The effect on engine performance of change in water-jacket outlet temperature

[Dominic]

http://naca.larc.nasa.gov/reports/1933/naca-tn-476/

If you read this, you will see that a reduction in coolant temperature does increase horsepower. When increasing the coolant temperature from 71degC and 90degC (160°F and 195°F) the engine lost 3-5% horsepower. When applied to our engines, that is roughly 5-10hp.

You will notice the fuel vaporization was higher, mechanical friction was lower, and fuel consumption dropped as the coolant temperature rose. This is easily explained though by the fact fuel vaporizes quicker in the heat, oils from 1933 were less pourable when cold, and the less dense intake charge allowed for less fuel to enter the cyl per stroke.

Please read this, all of you. I found it very informative and wanted to share it with the board. I hope some of you accept this paper as a fact and really learn something from it. [img]smile.gif[/img]

[ June 17, 2002: Message edited by: Dominic ]</p>

[DominusEtDeusNatus]

First of all this is an airplane engine being tested for different altitudes.

"friction horsepower decreases approximately linearly with increasing jacket temperature...this change in friction horsepower is primarily due to change in the viscosity of the oil...The brake power decreases with increasing jacket-water temperature at sea level, is nearly constant at 10,000 feet and increases at 20,000 feet...the percentage decrease for an increase in jacket water temperature from 35deg C to 95deg C being 5.7% at sea level...exhaust gases were cooled by injecting water"

Going from 203deg F down to 95deg F will give 5.7% on that engine. Decrease of 108deg F. Stock thermo is 195deg F and that is reduced to 160deg F. Decrease of 35deg. So you got 108deg vs 35deg.

Increase in jacket-water temperature:
decreases BSFC = good thing;
increases mechanical efficiency = good thing;
better vaporization of fuel = good thing.

If the engine is too cold you will loose power from poor vapourization of the fuel. Cooler intake is definitely good.

Is cooler engine good? How cool do you want it? Is there such a thing as too cool? At what temperature does that happen?

Good use of Google. [img]graemlins/thumbsup.gif[/img]

http://www.google.com/search?q=engin...e=UTF8&oe=UTF8

[Dominic]

<blockquote>quote:</font><hr>Originally posted by Dom:
[QB]First of all this is an airplane engine being tested for different altitudes.

<hr></blockquote>

Yes, I am only concerned with sealevel.
An airplane engine is still a watercooled internal combustion engine, and while the oils were far different in 1933 - the data presented is valuable. There is a such thing as too cold, I believe that is below 150-160degF for modern engines. Fuel vaporization is much less of an issue with injected engines, this was a carb'd engine keep in mind!

The increase in mechanical efficiency I can only attribute to the poorer oils used in 1933. I believe this might not hold true today using a synthetic oil.

[ June 17, 2002: Message edited by: Dominic ]</p>

[nova]

You have to be careful when dealing with a lot of the research NACA did. Most of the work they did with aerodynamics is still valid but a lot of work they did in other areas has been shown to be flawed in some way shape or form by more modern methods.