BiodieselBiodiesel is a domestically produced, renewable fuel that can be manufactured from vegetable oils, animal fats, or recycled restaurant grease for use in diesel vehicles. Biodiesel's physical properties are similar to those of petroleum diesel, but it is a cleaner-burning alternative. Using biodiesel in place of petroleum diesel, especially in older vehicles, can reduce emissions.

Basics

Biodiesel is a domestically produced, renewable fuel that can be manufactured from vegetable oils, animal fats, or recycled restaurant grease. It is a cleaner-burning replacement for petroleum diesel fuel. It is nontoxic and biodegradable.

Biodiesel is a liquid fuel often referred to as B100 or neat biodiesel in its pure, unblended form. Like petroleum diesel, biodiesel is used to fuel compression-ignition engines, which run on petroleum diesel. See the table for biodiesel's physical characteristics.

How well biodiesel performs in cold weather depends on the blend of biodiesel. The smaller the percentage of biodiesel in the blend, the better it performs in cold temperatures. Regular No. 2 diesel and B5 perform about the same in cold weather. Both biodiesel and No. 2 diesel have some compounds that crystallize in very cold temperatures. In winter weather, manufacturers combat crystallization in No. 2 diesel by adding a cold flow improver. For the best cold weather performance, drivers should use B20 made with No. 2 diesel manufactured for cold weather.

Biodiesel BlendsBiodiesel can be blended and used in many different concentrations, including B100 (pure biodiesel), B20 (20% biodiesel, 80% petroleum diesel), B5 (5% biodiesel, 95% petroleum diesel) and B2 (2% biodiesel, 98% petroleum diesel). B20 is a common biodiesel blend in the United States.

Low-Level BlendsASTM International develops specifications for conventional diesel fuel (ASTM D975). These specifications allow for biodiesel concentrations of up to 5% (B5). Low-level biodiesel blends, such as B5 are ASTM approved for safe operation in any compression-ignition engine designed to be operated on petroleum diesel. This can include light-duty and heavy-duty diesel cars and trucks, tractors, boats, and electrical generators.

B20B20 (20% biodiesel, 80% petroleum diesel) is the most common biodiesel blend in the United States. B20 is popular because it represents a good balance of cost, emissions, cold-weather performance, materials compatibility, and ability to act as a solvent. Using B20 provides substantial benefits and avoids many of the cold-weather performance and material compatibility concerns associated with B100. Most biodiesel users purchase B20 or lower blends from their petroleum distributors or biodiesel marketers. Biodiesel blends of 20% (B20) or higher qualify for biodiesel fuel use credits under the Energy Policy Act of 1992.

B20 and lower-level blends generally do not require engine modifications. Engines operating on B20 have similar fuel consumption, horsepower, and torque to engines running on petroleum diesel. B20

has a higher cetane number (a measure of the ignition value of diesel fuel) and higher lubricity (the ability to lubricate fuel pumps and fuel injectors) than petroleum diesel.

However, not all diesel engine manufacturers cover biodiesel use in their warranties (see the National Biodiesel Board's OEM Informationfor those that do support the use of biodiesel blends). Because diesel engines are expensive, users should consult their vehicle and engine warranty statements before using biodiesel. Biodiesel blends between B6 and B20 must meet prescribed quality standards—ASTM D7467 (summary of requirements).

B100, or neat biodiesel, contains about 8% less energy per gallon than petroleum diesel. For B20, this could mean a 1% to 2% difference, but most B20 users report no noticeable difference in performance or fuel economy. Biodiesel has some emissions benefits, especially for engines manufactured before 2010. For engines equipped with selective catalytic reduction (SCR) systems, the air quality benefits are the same whether running on biodiesel or petroleum diesel. However, biodiesel still offers better greenhouse gas (GHG) benefits compared to conventional diesel fuel. The emissions benefit is roughly commensurate with the blend level; that is, B20 would have 20% of the GHG reduction benefit of B100.

B100B100 and other high-level biodiesel blends are less common than B5 or B20 due to a lack of regulatory incentives and pricing. B100 can be used in some engines built since 1994 with biodiesel-compatible material for parts, such as hoses and gaskets. B100 has a solvent effect and it can clean a vehicle's fuel system and release deposits accumulated from previous petroleum diesel use. The release of these deposits may initially clog filters and require filter replacement in the first few tanks of high-level blends.

When using high-level blends, a number of issues can come into play. The higher the percentage of biodiesel above 20%, the lower the energy content per gallon. High-level biodiesel blends can also impact engine warranties, gel in cold temperatures, and suffer from microbial contamination in tanks. B100 use could also increase nitrogen oxides emissions, although it greatly reduces other toxic emissions.

B100 requires special handling and may require equipment modifications. To avoid engine operational problems, B100 must meet the requirements of ASTM D6751, Standard Specification for Biodiesel Fuel (B100) Blend Stock for Distillate Fuels (summary of requirements). ASTM Specification D6751 now includes a No.1-B and a No.2-B grade. The No.1-B grade has stricter limits on monoglycerides and filterability than the No.2-B grade. The No.1-B grade is a special purpose biodiesel grade for use in applications where low temperature operability is needed.

Biodiesel Production and DistributionBiodiesel is a legally registered fuel and fuel additive with the U.S. Environmental Protection Agency (EPA). EPA registration includes all biodiesel that meets ASTM D6751 and is feedstock neutral. The federal Renewable Fuel Standard requires at least 1 billion gallons of biomass-based diesel consumption in the U.S. (at this time, biodiesel comprises the vast majority of biomass-based diesel in the US). The RFS requires 1.3 billion gallons of biomass-based diesel in 2013.

Production

Biodiesel is produced from vegetable oils, yellow grease, used cooking oils, and tallow. The production process converts oils and fats into chemicals called long-chain mono alkyl esters, or biodiesel. These chemicals are also referred to as fatty acid methyl esters, and the process is referred to as transesterification. Roughly speaking, 100 pounds of oil or fat are reacted with 10 pounds of a short-chain alcohol (usually methanol) in the presence of a catalyst (usually sodium hydroxide [NaOH] or rarely, potassium hydroxide [KOH]) to form 100 pounds of biodiesel and 10 pounds of glycerin. Glycerin, which is used in pharmaceuticals and cosmetics, among other markets, is a co-product. Although the process is relatively simple, homemade biodiesel is not recommended. Diesel engines are expensive and risking damage, loss of warranty, and operational problems from fuel that does not meet rigorous ASTM D6751specifications is not wise.

Raw or refined plant oil, or recycled greases that have not been processed into biodiesel, are not biodiesel and should be avoided. Fats and oils (triglycerides) are much more viscous than biodiesel, and low-level vegetable oil blends can cause long-term engine deposits, ring sticking, lube-oil gelling, and other maintenance problems that can reduce engine life. (See Straight Vegetable Oil as a Diesel Fuel? (PDF) ).Research is currently focused on developing algae as a potential biodiesel feedstock, because it's expected to produce high yields from a smaller area of land than vegetable oils.

