Fuel Injection Systems Part 2

[Admiral_dk]

I can atest to reading everyone of your post about this subject - hoping for you to succed and me to be a bit viser on this field 

Agree with Dave - nice fast run - even and steady 

Per

[Roger B]

Thank you all for your interest and support   

I am happy in a strange way that the problems were due to my manufacturing errors rather than fundamental problems with the design 

I am moving this pump back to the two cylinder engine thread to work out a control linkage.

The updated design for petrol injection will remain on here. I have produced a couple of layouts for a horizontal and vertical version. They are based on an aluminium body with the hardened and lapped pump cylinder and delivery valve seating (red) Loctited in place. The pump tappet housing/ return stroke limit is made as a separate piece (blue with yellow bronze bush). There is a drain hole for any fuel leakage (green). I am not sure if the inlet valve will need a spring, obviously it will for the vertical version, and the union/seating may need to be something harder than brass. This has a conventional style camshaft rather than an excentric and stroke adjustment is via a wedge with a single pivot point. This will not be as linear as the earlier versions with a floating wedge, but equally the wedge can't keep popping out.

[Minh Thanh]

Hi Roger 1
 I think, with the vertical version, inlet valve: you need a spring in the ball valve - but the pressure is light, it just holds the ball valve in the closed position.
  For the horizontal version: no springs needed - you can make springs if you like

[Roger B]

Thank you Thanh 

My thoughts are much the same. I am not sure if I can avoid a spring in the horizontal version due to vibration  The current 360° twin is not that well balanced and I guess it is reaching around 8 000 rpm.

[Roger B]

As mentioned in the four stoke diesel thread I need to do some further work to improve the atomisation and spray angle of the injectors. I will keep to the current design but will experiment further with the needle angle and finish and with the springs.

The needles are turned from 2mm silver steel and like last time I will make two blanks, one on each end of a length of stock. The ends are centre drilled with a 0.5mm drill, turned down to 1.4mm and threaded M1.4. The shank is then supported with a brass bush while the section before the cone is turned down to 1mm. The cone is then turned, in this case 10° included angle, and parted off to give the required 1.6mm diameter at the end.

[Roger B]

The two needles have different lengths to allow some experiments with springs. I may have to make a slightly longer body as well. The next stage was to mill some feed slots in the guide are of the needle. In the first experiments I thought I could allow the needle to float but trials showed that this did not work. The most successful injector of that series was where I had drilled the spring seat 2.4mm instead of 2.5 mm so it centred the needle. The area of the slots is a little low for the fuel injection time and volume but seem to work.
The cones were then hardened and polished with a fine abrasive stone. I am hoping to do away with the grinding and polishing operations and just move onto lapping. Last time it didn't work but I had also moved from 1 Micron to 5 Micron lapping paste (don't change two things at the same time 
Next up I made some M1.4 nuts from 2mm brass hexagon. Luckily the swarf gnomes didn't get any 

[Admiral_dk]

It must be very hard to keep Deflection to a minimum @ those tiny sizes 

(don't change two things at the same time 

Always a prudent advise (that we always keep) if you need to know what is the reason you get a certain result 

Per

[jcge]

Hi Roger - I've thoroughly enjoyed reading about your methods and results in developing this injection system.

Viz. fuel leakage past the plunger (clearance to bore) - I understand that Bosch introduced (for racing Porsche's using PED6KL series pumps), a tiny oil passage to the side of the bore to create an "oil seal" due to high relative viscosity of the oil vs fuel in the tiny clearance between the plunger and bore. Also addressing lubrication of the plunger beyond the intrinsic lubricity of the fuel.

You can see it as a small diagonal passage in this sectioned plunger body assembly

Hope this info is useful to you
John

[Brendon M]

That probably also means you don't need as tight tolerances! (Or rather, it can handle a bit of wear over time), such a simple and elegant idea

[Roger B]

Thank you John, an interesting idea  I had thought about grinding a couple of oil retention grooves in the plunger as a next step. At the moment I am happy if it works at all before I start looking at extending the life span. Do you know how big the Bosch plunger is? I would guess around 6mm.

[Roger B]

The next step was to make some more nozzles. These were turned from 10mm stainless steel. 8mm Hex would possibly be better but I couldn't find any in sensible lengths and it doesn't take long to mill the hexagon at the end.

The bore is carefully reamed 1.4mm as the quality of the seat depends on the bore being as round as possible. The nozzles and needles are then identified with punch marks and fine grooves to keep them in pairs after lapping. They are lapped with 1 micron diamond paste thinned with light oil using the little Proxxon lathe and then cleaned up in the ultrasonic bath.

<a href="https://www.youtube.com/watch?v=p7-P_VkiGbw" target="_blank">http://www.youtube.com/watch?v=p7-P_VkiGbw</a>

<a href="https://www.youtube.com/watch?v=p7-P_VkiGbw" target="_blank">http://www.youtube.com/watch?v=p7-P_VkiGbw</a>

[jcge]

Hi Roger - the plungers for normally aspirated Porsches were 6mm and up to 7mm for 917 turbo.
Your success in running an engine at this scale is extrordinary in my opinion !!
Watching with great interest - thank you for posting your work for the world to see.
Regards
John

[Roger B]

Thank you John    A bit more on this.

I made a couple more injector bodies from 6mm brass hex. Now I have the tailstock die holder it can all be done on the little Proxxon lathe. The injectors I have made to this design have been very inconsistent    There is one good one which will run on the diesel and several that won't give consistent atomisation. Going back to the previous generation without the guided needle the one that worked best had the spring retained in a 2.4mm hole. As the bore of the spring was a close fit on the 1.4mm needle this acted as a guide. Now I have the guided needles a 'double' guide may be causing problems. I bored the spring seats out to 2.5 mm without obvious success    The springs are quite a close fit on the needles so maybe that is causing some restrictions  I have ordered some new springs with a 1.5mm bore 2.5mm OD, neither easy to find nor cheap 

I also needed to modify my test pump for higher pressures so I drilled a second hole twice the distance from the pivot. This will allow 5kg/50N on the 2mm plunger.

Finally an attempt to show my injector test method and a more spectacular way of checking the atomisation.

<a href="https://www.youtube.com/watch?v=KhNYT6AAsCI" target="_blank">http://www.youtube.com/watch?v=KhNYT6AAsCI</a>

<a href="https://www.youtube.com/watch?v=PcREpDLM64Q" target="_blank">http://www.youtube.com/watch?v=PcREpDLM64Q</a>

[RReid]

Switching from model engines to model flamethrowers?

[Kim]

That does look a little dangerous, Roger! 

Though I'm quite sure you keep flammable things far clear of your testing grounds!

Kim