R-R Merlin Intercooler Temperature

[PHN]

Hi,

I was reading about the Rolls-Royce Merlin and read that some of the later variants had an intercooler which cooled the fuel-air mixture as it came out from the superchargers and into the intake manifold. I was wondering if anyone knew the temperature of the fuel-air mixture in this intercooler. I have read that it used a 70-30 water-glycol mixture as coolant, which is the same as the main coolant system, but I have not found any values for the temperature. The temperature of the fuel-air charge just before it enters the cylinders is important as it affects the density of the charge and the subsequent power output.

 

[FLYBOYJ]

If this intercooler was using water/ glycol, the fluid temp going thru it would probably carry a value close to or a little less than the normal coolant system temp (on a P-38 with its allison, its between 125-250 degrees c, couldn't find anything on a Spit or Lanc, but most inline engines of the WWll period ran close to the same). Its hard to say what the temp of the air flowing out of this intercooler would be, probably just a few degrees cooler than ambient air temperature. Fuel/ air temp at the intake manifold is usually not monitored as the ambient (or in this case intercooler) air temp determines the fuel air mixture. Hotter air, the air is less dense, thus less fuel in the fuel/air mixture, cooler air, more dense, more fuel etc. With fuel injection, or a pressurized carburetor system, this is done automatically.

For supercharged engine performance, your going to watch cylinder head temp (if equipped) maniford pressure, engine RPM, and during high output you're going to watch oil and coolant temperatures as well. High engine temps and high intake manifold pressure will destroy an engine (like a merlin) quicker than you could say tally-ho!

 

[PHN]

Thanks for the reply. I suspect that the intercooler coolant temperature was similar to the main coolant temperature, due to the choice of similar coolants. The ethylene glycol is also justifiable as an antifreeze, however.

 

[FLYBOYJ]

Thanks for the reply. I suspect that the intercooler coolant temperature was similar to the main coolant temperature, due to the choice of similar coolants. The ethylene glycol is also justifiable as an antifreeze, however.

I would also guess that the glycol being used through the intercooler was "piped off" the engine cooling system, probably downstream of the engine radiator. I would love to see a schematic of this system.

 

[FLYBOYJ]

Spitfire IIA IIB with a Merlin XII engine - Max. radiator temp. - 120 degrees C

 

[KraziKanuK]

Thanks for the reply. I suspect that the intercooler coolant temperature was similar to the main coolant temperature, due to the choice of similar coolants. The ethylene glycol is also justifiable as an antifreeze, however.

I would also guess that the glycol being used through the intercooler was "piped off" the engine cooling system, probably downstream of the engine radiator. I would love to see a schematic of this system.

Spitfire: The History has a sketch of the intercooler system for a Griffon 61 in a Mk VIII. This was a trial a/c, JF317, one of the prototypes for the Mk XIV. Each radiator pod held a coolant radiator. Each pod held either a intercooler rad and a oil cooler rad. Can't remember which pod held which. The intercooler system was stand alone.

 

[FLYBOYJ]

There ya go....But, if the system was stand alone, how was the coolant circulated? Usually you will have an engine driven water pump (like on your car) circulating all cooling activities.

 

[KraziKanuK]

There ya go....But, if the system was stand alone, how was the coolant circulated? Usually you will have an engine driven water pump (like on your car) circulating all cooling activities.

You got it, pump for the IC system.

 

[FLYBOYJ]

Ah-ha!

 

[Tom Fey]

Author Dave Birch writes in "Rolls-Royce and the Mustang" that the air coming out of the Merlin 61 two-stage supercharger at 18lbs. boost was about 200°C (392°F) but was reduced to 120° (248°F) by the aftercooler for induction into the engine.