Biodiesel Benefits and ConsiderationsBiodiesel is a domestically produced, clean-burning, renewable substitute for petroleum diesel. Using biodiesel as a vehicle fuel increases energy security, improves public health and the environment, and provides safety benefits.

Energy Security and BalanceThe United States imports about half of its petroleum, two-thirds of which is used to fuel vehicles in the form of gasoline and diesel. Depending heavily on foreign petroleum supplies puts the United States at risk for trade deficits, supply disruption, and price changes. Biodiesel can be produced in the U.S. and used in conventional diesel engines, directly substituting for or extending supplies of traditional petroleum diesel.

Air QualityCompared with using petroleum diesel, using biodiesel in a conventional petroleum diesel engine substantially reduces tailpipe emissions of unburned hydrocarbons (HC), carbon monoxide (CO), sulfates, polycyclic aromatic hydrocarbons, nitrated polycyclic aromatic hydrocarbons, and particulate matter (PM). The reductions increase as the amount of biodiesel blended into diesel fuel increasesfor engines manufactured before 2010. Engines manufactured in 2010 and later have to meet the same emissions standards, whether running on biodiesel, diesel, or even natural gas. Selective catalytic

reduction (SCR)technology, which reduces nitrogen oxide (NOx) emissions to near zero levels, makes this possible. For these new technology engines, the emissions from diesel fuel are comparable to those from biodiesel and are very, very low. These new technology engines are some of the cleanest engines on the road. B100 provides the best emission reductions, but lower-level blends also provide benefits. B20 has been shown to reduce PM emissions 10%, CO 11%, and

unburned HC 21% (see graph) in older engines Learn more about Biodiesel Emissions.

Using biodiesel reduces greenhouse gas emissions because carbon dioxide released from biodiesel combustion is offset by the carbon dioxide sequestered while growing the soybeans or other feedstock. B100 use reduces carbon dioxide emissions by more than 75% compared with petroleum diesel. Using B20 reduces carbon dioxide emissions by 15%.

Greenhouse gas and air-quality benefits of biodiesel are roughly commensurate with the blend. B20 use provides about 20% of the benefit of B100 use. B100 use could increase nitrogen oxides emissions, although it greatly reduces other emissions.

Engine OperationBiodiesel improves fuel lubricity and raises the cetane number of the fuel. Diesel engines depend on the lubricity of the fuel to keep moving parts from wearing prematurely. One unintended side effect of the federal regulations, which have gradually reduced allowable fuel sulfur to only 15 ppm and lowered aromatics content, has been to reduce the lubricity of petroleum diesel. To address this, the ASTM D975 diesel fuel specification was modified to add a lubricity requirement (a maximum wear scar diameter on the high-frequency reciprocating rig [HFRR] test of 520 microns). Biodiesel can increase lubricity to diesel fuels at blend levels as low as 1%.

Before using biodiesel, be sure to check your engine warranty to ensure that higher-level blends of this alternative fuel don't void or affect it. High-level biodiesel blends can also have a solvency effect in engines that previously used petroleum diesel.

SafetyBiodiesel is nontoxic. It causes far less damage than petroleum diesel if spilled or released to the environment. It is safer than petroleum diesel because it is less combustible. The flashpoint for biodiesel is higher than 130°C, compared with about 52°C for petroleum diesel. Biodiesel is safe to handle, store, and transport.

ElectricityElectricity can be used to power all-electric vehicles and plug-in hybrid electric vehicles. These vehicles can draw electricity directly from the grid and other off-board electrical power sources and store it in batteries. Hybrid electric vehicles use electricity to boost fuel efficiency. Using electricity to power vehicles can have significant energy security and emissions benefits.

Electricity Fuel Basics

Electricity is considered an alternative fuel under the Energy Policy Act of 1992. Electricity can be produced from a variety of primary energy sources, including oil, coal, nuclear energy, moving water, natural gas, wind energy, and solar energy. Plug-in vehiclesare capable of drawing electricity from off-board electrical power sources (generally the electricity grid) and storing it in batteries. Though not yet widely available, fuel cell vehicles use hydrogen to cleanly generate electricity onboard the vehicle.

Powering Vehicles with ElectricityIn plug-in electric vehicles, onboard rechargeable batteries store energy to power electric motors. Vehicles that run only on electricity produce no tailpipe emissions. But there are emissions associated with the production of most of the country's electricity.

Fueling plug-in vehicles with electricity is currently cost effective compared to gasoline, especially if drivers take advantage of off-peak rates offered by many utilities. Electricity costs can vary by region, type of generation, time of use, and access point. Learn aboutfactors affecting electricity prices from the U.S. Energy Information Administration.

Electric Charging StationsMany plug-in vehicle owners will do the majority of their charging at home (or at fleet facilities, in the case of fleets). Some employers offer access to charging at the workplace. In many states, plug-in vehicle drivers also have access to public charging stations at libraries, shopping centers, hospitals, and businesses. Charging infrastructure is rapidly expanding, providing drivers with the convenience, range, and confidence to meet more of their transportation needs with plug-in vehicles.

Electricity Production and DistributionPlug-in hybrid electric vehicles (PHEVs) and all-electric vehicles (EVs) store electricity in batteries to power one or more electric motors. The batteries are charged primarily by plugging into off-board sources of electricity, produced from fossil fuels, nuclear energy, and renewable energy sources.

EVs and PHEVs in all-electric mode do not produce tailpipe emissions. However, there are emissions associated with the majority of electricity production in the United States. See theemissions section for more information.

ProductionMost of the electricity in the United States is produced by steam turbine generators at power plants from primary resources such as coal, natural gas, and nuclear energy. According to the U.S. Energy Information Administration, in 2012, 37% of the nation's electricity was generated by coal, 30% by natural gas, 19% by nuclear energy, and 1% by petroleum.

Electricity is also produced from renewable sources of energy, including hydropower, biomass, wind, geothermal, and solar power. Together, renewable energy sources generated about 12% of the country's electricity in 2012. Production capacity from renewable sources (excluding hydropower) has been increasing steadily over the last decade.

With the exception of photovoltaic (PV) generation, most of the primary sources of energy are used directly or indirectly to move the blades of a turbine connected to an electric generator. The turbine generator set converts mechanical energy to electrical energy. In the cases of coal, oil, natural gas, nuclear fission, biomass, geothermal and solar thermal, the heat produced by these primary resources is used to create steam, which moves the blades of the turbine. In the cases of hydro and wind power, turbine blades are acted upon directly by flowing water and wind, respectively. PV panels convert sunlight directly to electricity using semiconductors that exhibit the photovoltaic effect.

The sources of energy used to produce electricity vary from one geographic region to the next. To find out about the mix of fuels and other energy sources used in your area, see the emissions section. Learn more about electricity production from the U.S. Department of Energy's Energy Information Administration.

