Super V.E. for diesels

[oil pan 4]

It would appear the MAN diesel and Cummins are saying close to the same thing.
Man diesel was claiming air temps lower than 30'F to 40'F hurt fuel milage and cummins recomends staying above 20'F.
I knew cool air was good to a point, but never new what those numbers could be till now.

Cool air above 40'F and intake harmonics are the way to go.
Cold air intakes are good more often than not, just have to keep the air going into the enigne after the intercooler above 40'F.

I have a -40'C to +40'C temperature probe on order to put down in the intake manifold to get some real numbers.
I have the problem of 0'F temperatures in winter here.

[Daox]

What factors effect benefit from cold air and what factors penalize for it?

[Duffman]

Originally Posted by oil pan 4

It would appear the MAN diesel and Cummins are saying close to the same thing.
Man diesel was claiming air temps lower than 30'F to 40'F hurt fuel milage and cummins recomends staying above 20'F.
I knew cool air was good to a point, but never new what those numbers could be till now.

Cool air above 40'F and intake harmonics are the way to go.
Cold air intakes are good more often than not, just have to keep the air going into the enigne after the intercooler above 40'F.

I have a -40'C to +40'C temperature probe on order to put down in the intake manifold to get some real numbers.
I have the problem of 0'F temperatures in winter here.

My fuel economy on my diesel goes to crap in the cold, but I have no edea how much of it is idle time & warmup and hom much is the lower energy content of diesel and how much is intake temperature. I do have some -30C highway runs recorded but wind direction is a vairable as well. I do know that it is significant for me though.

[Duffman]

Originally Posted by oil pan 4

I was reading my cummins manual today and apperantly cummins recomends that when operating at +20'F or less to locate your intake inside the engine enclosure.
Also to use grill shutters below 32'F and a winter front below 0'F.

Our Macks at work say under hood air at -12C and winterfronts at -18C I believe.

[UFO]

Winter fuel is playing less and less of a role in reduced mileage in cold weather. The ULSD energy content is much closer to that of kerosene, the winter mixer.

[Diesel_Dave]

Originally Posted by Daox

What factors effect benefit from cold air and what factors penalize for it?

The cooler air benefits in 2 ways:

First cooler air means more dense air and therefore, you'll run a higher AFR (at least on most diesels--some more modern ones have some sophistcaed electronic controls). The higher AFR increases the combustion efficiency. Fundamentally, the thermodynamic benefit comes from the fact that mixtures with higher AFR have a higher specific heat ratio (gamma). Secondly, the lower air temperature itself increases the specific heat ratio and thus the combustion efficiency. You can see the dependence of specific heat ratio on temperature and AFR here (pg. 2392):
http://muhserv.atauni.edu.tr/makine/..._files/A/c.pdf
and the also the dependence of theoretical diesel efficiency on the specific heat ratio here:
The Diesel Engine


Now, for the downside:

In a diesel the ignition takes place due to compression, not due to spark as it does in a gasser. Therefore the ignition doesn't take place until the pressures and temperatures reach the point where the fuel evaporates and the mixture self-ignites. The time between when the fuel in injected and when ignites is the "ignition delay". Cooler air temps can prolong the ignition delay to the point where the ignition doesn't take place until very late in the cycle or, in extreme case, the ignition never happens and you get a misfire. Later combustion typically means lower efficiency because the heat release happens in a larger volume. Now, how much the ignition delay is affected depends on how cold it is as well as the type of fuel system. Newer common rail systems have extremely high injection pressures (30,000 psi+) so the ignition delays are very short and less affected by temperature. Also, many of the new systems will electronically advance the injection timing for cold air temps to compensate. The older mechanical fuel injection systems were more affected because the injection pressures were relatively low and the ignition delays were quite long.

[oil pan 4]

I think dave nailed it.
Just ran adiabatic compression for a 22:1 diesel like mine and with 0'F air the temperature in cylinder at TDC is only going to be like 860'F.
A more normal 18:1 compression diesel will only hit about 800'F.
40'F air in a 22:1 engine gives me 930'F and a 18:1 engine will hit 860'F.

The hotter the air the better, to a point.
800'F does not seem hot enough.

Originally Posted by Duffman

Our Macks at work say under hood air at -12C and winterfronts at -18C I believe.

Ok so we have Mack, cummins, Man and adaibatic calculations all saying air below 30'F isn't good and air in the >20'F range is bad.

Thats good enough for me.

Seems like we should try to shoot for <40'F IAT and keep it as cool as possible when the out side temperature is well above 40'F.

[tjts1]

Diesels already use tuned length manifolds.

[oil pan 4]

They aren't tuned for what we want.

[Diesel_Dave]

Originally Posted by tjts1

Diesels already use tuned length manifolds.

I've never seen one myself. Do you have any examples?

FYI, here's what the intake looks like on my Cummins:

The style is sometimes referred to as a "flower box"--similar to a flower box hanging off a window. The style has been known to be sub-optimal (performance wise), but the style has remained unchanged for decades because it's rugged, simple, and easy to manufacture.