Engine power increase via fuel injection: looking for some good info

[tomo pauk]

Hi,
I've learned on this site that some engines were using the additional fuel injected, in order to cool the fuel-air charge prior/during entering the intake ducts (so, a kind of ADI to increase manifold pressure? and therefore the power). IIRC some radial engines were able to do so. How about in-lines? Further: German engines using C3 injection?

Anyway, if someone has some good information, I look forward to read about that.

 

[wuzak]

Not sure about that Tomo.

I know that Pratt Whitney injected fuel into the eye of the compressor impeller when they went to fuel injection. I guess something similar occured with the Rolls-Royce injection carburettors later in the war.

We do know that Rolls-Royce engines did not use ADI operationally during the war - though some Packard engines may have. So I doubt RR would be injecting fuel after the supercharger and after-cooler.

As the fuel in most of the Allies' engines travelled through the supercharger I'm not sure it would have been of great benefit to them.

The German engines with direct fuel injection, on the other hand, may have benefitted from such injection.

 

[Shortround6]

We may be having a translation problem Tomo, as I am not sure what you are asking?

RR figured they were cooling the intake charge by either 21 or 25 degrees centigrade ( going by memory) by the fuel from the carburetor evaporating in the supercharger on the early Merlins (III-XX).

American and British "injection" carburetors injected the fuel into the eye of the supercharger and would get a similar benefit. Some extra fuel (over and above what was needed for combustion) was injected as an internal coolant, it may have helped cool the intake charge too. I haven't seen anything specific but that sure doesn't mean the documents don't exist. There is a limit to how much fuel you can use to do this though.
Some Idea of what was going on can gathered by the fact that some engines used "de-enrichment" circuits/settings that cut fuel flow when water injection was being used. Fuel flow was more in proportion to fuel burned rather than excess fuel being used as a coolant.

One Model of the BMW 801 did use a fuel injection nozzle into the supercharger air intake for cooling of the intake charge for more power. According to the 1946 "Jane's" ( German experts can chime in here) the 801D could be operated at 8.8lbs boost with this system in operation instead of 5.5lbs boost without it. Fuel was injected at the rate of approximately 14.3 gallons (imp?) per hour into the intake while overall fuel consumption went from 146 gallons an hour to 185 gallons (Imp) an hour. Power went from 1730hp to 1870hp.

Corrections would be welcome.

I hope this helps.

 

[Denniss]

1870PS = C3-injection used by Fw 190F/G JaBos and only permitted for low alts in the first supercharger gear. In mid 1944 all Fw 190 were available with erhöhte Notleistung without alt restriction, also available in the second supercharger gear. Power was increased to ~2000PS.
The fuel evaporation was use to cool the air prior to charging, somewhat similar to Water-Methanol injection.

 

[Shortround6]

We may have a translation problem here.

"The fuel evaporation was use to cool the air prior to charging, somewhat similar to Water-Methanol injection."

This cannot be right as the fuel (or Water-Methanol liquid) being sprayed into the induction air stream will have little evaporation or cooling effect. However as the fuel (W-M liquid) goes through the supercharger and the air heats up several hundred degrees the fuel (W-M liquid) does evaporate and absorb some of the heat and thus cool the intake charge. It is happening IN the supercharger itself and not afterwards in a separate component ( after cooler) or in the intake manifolds (although a small amount of heat transfer may be taking place).

We may have different meanings as to when the "charging" is taking place. Something like many Europeans will talk about the "distribution system" of an engine meaning the valves and intake manifolds while to an american the " distribution system" usually means the spark distribution. Coils, points, distributors, magnetos, wiring harness, etc. Nobody is "wrong" but it does get confusing at times because a word for word translation doesn't sometimes catch the difference.

 

[razor1uk]

I myself follow Phil Irving's defination of general engine namings...
Intake or exhaust ..valves/gear/drive/timing/system/tracts or pipes, lubrication, ignition and valve timing ...system(s)/gear/arrangement etc, small/little and big/bottom ends (of a conrod) and their similarly related gudegon crank bearing surfaces, crank with pistons and conrods.
Super-chargers a crank or motor powered induction compression systems.
Turbo's are exhaust Turbo(../Turbine driven )Super-chargers.
A supercharging turbo-super-charged engine - is one where the engine has its own mounted supercharger, that is 'fed' by a charged induction from a turbo-supercharger driven from the motors exhaust - so akin to the turbo with its own charger boosting the motors charger ala twin-charger style (not to be confussed with the twin-turbo or even a bi-turbo which is a different kettle of fish)...

Injectors of the 30's/40's were largely split between for most used; although I confess to not know many others..

