Fuel Injection Systems Part 2

[jcge]

Hi Roger

...... 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 .......

Rather than clutter up your thread, I've added a link here that you might find useful ...https://pbase.com/9146gt/the9146gt_28rsr_engine1_bosch_rsr_fuel_injectors_floating_needle

These PETROL injectors open at 15-18 bar.

Regards
John

[Roger B]

Thank you all 
 
The flame thrower test isn’t that risky. I move flammables out of range, the total fuel volume burnt is a couple of mm3, I have a damp towel to hand and if all else fails there is a fire extinguisher by the door.

My current injector design was loosely based on the Lucas petrol injector which is similar to the Bosch petrol one. This was fine for manifold injection spark ignition engines. I found that nozzle guidance was better for higher pressures which I based on the GM poppet diesel injector.

Manifold injection for a spark ignition engine is much easier as there is nearly a full crankshaft revolution for the fuel to vaporise before it has to ignite. Cylinder injection for compression ignition has only a few crankshaft degrees to atomise and ignite.

I also carried out some output trials on the diesel injection system, spinning the engine at various speeds with different electric drill and measuring the output from the injector with a measuring cylinder. The effect of leakage past the plunger is quite noticeable.  Testing that injector with the hand pump suggest an opening pressure of around 150 bar.

[Vixen]

Hello Roger,

Those conclusions make interesting reading, especially the lower time dependence of manifold injection v direct cylinder injection. Obvious perhaps,  when you think about it, but most of use don't think that far.

Oh! next time you do that exciting 'flammenwerfer' test/ experiment, why not try a dark as well as the light coloured background. It may make the flame front, even more visible and exciting to watch.

Just a thought

Mike

[RReid]

Oh! next time you do that exciting 'flammenwerfer' test/ experiment, why not try a dark as well as the light coloured background. It may make the flame front, even more visible and exciting to watch.

Or better yet, turn the lights off!

[jcge]

Hi Roger - I wasn't aware of the Lucas petrol injection system - thanks for enlightening me. And I agree completely re evaporation of the petrol in the inlet tract vs atomisation requirements for injection into the cylinder for diesel.I really posted that link as it gives a pretty good visual around component proportions (spring and pintle needle) for reference
I really do applaud your work on this - great stuff !!
John

[steamer]

ou  ou  ou!   12 cylinder manifold injection?     

[Roger B]

It's been done, just lots of little bits 

[Brendon M]

By golly, does that thing actually run!?

[steamer]

By golly, does that thing actually run!?

Word has it, it did and it sold at auction for $40K...

Though honestly....it's a poor representation of a 917 engine.....

[Roger B]

This is the only information I have on it:

https://rmsothebys.com/en/auctions/NY15/New-York---Driven-By-Disruption/lots/r1029/182098

Apparently it sold for $1000 per cc.

[Roger B]

As I am still waiting for the new injector springs here is an aside about another obscure petrol injection system.

I found the Simms MkII petrol injection system in a German Language Technical Book from 1966. Internet searches found a couple of references in Commercial Motor:

https://archive.commercialmotor.com/article/21st-october-1960/40/petrol-injection-by-simms

Petrol Injection By Simms
21st October 1960, Page 40
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
DETAILS of a petrol injection system which is simple and relatively cheap were announced on Wednesday by Simms Motor Units, Ltd. Whereas previous equipment of this type has been reserved for expensive high-performance cars because of its complexity and price, the Simms system, when supplied in large quantities, is to be offered to manufacturers at some £7 more than the cost of conventional carburettors. This, it could be applied equally to cars or petrol engined commercial vehicles.
It consists of a cam-operated plunger type pump driven from the camshaft gearing and a low-pressure injector which delivers fuel into the inlet manifold. Throttle pedal position provides quantitive control of the fuel injected, and output is modified for engine speed by a centrifugal governor and for load by a diaphragm actuated by manifold depression. A thermostatic control incorporated in the cooling jacket of the engine provides a form of automatic choke for cold starting.
The one pump will suffice for engines of any size, fuel delivery being altered by modification of the pump cam profiles.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
https://archive.commercialmotor.com/article/29th-october-1965/40/simms-to-make-and-market-petrol-injection-system