Electricity Transmission and DistributionElectricity in the United States travels long distances from generating facilities to local distribution substations through a transmission grid of nearly 160,000 miles of high-voltage transmission lines. Generating facilities provide power to the grid at low voltage, from 480V in small generating facilities to 22 kV in larger power plants. Once electricity leaves a generating facility, the voltage is increased, or "stepped up," by a transformer to minimize the power losses over long distances. As electricity is transmitted through the grid and arrives in the load areas, voltage is stepped down by transformers at distribution substations (ranges of 69 kV to 4.16 kV), and finally further lowered for use by customers (residential customers use 120V and 240V; commercial and industrial customers typically use 120V, 208V, and 480V).

Plug-In Vehicles and Electricity Infrastructure CapacityEVs and PHEVs represent a new source of demand for electricity. However, they are unlikely to strain much of our existing electricity infrastructure in the near term. Large increases in the number of these vehicles in the United States will not necessarily require the addition of new electricity-generation capacity or substantial upgrades to transmission and distribution infrastructure.

Demand for electricity rises and falls, depending on time of day and time of year. Electricity production, transmission, and distribution capacity must be able to meet demand during times of peak use; but most of the time, the electricity infrastructure is not operating at its full capacity. In the United States, roughly 50% of the generation capacity is used 100% of the time, while only 5% of the time (about 400 hours per year) generation greater than 90% of the capacity is used. Usually the most costly and inefficient generation is used during these peak periods. As a result, EVs and PHEVs have the potential to create little or no need for additional capacity, as long as they charge predominantly during off-peak times, such as late at night, when the electric load on the system is at a minimum.

According to a study by Pacific Northwest National Laboratory, existing U.S. electricity infrastructure has sufficient capacity to meet about 73% of the energy needs of the country's light-duty vehicles. According to deployment models developed by researchers at the National Renewable Energy Laboratory (NREL), the diversity of household electricity loads and electric vehicle loads should allow introduction and growth of the plug-in vehicle market while "smart grid" networks expand. These networks will provide the capability to monitor and protect residential distribution transformers from future vehicle impacts, ensure that charging occurs during off-peak periods, and reduce costs to utilities, grid operators, and consumers. The NREL analysis also demonstrated the potential for synergies between plug-in vehicles and distributed sources of renewable energy. For example, small-scale renewables, like solar panels on a rooftop, can both provide clean energy for vehicles and reduce demand on distribution infrastructure by generating electricity near the point of use.

Utilities, vehicle manufacturers, charging-equipment manufacturers, and researchers are working to ensure that EVs and PHEVs are smoothly integrated into the U.S. electricity infrastructure. Some utilities offer lower rates at off-peak times in order to encourage vehicle charging when electricity demand is lowest. Vehicles and many models of electric vehicle supply equipment (EVSE, or charging stations) can be programmed to restrict charging to off-peak times. "Smart" models are even capable of communicating with the grid, enabling them to charge automatically when electricity demand and prices are lowest.

Benefits and Considerations of Electricity as a Vehicle FuelHybrid and plug-in electric vehicles can help increase energy security, improve fuel economy, lower fuel costs, and reduce emissions.

Energy SecurityIn 2012, the United States imported about 40% of the petroleum it consumed, and transportation was responsible for nearly three-quarters of total U.S. petroleum consumption. With much of the world's petroleum reserves located in politically volatile countries, the United States is vulnerable to price spikes and supply disruptions.

Using hybrid and plug-in electric vehicles instead of conventional vehicles can help reduce U.S. reliance on imported petroleum and increase energy security. Hybrid electric vehicles (HEVs) typically use less fuel than similar conventional vehicles, because they employ electric-drive technologies to boost efficiency. Plug-in hybrid electric vehicles (PHEVs) and all-electric vehicles (EVs) are both

capable of using off-board sources of electricity, and almost all U.S. electricity is produced from domestic coal, nuclear energy, natural gas, and renewable resources.

Fuel EconomyHEVs typically achieve better fuel economy and have lower fuel costs than similar conventional vehicles. For example, the 2012 Honda Civic Hybrid has an EPA combined city-and-highway fuel economy estimate of 44 miles per gallon, while the estimate for the conventional 2012 Civic (four cylinder, automatic) is 32 miles per gallon. However, some HEV models employ hybrid technology to boost power rather than efficiency and consequently do not have substantial fuel economy advantages over similar conventional vehicles. Use the Find A Car tool on FuelEconomy.gov to compare fuel economy ratings of individual hybrid and conventional models.

PHEVs and EVs can reduce fuel costs dramatically because of the low cost of electricity relative to conventional fuel. Because they rely in whole or part on electric power, their fuel economy is measured differently than in conventional vehicles. Miles per gallon of gasoline equivalent (mpge) and kilowatt-hours (kWh) per 100 miles are common metrics. Depending on how they're driven, today's light-duty EVs (or PHEVs in electric mode) can exceed 100 mpge and can achieve 30-40 kWh per 100 miles.

The fuel economy of medium- and heavy-duty PHEVs and EVs is highly dependent on the load carried and the duty cycle, but in the right applications, they can maintain a strong fuel-cost advantage over their conventional counterparts as well.

Infrastructure AvailabilityPHEVs and EVs have the benefit of flexible fueling: They can charge overnight at a residence (or a fleet facility), at a workplace, or at public charging stations. PHEVs have added flexibility, because they can also refuel with gasoline or diesel (or possibly other fuels in the future) when necessary. Both types of vehicles can take advantage of distributed sources of renewable energy, such as solar panels on a rooftop.

Public charging stations are not as ubiquitous as gas stations, but charging equipment manufacturers, automakers, utilities, Clean Cities coalitions, municipalities, and government agencies are establishing a rapidly expanding network of charging infrastructure. The number of publicly accessible charging units surpassed 7,000 in 2012. Search for electric charging stations near you.

CostsAlthough fuel costs for hybrid and plug-in electric vehicles are generally lower than for similar conventional vehicles, purchase prices can be significantly higher. However, prices are likely to decrease as production volumes increase. And initial costs can be offset by fuel cost savings, a federal tax credit, and state incentives. The federal Qualified Plug-In Electric Drive Motor Vehicle Tax Creditis available for PHEV and EV purchases through 2014 (or until manufacturers meet certain thresholds of vehicle sales). It provides a tax credit of $2,500 to $7,500 for new purchases, with the amount determined by the size of the vehicle and capacity of its battery.

Use the Vehicle Cost Calculator to compare lifetime ownership costs of individual models of HEVs, PHEVs, EVs, and conventional vehicles.

EmissionsHybrid and plug-in electric vehicles can have significant emissions benefits over conventional vehicles. HEV emissions benefits vary by vehicle model and type of hybrid power system. EVs produce zero tailpipe emissions, and PHEVs produce no tailpipe emissions when in all-electric mode.

The life cycle emissions of an EV or PHEV depend on the sources of electricity used to charge it, which vary by region. In geographic areas that use relatively low-polluting energy sources for electricity production, plug-in vehicles typically have a life cycle emissions advantage over similar conventional vehicles running on gasoline or diesel. In regions that depend heavily on conventional fossil fuels for electricity generation, PHEVs and EVs may not demonstrate a strong life cycle emissions benefit. Use the Vehicle Cost Calculatorto compare life cycle emissions of individual vehicle models in a given location.

