Supporting > Engine Ancillaries
Porsche 12 Cylinder Fuel Injection
Vixen:
Ha Ha!! :ROFL: but don't forget the ring of bolts securing that engine to the transmission which itself is well attached to the tube chassis.
Mike
gerritv:
To throw another injection option into the fray, the Tecalumet system as used on e.g. BMC mini's :
Vixen:
Hello Dave,
Twelve individual injectors will dominate the engine, you just cannot make them small enough for them to disappear from sight.
I had a thought, that you could maybe consider reducing the number to four injectors, if we treat the 917 injection system as four, three cylinder engines. Each injector firing sideways into a single plenum chamber and throttle body, with three inlet trumpets above, then feeding down into a group of three cylinders. The injector pumps being based loosely on the Hunzinger and the "Schilling" solutions.
I went further and used Google Ai to do some calculations:
First, the air to fuel ratio (AFR) for methanol glow plug engines from max lean to max rich and max power. The wide FAR range of methanol fuel is amazing.
Then, the actual flow rate (quantity) of methanol fuel that needed to be delivered (at full speed) to the single injector feeding the group of three cylinders. Now have a good handle of the required ml/min.
Then, I asked about the fuel rail pressure needed to flow that quantity of fuel through 0.1mm, 0.15mm, and 0.2mm spray nozzles I mentioned in an earlier post. The smallest available 0.1mm nozzle shows a lot of promise.
Finally, I asked about the ideal air intake throat diameter for each of the three individual inlet trumpets. the suggested 5.0mm choke diameter does not seem unreasonable for a single 6.5cc cylinder.
I am still analysing the responses; There is a lot of detailed calculations and information to check; however the use of a 0.1mm spray nozzle at about 2.0 bar fuel rail pressure looks promising at full speed and also at a fast tick-over at a reduced pressure. :thinking: :thinking:
The problem I now have is I cannot simply cut and paste the full Google Ai responses due to formatting issues. I may be able to summarise the findings, if there is sufficient interest on the forum ( fuel injection is not a popular flavour with our steam engine brethren).
We all know by now, how careful you need to be in phrasing the correct question to an Ai bot, I have made a first attempt.
Cheers
Mike
Roger B:
I have translated some more about the Schillings system and it's set up procedure. His injectors fit into a M5 threaded hole in the inlet manifolds.
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
This is translated from the V12 DB 603 build notes in Hubert W. Schillings book:
Boxer-, Reihen- und V-Motoren als Modell published by VTH.
Intake manifolds, injection system
Pages 59, 60. Diagram on Page 14.
The injection system requires a bit of understanding: by way of explanation, it should be said that, in the strict sense, twelve carburettors are supplied with fuel depending on the engine speed. The wide ignition range of alcohol makes this possible. On the intake manifolds there are threaded holes for the injection nozzles. In reality, these are the adjustable main jets, because the fuel circulating in the system is sucked off here! The piping supplies the twelve nozzles via a manifold at low pressure; the pressure is set so that the nozzles are just wet - they must not drip. Two return valves ensure that the fuel does not flow back and thus allow air to enter the line system.
The system is very simple in design and works very reliably if all rules are observed and all screw connections are tight. The amount of fuel required for good running forms a curve that rises with increasing engine speed, i.e., it is not linear. A gear pump can never be so precise that it delivers a low-viscosity medium evenly from the very start. As the speed increases, the efficiency inevitably increases. In this way, a smaller amount automatically results for the idle range. The leakage therefore acts like the compensating jet in a carburettor. At higher speeds, the mixture automatically becomes richer. Thus, the running behaviour of the engine with model is purely a matter of adjustment.
The actual installation of the injection system is carried out as the final task once the engine is fully assembled. The two intake manifolds can be machined according to the drawing. The supplied nozzles do not need to be installed yet; one merely checks as a trial whether they can be screwed in.
