# Heat Release

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Heat release analysis is generally applied to compression ignition engines, although there is no reason why it cannot be used in spark ignition applications. Heat release analysis computes how much heat would need to have been added to the cylinder contents, in order to produce the observed pressure variations1.

Using the first law of thermodynamics it can be shown1,2,3:

(dQ_("net"))/(d theta)=gamma/(gamma-1) p (dV)/(d theta) + 1/(gamma-1) V (dp)/(d theta) (Equation 1)

where:
γ is the ratio of specific heats
Qnet is the net heat release rate in Joules per degree
p is the in-cylinder pressure in Pascals
V is the in-cylinder volume in cubic metres

By taking into account the effects of heat transfer to the cylinder walls, the gross heat release can be calculated:

(dQ_(gross))/(d theta)=(dQ_("net"))/(d theta)+(dQ_(ht))/(d theta) (Equation 2)

(dQ_(ht))/(d theta)=h(T-T_(wall)) (dA)/(d theta) (Equation 3)

where:
h is the heat transfer coefficient
T is the mean gas temperature in Kelvin, calculated from the equation of state (pV=mRT)
Twall is the mean cylinder wall temperature in Kelvin
A is the instantaneous heat transfer surface area of the combustion chamber in cubic metres

catool Implementation: See Return_Heat_Release_Data() in analysis.c

References:
1. Stone, R., "Introduction to Internal Combustion Engines," Macmillan Press Limited, Basingstoke, Hampshire, 1999.
2. Brunt, M. F. J., Rai, H., Emtage, A. L., "The Calculation of Heat Release Energy from Engine Cylinder Pressure Data," SAE Paper 981052, 1998.
3. Heywood, John, "Internal Combustion Engine Fundamentals," McGraw-Hill Book Company, New York, 1988.