The only picture and technical description are from the German book. I have translated it here:
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Petrol injection from Simms
 This British pump is built for small engines and correspondingly small injection quantities (5 mm2) and for very high speeds. With this new design, a major step has certainly been taken towards the further introduction of Petrol injection in small engines, especially with regard to the lower production costs compared to a conventional injection system.
 The fuel is injected into the intake manifold. Only one pump element and only one injection nozzle is required for all cylinders. Injection takes place in time with the suction strokes of the individual cylinders. In contrast to a conventional injection pump with pistons and cylinders, the Simms pump uses a kind of rubber ball, which is compressed by a ram and relaxes again through its own elasticity. Both a spring-loaded intake valve and a check valve protrude into this rubber ball. The quantity regulation of the fuel brought in by a feed pump is achieved by longer or shorter opening of the intake valve, The ram, which presses on the rubber ball, is lifted over a roller by a camshaft, The cam elevations are only a few tenths of a millimetre. The fuel metering according to speed and load is carried out according to the vacuum generated by a throttle valve in the intake duct. Facilities for cold start and fuel shutoff are planned.
 Also interesting is the associated injection nozzle, which differs from the others in that the path of the spring-loaded nozzle needle is limited by a soft ring made of synthetic rubber. The interaction of rubber disc and spring means that a very good atomization of the fuel at the nozzle opening is achieved at large and small flow rates, regardless of the prevailing injection pressure.
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
I guess that the rubber ball avoids any problems with sealing the plunger and has fairly low inertia which will be better for high speed operation. I can’t yet work out exactly what the rubber disc/ring in the injector does.

[Vixen]

Hello Roger,

Simms fuel injection systems are still manufactured with lots of stuff on the internet. There may be stuff about the Simms MK2 petrol injection system, with the squezzy rubber balls, but I have not had time to discover it yet.

Another high pressure pump with a squeezy rubber pump element is the Harben high pressure pump. They employ a small rubber tube for the pump. The rubber tube is squeezed by a hydraulic cylinder.   Have a look at        https://www.harbencalifornia.com/pumps/p-pump/        There is a description and animation in the bottom right hand corner.

I have often thought that a rubber tube diaphragm pump, similar to the Harben, could make the basis for a simpler petrol injection pump; without the need for all those precision fits. You would need to devise some variable throw into a petrol injection pump

More stuff for you to think about, if you think it has any merit.

Cheers 

Mike

[RReid]

This thread along with my own engine build have got me started reading up on mechanical FI more than I ever have before, starting from a near vacuum. The kind of info offered by you, Roger, and Vixen in the last couple of posts above are great and fall right into my hands!

I've looked at what I can find on the net about the SPICA system used by Alfa Romeo (not much), and the more well known Lucas system (quite a lot more). The Lucas "shuttle metering" looked well suited to model engine use and home shop building until I realized it relied on high fuel pressure (100 psi). Nope, not doing that.

Anyway, Thank You both for sparking and feeding my curiosity. Whether I will ever take on actually building an FI unit is an unknown at this time, but I no longer dismiss it out of hand!

[Roger B]

Hello Mike,

The second Commercial Motor article suggests that the Simms system was derived from the Marvel-Schebler petrol-injection system about which I can find even less. The Simms write up suggests that the pump stroke was a few tenths of a mm for a full size engine. I'm not sure how it could be reduced for a model sized system. The hardness of the rubber would also be critical to getting consistent results.

Hello Ron,

SPICA, Alfa Romeo, Kugelfisher, Peugeot and Bosch, Mercedes Benz and Porsche were all derived from standard diesel pumps with different control systems. They all offered a fairly direct control of the injection quantity using a helix spill system as long as the fuel was kept above it's vapour pressure. The injection pressure was generated in the pump plunger. The Lucas system used the pump shuttle for metering but the injection pressure was generated by the feed pump which meant there was a lot more pipework with petrol under moderate pressure. The metering shuttle should be fairly easy to make but the distribution ports would be more difficult. It also will only work with an even number of cylinders.

[Brendon M]

Hello

The "few tenths" is probably because the size of the rubber ball is large.

What if we considered this fuel injection similar to the low pressure mechanical fuel pump that feeds a carby, that uses a lever pressing on a rubber diaphragm to achieve pumping action?

Would be easier to scale that design down? And a wedge can be used to vary the amount of stroke for the ram that would press against the rubber.

Edit: gee whiz I thought I read through the last posts correctly, I see Vixen has proposed a similar design as well.

In all cases, the basis of these pumps is to remove high tolerance fits from the equation. Actually I now have an appreciation for the mechanical pump in my Toyota - for me the rubber diaphragm represents an obvious failure point, but so long as the rubber is OK it won't ever leak unlike a piston setup. Only problem is I probably can't buy new diaphragms for it.