Fuels energy density

Some of the desired properties of fuels, depending upon particular applications, include heal content, that is. Blus or calories released upon combustion per unit weight or volume of the fuel. Energy density is particularly important where a fuel is used in some form of vehicle where the fuel must he carried and thus part of the fuel is expended simply 10 transport itself. Cleanliness of burning is of major concern, not only in terms of pollutants that may be produced as the result of combustion, but... 

The presence of a prompt negative coefficient has two major effects on a large excursion that starts from normal operating conditions. First, in going from the normal operating fuel energy density to the point where... 

Figure 10. Effect of methanol concentration on fuel energy density for a DMFC single cell at 60 C using air as oxidant and methanol as fuel with various concentrations.

Figure 18. Plots of fuel energy density versus output current (A), power (B) and voltage (C) for a simulated DMFC system, respectively, which contains a 28-cell stack with 22 cm electrode area at 60 °C using air as oxidant and 1. OM methanol as fuel.

Several alternative methods have been considered in order to increase the energy density of natural gas and facilitate its use as a road vehicle fuel. It can be dissolved in organic solvents, contained in a molecular cage (clathrate), and it may be adsorbed in a porous medium. The use of solvents has been tested experimentally but there has been little improvement so far over the methane density obtained by simple compression. Clathrates of methane and water, (methane hydrates) have been widely investigated but seem to offer little advantage over ANG [4]. Theoretical comparison of these storage techniques has been made by Dignam [5]. In practical terms, ANG has shown the most promise so far of these three alternatives to CNG and LNG. 

The lower energy density of alternative fuels is even more problematic for aircraft. Methanol has been sug-... 

Another emerging area m biofuels is pyrolysis, which is the decomposition of biomass into other more usable fuels using a high-temperature anaerobic process. Pyrolysis converts biomass into charcoal and a liquid called biocrude. This liquid has a high energy density and is cheaper to transport and store than the unconverted biomass. Biocrude can be burned in boilers or used in a gas turbine. Biocrude also can be chemical by altered into other fuels or chemicals. Use of pyrolysis may make bioenergy more feasible in regions not near biomass sources. Biocrude is about two to four times more expensive than petroleum crude. 

It must he recognized, however, that hydrogen usage for transportation will always create a trade-off between energy efliciency (fuel economy) and energy density (range), whereas this trade-off is non-existent for other applications. 

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