Liquid fuels, advantages

In the United States, in particular, recent legislation has mandated sweeping improvements to urban air quality by limiting mobile source emissions and by promoting cleaner fuels. The new laws require commercial and government fleets to purchase a substantial number of vehicles powered by an alternative fuel, such as natural gas, propane, electricity, methanol or ethanol. However, natural gas is usually preferred because of its lower cost and lower emissions compared with the other available alternative gas or liquid fuels. Even when compared with electricity, it has been shown that the full fuel cycle emissions, including those from production, conversion, and transportation of the fuel, are lower for an NGV [2]. Natural gas vehicles offer other advantages as well. Where natural gas is abundantly available as a domestic resource, increased use... 

The major advantage of Fischer Tropsch diesel, compared to natural gas, lies in its liquid nature. It does not need special infrastructure and compression like CNG does, and unlike LNG, once converted, it is a liquid fuel that can be treated like any other liquid fuel. However, because the GTL process is more complex than traditional refining, it requires low-cost natural gas priced at less than 1 per million BTUs to remain cost-competitive. Without stranded gas, sources sold at a large discount compared to crude oil, GTL diesel would be considerably more expensive than traditionally refined diesel fuel. 

Regional scarcities of coal initially drove these uses. As petroleum became more abundant and as its price fell, oil became more attractive. In firing boilers, fuel oil possessed only a slight advantage over good-quality coal in Btus per unit volume. But liquid fuels were much easier to handle and store than coal. Competitive pressures kept the prices per Btu of residual oil and coal quite close. 

LPG has many advantages over the alternative liquid fuels, and is regarded as a premium fuel . Some of the premium characteristics are ... 

Biodiesel may be represented chemically as a mixture of fatty acid methyl esters. It is a naturally derived liquid fuel, produced from renewable somces which, in compliance with appropriate prescriptions, may be used in place of diesel fuel for both internal combustion engines and for producing heat in boilers. The advantages, especially environmental, which can potentially result from the widespread use of biodiesel, are manifold ... 

Others affirm the superiority of direct hydrogen, but feel that liquid fuels such as methanol are the answer for the near future. If methanol is used directly, there has to be an onboard reformer and a revised infrastructure to deliver it. But methanol does have some advantages. There is excess generating capacity, and it s the least expensive fuel to transport. Some 70% of the world s oil is in OPEC countries, and 65% of it is in the Persian Gulf. If we switch to methanol, which is produced from natural gas, we can diminish that dependency. 

Fuel cells using directly liquid fuels are advantageous in this aspect. Methanol, formaldehyde (water solution), formic acid (water solution) and hydrazine are among fuels relatively easy to oxidize electrochemically. Alcohol and hydrocarbon with larger molecular weight are much harder to oxidize completely to C02- Other qualifications to be considered are price, availability, safety, energy density and ease of handling. 

High-performance liquid chromatography (HPLC), followed by GC/MS, has been used to fractionate and then quantitate the aliphatic and aromatic hydrocarbons present in liquid fuel precursors in order to determine the fuel potential of the compounds. Kerosene had the advantage of not requiring any sample preparation. Other light fuel oils may require the use of methylene chloride as a solvent prior to HPLC analysis (Lamey et al. 1991). The sensitivity, precision, and recovery of this method were not reported. 

One major advantage of DME use is that it can be stored as a high-density liquid phase at modest pressures (around 5 atm) and delivered as a gas-phase fuel in a pumpless operation. Therefore, the use of DME can potentially combine the advantages of easy fuel delivery of pressurized hydrogen and the high energy density storage of liquid fuel. In addition, DME is less toxic than methanol. 

Several studies have recently reported on the technical viability and economics of fuel cell systems for various applications. " A variety of designs are under development, but all rely on a H2-rich gas stream. Transportation and storage of H2 is one of the key issues that must be overcome, " and is an important reason for the interest in reformed liquid fuels, which can take advantage of a well-developed existing infrastructure to provide H2. 

Methanol s major advantages in vehicular use are that it is a convenient, familiar liquid fuel that can readily be produced using well-proven technology. It is a fuel for which vehicle manufacturers can, with relative ease, design a vehicle that will outperform an equivalent gasoline vehicle and obtain an advantage in some combination of emission reduction and efficiency improvement [1.7]. 

Despite many advantages of using ethanol produced from biomass as a fuel (it is a high-energy, clean-burning, and totally renewable liquid fuel), it will only substitute gasoline if it is economically competitive. Thus, there is an increased interest in the optimization of all the steps of ethanol production. 

Methanol has a number of advantages for powering fuel cell vehicles. As the 2001 study for the caFCP noted, these include methanol s immediate availability without new upstream infrastructure, high hydrogen-carrying capacity, and ability to be readily stored, delivered, and carried on-board without pressurization. 22 In short, our transportation system and its infrastructure favor liquid fuels. Fuel cell vehicles with onboard methanol reformers would have very low emissions of urban air pollutants. Daimler-Chrysler has introduced demonstration fuel cell vehicles that convert methanol to hydrogen on board. 

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