What is the ideal intake air temp in relation to the outside air cooling at the intercooler? Maybe it makes so little difference it's not worth the hassle? Winter time fuel mileage does go down so maybe just a winter front is all that is needed below what temp?

 

Lets see if I can confuse the issue with some too elementry information. In a gas engine, the colder air carries more dense oxygen which may pick up the efficiency some. But a diesel runs on heat, the colder the intake temp the colder the combustion temp. I am sure that the engines are engineered to run at a specific temperature. Obviously this temperature is above freezing for optimum efficiency.

 

You guys got me to thinking so I ran some compression temperature numbers for comparison.

First off, it seems the boost value does not matter for compression temperature. What does matrer is only the compression ratio and the IAT. Certainly the compression pressure goes up with boost, in fact the pressure doubles for every 14.7 psi of boost. With zero boost the compression pressure should be about 250 psi.

For an assumption I said IAT was Ambient Temperature + 30F and that 14.7 psia was Ambient Pressure. I could not remember the CTD compression ratio so I assumed it was 18:1 with a compression efficientcy of 90%.

Hopefully these are ball park numbers in degrees F:

AMB = Ambient Temperature
CBT = Combustion Temperature (Cumminsbustion)

AMB = -20
CBT = 605

AMB = 0
CBT = 650

AMB = 20
CBT = 695

AMB = 40
CBT = 740

AMB = 60
CBT = 786

AMB = 80
CBT = 831

AMB = 100
CBT = 876

AMB = 120
CBT = 922

Jim

 

the commercial B engine has one point lower compresson than the Dodge engine and is 16 and change, do not remember the exact pressure.

 

So what's optimum CBT for diesel fuel?

 

Heck the air entering the air box on my 06 comes in thru the grill !Either way its cold in the winter.It enters behind the passenger headlight,it was engineered that way.So what now ? Did DODGE screw up ?

 

Nope. Just wonderd? Cold weather seems to decrease mileage so get warm air from inside the motor compartment. When it's warmer get it outside. What temp is optimum though?

 

Using Jim's math and assumptions, optimum combustion temperature (which I would rephrase as "optimum #2 diesel compression ignition temperature") is 825*F-875*F.

This would correspond to Cummins recommendation for most efficient ambient air operating temperature of ~75*F-95*F on their industrial engines.

 

Dude - I don't think you're allowed to post that... might want to edit before the mods do.

 

We really can't make the air cooler than outside without extra stuff but we can keep it above 75 if we wanted to. The winter mpg drop might possible be fixable.
I've noticed since I put the fan in my intake the IAT has droped 2-5deg. Also noticed that when the motor is allready hot and I start it the IAT temp is allways very hot, but with the fan on it cools down a lot faster.

 

Sure, that's because the intake tract is heat-soaked.

 

Yeah, I noticed the heat soaking also.

Jim

 

Yes heat soaking couldn't come up with the word. Since I put the intake fan in the temp drops much quicker, and doesn't get as hot in stop and go traffic.