Effect of Air Temperature on Power
#1
Effect of Air Temperature on Power
bmf wrote on 09-18-2002 11:45 PM:
Tomcat, quick question, for every 10 degree drop in temp. what is the expected percent of horsepower gain?
Thanks bmf
Tomcat, quick question, for every 10 degree drop in temp. what is the expected percent of horsepower gain?
Thanks bmf
The way to answer your question is to calculate the density ratio.
D.R. = (T1 + 460)/(T2 + 460)
eg. if you reduce air temperature from 85F to 75F
D.R. = (85 + 460)/(75 + 460) = 545/535 = 1.0187
That's about a 2% increase in density, meaning each cubic foot of air drawn into the engine has almost 2% more oxygen molecules.
IF you add more fuel in proportion, or you were a bit too rich before, you will make about 2% more power.
This type of calculation is used to report engine HP at "standard conditions". For example, an engine might be tested on the dyno with 85F air on a day when the air is humid and the atmospheric pressure is low. The actual dyno reading will be converted to the HP that the engine would have achieved at say 65F, normal atmospheric pressure and no humidity. This will increase the reported dyno HP, but on a hot humid day in the summer, the engine will deliver the lower actual number.
Since altitude has a significant effect on atmospheric pressure (higher altitude = lower pressure = less oxygen molecules in a cubic foot), HP is reduced, and fuel flow must be reduced or the engine will run rich.
Thread
Thread Starter
Forum
Replies
Last Post
Mr. Demeanor
General Boating Discussion
1
02-11-2004 11:59 PM