Rolls Royce Fuel Injection

[Admiral Beez]

Wikipedia reports that the Griffon 101 used on the postwar Spiteful Mk.XVI (shown below) had fuel injection.

Why did it take so long to put fuel injection on a Rolls Royce engine? And why never on the Merlin? The short answer of course is that the Merlin and Griffon (and Meteor and Meteorite for that matter) did just fine without fuel injection, but it must have been seen as a needed push for the Spiteful. Not the Seafang though, only carburetors.

Wikipedia also says the Napier Sabre had fuel injection, however I think this is inaccurate, being more of a traditional carburetor with added pressure injection. So I wonder how accurate Wikipedia is being with the fuel injected Griffon.

 

[Shortround6]

During the war (and very early in it) RR had looked at Fuel injection of the German type (direct injection) and rejected for a number of reasons. Some may have been good, some may have been cover your ass reasons. The British carburetors and American single point/pressure injection carbs were much easier to make requiring hundreds fewer parts. The evaporation of the fuel in the supercharger lowered the intake mixture temperature by 25 degrees C on the early Merlins and RR was very hesitant to give that up. Granted the mixture distribution was not all it could be with simpler systems.
Please do not confuse the German Fuel injection of WW II with modern automobile fuel injection. It was entirely mechanical and relied on pretty much the same sensors as the Carburetor engines did. It could be adjusted so that cylinder 6 got a few percent more or less fuel than cylinder 7 but once the difference was adjusted in, that is where stayed, at all rpms and at all altitudes and manifold pressures.

The battle between fuel injection and carburetors lasted through the 50s and into the 60s on cars. Fuel injection could often outperform cheap carburetors or set ups where one carb supplied more than one cylinder. On engines that could be equipped with one carburetor barrel per cylinder there was often very little difference in power and often difference in drivability or power band with the favor going to the carburetors.

 

[Admiral Beez]

It could be adjusted so that cylinder 6 got a few percent more or less fuel than cylinder 7 but once the difference was adjusted in, that is where stayed, at all rpms and at all altitudes and manifold pressures.

Interesting, thanks S Shortround6 . Would it have been beneficial to be able to adjust the mechanical fuel injector's mixture in flight? Presumably better HA/LA mixture could then be dialled in.

Without the ability to adjust fuel flow, once Miss Shilling's orifice was in service I see little benefit of direct injection over carburetors.

 

[wuzak]

Certainly the Rolls-Royce engines used injection type carburetors during the war.

Rolls-Royce Merlin (2-stage 2-speed)
Model: Merlin 66 (RM 10 SM).

Carburetion: 1 Rolls-Royce Bendix-Stromberg BD-44-1 2-barrel injection type updraft carburetor with automatic mixture control and progressive boost control.

Rolls-Royce Merlin (2-stage 2-speed)
Model: Merlin 130 (RM 14 SM).

Carburetion: 1 Rolls-Royce-S.U. variable-stroke fuel injection pump with injection through 1 nozzle into eye of supercharger impeller. Downdraft air intake. Automatic fuel-air ratio cottlt'ol

http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Merlin.pdf


Rolls-Royce Griffon (1-stage 2-speed)
Model: Griffon VI (RG 14 SM)

Carburetion: 1 S.U. AVT-44/203 Z-barrel updraft injection type carburetor with automatic mixture control and progressive boost control.

Rolls-Royce Griffon (2-stage 2-speed)
Model: Griffon 69 (RG 4 SM)

Carburetion: Rolls-Royce Bendix-Stromberg 9T-40-1 3-barrel updraft injection type carburetor, with injection through 8 nozzles into eye of first-stage supercharger impeller. Automatic mixture control and progressive boost control.

http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Griffon.pdf

The Rolls-Royce Griffon 69 had the same injection system as the 61 and 65, which were used in Spitfire XIVs and XIXs, but a different reduction ratio.

Other models had injection into the air intake of the carburetor itself.

Packard Merlins all had injection type carburetors. This was because the carburetor was sourced locally and not built to British designs.

Rolls-Royce, of course, had the heightened imperative of production over improvement. And many of their Merlins went into aircraft that would not need to manoeuvre in such a way that required the ability to operate in negative-G (such as bombers).

 

[Admiral Beez]

Certainly the Rolls-Royce engines used injection type carburetors during the war.

Rolls-Royce Merlin (2-stage 2-speed)
Model: Merlin 66 (RM 10 SM).

Carburetion: 1 Rolls-Royce Bendix-Stromberg BD-44-1 2-barrel injection type updraft carburetor with automatic mixture control and progressive boost control.

Rolls-Royce Merlin (2-stage 2-speed)
Model: Merlin 130 (RM 14 SM).

Carburetion: 1 Rolls-Royce-S.U. variable-stroke fuel injection pump with injection through 1 nozzle into eye of supercharger impeller. Downdraft air intake. Automatic fuel-air ratio cottlt'ol

http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Merlin.pdf


Rolls-Royce Griffon (1-stage 2-speed)
Model: Griffon VI (RG 14 SM)

Carburetion: 1 S.U. AVT-44/203 Z-barrel updraft injection type carburetor with automatic mixture control and progressive boost control.

Rolls-Royce Griffon (2-stage 2-speed)
Model: Griffon 69 (RG 4 SM)

Carburetion: Rolls-Royce Bendix-Stromberg 9T-40-1 3-barrel updraft injection type carburetor, with injection through 8 nozzles into eye of first-stage supercharger impeller. Automatic mixture control and progressive boost control.

http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Griffon.pdf

The Rolls-Royce Griffon 69 had the same injection system as the 61 and 65, which were used in Spitfire XIVs and XIXs, but a different reduction ratio.

Other models had injection into the air intake of the carburetor itself.

