Supercharger exit temperatures - general ranges

[yosimitesam]

I've searched here (and elsewhere) and either get no hits or too many useless hits on this subject: What are the "average" supercharger entrance/exit temperatures in WWII high-performance engines?. I've found a few references that indicate the exit termperature from the intercooler on a Merlin to be around 90-degF (32-degC) but I'm unsure if this is reliable. Many engines have a "built-in" supercharger without an aftercooler which must surely increase the charge temp again after exiting an auxillary intercooler/aftercooler,etc. I'm just interested in the general temperature ranges at points along the whole "supercharge train" for some typical engines. I realize this can vary based on octane (resistance to detonation) of the fuel and compression ratio etc., but can't seem to find authoritative numbers. I'm hoping Calum Douglas' new book (if it ever becomes available) might have some data on this. Thanks to everyone for contributing to this astounding resource called a forum, which always is a great way for me to "waste some time" (wife's words) just by picking some random thread topic to read.

 

[Koopernic]

I've searched here (and elsewhere) and either get no hits or too many useless hits on this subject: What are the "average" supercharger entrance/exit temperatures in WWII high-performance engines?. I've found a few references that indicate the exit termperature from the intercooler on a Merlin to be around 90-degF (32-degC) but I'm unsure if this is reliable. Many engines have a "built-in" supercharger without an aftercooler which must surely increase the charge temp again after exiting an auxillary intercooler/aftercooler,etc. I'm just interested in the general temperature ranges at points along the whole "supercharge train" for some typical engines. I realize this can vary based on octane (resistance to detonation) of the fuel and compression ratio etc., but can't seem to find authoritative numbers. I'm hoping Calum Douglas' new book (if it ever becomes available) might have some data on this. Thanks to everyone for contributing to this astounding resource called a forum, which always is a great way for me to "waste some time" (wife's words) just by picking some random thread topic to read.

It's an adiabatic process. Means no heat is added except by work.
Adiabatic process - Wikipedia
There is a nice example of the pressure increase and temperature increase for a 10:1 compression ratio. Pressure goes up 25.1 x and temperature from 300K->753K.


Supercharger - Wikipedia
The above wikipedia article says for a 24C inlet temperature 10psi boost (at sea level) will produce 71C.

 

[Dash119]

I'm hoping Calum Douglas' new book (if it ever becomes available) might have some data on this.

I believe that book is now available.

 

[Deleted member 68059]

I've searched here (and elsewhere) and either get no hits or too many useless hits on this subject: What are the "average" supercharger entrance/exit temperatures in WWII high-performance engines?

Assume abiabatic efficiency of 60>75% depending on the supercharger, then assume 30>40% intercooling. Obviously totally dependant on boost, efficiency
of the compressor, fuel or water injected before the compressor or not etc etc etc etc

(that basically means calculate the temp rise adibatic, then multiply that rise by about a third, then remove about 35% of whatever that rise is
to guess what the post-chargecooler temp is).

These temps are at 16,500ft which is the lowest efficiency point (before the change to 2nd SC gear)

EG 2stg Merlin at 54" HG boost, 3000rpm, at rich mixture, giving 1270bhp.

Temp after 2nd stage = 127 Deg C
Temp after Chargecooler = 82 Deg C

A German test of the 2st Merlin at 61" HG, 3000rpm about 1300bhp
Temp after 2nd stage = 148 Deg C
Temp after Chargecooler = 75 Deg C

Later Merlins with much higher boost will obviously have higher temps.

One can also relate this rise for a given supercharger by the following formula (which changes depending
on the supercharger in question).

T_out = T_Inlet + 0.79 x (supercharger tip speed squared / 10000) -25

For rise in temp simple re-arrange for T_out - Tin = 0.79... etc

Basically 0.79 relates to the efficiency, and the -25 is to account for the cooling created
by feeding fuel into the compressor eye. Temps are Deg C and speed is ft/second. You
can find that in the Hooker book by RRHT on superchargers and other wartime documents. For
other superchargers the 0.79 changes (if its more efficient it might be 0.77 or something, and
if there is no fuel added before the compressor you dont have the -25 etc)

This tells you the temp after the compressor but NOT the impact of the chargecooler.

As for my book, its been printed and has already been sent to anyone who bought one. If you bought from Amazon in the USA etc
they dont "know" that yet as the books are on their way to their distribution centres in bulk on a ship, they wont show it as "available"
until they get them, break the boxes down and stock their own shelves. To be honest my book isnt really designed to tell you
data like that for every engine, its not really a "data-tables" sort of book. It may well have some figures on it as part of the
narrative somewhere, I cant remember as its so huge I cant memorise everything thats in it now...

 

[tomo pauk]

...

As for my book, its been printed and has already been sent to anyone who bought one. If you bought from Amazon in the USA etc
they dont "know" that yet as the books are on their way to their distribution centres in bulk on a ship, they wont show it as "available"
until they get them, break the boxes down and stock their own shelves. To be honest my book isnt really designed to tell you
data like that for every engine, its not really a "data-tables" sort of book. It may well have some figures on it as part of the
narrative somewhere, I cant remember as its so huge I cant memorise everything thats in it now...

Calum - any ETA on the book for people that ordered at Mortons, shipment to European Union (Croatia specifically)?

 

[Deleted member 68059]

Calum - any ETA on the book for people that ordered at Mortons, shipment to European Union (Croatia specifically)?

Hmm well I know people in France have started getting them now, Germany not yet... so I guess in the next week ?

