Author Topic: Fuel injection systems  (Read 36966 times)

Offline Roger B

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Re: Fuel injection systems
« Reply #150 on: January 07, 2018, 11:04:56 AM »
I put the system back together and got it primed. The atomisation looks reasonable, but operation was not consistent. I think that there is still a problem with turbulence in the inlet port when the spill helix opens. I removed the fuel inlet flexible pipe and small droplets were shooting out. I'm not sure if they are visible in the video  ::)
According to the calculated injector spring load, 14N, the injector needle was opening at around 60 Bar.


Best regards

Roger

Offline Admiral_dk

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Re: Fuel injection systems
« Reply #151 on: January 07, 2018, 09:27:56 PM »
The spray Looks fine - so far so good  :ThumbsUp:

Best wishes with the rest  :)

Per

Offline fumopuc

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Re: Fuel injection systems
« Reply #152 on: January 08, 2018, 07:06:55 PM »
"Spannend"
Great project with a lot of interesting challenges.
Kind Regards
Achim

Offline Laurentic

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Re: Fuel injection systems
« Reply #153 on: January 25, 2018, 11:00:21 PM »
Can't believe you are still trucking on Roger, gees but you have some stamina and application.  More than 1 1/2 years on and you are still at it like a dog with a bone, well done that man, you have my admiration and respect, many a lessor man would have given up, but I am so pleased you are staying the course as you seem, little by little, to be winning.  Like how many body's have you made, I've lost count.  Really willing you on here, wanting and hoping you will finally succeed.  Where do you buy all your small - tiny even - drills, reamers and laps from?  Haven't been able to source them in the UK myself so far.

Cheers, Chris

Offline Roger B

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Re: Fuel injection systems
« Reply #154 on: January 26, 2018, 08:43:08 AM »
Thank you all for your continuing interest in this somewhat long term project. I knew at the start it wasn't going to be easy  ::)

Chris, there have only been 5 or 6 pump bodies so far, but I made around 10 simpler versions when I was learning how to ream.

The 0.35mm drills came from a workshop clear out at work but are also available from Brütsch-Rüegger where I get the other drills:

https://www.brw.ch/3/BRW-ToolShop/1/Category/417/Product/Details/P_20532/Twist-drill-TITEX?pSearchId=18968cfa-1ccc-42c5-8874-feaaffc72f38&pOnlyPromotion=False

The 0.01 step reamers are from the same source:

https://www.brw.ch/3/BRW-ToolShop/1/Category/523/Product/Details/P_189574/Machine-reamer-MAGAFOR?pSearchId=375fe529-1341-4eb3-a3b8-cdaec2ffe2f5&pOnlyPromotion=False

As are the pin gauges:

https://www.brw.ch/3/BRW-ToolShop/1/Category/194/Product/Details/P_18228/Pin-gauges-MT?pSearchId=a6f6ce3f-a392-4ebb-86b7-5dd855770f9b&pOnlyPromotion=False

The needle eye laps are from Acro in the USA (I also use their barrel laps for engine cylinders):

http://acrolaps.com/index_007.htm

Best regards

Roger

Offline Laurentic

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Re: Fuel injection systems
« Reply #155 on: February 02, 2018, 02:33:02 PM »
 Many thanks for the info Roger, been away for a few days and only just catching up - will take a look at the links you gave right away.

Cheers, Chris

Offline Roger B

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Re: Fuel injection systems
« Reply #156 on: February 28, 2018, 08:09:24 PM »
Not much is happening on here at the moment as I need to do some more trials with the horizontal engine but with -10°C and snow they are going to have to wait. I am continuing to modify the variable stroke pump to fit on the diesel. The problem with this is that the start of injection varies with the stroke. Maybe ok maybe not  :headscratch: I have made a new plunger from the other half of the pin gauge with a larger flange to suit the same spring type as the helix pump.
While doing this I did find that the inlet union to the pump was a failed delivery valve body and had been drilled out to ~3.3mm giving a reservoir above the pump inlet. I will modify the helix pump to match.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #157 on: April 14, 2018, 07:44:30 AM »
I modified the backplate of the variable stroke pump so I could access the unions if it is fitted to the diesel. Hopefully the helix pump will work though ::)
The inlet union of the helix pump was opened out to 3.2mm to hopefully give a space for surge/turbulence during spill. I then refitted the injection system to my horizontal engine. Previously the injector was vaguely held in place by the fuel pipe so I decided to make a proper clamp to keep the O ring compressed and remove the variable air leak. Ready for another trial  :)
Best regards

Roger

Online Vixen

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Re: Fuel injection systems
« Reply #158 on: April 14, 2018, 10:08:49 AM »
Hi Roger,

Top marks for your persistence. A direct fuel injected model engine will be a remarkable achievement.

When you have a spare moment, could you please post the latest schematic of your injection system.

I for one, and I am sure there are others, have lost track of where all these individual piece parts and modified parts fit into the system.