Bosch direct injectors - sparying directly in/on the openeng intake valve or/for each cylinders intake.
The injector was mounted slightly upstream from the valve guides within the monoblock cylinder heads, and so could in the most minimal way possible, be though of as after cooling; thats not say that the fuel which happened to contact the internal surface areas of the intake port and cylinder did not have a some small cooling affect...

Stormberg Injected Carb - was largely a pressurised fuel injection within a carburettor metering system.
Partially controlled fuel by airflow speeds carburettor slide/needle meterings IIRC, was normally mounted after the Super-charger to give after charge cooling, and to lessen fire/sparking/flash-back risk if injected ahead of the -chargers impellor.
Weren't the injectors for the Stormberg ..or is it Stromberg, by Bendix - or whom bourght out and rebranded the Bosch-US company?

Miss Shillings Orifice - non injected, but likely with (partial) pressure fed float chambers that had a washer (the 'Orifice' as thought attributed to, by Miss Shilling) to impede fuel escape from the bowls during negative Gs, giving such fitted Merlins 'injection' like nose over abilities - albeit beifly as the fuel tanks and fuel supply lines waren't '-G' redsigned to counted air or bubble ingestion.

 

[Gixxerman]

Miss Schillings Orifice

razor1uk

I think you'll find it's Miss Shilling's orifice (or Tillys orifice).......unless it's another case of identical physics appearing in 2 places simultaneously a lady with a fairly similar name came up with the same thing in Germany or Austria?

 

[razor1uk]

Wrong language typo, so used to reading messerschmitt this and that etc...

 

[Shortround6]

The best place to put fuel into the air to cool the charge is at the entrance to the supercharger. Trying to squirt fuel into cold air (below freezing at altitude and even to -30 or -40 degrees) isn't going to do much except puddle fuel in the bottom of the ducts (fire hazard) until you reach the supercharger. The supercharger is where the air/mixture is heated. With fuel in the supercharger the fuel can absorb heat as it is being created and in the turbulence of the spinning impeller. Injecting fuel after the supercharger into the already hot air or mixture may do some good but not as much. The Fuel droplets have less time to mix with the air/mixture and absorb the heat (vaporize) and can give mixture distribution problems. V-12s had enough of those. One cylinder in a bank of 6 always gets more or less air than the others. Same with radials. IN the 20s the radials used slow turning (comparatively) impellers to help make sure all cylinders got a even share of the same mixture as much as they were there to increase pressure.

 

[wuzak]

Bosch direct injectors - sparying directly in/on the openeng intake valve or/for each cylinders intake.
The injector was mounted slightly upstream from the valve guides within the monoblock cylinder heads, and so could in the most minimal way possible, be though of as after cooling; thats not say that the fuel which happened to contact the internal surface areas of the intake port and cylinder did not have a some small cooling affect...

You sure about where the direct injectors work?

What you describe is port injection. Direct injection is usually defined as fuel being injected directly into the cylinder - not through a port. Direct injection was common in Diesels at the time, so I would think that the petrol version would follow the same principle.

 

[GregP]

When you say "injected fuel into the supercharger," many people may not know what you mean. But, MANY people may have a swimming pool. If you turn on the pool spray, it pumps the water out of the pool, into a sprayer INTO THE AIR and back into the pool. The pool gets cooler in time, due to aireation, which includes some evaporation.

I am describing a centfifugal supercharger, not a roots, screw, or any other type. Most of the engines of WWII used a centrifugal unit on the crankshaft.

The "injector" carburetor is similar. It has a steel peg with a round disc on the end. The fuel runs down around the steel peg under pressure and impacts the disc. It turns into a circular spray pattern and gets sucked into the impeller of the supercharger somehwat cooler than the fuel temp when it arrived at the injector, and then gets compressed in the suopercharger and routed down the intake manifold where it SHOULD get diverted to each cylinder in EXTACTLY the same fuel-to-air ratio.

Doesn't always happen that way. Sometimes the spray mixture impacts a curved surface (in the intake manifold) and gets diverted in unrecognized ways so that one cylinder is lean and another is rich. Perhaps more than one or two.

Then you get rough running and mission aborts due to engine roughness. Sometimes the situation is simply the way the engine runs at that time in the design. When it gets fixed, the missions run MUCH better with many fewer aborts.

It took one year for the P-38's in Europe to be fixed (intake and backfiring issues) , and by then, the P-51's were there and the P-38's were transferred to the Pacific Theater where they excelled.

 

[razor1uk]

My mistake, I thought the DB's used direct injection, as in directly over/across the opened valves, hell of a gaff by me there...
So the induction side of the banks are naturally inside the V, and under the slightly offset plenum bifrucated ducting from the charger. I suppose the right side of this pic (below) is the induction/intake side, and the injector is just spraying above and partially onto the open valve then to atomise and create some swirl dispersion...