Test Run
Pages 61,62
Before the first start, be sure to provide the engine with a firm stand so that it won’t move. The fuel container and oil tank should also be properly fixed. We know that one eagerly awaits the first pops and bangs and can hardly wait for the machine to run. However, one must restrain oneself and do everything for one’s own safety and that of the equipment. Ensuring the ignition current is also important. We did this using a transformer that we built ourselves. An on/off switch is a must. By the way: current should be measured; a visual check of whether the plugs are glowing is primitive. Everything primitive should be forgotten when doing this work. A second person is also required. Hand signals for communication are agreed upon beforehand.
You may consider these notes to be rambling; that is your business. But we would like to point out that around 20 hp are normally released. The propeller will cleanly chop off an arm if it gets in the way - quite apart from the damage to the engine.
Now for the start. First, we make sure (transparent connecting hoses are very helpful) that lubricating oil is flowing. Then the fuel system must be bled.
We did it like this: (of course with the ignition switched off) we held the fuel tank up, turned the engine over, and opened the nozzle fittings (the nozzle needles remain closed for now). Then, one after another, we tightened the fittings as soon as fuel emerged free of bubbles. Keep turning (do not stop), briefly disconnect the check valve after the fuel manifold until fuel emerges, then reconnect it. If both check valves seal properly, the system is bled you can start. To do this, all nozzle needles are opened half a turn, and the locknut is lightly tightened.
When the engine emits its first sounds, with the throttle valve only slightly open, give it a very brief burst of throttle. If the engine then dies, the nozzles must be opened another half turn. This procedure is repeated until the engine runs steadily at low throttle. Now check with your finger (this works well) whether all cylinders are running. Those that are not yet firing are given more fuel by further opening the nozzles until they run. During this procedure, the ignition naturally remains switched on. These adjustments require a great deal of sensitivity; especially opening the nozzles must be done very carefully.
We initially carried out the starting process with a flywheel, using a modified car starter. This gave the whole thing a bit more force. Later, the engine was started by hand with a three-blade propeller of about 80 cm diameter. This is very dangerous and not recommended!
Vixen:
Air-to-Fuel Ratios (AFR) for Methanol Glow Plug Engines According to Google Ai
This may be of interest to all i/c engine owners and is not specific to just Fuel Injection
The question given to Google Ai was:
1 Create a table showing the air to fuel ratio (AFR) for a small four stroke engine with glow plug ignition running on methanol fuel. Show the AFR ratios for the following conditions: a, max lean b, max economy c, max power d, max acceleration and e, max rich running conditions.
Google Ai came back with:
The stoichiometric Air-Fuel Ratio (AFR) for pure methanol is approximately 6.47:1
Small four-stroke engines using glow plug ignition and methanol fuel operate at significantly richer mixtures than stoichiometric. This richness is essential for internal cooling, as methanol has a very high latent heat of evaporation, and for maintaining the catalytic reaction on the glow plug element.
Condition Description AFR (Air:Fuel) by weight
Max Lean Limit before flameout/overheating 6.79:1
Max Economy Slightly rich for safety/stability 6.15:1
Max Power Peak BMEP and critical cooling 4.85:1
Max Acceleration Extra enrichment for transient response 4.53:1
Max Rich Limit of combustion (four-stroking) 3.56:1
Key Technical Considerations:
Cooling Requirements: Methanol engines rely on excess fuel to manage cylinder head temperatures. Running at the "Max Lean" limit in a small air-cooled engine can lead to rapid thermal failure.
Glow Plug Heat: The ignition timing in these engines is determined by the temperature of the glow plug. A mixture that is too lean will cause advanced ignition (knocking), while a "Max Rich" mixture can "drown" the plug, causing the engine to stall.
Lubrication: Small glow engines typically use fuel containing 15%–20% oil (castor or synthetic). The AFR values above refer to the total "fuel" (methanol + oil) mixture.
Interesting stuff :thinking: :thinking:
Mike
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version