Page 258 - Advanced thermodynamics for engineers

11.4 CONCLUDING REMARKS 245

11.3 ENTHALPY OF REACTION
The enthalpies of reaction of some commonly encountered fuels are given in Table 11.2. These have
been taken from a number of sources and converted to units consistent with this text where necessary.
There are a number of interesting observations that can be made from this table, viz.
• the enthalpies of reaction of many of the hydrocarbon fuels on a basis of mass are very similar,
and around 44,000 kJ/kg;
• the stoichiometric air–fuel ratios of many basic hydrocarbon fuels lie in the range 13:1 to 17:1;
• some of the fuels have positive enthalpies of formation;
• all of the fuels have negative enthalpies of reaction;
• the enthalpies of reaction of the alcohols are less than those of the non-oxygenated fuels, simply
because the oxygen cannot provide any energy of reaction;
• the commonly used hydrocarbon fuels are usually mixtures of hydrocarbon compounds.

11.4 CONCLUDING REMARKS
It has been shown that the energy released by a fuel is contained in it by virtue of its structure, i.e. the
bonds between the atoms. It is possible to assess the enthalpies of formation or reaction of a wide range
of fuels by considering the chemical structure of the bonds in the compound.
A table of enthalpies of formation and reaction for common fuels has been given (Table 11.2).