The message
from Phil Addison contains these words:

AIUI the calorific value is defined as the total heat obtained by
complete burning, so it should be immaterial whether we react in a flame
or below 100C - so long as we capture all the heat produced. In an ideal
calorific heat measurement, all the material of combustion would be
captured, and the before and after temperatures would be the same. This
definition implies capturing the latent heat, though I admit to not
having checked to see if it is the accepted definition.

My 'Mechanical Engineers Handbook' claims to have been completely
revised in 1973 and that distinguishes between Higher and Lower
Calorific Values.

The following is based on the section on combustion.

On Combustion Efficiency (in engine or combustor) may be defined 3 ways:

In non flow combustors
- Actual volumetic %age of CO2/
Max. possible

In flow combustors
- Actual temp. rise in the combustion chamber/
Max poss. rise with same air/fuel ratio

In heating devices
- Actual heat transfer to working substance/
Max. poss. heat transfer in an isothermal reaction

--
Roger