2) Fuel leaks past the plunger.

I accept that there will always be leakage past a metal pump plunger in a metal barrel. This could possibly be reduced by using some form of seal around the end of the plunger but I think that would be another level of technology with a 2mm diameter seal  :headscratch:

The other option is to manage the leakage. With the current vertical layout the fuel leakage flows down onto the operating mechanism and washes the lubricant away resulting in wear and seizing. This would be less critical with diesel which has some lubricating properties. My first two injection systems have/had horizontal pumps so that leakage past the plunger does not get into the mechanism.

Maybe a new design with the pump horizontal would be better as it would allow for the fuel leakage to by led away from the mechanism.

3) Stroke/volume control and the inlet port.

My first pump designs were based on full sized diesel pumps where the inlet valve is a port in the side of the pump barrel. This removes the need for an actual inlet valve and any sealing problems. It also allows for a precise control of start of injection which is necessary for true diesel operation. For operation on petrol  (gas, benzine) it creates a problem as the cylinder is under vacuum when the port opens causing the petrol to vaporise. This can be solved, as in full size practise, by pressurising the fuel above its vapor pressure ~0.8 bar/10psi.

Controlling the volume by controlling the pump stroke works and is quite simple but does not give constant timing, which is not a problem for manifold petrol injection. It is however very sensitive to wear in the operating mechanism. Even if the actual working stoke remains the same increased clearances in pivots etc. reduce the delivered volume. When the working stroke is around 0.2mm this is a problem.

Controlling the volume with a helix ground in the plunger is more complicated. It gives a constant start of injection point and seems fairly linear. This seemed to work ok with diesel, but with petrol the leakage past the plunger washed the lubricant away from the rack and gear make the movement stiff and jerky.

Next steps.

I think I need to split the development into two streams:

a) The helix controlled pump for diesel, continuing on the current path but using a simple hardened sleeve.

b) A horizontal pump with separate inlet and delivery valves for petrol. This will reduce the sensitivity to wear in the operating mechanism, hopefully remove the need for a separate pressure feed pump and allow separation of the leakage past the plunger.

The picture are taken from the two cylinder engine thread so the numbers are out of sequence.
Best regards

Roger

Offline Admiral_dk

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Re: Fuel Injection Systems Part 2
« Reply #14 on: March 09, 2022, 11:51:33 AM »
I can think of one more option - an up-side-down pump - that way leaking fuel do not wash the moving parts ....  Sad to say that is all I can come up with right now  :-[

Per