Fuel injection systems

[Roger B]

Most of my future projects require fuel injection systems, both paraffin (kerosene) and diesel. These will be around 20 - 25 cc per cylinder and as the smallest commercial engines with mechanical injection are around 200 cc per cylinder I decided that I need to start experimenting and developing some manufacturing techniques.
The first step will be a fuel pump and injector hopefully suitable for a 25 cc engine. The fuel pump will have a plunger diameter of 2mm and a target stroke of 2mm. The injector will have 1.5mm diameter needle with a 0.35mm diameter nozzle.
I hope to trial this on my current horizontal engine injecting petrol into the inlet with a later step of injecting paraffin into a vaporiser.
This will require lower pressures than for direct injection in a diesel engine, but petrol is of low viscosity and has no lubricating properties.
I have made a start on the injector with a body from 10mm square black bar. To make the nozzle concentric I need to drill the hole from the needle side so I had a go at drilling a deep (12mm) hole in the end of some brass bar turned down to 1.5 mm diameter. This seemed to work (the centre drill has a 0.5mm diameter tip.
Next I need to look at making a needle and seat cutting tool from hardened silver steel (drill rod).

[Roger B]

I had decided to try and grind the D bit and the needle as with these small sizes even at full speed (2000rpm) the cutting speed is minimal. For a previous project I had made a tool post support for my Proxxon hand tool, this is not so rigid but was sufficient for some trials.

The lathe bed was protected with a sheet of plastic covered with a damp paper towel. I arranged the setup so that the sparks would be downwards. This required running the lathe in reverse.

I was able to grind 30° and 45° points as well as parallel without the Proxxon colliding with anything.

The D bit was hand filled to half thickness and then hardened by heating to dull orange and quenching in water.

I am happy with the basic techniques but they will need some refinement.

[Roger B]

Next I tried some of the steps for making a nozzle to see if I could drill the 0.35mm hole from inside.

Starting with some 6mm round brass I drilled a 1. mm hole 20mm deep and then reamed it out to 1.5mm. Using my D bit I then went down to 24mm which would leave around 1mm for the nozzle hole.

Finally I put my nozzle drill in, marked the expected starting depth with a marker pen, put a drop of oil on the brass shaft, started the lathe at 2000rpm and carefully pecked until the resistance went away.

The drill came out complete and removing the bar showed the hole had gone through   

[Admiral_dk]

Hi Roger

Very interesting project - many has tried and few has succeeded in making a working injection system in miniature size.

I for one hope that you will be among them   

That way the rest of us can learn     ..... 

[Roger B]

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 

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 .

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 

[jerry kieffer]

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 

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 .

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

[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

[Roger B]

Thank you Lohring, those are some interesting variable stroke linkages to think about    I guess that flash steam uses a significant quantity of water. I am looking a maximum of 2 - 3 mm³ per stroke.

These are the pump mechanisms I have been looking at. The Lanz pump uses a wedge between the eccentric and the plunger to vary the working stroke. The Benz pump uses a linkage to vary the stroke and the timing. The Compur pump has a separate spill valve and also allows the timing to be varied.

The Lanz picture is taken from 'Lanz von 1859 bis 1929' by Kurt Häfner  (Franckh-Kosmos)

The Benz picture is taken from 'Schlepper' by Armin Bauer (Bechtermünz Verlag)

The Compur  pump is taken from 'The Modern Diesel' Fifth Edition (Iliffe & sons Ltd)

[Graham Meek]

Hi Roger,

Yes my Diesel is coming along, but my progress is very slow, the injector pump has been a bit of a stumbling block up until recently. I had been going down the variable stroke route and tried all sorts of different designs. Then talking to Jim at Woodward's he suggested restricting the in-flow. Apparently this was how they used to vary the fuel supply in the very beginning. He said the type of engine that I am building is not going to have such a demanding injection regime as one fitted to a vehicle.

I have therefore been experimenting with some differential screw thread combinations to give me a range of fuel supply that I think the engine will need.

The real problem now is getting this design to fit my engine, I do not want end up with an injection pump as big as the 10 cc engine.

My best regards
Gray,

[Roger B]

Hi Gray,

I choose to start at around 25 cc as the biggest I could comfortably make with my machines to give me more chance of getting the bits to fit.

I have looked at a couple of simple variable stroke mechanisms, but the problem is keeping the angle of injection commencement the same (or similar. I don't know how important this really is  ). I am probably going to try a cam like the one on the Benz pump where the working angle is quite small to start with. This should also give a quick pump stroke (less time to leak    )

[Graham Meek]

Hi Roger,

Several years ago when I started out on my Diesel engine design I came across the engine below. The photograph was all the information I could find, not helped with my limited knowledge of German. I was wondering if you, or anyone else on the Forum has come across this engine before and knows more about the design?

My best regards
Gray,

[Roger B]

Hi Gray,

A limited search suggests that the drawing you have is an Eisfeld. I have a short German description that I will translate later, but it suggests that it was 15cc, ran, but was too heavy to fly.

http://www.kleinstmotoren.eu/histori15.html

I have attached a picture of a petrol Eisfeld engine, there are similarities.