BatteriesLike the engines in conventional vehicles, the advanced batteries in plug-in electric vehicles are designed for extended life but will wear out eventually. Several manufacturers of plug-in vehicles are offering 8-year/100,000 mile battery warranties. Test and simulation (PDF) results from the National Renewable Energy Laboratory indicate that today’s batteries may last 12 to 15 years in moderate climates (eight to 12 years in extreme climates).Check with your dealer for model-specific information about battery life and warranties. Although manufacturers have not published pricing for replacement batteries, some are offering extended warranty programs with monthly fees. If the batteries need to be replaced outside the warranty, it may be a significant expense. Battery prices are expected to decline as battery technologies improve and production volumes increase.

EthanolEthanol is a renewable fuel made from corn and other plant materials. The use of ethanol is widespread—almost all gasoline in the U.S. contains ethanol in a low-level blend. Ethanol is also available as E85—a high-level ethanol blend—for use in flexible fuel vehicles.

Ethanol Fuel Basics

National Biofuels Action Plan (PDF)

Ethanol is a renewable fuel made from various plant materials collectively known as "biomass." More than 95% of U.S. gasoline contains ethanol in a low-level blend to oxygenate the fuel and reduce air pollution.

Ethanol is also available as E85, or high-level ethanol blends. This fuel can be used in flexible fuel vehicles, which can run on high-level ethanol blends, gasoline, or any blend of these.

There are several steps involved in making ethanol available as a vehicle fuel:

Biomass feedstocks are grown, collected and transported to an ethanol production facility Ethanol is produced from feedstocks at a production facility and then transported to a

blender/fuel supplier Ethanol is mixed with gasoline by the blender/fuel supplier and distributed to fueling stations.

Ethanol as a vehicle fuel is not a new concept. Henry Ford and other early automakers suspected it would be the world's primary fuel before gasoline became so readily available. Today, researchers agree ethanol could substantially offset our nation's petroleum use. In fact, studies have estimated that ethanol and other biofuels could replace 30% or more of U.S. gasoline demand by 2030.

The use of ethanol is required by the federal Renewable Fuel Standard (RFS).

Fuel PropertiesEthanol (CH3CH2OH) is a clear, colorless liquid. It is also known as ethyl alcohol, grain alcohol, and EtOH. (See Fuel Properties search.) Ethanol has the same chemical formula regardless of whether it is produced from starch- and sugar-based feedstocks, such as corn grain (as it primarily is in the United States), sugar cane (as it primarily is in Brazil), or from cellulosic feedstocks (such as wood chips or crop residues).

Ethanol has a higher octane number than gasoline, providing premium blending properties. Minimum octane number requirements prevent engine knocking and ensure drivability. Low-level ethanol blends generally have a higher octane rating than unleaded gasoline. Low-octane gasoline is blended with 10% ethanol to attain the standard 87 octane requirement. Ethanol is the main component in high-level ethanol blends. (See E85 Specification to learn more.)

Per unit volume, ethanol contains about 30% less energy than gasoline. E85 contains about 25% less energy than gasoline. High-level ethanol blends contain less energy per gallon than does gasoline, to varying degrees, depending on the volume percentage of ethanol in the high-level blend.

Ethanol Energy BalanceIn the United States, ethanol is primarily produced from the starch in corn grain. Recent studies using updated data about corn production methods demonstrate a positive energy balance for corn ethanol, meaning that fuel production does not require more energy than the amount of energy contained in the fuel

Cellulosic ethanol, which is produced from non-food-based feedstocks, is expected to improve the energy balance of ethanol, because non-food-based feedstocks are anticipated to require less fossil fuel energy to produce ethanol. Biomass used to power the process of converting non-food-based feedstocks into cellulosic ethanol is also expected to reduce the amount of fossil fuel energy used in production. Another potential benefit of cellulosic ethanol is that it results in lower levels of life cycle greenhouse gas emissions. (Find out more about emissions related to ethanol.)

Ethanol Benefits and ConsiderationsEthanol is a renewable, domestically produced transportation fuel. Whether used in low-level blends, such as E10 (10% ethanol, 90% gasoline), or in E85 (a gasoline-ethanol blend containing 51% to 83% ethanol, depending on geography and season), ethanol helps reduce imported oil and greenhouse gas emissions. Like any alternative fuel, there are some considerations to take into account when contemplating the use of ethanol.

Energy SecurityIn 2012, the United States imported about 40% of the petroleum it consumed, and transportation was responsible for nearly three-quarters of total U.S. petroleum consumption. Depending heavily on foreign petroleum supplies puts the United States at risk for trade deficits, supply disruption, and price changes. The Renewable Fuels Association's 2013 Ethanol Industry Outlook (PDF)  calculated that, from 2005 through 2012, ethanol increased from 1% to 10% of gasoline supply.Fuel Economy and PerformanceA gallon of ethanol contains less energy than a gallon of gasoline. The result is lower fuel economy than a gallon of gasoline. The amount of energy difference varies depending on the blend. For example, E85 has about 27% less energy per gallon than gasoline (mileage penalty lessens as ethanol content decreases). However, because ethanol is a high-octane fuel, it offers increased vehicle power and performance.

To learn more about fuel economy, GHG scores, and EPA smog scores for flexible fuel vehicles (FFVs), visit FuelEconomy.gov, or see the Clean Cities 2013 Vehicle Buyer's Guide (PDF) .Job OpportunitiesEthanol production creates jobs in rural areas where employment opportunities are needed. According to the Renewable Fuels Association, ethanol production in 2012 added more than 365,000 jobs across the country, $40.6 billion to the gross domestic product, and $28.9 billion in household income. Lower EmissionsThe carbon dioxide released when ethanol is burned is balanced by the carbon dioxide captured when the crops are grown to make ethanol. This differs from petroleum, which is made from plants that grew millions of years ago. On a life cycle analysis basis, corn-based ethanol production and use

reduces greenhouse gas emissions (GHGs) by up to 52% compared to gasoline production and use. Cellulosic ethanol use could reduce GHGs by as much as 86%.

Equipment and AvailabilityMore than 95% of the gasoline sold in the United States contains low levels of ethanol. Low-level blends require no special fueling equipment, and they can be used in any conventional gasoline vehicle.

The equipment used to store and dispense ethanol blends above E10 is the same equipment used for gasoline with modifications to some materials. All equipment used in the handling, storing, and dispensing of these blends must be designed specifically for such use. See the Handbook for Handling, Storing, and Dispensing E85 and Other Ethanol-Gasoline Blends (PDF)  for detailed information on compatible equipment.FFVs (which can operate on E85, gasoline, or any blend of the two) are available nationwide as standard equipment with no incremental costs, making them an affordable alternative fuel vehicle option. However, because most U.S. ethanol plants are concentrated in the Midwest, fueling stations offering E85 are predominately located in that region. Find E85 fueling stations in your area.

HydrogenHydrogen is a potentially emissions-free alternative fuel that can be produced from diverse domestic energy sources. Research is under way to make hydrogen vehicles practical for widespread use.

