Author Topic: Fuel injection systems  (Read 52511 times)

Offline fumopuc

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Re: Fuel injection systems
« Reply #105 on: December 11, 2016, 07:29:21 AM »
I am following with interest.
Kind Regards
Achim

Offline BillTodd

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Re: Fuel injection systems
« Reply #106 on: December 11, 2016, 02:43:13 PM »
Quote
bubbles in the fuel pipe to the injection pump  ::) As far as I can see the only possible air leak
May not be air , could be fuel vapour if the pressure is low.

Bill
Bill
wy omnibus Latinis taurus stercore?

Offline Roger B

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Re: Fuel injection systems
« Reply #107 on: December 11, 2016, 02:52:59 PM »
Thank you  :ThumbsUp:

Brendom, the diagram was the helix unrolled and scaled up 10 times. It was unrolled along the long edge and as it was 2mm diameter it is 2 x pi x 10 = 62.83. The other direction was the pitch, 4mm so times 10  = 40 mm. This diagram then gave me the helix angle, 32░ and allowed me to see how it would work with the 1mm port in the pump. The pump stroke will be 3mm so the first mm closes the port and the next two mm will do the pumping. As soon as the port reaches the helix the pressure will drop and the pumping will stop.

The next thing was to try and grind a trial helix  ::) I added a few holes to the Hobbymat milling support angle plate so I could mount the compound slide along the axis of the lathe and at the helix angle. The 4mm pitch required the change gears to step up 1-4. I found a suitable set up with the available gears, 70-35 and 60-30, but the arm hit the spindle before I could get a good mesh. As the foul point was just rough cast a quick bit of filing made enough clearance.
The actual feeding will be done with the leadscrew handle so I left the drive belt off and the lathe unplugged. I also made a quick 'sanity check' that four turns of the leadscrew handle gave one turn of the chuck.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #108 on: December 11, 2016, 02:59:44 PM »
I made an initial attempt on a piece of unhardened 2mm silver steel. I let the wheel cut in both directions but that may have been a mistake due to the general play and lack of rigidity of my set up. The second attempt on a hardened scrap plunger was made with a different grinding wheel held in a collet rather than the drill chuck. This time I only cut on the in stroke. The cut was taken to 0.5mm deep in 0.05mm steps. I think that it was harder to get a good picture of the helix than it was to make it  :headscratch:
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #109 on: December 11, 2016, 03:02:43 PM »
Thank you Bill, I was coming to that conclusion as well. The only mechanical petrol injection systems I know of (Lucas and SPICA) fed the petrol into the metering pump under pressure rather than a very small head. At least vaporisation shouldn't be a problem with diesel fuel  ::)
Best regards

Roger

Offline Graham Meek

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Re: Fuel injection systems
« Reply #110 on: December 11, 2016, 06:21:39 PM »
Hi Roger,

You are to be congratulated on your progress.

I have been looking in from time to time but totally missed the engine running. You have been busy, and I like your helical groove. You are doing some real methodical trail blazing as regards the small "True Diesel" engine. I do hope that one day you will publish your design.

My best regards
Gray,

Offline Don1966

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Re: Fuel injection systems
« Reply #111 on: December 11, 2016, 06:46:00 PM »
That's awesome Roger and congrats I do hope you perfect it. Great following your progress...... :praise2:

Don

Offline philjoe5

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Re: Fuel injection systems
« Reply #112 on: December 11, 2016, 10:40:27 PM »
Fantastic Roger.  A real leading edge effort at fueling these small engines :ThumbsUp:

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline BillTodd

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Re: Fuel injection systems
« Reply #113 on: December 12, 2016, 12:01:28 AM »
Bill
wy omnibus Latinis taurus stercore?

