Chapter 4 Energetic Efficiency of Biofuel Production 4.1 Thermal Properties of Biofuels Both primary and secondary biofuels have to assure specified requirements concern- ing their properties. Since the biofuels can exist in solid, liquid, and gaseous forms, some of the characteristics are very different, some are universal for all types of fuels. The variety of properties for technical, as well as market purposes are carefully stan- dardized [1]. The most important property is calorific value (heating value). As shown in numer- ous research the calorific value results of chemical composition of a fuel. Many for- mulas have been proposed to describe the correlation between heating value, and elemental or on proximate data on the fuel composition. Two main cases of calorific value are distinguished: the higher heating value (also called gross calorific value) and low heating value (also called net calorific value). Those calorific values differ because the majority of fuels contain hydrocarbons, which causes the combustion gases to contain water. Evaporation of this water consumes some part (dependent upon hydrogen content) of energy released during combustion of the fuel. High calorific value is determined in such a way that the corresponding amount of latent heat of evaporation is not subtracted from reaction heat. Low calorific value, in turn, corresponds to this amount of energy, which remains after evaporation of water, and is available to the user. Another contribution of the same type comes from mois- ture—the molecules of water absorber by the fuel. The methods of determination of both calorific values as well as their precise definitions are given in appropriate standards (e.g., ISO1213-2:1992) [2]. Correlation between the chemical composition of a fuel and its calorific value was first studied by Dulong, whose historical equation can be written in the following form [3]: © Springer Nature Switzerland AG 2019 A. Wasiak, Modeling Energetic Efficiency of Biofuels Production, Green Energy and Technology, https://doi.org/10.1007/978-3-319-98431-5_4 35