Hydrogen BasicsHydrogen (H2) is a potentially emissions-free alternative fuel that can be produced from domestic resources. Although not widely used today as a transportation fuel, government and industry researchers are working toward the goal of clean, economical, and safe hydrogen production and fuel-cell electric vehicles. For more information, seefuel properties and the Hydrogen Analysis Resource Center.

Hydrogen is locked up in enormous quantities in water (H2O), hydrocarbons (such as methane, CH4), and other organic matter. Efficiently producing hydrogen from these compounds is one of the challenges of using hydrogen as a fuel.

Currently, steam reforming of methane (natural gas) accounts for the majority of the hydrogen produced in the United States. Almost all of the hydrogen produced here each year is used for refining petroleum, treating metals, producing fertilizer, and processing foods. Hydrogen has been used for space flight since the 1950s. Learn more about hydrogen and fuel cells from the National Aeronautics and Space Administration.

Hydrogen also can be used to power fuel cell electric vehicles, which are zero-emission vehicles. Major research and developmentefforts are aimed at making fuel cell electric vehicles practical for widespread use.

Learn more about hydrogen and fuel cells from the Fuel Cell Technologies Office.

Hydrogen as an Alternative FuelHydrogen is considered an alternative fuel under the Energy Policy Act of 1992. The interest in hydrogen as an alternative transportation fuel stems from its ability to power fuel cells in zero-emission electric vehicles, its potential for domestic production, and the fuel cell vehicle's potential for high efficiency—it's two to three times more efficient than an internal combustion engine. Learn more aboutfuel cells (PDF) .The energy in 2.2 pounds (1 kilogram) of hydrogen gas is about the same as the energy in 1 gallon of gasoline. Because hydrogen has a low volumetric energy density, it is important for a fuel cell vehicle to store enough fuel onboard to have a driving range comparable to conventional vehicles. Some hydrogen storage technologies are available and undergoing more research and demonstration. These technologies include compressing gaseous hydrogen in high-pressure tanks at up to 10,000 pounds per square inch. Other storage technologies are under development, including bonding hydrogen chemically with a material such as metal hydride, or low temperature sorbent materials. Learn more about hydrogen storage (PDF) .

Source: Hydrogen.energy.gov

Most of the few currently operating hydrogen fueling stations are in California. Find hydrogen fueling stations near you.

Hydrogen Production and DistributionAlthough abundant on earth as an element, hydrogen is almost always found as part of another compound, such as water (H2O) and must be produced from the compounds that contain it. Once produced, hydrogen can be used along with oxygen in a fuel cell to create electricity by an electrochemical process.

ProductionHydrogen can be produced from diverse, domestic resources including fossil fuels, biomass, and other renewable energy technologies. The environmental impact and energy efficiency of hydrogen depends on how it is produced. Some projects are underway to decrease costs associated with hydrogen production (PDF) .There are a number of ways to produce hydrogen:

Natural Gas Reforming : Synthesis gas, a mixture of hydrogen, carbon monoxide, and a small amount of carbon dioxide, is created by reacting natural gas with high-temperature steam or by partial oxidation. The carbon monoxide is reacted with water to produce additional hydrogen. This method is the cheapest, most efficient, and most common for producing hydrogen. Natural gas reforming using steam accounts for about the majority of hydrogen produced in the United States annually.

Electrolysis : An electric current splits water into hydrogen and oxygen. If the electricity is from renewable sources, such as solar or wind, the resulting hydrogen will be considered renewable as well, and have numerous emissions benefits.

Gasification : Coal or biomass is reacted with high-temperature steam and oxygen in a pressurized gasifier and converted into gaseous components. The resulting synthesis gas contains hydrogen and carbon monoxide, which is reacted with steam to produce more hydrogen.

Renewable Liquid Reforming : Renewable liquid fuels, such as ethanol, are reacted with high-temperature steam to produce hydrogen near the point of end use.

Fermentation : Biomass is converted into sugar-rich feedstocks that can be fermented to produce hydrogen.

A number of hydrogen production methods are in development:

High-Temperature Water Splitting : High temperatures generated by solar concentrators or nuclear reactors drive chemical reactions that split water to produce hydrogen.

Photobiological Water Splitting : Microbes, such as green algae, consume water in the presence of sunlight, producing hydrogen as a byproduct.

Photoelectrochemical Water Splitting :Photoelectrochemical systems produce hydrogen from water using special semiconductors and energy from sunlight.

The major hydrogen-producing states are California, Louisiana, and Texas. Almost all of the hydrogen produced in the United States is used for refining petroleum, treating metals, producing fertilizer, and processing foods.

The primary challenge for hydrogen production is reducing the cost of production technologies to make the resulting hydrogen cost competitive with conventional transportation fuels. Government and industry research and development projects are reducing the cost as well as the environmental impacts of hydrogen production technologies. Learn more about hydrogen production from the Fuel Cell Technologies Office and the National Renewable Energy Laboratory.

DistributionMost hydrogen used in the United States is produced at or close to where it is used—typically at large industrial sites. As a result, there is not yet an effective infrastructure for distributing hydrogen to the nationwide network of fueling stations required for the widespread use of fuel cell electric vehicles.

Currently, hydrogen is distributed through three methods:

Pipeline: This least-expensive way to deliver large volumes of hydrogen is limited—with only about 700 miles of U.S. pipelines located near large petroleum refineries and chemical plants in Illinois, California, and the Gulf Coast.

High-Pressure Tube Trailers: Transporting compressed hydrogen gas by truck, railcar, ship, or barge in high-pressure tube trailers is expensive and used primarily for distances of 200 miles or less.

Liquefied Hydrogen Tankers: Cryogenic liquefaction enables hydrogen to be transported more efficiently over longer distances by truck, railcar, ship, or barge compared with using high-pressure tube trailers, even though the liquefaction process is expensive. If not used at a sufficiently high rate at the point of consumption, liquified hydrogen periodically boils off from its containment vessels. This fact requires that the hydrogen delivery and consumption rates are carefully matched.

Creating an infrastructure for hydrogen distribution and delivery (PDF)  to thousands of individual fueling stations presents many challenges. Because hydrogen contains less energy per unit volume than all other fuels, transporting, storing, and delivering it to the point of end-use is more expensive. Building a new hydrogen pipeline network involves high initial capital costs, and hydrogen's properties present unique challenges to pipeline materials and compressor design. However, because hydrogen can be produced from a wide variety of resources, regional or even local production of hydrogen can maximize use of local resources and minimize distribution challenges, and the use of petroleum.There are tradeoffs between centralized and distributed production to consider. Producing hydrogen centrally in large plants cuts production costs but boosts distribution costs. Producing hydrogen at the

point of end-use—at fueling stations, for example—cuts distribution costs but boosts production costs because of the cost to construct on-site production capabilities.

Government and industry research and development projects are overcoming the barriers to efficient hydrogen distribution. Learn more about hydrogen distribution from the Fuel Cell Technologies Office.

