Merlin with fuel injection

Hi Pete, I recall (getting older now….) a RR engineer on a programme long ago, possible Robby Coltranes trains planes and automobiles featuring black 6, who on being asked about the DB601’s multi-point fuel injection efficiency vs the single point on the later Merlins, stated that as it was injected into the eye of the supercharger (Merlin), the increased charge density resulting, was much more efficient than when directed at the inlet, evolving much more power and efficiency as a result?

Any ideas?

Yes, putting it simply, the fuel in the mixture evaporates as it passes through the supercharger and cools the charge quite significantly, like an intercooler. The result being you get more fuel air mixture into the cylinders for no more effort on the part of the supercharger, cooler mixture takesup less room, effectively. This is one reason why the DB601 is a larger displacement for the same power output as an early Merlin, combined with a less efficient supercharger. That’s not the whole story though, because the DB fuel pump is very efficient and the engine contains an amount of magnesium, making it no heavier than the Merlin. They were very closely matched around 1940.

Pete

As Peter Verney pointed out, it did go into widespread production on the 100 series Merlin, and it did not increase the power output.
Griffons also used a mixture of carburettor / injection carb / injection pump.

Pete

Hi Pete, I recall (getting older now….) a RR engineer on a programme long ago, possible Robby Coltranes trains planes and automobiles featuring black 6, who on being asked about the DB601’s multi-point fuel injection efficiency vs the single point on the later Merlins, stated that as it was injected into the eye of the supercharger (Merlin), the increased charge density resulting, was much more efficient than when directed at the inlet, evolving much more power and efficiency as a result?

Any ideas?

As Peter Verney pointed out, it did go into widespread production on the 100 series Merlin, and it did not increase the power output.
Griffons also used a mixture of carburettor / injection carb / injection pump.

Pete

Yes: fuel injection would not provide that much extra power – if any.

Hi

Thanks for the responses. It would have been interesting if this had gone into production – for instance would have the Griffon been needed

Roger

🙁

Roger,

Spitfire Mk9 En114 lost on a test flight from Rolls Royce was fitted with a fuel injection system, this was found along with the engine last year.

Gareth

I did wonder if it was referring to an experimental set up, or whether the reference was to the Bendix injection carburettor fitted to most Mk9s, which was essentially a low pressure metering diaphragm carb feeding an injection nozzle, not unlike the principle of a chain saw carb.
I think that aircraft on test had an SU mechanical single point pump as fitted to later 100 series as mentioned, but so many ideas were test flown, I would like to see that engine if it is possible.

Pete

The Merlin fuel injection system was a single nozzle directed at the root of the supercharger vanes as stated previously not the PI systems of modern day but a vast improvement on the carb.

Hi

Heard a story today that a Spitfire crash site has revealed a Merlin 60 series fitted with fuel injection. Does anyone know if this is correct and if so why wasn’t this made a permanent feature on the Merlin

Thanks in advance for any information

Roger

Roger,

Spitfire Mk9 En114 lost on a test flight from Rolls Royce was fitted with a fuel injection system, this was found along with the engine last year.

Gareth

its not fuel injection as we would know it; its a very early form.

I doubt that anybody is assuming that it’s 3,000-psi direct injection controlled at the injector by piezioelectric microchips, or whatever they’re called on a 2012 Mercedes or Lexus…but the important thing about fuel injection, early form or late, is that it’s not a carburetor. I’ve driven racecars with some inarguably primitive forms of FI, but it was pretty effective nonetheless.

I’m sure Peter will be along in a minute, but its not fuel injection as we would know it; its a very early form.

Bruce

I believe all the Merlin 1XX series had fuel injection. A different procedure was needed in the event of a wet start. I vividly remember a night start in a Mosquito NF36 with the Merlin 113/4 engines. When the engine did not pick up fuel was being pumped through and collected in the exhaust shroud. Then of course the engine fired and set light to this pool of fuel. The book said, in that event, keep the engine running and the prop wash will blow the fire out 😮
It had to be the starboard engine and I sat there petrified as this blazing fuel ran back over the wing just outside my window. :(:o