Mike.  :ThumbsUp: :ThumbsUp: :ThumbsUp:
« Last Edit: April 14, 2018, 10:27:12 AM by Vixen »
It is the journey that matters, not the destination

Offline Roger B

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Re: Fuel injection systems
« Reply #159 on: April 14, 2018, 04:31:21 PM »
Thank you Mike  :ThumbsUp:  :ThumbsUp: Here is a summary of where I am today:

First system:

2mm bore variable stroke pump with 1mm diameter inlet port and ball delivery valve. Stroke adjustment 0-3 mm. The bore is drilled reamed and lapped. The plunger is made from a commercial pin gauge. I started out using hardened and lapped silver steel but had problems with a non-circular piece and at 11 chf each which will give 2 plungers they seem the best option.

The pump is driven by an eccentric to give a long injection period while the inlet valve is open.

Plain bodied injector with 1.5mm diameter needle ground down to 1mm. 0.35mm diameter nozzle. The nozzle seating is 60° and the needle 50° to give a line seal at the entrance to the nozzle bore. Adjustable spring tension, opening pressure around 15 bar. The needle is made from hardened and lapped silver steel.

This operated successfully as manifold petrol injection but required a feed pump to avoid vaporisation of the petrol.

Second system:

This pump has a helix ground in the plunger following full size practice. The plunger is rotated by a rack and gear. The gear is wide enough to allow for the 3mm stroke of the pump.

This pump can be driven by the eccentric for manifold injection or by a fast-acting cam for diesel injection.

The injector is the same as above except for a mounting flange to fit to the diesel cylinder head. A stronger spring can be fitted to give a higher release pressure (estimate 60 bar)

This has also run successfully as manifold petrol injection.

Reaming:

Reaming the bores has required significant development of my technique to avoid bell mouthing. I am following the manufacturers recommended speed and feeds for the reamers which are higher and lower respectively than I had been using. The drill size is important as is a slight lead on the hole. I found that a floating reamer holder gave less bell mouthing but was expensive.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #160 on: April 14, 2018, 04:41:24 PM »
I made some trials with the helix pump today. As ever priming is a problem and I have a small leak from the inlet union to the fuel pump due to partially stripped threads  ::) I may need to make a new pump body  :(

It ran well and would run between 1500 and 6000rpm at the same setting of the pump  :)


I then connected the load bank and was getting nearly 8A into 1ohm so around 64W. Previously I achieved a maximum of 80W using the same carb as I am using for a throttle. This was at the same setting of the pump as before.


Finally it settled down to a 1500rpm idle still at the same setting.


There were some problems with the feed pump. It seemed to keep pumping/clicking even into a closed pipe which resulted in the fuel overheating and vaporising  ::)

Generally a good day  :wine1:
Best regards

Roger

Online Vixen

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Re: Fuel injection systems
« Reply #161 on: April 14, 2018, 07:12:10 PM »
Roger

Thanks for the update on your design and experiments

MIke
It is the journey that matters, not the destination

Offline Roger B

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Re: Fuel injection systems
« Reply #162 on: April 15, 2018, 01:55:05 PM »
I tried to determine the working stroke of the injection pump. During the trials moving the rack up and down by one tooth each way produced too rich and too lean. Looking down the inlet port the start of injection was fairly easy to see but when the helix was exposed was more of a problem. I took the following measurements which I expect are too large due to chamfers on the edges:
Best running 1.2mm
1 tooth rich 1.5mm
1 tooth lean 0.8mm
With the variable stroke pump I estimated 0.5mm

I then decided to see if I could rescue the damaged thread. I set the body up on the mill and removed the damaged thread with a 5mm end mill. The hole was then tapped M6x0.5 and I made a bush to take it back to M5x0.5. This has been Loctited in and is curing.
Best regards

Roger

Offline Admiral_dk

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Re: Fuel injection systems
« Reply #163 on: April 15, 2018, 05:26:46 PM »
Still following along and glad to see some progress for you  :ThumbsUp:

The measurement will be extremely difficult if you insist on doing it geometrically - as you say yourself - how about camfers etc. ....

In my book you will have to ensure a reasonable constant rpm over a certain amount of time and measure the amount of fuel drawn from the tank / how long it will run on a known amount of fuel at a constant rpm.
I would use a calibrated syringe or laboratory "beaker" with a fine graded scale as the fuel tank.

Best wishes

Per

Offline Roger B

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Re: Fuel injection systems
« Reply #164 on: April 16, 2018, 08:42:57 AM »
Thank you Per  :ThumbsUp:

The stroke measurements were more to confirm the mechanical design was ok and I was not reaching a limit. Making a proper test rig so I could also see how much the output varied with speed due to leakage would be interesting but is almost a project in itself  ::)

I was surprised how flexible the engine was with a fixed stroke set on the pump. It was better than with the carb (although the carb is not properly calibrated to the engine). I suppose that a metering pump takes speed out of the fuel map equation, the same amount of fuel will be injected per stroke however fast the engine is running. Throttle position and load may then by partially compensated for by the speed related leakage  :headscratch:  :headscratch:
Best regards

Roger