Hydrogen Benefits and ConsiderationsHydrogen can be produced from diverse domestic resources with the potential for near-zero greenhouse gas emissions. Once produced, hydrogen generates power without exhaust emissions in fuel cells. It holds promise for growth in both the stationary and transportation energy sectors.

Energy SecurityThe United States relies heavily on foreign oil to power its transportation sector. Transportation accounts for about 71% of the U.S. petroleum consumption and our country imported about 40% of the petroleum it consumed in 2012. With much of the worldwide petroleum reserves located in politically volatile countries, the United States is vulnerable to supply disruptions.

Hydrogen can be produced domestically from resources like natural gas, coal, solar energy, wind, and biomass. When used to power highly efficient fuel cell electric vehicles, hydrogen holds the promise of offsetting petroleum in transportation.

Public Health and EnvironmentAbout half of the U.S. population lives in areas where air pollution levels are high enough to negatively impact public health and the environment. Emissions from gasoline and diesel vehicles—such as nitrogen oxides, hydrocarbons, and particulate matter—are a major source of this pollution. Hydrogen-powered fuel cell vehicles emit none of these harmful substances. Their only emission is H2O—water and warm air.

The environmental and health benefits are even greater when hydrogen is produced from low- or zero-emission sources, such as solar, wind, and nuclear energy and fossil fuels with advanced emission controls and carbon sequestration. Because the transportation sector accounts for about one-third of U.S. carbon dioxide emissions (which contribute to climate change), using these sources to produce hydrogen for transportation can slash greenhouse gas emissions. Learn more about hydrogen emissions.

Fuel StorageHydrogen has the highest energy content by weight of any fuel, but its energy content by volume is low. This fuel property makes storing hydrogen a challenge because it requires high pressures, low temperatures, or chemical processes to be stored in small spaces. Overcoming this challenge is important for light-duty vehicles because they often have limited size and weight capacity for fuel storage.

The storage capacity for hydrogen in light-duty vehicles should enable a driving range of more than 300 miles to meet consumer needs. Because hydrogen has a low volumetric energy density compared with gasoline, storing this much hydrogen on a vehicle currently requires a larger tank than most conventional vehicles. Learn more about hydrogen storage challenges from the Fuel Cell Technologies Program.

Production CostsTo be competitive in the marketplace, the cost of fuel cells will have to decrease substantially without compromising vehicle performance. See the Department of Energy Hydrogen and Fuel Cells Office Plan for plans and projections for the future of hydrogen and fuel cells.

Natural GasNatural gas is a domestically produced gaseous fuel, readily available through the utility infrastructure. This clean-burning alternative fuel can be used in vehicles as either compressed natural gas (CNG) or liquefied natural gas (LNG).

Natural Gas Fuel Basics

Natural gas is an odorless, nontoxic, gaseous mixture of hydrocarbons—predominantly methane (CH4). It accounts for about a quarter of the energy used in the United States. About one-third goes to residential and commercial uses, such as heating and cooking; one-third to industrial uses; and one-third to electric power production. Although natural gas is a clean-burning alternative fuel that has long been used to power natural gas vehicles, only about one-tenth of 1% is used for transportation fuel.

In recent years, 80% to 90% of the natural gas used in the United States was domestically produced. Most natural gas is drawn from wells or extracted in conjunction with crude oil production. Natural gas can also be mined from subsurface porous rock reservoirs through extraction processes, such as hydraulic fracturing (see a list of supplemental sources from EIA). Renewable natural gas is an emerging fuel produced from decaying organic materials, such as waste from plants, landfills, wastewater, and livestock.

CNG and LNG as Alternative FuelsTwo forms of natural gas are used in vehicles: CNG and LNG. Both are clean-burning, domestically produced, relatively low priced, and widely available. Because of the gaseous nature of this fuel, when stored onboard a vehicle, it must be in either a compressed gaseous (CNG) or liquefied (LNG) state. CNG and LNG are considered alternative fuels under the Energy Policy Act of 1992.

Natural gas is sold in units of diesel or gasoline gallon equivalents (DGEs or GGEs) based on the energy content of a gallon of gasoline or diesel fuel.

Compressed Natural GasTo provide adequate driving range for a vehicle, CNG is stored in cylinders at a pressure of 3,000 to 3,600 pounds per square inch. A CNG-powered vehicle gets about the same fuel economy as a

conventional gasoline vehicle on a gasoline gallon equivalent basis. A GGE equals about 5.66 pounds of CNG. CNG is used in light-, medium-, and heavy-duty applications.

Liquefied Natural GasLNG is produced by purifying natural gas and super-cooling it to -260°F to turn it into a liquid. Because it must be kept at cold temperatures, LNG is stored in double-walled, vacuum-insulated pressure vessels. LNG is good for trucks needing a longer range because liquid is more dense than gas (CNG) and, therefore, more energy can be stored by volume in a given tank. LNG is typically used in medium- and heavy-duty vehicles; a GGE equals about 1.5 gallons of LNG.

Natural Gas Production and DistributionMost natural gas consumed in the United States is domestically produced. The vast majority of natural gas in the U.S. is considered a fossil fuel because it is made from sources formed over millions of years by the action of heat and pressure on organic materials.

ProductionNatural gas is primarily extracted from gas and oil wells, while smaller amounts can be made from supplemental sources, such as biomass and coal. Gas trapped in subsurface porous rock reservoirs is extracted via drilling. Gas streams produced from oil and gas reservoirs contain natural gas, liquids, and other materials. Also, advances in hydraulic fracturing technologies enabled access to large volumes of natural gas from shale formations.

The U.S. Environmental Protection Agency (EPA) is working to ensure that natural gas extraction does not come at the expense of public health and the environment (see EPA's hydraulic fracturing information).

Once extracted, the gas is separated from free liquids, such as crude oil, hydrocarbon condensate, water, and entrained solids. The separated gas is further processed to meet specified requirements. For example, natural gas for transmission companies must generally meet certain pipeline quality specifications with respect to water content, hydrocarbon dewpoint, heating value, and hydrogen-sulfide content.

Although natural gas is a mixture of hydrocarbons, it is predominantly made up of methane (CH4). As delivered through thepipeline system, natural gas also contains additional hydrocarbons, such as ethane and propane, as well as other gases, such as nitrogen, helium, carbon dioxide, hydrogen sulfide, and water vapor. (See the Fuel Properties.)

A dehydration plant controls water content, a gas-processing plant removes certain hydrocarbon components to hydrocarbon dewpoint specifications, and a gas-sweetening plant removes hydrogen sulfide and other sulfur compounds (when present).

DistributionThe United States has a vast natural gas distribution system, which can quickly and economically distribute natural gas to and from almost any location in the lower 48 states. Gas is distributed using 300,000 miles of transmission pipelines (see map), while an additional 1.9 million miles of distribution pipes transport gas within utility service areas. The distribution system also includes thousands of

delivery, receipt, and interconnection points; hundreds of storage facilities; and more than 50 points for exporting and importing natural gas.

