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Alternative fuels, also known as non-conventional and advanced fuels, are derived from sources other than petroleum. Alternative fuels include gaseous fossil fuels like propane, natural gas, methane, and ammonia; like biodiesel, bioalcohol, and refuse-derived fuel; and other like hydrogen and electricity.
These fuels are intended to substitute for more carbon intensive energy sources like gasoline and Diesel fuel in and can help to contribute to decarbonization and reductions in pollution. Alternative fuel is also shown to reduce non-carbon emissions such as the release of nitric oxide and nitrogen dioxide, as well as sulfur dioxide and other harmful gases in the exhaust. This is especially important in industries such as mining, where toxic gases can accumulate more easily.
Ammonia is the simplest molecule that carries hydrogen in a liquid form. It is carbon-free and can be produced using renewable energy. Ammonia can become a transitional fuel soon because of its relative easiness of storage and distribution.
Carbon-neutral fuels have been proposed for distributed storage for renewable energy, minimizing problems of wind and solar intermittency, and enabling transmission of wind, water, and solar power through existing natural gas pipelines. Such renewable fuels could alleviate the costs and dependency issues of imported fossil fuels without requiring either electrification of the vehicle fleet or conversion to hydrogen or other fuels, enabling continued compatible and affordable vehicles. Germany has built a 250-kilowatt synthetic methane plant which they are scaling up to 10 megawatts. Audi has constructed a carbon neutral liquefied natural gas (LNG) plant in Werlte, Germany. The plant is intended to produce transportation fuel to offset LNG used in their A3 Sportback g-tron automobiles, and can keep 2,800 metric tons of CO2 out of the environment per year at its initial capacity. Other commercial developments are taking place in Columbia, South Carolina, Camarillo, California, and Darlington, England.
The least expensive source of carbon for recycling into fuel is flue-gas emissions from fossil-fuel combustion, where it can be extracted for about US $7.50 per ton. Automobile exhaust gas capture has also been proposed to be economical but would require extensive design changes or retrofitting. Since carbonic acid in seawater is in chemical equilibrium with atmospheric carbon dioxide, extraction of carbon from seawater has been studied. Researchers have estimated that carbon extraction from seawater would cost about $50 per ton. Carbon capture from ambient air is more costly, at between $600 and $1000 per ton and is considered impractical for fuel synthesis or carbon sequestration.
Nighttime wind power is considered the most economical form of electrical power with which to synthesize fuel, because the load curve for electricity peaks sharply during the warmest hours of the day, but wind tends to blow slightly more at night than during the day. Therefore, the price of nighttime wind power is often much less expensive than any alternative. Off-peak wind power prices in high wind penetration areas of the U.S. averaged 1.64 cents per kilowatt-hour in 2009, but only 0.71 cents/kWh during the least expensive six hours of the day. Typically, wholesale electricity costs 2 to 5 cents/kWh during the day. Bloomberg Energy Prices Bloomberg.com (compare to off-peak wind power price graph.) Retrieved September 7, 2012. Commercial fuel synthesis companies suggest they can produce fuel for less than petroleum fuels when oil costs more than $55 per barrel. The U.S. Navy estimates that shipboard production of jet fuel from nuclear power would cost about $6 per gallon. While that was about twice the petroleum fuel cost in 2010, it is expected to be much less than the market price in less than five years if recent trends continue. Moreover, since the delivery of fuel to a carrier battle group costs about $8 per gallon, shipboard production is already much less expensive. However, U.S. civilian nuclear power is considerably more expensive than wind power.Sovacool, B.K. (2011). Contesting the Future of Nuclear Power: A Critical Global Assessment of Atomic Energy, World Scientific, p. 126. The Navy's estimate that 100 megawatts can produce 41,000 gallons of fuel per day indicates that terrestrial production from wind power would cost less than $1 per gallon.
Another fuel is formic acid. The fuel is used by converting it first to hydrogen and using that in a fuel cell. Formic acid is much more easy to store than hydrogen.
Propane as an automotive fuel shares many of the physical attributes of gasoline while reducing tailpipe emissions and well to wheel emissions overall. Propane is the number one alternative fuel in the world and offers an abundance of supply, liquid storage at low pressure, an excellent safety record and large cost savings when compared to traditional fuels.
Propane delivers an octane rating between 104 and 112 depending on the composition of the butane/propane ratios of the mixture. Propane autogas in a liquid injection format captures the phase change from liquid to gas state within the cylinder of the combustion engine producing an "intercooler" effect, reducing the cylinder temperature and increasing air density. The resultant effect allows more advance on the ignition cycle and a more efficient engine combustion.
Propane lacks additives, detergents or other chemical enhancements further reducing the exhaust output from the tailpipe. The cleaner combustion also has fewer particulate emissions, lower NOx due to the complete combustion of the gas within the cylinder, higher exhaust temperatures increasing the efficiency of the catalyst and deposits less acid and carbon inside the engine which extends the useful life of the lubricating oil.
Propane autogas is generated at the well alongside other natural gas and oil products. It is also a by-product of the refining processes which further increase the supply of Propane to the market.
Propane is stored and transported in a liquid state at roughly of pressure. Fueling vehicles are similar to gasoline in the speed of delivery with modern fueling equipment. Propane filling stations only require a pump to transfer vehicle fuel and do not require expensive and slow compression systems when compared to compressed natural gas which is usually kept at over .