Offline Roger B

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Re: Fuel injection systems
« Reply #114 on: December 12, 2016, 01:50:21 PM »
Thank you all  :ThumbsUp:

I looked up the vapour pressure of petrol and it is around 0.5 Bar at normal temperatures. When the plunger on the 'jerk' type pump returns it will create a vacuum which will certainly vapourise the fuel. If the feed pressure is not higher than the vapour pressure the vapour will remain and this is probably what I have been seeing in the feed pipe. Petrol vapour is around three times the density of air. The initial air bubbles I get when I prime the system tend to flow back up into the tank. The bubbles when running tend to float just above the intake pipe.
The SPICA (Alfa Romeo) and Bosch (Mercedes Benz) mechanical petrol injection systems both fed the metering pump at around 1 Bar which should be enough to overcome the vapour pressure.

Based on this I think that my current metering is probably fairly random and I will need a pressure fed system to get consistent results. The vapour pressure of diesel fuel is much lower so vaporisation won't be a problem but I don't think that I am ready for that step yet.

Next challenge: Design and build a ~1 Bar constant pressure petrol feed pump that can be fitted on my horizontal engine (which already has two unplanned pumps  ::) ). Another option may be a separate electric feed pump, but the more pressurised petrol I have around the more nervous I become  :zap:
Best regards

Roger

Offline Admiral_dk

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Re: Fuel injection systems
« Reply #115 on: December 12, 2016, 02:20:15 PM »
Congratulations Roger - nice step forward  :praise2:

All diesel engines I know of has a feed pump before the metering pump - often together with the filtering system .....

Best wishes

Per

Offline Graham Meek

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Re: Fuel injection systems
« Reply #116 on: December 13, 2016, 11:00:44 AM »
Hi Roger,

You could pressurise the delivery by raising the height of the fuel tank above the pump. You might find in doing this that by increasing the tank volume you can also influence the amount of pressure. I am not saying this will give you what you need, but you can do this with relatively little work and it might prove your theory.

My best regards
Gray,

Offline Roger B

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Re: Fuel injection systems
« Reply #117 on: December 13, 2016, 07:29:14 PM »
Hi Gray,

I think I will need a few meters of head to overcome the vapour pressure. I am looking at a couple of electric pump options, one from Conrad:

http://www.conrad.ch/ce/de/product/224413/Kavan-Kraftstoff-Zahnradpumpe-Foerdermenge-18-lmin?ref=list

This is capable of 3.8 Bar however it is not continuously rated at full output. It may be ok on reduced voltage but would need a pressure regulating/release valve. It is suitable for petrol and diesel fuel.

The other slightly larger option is an automotive pump:

http://www.fuelpumpsonline.co.uk/facet-solid-state-fuel-pump-40107-70-10psi-9-p.asp

I used to use Facet (or Bendix as I think they were then) fuel pumps on my competition cars and they are certainly robust and reliable. There are other versions available up to 15psi/1 Bar.

I am tempted by the Facet pump as I am certain it will do what I want. I will just have to make some NPT adaptors.

« Last Edit: December 19, 2016, 11:36:24 PM by Roger B »
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #118 on: January 20, 2017, 08:48:43 PM »
I have purchased a Facet pump with a 10psi rating along with a couple of 1/8" NPT fittings that I will be able to adapt. As the R&D Dept is closed again due to snow the next tests may be a month or two away.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #119 on: January 25, 2017, 07:48:30 PM »
The 1/4 NPT fittings that came with the fuel pump had 5.5mm bores and the connections I wanted to use had M5 or M5 x 0.5 threads so I had to make a couple of adaptors from some 8mm brass hex. The fittings were tapped M6 x 0.5 to allow for future developments.
I have fitted the pump to the engine base and connected it up. The copper pipe was bent using my old Girling former (Autojumble? Don't remember  ::) ) and I had purchased some small bore automotive fuel hose that is supposed to be OK with Petrol, Diesel and Alcohol to connect to the tank. The pump will be switched together with the coil.
« Last Edit: January 26, 2017, 08:02:57 AM by Roger B »
Best regards

Roger