Most natural gas fueling stations dispense compressed natural gas (CNG), which is compressed on site in most cases. The availability of liquefied natural gas (LNG) stations is more limited. Most LNG users are fleets that have LNG infrastructure dedicated to their vehicles. Only a few large-scale liquefaction facilities provide LNG fuel for transportation nationwide. LNG must be delivered to stations via truck.

PropanePropane, also known as liquefied petroleum gas (LPG) or autogas, has been used worldwide as a vehicle fuel for decades. It is stored as a liquid, and propane fueling infrastructure is widespread.

Propane Fuel Basics

Also known as liquefied petroleum gas (LPG) or autogas, propane is a clean-burning, high-energy alternative fuel that's been used for decades to power light-, medium- and heavy-dutypropane vehicles.

Propane is a three-carbon alkane gas (C3H8). It is stored under pressure inside a tank and is a colorless, odorless liquid. As pressure is released, the liquid propane vaporizes and turns into gas that is used for combustion. An odorant, ethyl mercaptan, is added for leak detection. (See fuel properties.)

Propane has a high octane rating and excellent properties for spark-ignited internal combustion engines. It is non-toxic and presents no threat to soil, surface water, or groundwater. Propane is produced as a by-product of natural gas processing and crude oil refining. It accounts for about 2% of the energy used in the United States. Of that, less than 2% is used for transportation fuel. Its main uses include home and water heating, cooking and refrigerating food, clothes drying, powering farm and industrial equipment. Rural areas without natural gas service commonly rely on propane as a residential energy source. The chemical industry uses propane as a raw material for making plastics and other compounds.

Propane as an Alternative FuelInterest in propane as an alternative transportation fuel stems mainly from its domestic availability, high-energy density, clean-burning qualities, and its relatively low cost. It is the world's third most common engine fuel and is considered an alternative fuel under theEnergy Policy Act of 1992.

Autogas is a mixture of propane with smaller amounts of other gases. According to the Gas Processors Association's HD-5 specification for propane, it must consist of at least 90% propane, no more than 5% propylene, and 5% other gases, primarily butane and butylene. (See fuel properties.)

Propane is stored onboard a vehicle in a tank pressurized to about 150 pounds per square inch—about twice the pressure of an inflated truck tire. Under this pressure, propane becomes a liquid with an energy density 270 times greater than the gaseous form. Propane has a higher octane rating than gasoline, which can decrease engine knock. However, it has a lower Btu rating than gasoline, so it takes more fuel to drive the same distance. Propane's clean burning characteristics allow the engine to have increased service life.

Propane Production and DistributionPropane is a by-product of natural gas processing and crude oil refining with almost equal amounts of production derived from each of these sources. Most of the propane consumed in the United States is produced in North America and shipped from its production point to distribution terminals.

ProductionPropane is produced from liquid components recovered duringnatural gas processing. These components include ethane, methane, propane, and butane, as well as heavier hydrocarbons. Propane and butane, along with other gases, are also produced during crude oil refining.

DistributionPropane is shipped from its point of production to bulk distribution terminals via pipeline, railroad, barge, truck, or tanker ship. Propane dealers fill trucks at the terminals and distribute propane to end users, including retail fuel sites.

Propane Benefits and ConsiderationsAlso known as liquefied petroleum gas (LPG), propane is a domestically produced, well-established, clean-burning fuel. Using propane as a vehicle fuel increases energy security, provides convenience and performance benefits, and improves public health and the environment.

Energy SecurityIn 2012, the United States imported about 40% of the petroleum it consumed and transportation accounted for more than 70% of total U.S. petroleum consumption. With much of the worldwide petroleum reserves located in politically volatile countries, the United States is vulnerable to supply disruptions.

Fueling vehicles with propane is one way to diversify U.S. transportation fuels. The vast majority of propane consumed in the United States is produced here and distributed via an established infrastructure. Using propane vehicles instead of conventional vehicles reduces U.S. dependence on foreign oil and increases energy security.

Vehicle and Infrastructure AvailabilityA variety of light-, medium-, and heavy-duty propane vehicle models are available through original equipment manufacturers (OEMs) and select dealerships. For options, see the Heavy-Duty Vehicle and Engine Search, the Light-Duty Vehicle Search, and the Clean Cities Vehicle Buyer's Guide (PDF) .OEM-delivered, light-duty propane vehicles can cost several thousand dollars more than comparable gasoline vehicles. The cost of propane is lower than gasoline so the return on investment can be quick. Fleets and consumers also have the option of economically, safely, and reliably converting existing light-, medium-, and heavy-duty gasoline or diesel vehicles for propane operation using

qualified system retrofitters. It's critical that all vehicle and engine conversions meet the emissions and safety regulations and standards instituted by the U.S. Environmental Protection Agency, the National Highway Traffic Safety Administration, and state agencies like the California Air Resources Board. Learn aboutpropane vehicle conversions.

Although propane is widely available in the United States, public vehicle fueling infrastructure is limited. Fleets can work with local propane marketers to establish the fueling infrastructure. Costs will depend on the fuel contract and the complexity of the equipment being installed.

Fuel Economy and PerformanceTypically in fleet applications, propane costs less than gasoline and offers a comparable driving range to conventional fuel. Although it has a higher octane rating than gasoline rating (104 to 112 compared with 87 to 92 for gasoline), and potentially more horsepower, it has a lower Btu rating than gasoline, which results in lower fuel economy.

Low maintenance costs are one reason behind propane's popularity for high-mileage vehicles. Propane's high octane and low-carbon and oil-contamination characteristics have resulted in greater engine life than conventional gasoline engines. Because the fuel's mixture of propane and air is completely gaseous, cold start problems associated with liquid fuel are reduced.

Public Health and EnvironmentPropane is nontoxic, nonpoisonous, and insoluble in water. Compared with vehicles fueled by conventional diesel and gasoline,propane vehicles can produce lower amounts of some harmful air pollutants and greenhouse gases, depending on vehicle type, drive cycle, and engine calibration. Learn more about propane emissions.

Compressed Air

A compressed air car is a car that uses a motor powered by compressed air. The car can be powered solely by air, or combined (as in a hybrid electric vehicle) with gasoline, diesel, ethanol, or an electric plant withregenerative braking.

Engines[edit]Main article: Compressed air engine

Compressed air cars are powered by motors driven by compressed air, which is stored in atank at high pressure such as 30 MPa (4500 psi or 310 bar). Rather than driving engine pistons with an ignited fuel-air mixture, compressed air cars use the expansion of compressed air, in a similar manner to the expansion of steam in a steam engine.

There have been prototype cars since the 1920s, with compressed air used in torpedo propulsion .

Storage tanks[edit]Main article: Compressed air tank

In contrast to hydrogen's issues of damage and danger involved in high-impact crashes, air, on its own, is non-flammable. It was reported on Seven Network's Beyond Tomorrow that on its own carbon-fiber is brittle and can split under sufficient stress, but creates no shrapnel when it does so. Carbon-fiber tanks safely hold air at a pressure somewhere around 4500 psi, making them comparable to steel tanks. The cars are designed to be filled up at a high-pressure pump.

