Author Topic: Fuel injection systems  (Read 20127 times)

Offline fumopuc

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Re: Fuel injection systems
« Reply #120 on: January 26, 2017, 06:57:41 PM »
Waiting for the next pops.
Kind Regards
Achim

Offline Roger B

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Re: Fuel injection systems
« Reply #121 on: January 28, 2017, 06:33:48 PM »
The weather was kind today so I was able to try the new fuel pump. It was quite difficult to get all the air out as it is designed to feed into an open float chamber rather than a closed system. In the end I used a temporary pipe to circulate the fuel back to the tank for a couple of minutes.
The response was quite different, I was able to reduced the pump working stroke from maximum (around 1.5mm) to ~0.5mm. It would also run quite steadily without needing frequent adjustments or restarts.
The throttle response is also quite interesting, off load it will run over quite a wide speed range without needing to adjust the pump stroke. I haven't tried this system under load and may wait until I have the helix spill system working as it will be quicker to adjust/respond.

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

<a href="http://www.youtube.com/watch?v=bI5pCyaTkbY" target="_blank">http://www.youtube.com/watch?v=bI5pCyaTkbY</a>
Best regards

Roger

Offline Admiral_dk

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Re: Fuel injection systems
« Reply #122 on: January 28, 2017, 07:47:11 PM »
Wonderful Roger - it sounds very good with a very even running / firing  :ThumbsUp:

Offline Roger B

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Re: Fuel injection systems
« Reply #123 on: February 07, 2017, 09:07:13 PM »
The next step was to work out a control rack system for the metering helix. I had some 0.5 Mod 20 tooth pinions for the diesel engine lubrication pump with a 5mm bore. The projection on the fuel pump body is also 5mm but unfortunately the one I have already was only rough turned to support a spring not finish turned as a bearing surface. It will work for the first trials.

I could purchase some 0.5 Mod rack, 4mm x 4mm from Conrad. I cut off 30mm and milled it down to 3mm thick. The boss of the pinion was turned down to 7mm for a return spring. I decided to leave the existing system intact and start again on a new 5mm thick aluminium back plate. This now has fixing holes to attach to my horizontal engine, fixings for the pump body and a couple of slots for the rack. This all fits together and has 13mm rack travel which is around 150° rotation.

I need to devise a coupling between the pinion and the pump plunger and make a fixed guide rod for the excentric in place of the existing variable stroke one.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #124 on: February 16, 2017, 06:54:27 PM »
Having recently purchased a 4 jaw self centring chuck I thought I would see how it helped with the new excentric guide, new injection pump body and new injector body.

The excentric guide and injection pump both have the bore offset 1mm in both directions. This was easily resolved with two 2mm thick aluminium shims. Set up time effectively zero. The stub on the injection pump was finish turned to a good running fit for the rack pinion. I also turned a 0.8 mm deep 7mm dia. recess on the end of the body to locate the return spring. The 5mm dia. stub will then be held in a collet to machine the bore and the delivery valve recess and seat.

The injector body was even easier as it is concentric. The bore for the nozzle was drilled 5.9mm and then reamed 6mm. The end was flattened to the correct depth with a 6mm end mill. The top of the body was then opened out to 7mm and tapped M8 x 1
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #125 on: March 26, 2017, 07:36:05 PM »
I'm still struggling with this one. I tried reaming out the next pump body with the tailstock clamped as tight as possible this resulted in the bore being even more oversize. The 1.97 plug gauge would pass through a nominal 1.95 reamed hole. I think that I will have to get a floating reamer holder  ::) £ £ £
I decided to continue with the body anyway. I turned a bronze bush to fit the tappet guide and then set the tappet guide and the pump body in the Proxxon to drill and tap the fixing holes. The centre drill tip broke off in the pump body  :facepalm:  I couldn't get the broken bit out, so another trial piece  :( At least it's only 25mm of 10x10mm black bar.
I then turned up the start of another injector nozzle and spring plug. I will wait for the floating reamer holder before I finish the injector (and the pump)
Best regards

Roger

Online Tennessee Whiskey

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Re: Fuel injection systems
« Reply #126 on: March 26, 2017, 07:38:31 PM »
Roger, make sure you aren't bottoming out the reamer, this will cause an oversized hole.

