The tutor examines the idea that internal combustion engines are more efficient in cold weather.
An upper limit for efficiency of an internal combustion engine is
eff = (Tcombust – Tsurrounding)/Tcombust
Tcombust is the temp of the combustion cylinder
Tcombust, Tsurrounding both in degrees Kelvin (Celsius + 273).
Let’s imagine a diesel engine, whose average internal cylinder temperature might be around 1600°C. Then at outdoor temp of 25°C (293K) we have
eff = (1873 – 298)/1873 = 84.1%
Likewise, at outdoor temp -25°C we have
eff = (1873 – 248)/1873 = 86.8%
The 2.7% increase in efficiency at -25°C vs 25°C may be noticeable to an operator.
White, J. Edmund. Physical Chemistry: College Outline Series. New York: Harcourt Brace Jovanovich, 1987.
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.