Fuel, thermochemical properties

A comparison of the characteristics associated with propellant burning, explosive detonation, and the performance of conventional fuels (see Coal Gas, NATURAL Petroleum) is shown ia Table 1. The most notable difference is the rate at which energy is evolved. The energy Hberated by explosives and propellants depends on the thermochemical properties of the reactants. As a rough rule of thumb, these materials yield about 1000 cm of gas and 4.2 kj (1000 cal) of heat per gram of material. 

Now it is important to stress that, whereas the laminar flame speed is a unique thermochemical property of a fuel-oxidizer mixture ratio, a turbulent flame speed is a function not only of the fuel-oxidizer mixture ratio, but also of the flow characteristics and experimental configuration. Thus, one encounters great difficulty in correlating the experimental data of various investigators. In a sense, there is no flame speed in a turbulent stream. Essentially, as a flow field is made turbulent for a given experimental configuration, the mass consumption rate (and hence the rate of energy release) of the fuel-oxidizer mixture increases. Therefore, some researchers have found it convenient to define a turbulent flame speed, S T as the mean mass flux per unit area (in a... 

The NIST Chemical Kinetics Model Database web site (http //kinetics.nist. gov/CKMech/) is a good resource for chemical kinetic models, thermochemical property data, and elementary rate coefficients. The book Gas-Phase Combustion Chemistry edited by W. C. Gardiner, Ir. (Springer-Verlag, NY, 1999) also lists many detailed mechanisms for different fuels that are available in technical papers and from the Internet. 

A core aspect of the model is the determination of the chemical conversion of gasifier SG to hydrogen by the RP. For conditions where steam availability is not limiting, the chemical conversion relates to the difference between the initial and final combustion/fuel ratio of the fuel gas. The initial CP/SG ratio is determined by the gasifier and the biomass feedstock. The final CP/SG ratio is determined by the thermochemical properties of the metal oxide material. Ideally the difference between the initial (CP/SG),and final (CP/SG)j , ratios should be as large as possible. In reality the availability of steam for the re-oxidation of the metal oxide is limiting for conditions where the difference in the CP/SG ratios are large. 

All these fuels belong to a group of high-energy-density fuels with compact molecular structure rendered by the presence of pentacyclic cages. They are stable and nonvolatile at room temperature and pressure. Three formulations are solid and the fourth is a viscous liquid. Their S3mthesis and molecular structure analysis that uses X-ray crystallographic methods have been described by Marchand [5, 6]. Their molecular structure and physical properties are presented briefly below. Measured thermophysical and thermochemical properties follow. 

A new class of pentacyclic HED fuels was analyzed and some thermophysical and thermochemical properties have been measured. The main findings were as follows ... 

Now it is important to stress that, whereas the laminar flame speed is a unique thermochemical property of a fuel-oxidizer mixture ratio, a turbulent flame speed is a function not only of the fuel-oxidizer mixture ratio, but also of the flow characteristics and experimental configuration. Thus, one encounters great difficulty... 

Pyrolysis of biomass is a thermochemical conversion technology of solid biomass into a liquid ( pyrolysis oil , bio-oil ). This liquid can be used as a fuel with properties comparable to (crude) mineral oils. The pyrolysis process itself is not subject to this paper, the technology is described in (6), where there is also given a equation for calculating the cost of the pyrolysis oil depending on plant size and feedstock price. 

Table 1 Thermochemical properties of various bioenergy feedstocks and fuels...

Jenkins, B.M., Ebeling, J.M., 1985. Thermochemical properties of biomass fuels. CaUforaia Agriculture 14—16. 

We saw in Case study 1.1 that photosynthesis and the oxidation of organic molecules are the most important processes that supply energy to organisms. In this section we begin our quantitative study of biological energy conversion by assessing the thermochemical properties of fuels. 

The NASA polynomials are usually fitted in the temperature range 300 to 5000 K. The reason for choosing this range is practical. Combustion calculations require thermodynamic and thermochemical properties between room temperature and 3000 or (for special fuels or detonations) 4000 K. In the course of automatic calculations, as well as in some exotic conditions such as spaceship reentry, knowledge of properties to 6000 K is required. Thus, the polynomials discussed here follow the bulk of existing tables (such as JANAF and TSIV as discussed later) by being fit in the range 300-5000 K. Extrapolation to 6000 K is easily done with little error. Extrapolation below 300 K, seldom needed in combustion research, is less accurate. In some cases the polynomials were fit up to 3000 K only. 

The preheating of solid fuel and the ash cooling are not included in the thermochemical conversion process. The basic criteria for these four thermochemical conversion reactions are that the solid-fuel convertibles (or moisture, char, volatiles) are converted from the solid phase into the interstitial gas phase and finally to the offgases (Figure 16 and Figure 19). The part of the solid-fuel convertibles that is converted into the interstitial gas phase is defined as the conversion gas [3]. The conversion gas is associated with two important physical properties, namely the empirical stoichiometry [CxHyOz] and the mass flux [kg/m s]. 

The active layer must provide the required activity, selectivity and thermochemical stability properties. Different active phases can be adopted depending on the operating constraints and the fuel type. In the following we will mainly focus on CH4 (i.e. the main constituent of natural gas) as the reference fuel for GT applications. In this respect, the combustion catalysts that have been most extensively investigated for configurations based on lean combustion concepts are PdO-based systems and metal-substituted hexaaluminates. 

The requirements for selecting a fuel and oxidizer as a liquid bipropellant system are usually a compromise between the demands of the vehicle system, the propulsion system, and the propellants themselves. The vehicle and propulsion system will determine performance levels, physical property requirements, thermal requirements, auxiliary combustion requirements, degree of storability and package-ability, hypergolicity, etc. The final propellant selection must not only satisfy such requirements but is also dictated by thermochemical demands which the fuel and oxidizer make on each other. Frequently, specifically required properties are achieved through the use of chemical additives and/or propellant blending. 

Addn of small quantity, such as 0.1%, of Centr 2 to motor fuels improves their antiknock properties) 15)Perez Ara(1945), 423 (Some props) l6)J.Taylor et al, JPhysCollChem 51, 590(1947)(Some thermochemical props)... 

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