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Fuel injection systems

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jerry kieffer:

--- Quote from: Roger B on May 03, 2015, 08:04:50 PM ---Thank you  :)

I am well aware of the level of the challenge I have set myself  ::) From these first trials I need to improve the finish and fit by an order of magnitude to have any chance of success  :headscratch:

Maybe my machines and I can reach this, but anyway it will be good experience. The 1.5mm silver steel I am using is actually 1.49 mm. This is within specification,  but if my 1.5mm reamer cuts on size the clearance is already too much before I start lapping/polishing.

I have source of reamers in 0.01mm steps, but they are not cheap  :( Acrolaps also supply needle laps in this size range so I have some ideas for the next steps.

Valves for the injection pump are another challenge. The current Bosch type jerk pump with the spiral spill edge is out of the question in this size. I need to look to earlier designs with inlet and exhaust valves with variable stroke or fixed stroke with a separate spill valve. The earliest Benz design I have a drawing of used cone valves and the Lanz Bulldog used cone valves backed up with ball valves. Good cone valves 3 or 4 mm in diameter will be interesting to make :thinking: .

I am always happy for people to learn from me, even if it is how not to do things  ;)

Suggestions of how to do things better are also welcome  :)

Roger
  I suspect that your .35mm injector hole is far to large to get the spray needed for air saturation if that is the final hole size.

For example.
                   My 1/8th scale grease fittings have a .25mm passage with ball and spring and the 1/8th scale grease gun easily pumps regular grease through them.       I suspect with Diesel fuel you will need to be less than .1 mm but a good starting point for experimentation.         

Jerry Kieffer

--- End quote ---

Roger B:
Thank you for the interest Jerry.  My intention (hope) is that this will operate more like a pintle injector with the actual orifice being the annulus between the nozzle hole and the point of the needle (hence the 30 needle and the 45 needle seat). The 0.35 mm hole is much to big to act as a conventional jet. Full size engines tend to be around 0.2mm so in this size I think it would have to be less than 0.1mm (outside my current abilities  :(  ).

Graham Meek:
Hi Roger,

A tip given to me by a Designer at Woodward's Diesel engines was to have a Pintle nozzle for a small engine. That way the orifice can be more easily controlled as the pintle diameter can be made just a shade smaller than the hole. Some of the full size Pintles were tapered, such that as the pintle lifted off the seat the taper closed the orifice slightly thereby giving a finer spray. The biggest problem I have had is seeing the pintle to grind the shape and to get a very fine finish. My latest attempts have been with Diamond charged rotary lap after rough grinding which has given a big improvement, but it is still early days, I hope this helps.

My best regards
Gray,

Roger B:
Thank you Gray, If I remember correctly you are also working on a diesel engine (along with everything else  :) )

lohring:
I've been thinking about variable stroke pumps for flash steam engine control.  There is a lot of information if you search on variable stroke or variable valve mechanisms.  The Pattakon site (http://www.pattakon.com/) has a lot of ideas for variable valve lift.  My favorite variable stroke pump designs are pictured below.  The first two pictures are the same mechanism.  The last picture is the valve timing method used on large marine diesels.

Lohring Miller

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