 

[Koopernic]

Assume abiabatic efficiency of 60>75% depending on the supercharger, then assume 30>40% intercooling. Obviously totally dependant on boost, efficiency
of the compressor, fuel or water injected before the compressor or not etc etc etc etc

(that basically means calculate the temp rise adibatic, then multiply that rise by about a third, then remove about 35% of whatever that rise is
to guess what the post-chargecooler temp is).

These temps are at 16,500ft which is the lowest efficiency point (before the change to 2nd SC gear)

EG 2stg Merlin at 54" HG boost, 3000rpm, at rich mixture, giving 1270bhp.

Temp after 2nd stage = 127 Deg C
Temp after Chargecooler = 82 Deg C

A German test of the 2st Merlin at 61" HG, 3000rpm about 1300bhp
Temp after 2nd stage = 148 Deg C
Temp after Chargecooler = 75 Deg C

Later Merlins with much higher boost will obviously have higher temps.

One can also relate this rise for a given supercharger by the following formula (which changes depending
on the supercharger in question).

T_out = T_Inlet + 0.79 x (supercharger tip speed squared / 10000) -25

For rise in temp simple re-arrange for T_out - Tin = 0.79... etc

Basically 0.79 relates to the efficiency, and the -25 is to account for the cooling created
by feeding fuel into the compressor eye. Temps are Deg C and speed is ft/second. You
can find that in the Hooker book by RRHT on superchargers and other wartime documents. For
other superchargers the 0.79 changes (if its more efficient it might be 0.77 or something, and
if there is no fuel added before the compressor you dont have the -25 etc)

This tells you the temp after the compressor but NOT the impact of the chargecooler.

As for my book, its been printed and has already been sent to anyone who bought one. If you bought from Amazon in the USA etc
they dont "know" that yet as the books are on their way to their distribution centres in bulk on a ship, they wont show it as "available"
until they get them, break the boxes down and stock their own shelves. To be honest my book isnt really designed to tell you
data like that for every engine, its not really a "data-tables" sort of book. It may well have some figures on it as part of the
narrative somewhere, I cant remember as its so huge I cant memorise everything thats in it now...

A note for other readers: 54 inches of Mercury is 11.36psig and 60 inches about 14.5psig. These temperatures are much higher than my Wikipedia derived example which gave a 71C exit temperature with 10psig (51 inches hg) boost at sea level with ambient at 24C. This is because
in the example above the Merlin is at 16500 ft where air pressure is much lower (55%) than at sea level so the pressure ratio is much higher.

important to note that the extremely high pressures used on the Rolls Royce engines lead to an enormous amount of jet thrust. Recoil nozzles, a topic in itself.

 

[GregP]

Hi Calum,

In a post previously, I said I wanted a copy of your book, but I missed the title. I am assuming above I can find it on Amazon?

Nevermind, found it in plain sight. Figures.

 

[overbeck]

This report has some temperature data for a V-1710 with 9.6:1 supercharger gears.

 

[yosimitesam]

Thanks for all the replies. This is exactly the information I was looking for. The one instance I found in my own research for the Merlin was probably in degC and not degF as it stated. I thought it sounded too low as 90F is close to "balmy" and my gut feeling was that the temps had to be much, much higher in normal operations. Thanks, again, for all the replies.

 

[J_P_C]

Hmm well I know people in France have started getting them now, Germany not yet... so I guess in the next week ?

just received it today in Poland but my wife took as a prisoner untill Xmas - bummer i would call this curse of 2020 ......

 

[xylstra]

I've searched here (and elsewhere) and either get no hits or too many useless hits on this subject: What are the "average" supercharger entrance/exit temperatures in WWII high-performance engines?. I've found a few references that indicate the exit termperature from the intercooler on a Merlin to be around 90-degF (32-degC) but I'm unsure if this is reliable. Many engines have a "built-in" supercharger without an aftercooler which must surely increase the charge temp again after exiting an auxillary intercooler/aftercooler,etc. I'm just interested in the general temperature ranges at points along the whole "supercharge train" for some typical engines. I realize this can vary based on octane (resistance to detonation) of the fuel and compression ratio etc., but can't seem to find authoritative numbers. I'm hoping Calum Douglas' new book (if it ever becomes available) might have some data on this. Thanks to everyone for contributing to this astounding resource called a forum, which always is a great way for me to "waste some time" (wife's words) just by picking some random thread topic to read.

A lot of the intermediate temperature gradation after the supercharger discharge depends on the intercooler type. I would like some stats on typical installation weight for the inter/after-cooler section, with inter-connecting manifolding separated out of the numbers. Maybe someone has this? Example, the GE CH-5 turbo-supercharger.

 

[elbmc1969]

"By the way, it's my book of the year. In every way a fantastic history of engine design, and in particular one that highlights the many innovations needed in high-performance fighter engines."
--Lee Brimmicombe-Wood, designer of The Burning Blue and the Wing Leader series

"What Lee said.

It is the best thing I've read in a long time."
--Andrew Brazier, some dude

"It's only in the last year or so I've begun to appreciate the importance of radiator design in liquid-cooled engines. We've known from Baughen's book how the French, who had many problems with developing power from their engines, were further hamstrung by poor radiator design. But Douglas really shows how Rolls Royce became a leader in compact, low-drag radiator design and the Germans were way behind, and really suffered with their radiators for the DB 600 series aboard the Bf 109."
--Lee Brimmicombe-Wood