While looking at some pics of es44ac rooftops, I noticed that some units had a raised air-air heat exchanger while some did not. For example UP 7605 has a raised air-air heat exchanger while UP 7832 does not. The same was for BNSF es44acs. Why would there be two different styles/types of air-air heat exchangers on the same locomotive that is from the same railroad? Is it like how there were flared and non flared radiators on UP sd70ms? Also, what is an air-air heat exchanger? I did google it and look on wikipedia and I managed to find some information on them but I am still not clear as to what their function is.
What an Air to Air is is basically a radiator for the INTAKE air of the Engine after it has been Turbocharged. Turbocharging raises the temprature of the air passing it thru an Air to Air lowers the temp and lowers the intake air temp and allows for more complete combustion and therefore lowers EMMISIONS and makes the engine more effiecent. They have been used for YEARS on OTR trucks and have had few issuses except when a bird Deer Moose or other large animal and or vechiles go thru them. As tgo certain units having a raised vs non raised could be a desgin change mid stream to a better design that happens as the egineers come up with better designs.
Firstly I checked some photos and there is a small duct, about 3" high, 2 feet by four feet surrounding the outlet from the twin fans that pull the air through the intercooler on 7605 (and 7608) and not on 7832. I am not sure what the function of this duct is but it might improve the fan efficiency a little.
The basic intercooler is unaltered and is the same on all ES locomotives including the Australian ES44DCi units (which have a bigger AC6000 size radiator).
The intercooler (or aftercooler, or charge air cooler) lowers the temperature of the air AFTER it has been compressed in the turbocharger. All GE engines since the FDL in the U25 have had intercoolers, but all intercoolers on FDL engines (up to the Dash 9s and AC4400s) were air to water intercoolers where water (cooled in the engine radiator) cooled the air between the turbocharger and the cylinders.
Using air instead of water means that the radiator no longer has to cool the intercooler water and the water no longer needs to be carried around. The intercooler itself is larger and heavier and very large air ducts are needed between the turbocharger and the intercooler. GE were able to fit the air to air intercooler because there was space available where the shorter EVO 12 replaced the FDL 1
Being nitpicky here…
Aftercooler is the correct name for the air-air heat exchanger on the ES44ACs as it comes after the compressor. An intercooler technically refers to a charge air cooler placed between two or more stage of compression (quite a few WW2 aircraft engines had two stages of compression).
Intercooler is the name used in most automotive applications, but I’ll rely on GE describing the device as an intercooler in their EVO locomotive brochure.
And since the air will be compressed again in the cylinder (they don’t call diesels “compression ignition” for nothing, this intercooler is between two stages of compression.
But I agree that a number of piston aero engines had more than one stage of compression BEFORE the cylinders.
M636C
Cooler intake air makes for a denser charge - i.e. more oxygen available for combustion - less emissions and a more complete burn for more power. A turbocharger is more of a ‘pump’ than a ‘compressor’, even though some compression does take place. The intercooler reduces the temperature of the turbo output, in order to cram more into the cylinder (charge).