Energy density of fuels

Q = energy density of fuel at the melting point (joules/gm)... 

In the present study, the energy density of a DMFC single cell is defined as the experimental energy density of fuel neglecting the energies provided by the external equipment to pump air and fuel, and to maintain the cell s temperature and humidity. 

Fuel Cells, Principles and Thermodynamics, Table 2 Electromechanical energy density of fuels ... 

Storage method Energy density of fuel Storage efficiency (%) Net energy density... 

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-... 

Liquid hydrazine, 13 586 Liquid hydrocarbons, in fluidized-bed processes, 20 169-170 Liquid hydrogen delivery of, 13 853 energy density of, 13 839 physical and thermodynamic properties of, 13 762-763t as a rocket fuel, 13 800 storage of, 13 785-786 Liquid hydrogen sulfide, 23 630, 633 Liquid hydrogen tank levitation system, 23 866... 

Other battery technologies include sodium-sulfur which was used in early Ford EVs, and zinc-air. Zinc appeared in GM s failed Electrovette EV in the late 1970s. Zinc-air batteries have been promoted by a number of companies, including Israel s Electric Fuel, Ltd. Zinc is inexpensive and these batteries have six times the energy density of lead-acid. A car with zinc-air batteries could deliver a 400 mile range, but the German postal service found that these batteries cannot be conventionally recharged. 

Figure 9.3. Energy densities of various alternative fuels (LHY) (LPG 50% propane, 50% butane natural gas 83% methane).

Due to the high hydrogen storage capacity of the ammonia molecule (17.7 wt% equal to an energy density of 4,318 Wh kg 1), its decomposition is intensely investigated for COx-free hydrogen production for mobile fuel cell applications [146]. However, compared with the well-established Haber Bosch process for ammonia synthesis, its decomposition is underdeveloped and requires substantial improvements before it can be considered as a practical contribution to the energy supply toolbox. 

One of the main reasons is the low power density of fuel cells. Power density, defined as power produced per unit weight or unit volume of the power source, is one of the most important factors for a power source for transportation as well as energy density, defined as energy produced per unit weight or volume. As for fuel cells, unlike batteries, energy density would not be such a serious problem as power density because energy density can be increased when more fuel is loaded. 

Methanol can be nsed as one possible replacement for conventional motor fuels. The use of methanol as a motor fuel received attention during the oil crises of the 1970s due to its availability and low cost. Methanol is an attractive fuel it is hquid at room temperature, it has limited toxicity, high energy density, and is an inexpensive energy source (Shukla et al., 1998). Methanol is a favored fuel as it has twice the energy density of liquid hydrogen and since it is a liquid at normal ambient temperatures and it can thus be stored and transported easily and inexpensively (Collins, 2001). 

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