Packard Merlins all had injection type carburetors. This was because the carburetor was sourced locally and not built to British designs.

Rolls-Royce, of course, had the heightened imperative of production over improvement. And many of their Merlins went into aircraft that would not need to manoeuvre in such a way that required the ability to operate in negative-G (such as bombers).

Taking all this into account, I wonder why they bothered with direct injection in the Spiteful and IIRC the Shackleton .

 

[wuzak]

Taking all this into account, I wonder why they bothered with direct injection in the Spiteful and IIRC the Shackleton .

The answer is they didn't.

The Wiki article you referenced in the OP says:

• Griffon 101

2,420 hp (1,805 kW); Two-stage, three-speed supercharger using Low Supercharger (L.S), Moderate Supercharger (M.S), or Full Supercharger (F.S); reduction gear ratio 4.45; Rolls-Royce fuel injection system. Used on Spiteful Mk.XVI.

It does not say that it is direct injection.

 

[Shortround6]

Interesting, thanks S Shortround6 . Would it have been beneficial to be able to adjust the mechanical fuel injector's mixture in flight? Presumably better HA/LA mixture could then be dialled in.

Without the ability to adjust fuel flow, once Miss Shilling's orifice was in service I see little benefit of direct injection over carburetors.

The injector pump as a whole did adjust in flight. each injector could be tuned (varied) to it's cylinder on the ground, but in the air all the injectors were leaned or richened the same amount. They were in a rack or body and and the "adjustment" either raised and lowered or rotated the injector pump bodies in the rack or housing.

The German system gave the pilot one less thing to worry about, shove the power lever forward and the air inlet opened up, the injector pump threw more fuel per stroke of the pump and the engine made more power. A barometric capsule was also linked to the pump to decrease the amount of fuel per stroke as the altitude increased or the manifold pressure dropped.

 

[pbehn]

As S/R posted, the difference between the two wasn't that direct fuel injection was automatically superior until the late 1970s early 1980s but that superiority relied on computer chips and lots of sensors. I owned a car with the ubiquitous "twin choke Webers" which the second oil crisis saw the end of, you just cant take a 4MPG road car seriously.

 

[Admiral Beez]

The answer is they didn't.

The Wiki article you referenced in the OP says:

• Griffon 101

2,420 hp (1,805 kW); Two-stage, three-speed supercharger using Low Supercharger (L.S), Moderate Supercharger (M.S), or Full Supercharger (F.S); reduction gear ratio 4.45; Rolls-Royce fuel injection system. Used on Spiteful Mk.XVI.

It does not say that it is direct injection.

Interesting, thanks. I wonder why they bother calling out RR fuel injection on the Griffon 101 if it's just another pressure injected carburetor as the other Griffons.

 

[Shortround6]

As S/R posted, the difference between the two wasn't that direct fuel injection was automatically superior until the late 1970s early 1980s but that superiority relied on computer chips and lots of sensors. I owned a car with the ubiquitous "twin choke Webers" which the second oil crisis saw the end of, you just cant take a 4MPG road car seriously.

true but the Webers, if properly set up, could give many of the mechanical fuel injection systems a run for their money.

 

[pbehn]

true but the Webers, if properly set up, could give many of the mechanical fuel injection systems a run for their money.

Mine was a road car, whatever is true about power output, my Hillman Hunter GLS thew an awful lot of petrol straight out of the exhaust unburned.

 

[Admiral Beez]

The Germans, Japanese, Soviets, Italians (Fiat Tifone) and US used direct injection in at least some of their WW2 aero engines. Why not the Brits?

 

[wuzak]

Interesting, thanks. I wonder why they bother calling out RR fuel injection on the Griffon 101 if it's just another pressure injected carburetor as the other Griffons.

The system of sensors and control systems are of Rolls-Royce design/specification, I would guess.

 

[wuzak]

As S/R posted, the difference between the two wasn't that direct fuel injection was automatically superior until the late 1970s early 1980s but that superiority relied on computer chips and lots of sensors. I owned a car with the ubiquitous "twin choke Webers" which the second oil crisis saw the end of, you just cant take a 4MPG road car seriously.

true but the Webers, if properly set up, could give many of the mechanical fuel injection systems a run for their money.

The electronic fuel injection systems that started appearing in the 1970s were not direct injection, but either port injection or throttle body injection. The latter could be considered a injection carburettor system.

Direct injection systems after WW2 and up to the 1960s (in road cars) were mechanical injection type, similar to what was used on aero engines during WW2.

Race cars sometimes used mechanical direct fuel injection, and that continues today in some categories (such as drag racing).

Modern direct injection systems are EFI and started appearing in the 1990s/early 2000s.

 

[wuzak]

The Germans, Japanese, Soviets, Italians (Fiat Tifone) and US used direct injection in at least some of their WW2 aero engines. Why not the Brits?

Charge cooling.

 

[Sid327]

Charge cooling.

I think "SR6'' already mentioned that RR at the time looked into mechanical F.I. and decided they could make better power using a carb.

I don't think many engines came close to matching the Merlin in spite of this.

 

[tomo pauk]

The Germans, Japanese, Soviets, Italians (Fiat Tifone) and US used direct injection in at least some of their WW2 aero engines. Why not the Brits?

High cost to make, time consuming to make, lack of expertise.

 

[Milosh]

One would think those reasons would be obvious Tomo.

 

[Admiral Beez]

High cost to make, time consuming to make, lack of expertise.

The Brits were leading in jet propulsion, radar/sonar, computers, piston aero engines, pressure injected carburetors, sleeve valves, etc, etc. I assume a preceived lack of ROI is the leading driver rather than a lack of treasure, time or talent.

 

[tomo pauk]

One would think those reasons would be obvious Tomo.

Still feel that way?