In a vehicle format, propane autogas can be retrofitted to almost any engine and provide fuel cost savings and lowered emissions while being more efficient as an overall system due to the large, pre-existing propane fueling infrastructure that does not require compressors and the resultant waste of other alternative fuels in well to wheel lifecycles.
Conventional CNG is a fossil fuel. New technologies such as horizontal drilling and hydraulic fracturing to economically access unconventional gas resources, appear to have increased the supply of natural gas in a fundamental way.
Renewable natural gas or biogas is a methane-based gas with similar properties to natural gas that can be used as transportation fuel. Present sources of biogas are mainly , sewage, and animal/agri-waste. Based on the process type, biogas can be divided into the following: biogas produced by anaerobic digestion, landfill gas collected from landfills, treated to remove trace contaminants, and synthetic natural gas (SNG).
Natural gas and hydrogen are both lighter than air and can be mixed together.
Nuclear power generally requires a nuclear reactor to heat a working fluid such as water, which is then used to create steam pressure, which is converted into mechanical work for the purpose of generating electricity or propulsion in water. Today, more than 15% of the world's electricity comes from nuclear power, and over 150 nuclear-powered naval vessels have been built.
In theory, electricity from nuclear reactors could also be used for propulsion in space, but this has yet to be demonstrated in a space flight. Some smaller reactors, such as the TOPAZ nuclear reactor, are built to minimize moving parts and use methods that convert nuclear energy to electricity more directly, making them useful for space missions, but this electricity has historically been used for other purposes. Power from nuclear fission has been used in a number of spacecraft, all of them uncrewed. The Soviets up to 1988 orbited 33 nuclear reactors in RORSAT military radar satellites, where electric power generated was used to power a radar unit that located ships on the Earth's oceans. The U.S. also orbited one experimental nuclear reactor in 1965, in the SNAP-10A mission.
For a list of experimental and presently-operating thorium-fueled reactors, see .
Hydrogen and formic acid
Hydrogen is an emissionless fuel. The byproduct of hydrogen burning is water, although some mono-nitrogen oxides NOx are produced when hydrogen is burned with air.
Hydrogen/compressed natural gas mixture
HCNG (or H2CNG) is a mixture of compressed natural gas and 4–9 percent hydrogen by energy.
Hydrogen could also be used as Oxyhydrogen for better combustion characteristics of Diesel engine. Hydroxy gas is obtained through electrolysis of water.
Compressed air
The Pneumatic motor is an emission-free piston engine using compressed air as fuel.
Propane autogas
Propane is a cleaner burning, high-performance fuel derived from multiple sources. It is known by many names including propane, LPG (liquified propane gas), LPA (liquid propane autogas), Autogas and others. Propane is a hydrocarbon fuel and is a member of the natural gas family.
Compressed natural gas
Compressed natural gas (CNG) and liquefied natural gas (LNG) are two cleaner combustible alternatives to conventional liquid automobile fuels.
Compressed natural gas fuel types
CNG vehicles can use both renewable CNG and non-renewable CNG.
Practicality
CNG powers more than 5 million vehicles worldwide, and just over 150,000 of these are in the U.S. American usage is growing at a dramatic rate.
Environmental analysis
Because natural gas emits less smog-forming pollutants than other fossil fuels when combusted, cleaner air has been measured in urban localities switching to natural gas vehicles. Tailpipe can be reduced by 15–25% compared to gasoline, diesel. The greatest reductions occur in medium and heavy duty, light duty and refuse truck segments.
reductions of up to 88% are possible by using biogas.
Nuclear power and radiothermal generators
Nuclear reactors
Nuclear power is any nuclear technology designed to extract usable energy from atomic nuclei via controlled nuclear reactions. Currently, the only controlled method uses nuclear fission in a fissile fuel (with a small fraction of the power coming from subsequent radioactive decay). Use of nuclear fusion for controlled power generation is not yet practical, but is an active area of research.
Thorium fuelled nuclear reactors
Thorium-based nuclear power reactors have also become an area of active research in recent years. It is being backed by many scientists and researchers, and Professor James Hansen, the former Director at NASA Goddard Institute for Space Studies has reportedly said, "After studying climate change for over four decades, it's clear to me that the world is heading for a climate catastrophe unless we develop adequate energy sources to replace fossil fuels. Safer, cleaner and cheaper nuclear power can replace coal and is desperately needed as an essential part of the solution". Thorium is 3–4 times more abundant within nature than uranium, and its ore, monazite, is commonly found in sands along bodies of water. Thorium has also gained interest because it could be easier to obtain than uranium. While uranium mines are enclosed underground and thus very dangerous for the miners, thorium is taken from open pits. Monazite is present in countries such as Australia, the United States and India, in quantities large enough to power the earth for thousands of years. As an alternative to uranium-fuelled nuclear reactors, thorium has been proven to add to proliferation, produces radioactive waste for deep geological repositories like technetium-99 (half-life over 200,000 years), and has a longer fuel cycle.
Radiothermal generators
In addition, have been used as alternative fuels, on both lands, and in space. Their use on land is declining due to the danger of theft of isotope and environmental damage if the unit is opened. The decay of radioisotopes generates both heat and electricity in many space probes, particularly probes to outer planets where sunlight is weak, and low temperatures is a problem. Radiothermal generators (RTGs) which use radioisotopes as fuels do not sustain a nuclear chain reaction, but rather generate electricity from the decay of a radioisotope.
See also
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