 

[rinkol]

I recall reading that the Germans adopted fuel injection after BMW reported a 6% improvement in fuel economy by fitting fuel injection to a BMW VI engine (try searching on the web).

The WWII era literature differs as to the benefits of fuel injection. Heron criticised it on the grounds that it did not provide as much charge cooling as could be obtained with a carburettor (he noted that US tests of captured DB engines showed no increase in achievable boost/power when the engines were adjusted to run rich). This may have been why the arrangement of spraying additional fuel into the supercharger of the BMW 801 engine was used. On the other hand, direct fuel injection had some important benefits:

- reduction or elimination of problems with uneven air/fuel ratios (a major issue with early R-3350s - supposedly early versions of this engine that used fuel injection may have had reduced power, but had better reliability);
- elimination of the need for a carburetor choke (and the accompanying presure drop);
- elimination of backfiring problems.

The Soviets adopted the German technology on their later engines - presumably they found it worthwhile.

Modern automotive experience seems to favor direct fuel injection ("solid fuel injection" seems to be the current term).

 

[wuzak]

elimination of the need for a carburetor choke (and the accompanying presure drop);

There still needs to be some kind of throttle - and in WW2 that would still usually be a butterfly valve, like that used in carburettors. Most FI engines today, even with all the fancy electronics, still use throttles. Only a few with adjustable valve control do without - such as BMW's valvetronic.

Rolls-Royce tried to operate the Crecy without a throttle, by just adjusting teh fuel mixture injected in the cylinders, but found that they could not.

- elimination of backfiring problems.

That would be a major benefit. Engine like the Merlin used backfire screens over the inlet ports - which would definitely cause a pressure drop.

 

[GregP]

Actually I was talking about Allison and Merlin/Griffon "injection carburetors," not the Daimler-Benz variety. I hear they were "feul injected," but am not familiar with the system.

Still, it has a supercharger, so the fuel HAS to be injected into the impeller ... unles they had individuakl cylinder fuel injection, which I seriously dount. The "fuel injection" in the DB siomply didn;t care if was upright or inverted, making me believe the difference was the fuel pickup and the fuel punp. Once you get fuel to the impeller intake, then there is no "up or down" to the intake manifold. All it does is route the air-fuel mixture to the cylinders under pressure and, when the intale valves open, the mixture is pushed in by the manifold pressure.

They CERTAINLY didn't have digital fuel injection like we do today.

 

[wuzak]

Actually I was talking about Allison and Merlin/Griffon "injection carburetors," not the Daimler-Benz variety. I hear they were "feul injected," but am not familiar with the system.

Still, it has a supercharger, so the fuel HAS to be injected into the impeller ... unles they had individuakl cylinder fuel injection, which I seriously dount. The "fuel injection" in the DB siomply didn;t care if was upright or inverted, making me believe the difference was the fuel pickup and the fuel punp. Once you get fuel to the impeller intake, then there is no "up or down" to the intake manifold. All it does is route the air-fuel mixture to the cylinders under pressure and, when the intale valves open, the mixture is pushed in by the manifold pressure.

They CERTAINLY didn't have digital fuel injection like we do today.

The DB 601/603/605s, BMW 801 and Jumo 211/213 al had direct fuel injection Greg - the fuel was injected directly into the cylinder. It was mechanically operated not electronically.

 

[GregP]

OK, Wuzak. Can you describe the system?

What sort of fuel controller did they have?No problem compressing the AIR ... but how was the fuel atomized and injected into individual cylinders?

Just curious, not trying to argue since I have never worked on a DB series inverted V-12. I assume fuel pressure and tube diameter determined the fuel flow along with the orifice / nozzle into the cylinder. It MUST have been adjustable or they could not have used multiple fuel grades.

 

[wuzak]

I don't have the details on how teh system worked Greg. I would guess that a cam was used to trigger the injectors.

In any case, in this image you can see one of the fuel injectors labelled (lower right of the image)

http://www.flightglobal.com/airspac...s/images/5677/daimler-benz-db601n-cutaway.jpg

 

[cimmex]

Can't help with the injection pump for DB engines but a good description of the BMW801 one is here:
BMW 801 Fuel Injection Pump

cimmex

 

[Shortround6]

The German engines used direct fuel injection into the cylinders. The injection pump used a piston/cylinder for each engine cylinder and the pump pistons were driven by a a camshaft. A number of articles can be found in the "Flight" magazine archives. A good description starts on Page 46 of the Jan 18, 1940 issue for the Jumo 211 system.