Eric

Offline Roger B

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Re: Fuel injection systems
« Reply #127 on: March 26, 2017, 07:52:37 PM »
Thank you Eric  :ThumbsUp: It's a through hole, but I am trying to work to micron tolerances and it appears that the reamer has to be aligned to better than the desired tolerance to get the best results  ::) I'm still in the learning phase on this, but think I am going to have to spend some money  :headscratch:
Best regards

Roger

Offline freefuel

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Re: Fuel injection systems
« Reply #128 on: May 06, 2017, 11:56:29 PM »
Hi Roger,

for small holes have you taken a look at EDM wire cutters? the process might prove you with the ability to cut holes smaller then your tools permit.

https://en.wikipedia.org/wiki/Electrical_discharge_machining

Offline Roger B

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Re: Fuel injection systems
« Reply #129 on: May 15, 2017, 09:17:27 AM »
Thank you for that. The link suggests that EDM drilling will work down to around 0.3mm which I can currently drill. I am not sure if there is a need to go any smaller. Full size nozzles tend to be around 0.2 mm but I think that attempting to scale them down would just result in frequent blockages.
I chose to use an open needle valve (Pintle type) as the annulus gives quite a fine opening. Graham Meek is also working in the same direction.
I am not completely sure of the Physics/Fluid Dynamic but for a small engine the fuel pressure and penetration must be less than for a full size one otherwise the fuel will just be sprayed onto the combustion chamber walls or the piston.
Best regards

Roger

Offline freefuel

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Re: Fuel injection systems
« Reply #130 on: May 15, 2017, 03:05:45 PM »
the trend in modern diesel fuel injector design is for even finer fuel droplet size to maximize combustion efficiency, this is a problem compounded by our desire to use much smaller displacements and thus combustion chambers. it's a physics problem we are working against, in that we are not scaling the molecules of fuel and air we are working with down with our machines.

from what I can recall about full size diesel engines is that the injection pressures have increased as the nozzle orifice sizes have decreased to produce smaller fuel droplets. another major innovation has been the introduction of the multi event injection procedure, where a series of small injections precede the main delivery of fuel. doing do permits better control of the combustion chamber temps and noise reduction.

some more fun reading material, http://www.mmsonline.com/articles/non-traditional-methods-for-making-small-holes and https://en.wikipedia.org/wiki/Electron_beam_machining
« Last Edit: May 16, 2017, 02:26:43 AM by freefuel »

Offline Roger B

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Re: Fuel injection systems
« Reply #131 on: July 04, 2017, 06:48:43 PM »
Having learnt how to ream holes accurately (see the floating reamer holders thread) and had the engine running as a petrol engine it was time to move back to the injection system.

I started yet another pump body, this time with the correct size drilled hole and controlling the reamer at the correct feed rate with a floating holder I got a good bore without bellmouthing.

I then used the same experiences on the injector nozzle. Drilling 1.4mm was too much, the 1.45mm reamer passed straight through. Using a 1.3mm drill produced an acceptable result. I don't have a 1.46mm pin gauge, but the 1.47 didn't enter.

I then cut the seating with my previously made D bit, taking more care over the hole depths than on the last attempt.
Best regards

Roger

Offline Roger B

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Re: Fuel injection systems
« Reply #132 on: July 04, 2017, 06:53:28 PM »
The nozzle was then drilled 0.35mm with the same drill as before. I then moved onto the flange for the injector body as this one will have to be clamped to the cylinder head rather than just resting in the inlet manifold. This was done the traditional way with hacksaw, files and filing buttons rather than setting up the mill.
Best regards

Roger

Offline Brendon M

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Re: Fuel injection systems
« Reply #133 on: July 19, 2017, 11:42:41 AM »
I am amazed that a 0.35mm drill bit actually drills and not simply disintegrate. How do you do it?
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Offline Roger B

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Re: Fuel injection systems
« Reply #134 on: July 20, 2017, 05:45:15 PM »
No real problems. I am drilling less than a millimetre through brass. These are some good quality drills, some of the cheaper ones I looked at did not have real points and would not cut. I would have liked to have used a higher speed but my lathe will only reach 2000rpm.
Best regards

Roger