Energy density[edit]

Compressed air has relatively low energy density. Air at 30 MPa (4,500 psi) contains about 50 Wh of energy per liter (and normally weighs 372g per liter). For comparison, a lead–acid battery contains 60-75 Wh/l. A lithium-ion battery contains about 250-620 Wh/l. Gasolinecontains about 9411 Wh per liter;[1] however, a typical gasoline engine with 18% efficiency can only recover the equivalent of 1694 Wh/l. The energy density of a compressed air system can be more than doubled if the air is heated prior to expansion.

In order to increase energy density, some systems may use gases that can be liquified or solidified. "CO2 offers far greater compressibility than air when it transitions from gaseous to supercritical form."[2]

Emissions[edit]

Compressed air cars are emission-free at the exhaust. Since a compressed air car's source of energy is usually electricity, its total environmental impact depends on how clean the source of this electricity is. Different regions can have very different sources of power, ranging from high-emission power sources such as coal to zero-emission power sources such as wind. A given region can also change its electrical power sources over time, thereby improving or worsening total emissions.

However a study showed that even with very optimistic assumptions, air storage of energy is less efficient than chemical (battery) storage.[3]

Advantages[edit]

The principal advantages of an air powered

It uses no gasoline or other bio-carbon based fuel. Refueling may be done at home,[4] but filling the tanks to full pressure would require compressors

for 250-300 bars, which are not normally available for home standard utilization, considering the danger inherent at these pressure levels. As with gasoline, service stations will eventually have the necessary air facilities. Those will use energy produced at large centralized powerplants, potentially making it less costly and more effective to manage emissions than from individual vehicles.

Compressed air engines reduce the cost of vehicle production, because there is no need to build a cooling system, spark plugs, starter motor, or mufflers.[5]

The rate of self-discharge is very low opposed to batteries that deplete their charge slowly over time. Therefore, the vehicle may be left unused for longer periods of time than electric cars.

Expansion of the compressed air lowers its temperature; this may be exploited for use asair conditioning.

Reduction or elimination of hazardous chemicals such as gasoline or battery acids/metals Some mechanical configurations may allow energy recovery during braking by compressing and

storing air. Sweden’s Lund University reports that buses could see an improvement in fuel efficiency of up to

60 percent using an air-hybrid system[6] But this only refers to hybrid air concepts (due to recuperation of energy during braking), not compressed air-only vehicles.

Disadvantages[edit]

The principal disadvantages are the additional steps of energy conversion and transmission, because each inherently has loss. For combustion engine cars, the energy is lost when chemical energy in fossil fuels are converted by the engine to mechanical energy. For electric cars, a power plant's electricity (from whatever source) is transmitted to the car's batteries, which then transmits the electricity to the car's motor, which converts it to mechanical energy. For compressed-air cars, the power plant's electricity is transmitted to a compressor, which mechanically compresses the air into the car's tank. The car's engine then converts the compressed air to mechanical energy.

Additional concerns:

When air expands in the engine it cools dramatically and must be heated to ambient temperature using a heat exchanger. The heating is necessary in order to obtain a significant fraction of the theoretical energy output. The heat exchanger can be problematic: while it performs a similar task to an intercooler for an internal combustion engine, the temperature difference between the incoming air and the working gas is smaller. In heating the stored air, the device gets very cold and may ice up in cool, moist climates.

This also leads to the necessity of completely dehydrating the compressed air. If any humidity subsists in the compressed air, the engine will stop due to inner icing. Removing the humidity completely requires additional energy that cannot be reused and is lost. (At 10g of water per m3

air -typical value in the summer- you have to take out 900 g of water in 90 m3; with a vaporization enthalpy of 2.26MJ/kg you will need theoretically minimally 0.6 kWh; technically, with cold drying this figure must be multiplied by 3 - 4. Moreover, dehydrating can only be done with professional compressors, so that a home charging will completely be impossible, or at least not at any reasonable cost.)

Conversely, when air is compressed to fill the tank, its temperature increases up. If the stored air is not cooled while the tank is being filled, then when the air cools off later, its pressure decreases and the available energy decreases.To mitigate this, the tank may be equipped with an internal heat-exchanger in order to cool the air quickly and efficiently while charging.Alternatively, a spring may be used to store work from the air as it is inserted in the tank, thus maintaining a low pressure difference between the tank and recharger, which results in a lower temperature raise for the transferred air.[citation needed]

Refueling the compressed air container using a home or low-end conventional air compressor may take as long as 4 hours, though specialized equipment at service stations may fill the tanks in only 3 minutes.[4] To store 2.5 kWh @300 bar in 300 liter reservoirs (90 m3 of air @ 1 bar), requires about 30 kWh of compressor energy (with a single-stageadiabatic compressor), or approx. 21 kWh with an industrial standard multistage unit. That means a compressor power of 360 kW is needed to fill the reservoirs in 5 minutes from a single stage unit, or 250 kW for a multistage one.[7] However, intercooling and isothermal compression is far more efficient and more practical than adiabatic compression, if sufficiently large heat exchangers are fitted. Efficiencies of up to 65% might perhaps be achieved,[8] (whereas current efficiency for large industrial compressors is max. 50% )however this is lower than the Coulomb's efficiency with lead acid batteries.

The overall efficiency of a vehicle using compressed air energy storage, using the above refueling figures, is around 5-7%.[citation needed] For comparison, well to wheel efficiency of a conventional internal-combustion drivetrain is about 14%,[9]

Early tests have demonstrated the limited storage capacity of the tanks; the only published test of a vehicle running on compressed air alone was limited to a range of 7.22 km.[10]

A 2005 study demonstrated that cars running on lithium-ion batteries out-perform both compressed air and fuel cell vehicles more than threefold at the same speeds.[11] MDIclaimed in 2007 that an air car will be able to travel 140 km in urban driving, and have a range of 80 km with a top speed of 110 km/h (68 mph) on highways,[12] when operating on compressed air alone, but in as late as mid-2011, MDI has still not produced any working prototype.

A 2009 University of Berkeley Research Letter found that "Even under highly optimistic assumptions the compressed-air car is significantly less efficient than a battery electric vehicle and produces more greenhouse gas emissions than a conventional gas-powered car with a coal intensive power mix." However, they also suggested, "a pneumatic–combustion hybrid is technologically feasible, inexpensive and could eventually compete with hybrid electric vehicles."[13]

Crash safety[edit]

Safety claims for light weight vehicle air tanks in severe collisions have not been verified. North American crash testing has not yet been conducted, and skeptics question the ability of an ultralight vehicle assembled with adhesives to produce acceptable crash safety results. Shiva Vencat, vice president of MDI and CEO of Zero Pollution Motors, claims the vehicle would pass crash testing and meet U.S. safety standards. He insists that the millions of dollars invested in the AirCar would not be in vain. To date, there has never been a lightweight, 100-plus mpg car which passed North American crash testing. Technological advances may soon make this possible, but the AirCar has yet to prove itself, and collision safety questions remain.[14]

The key to achieving an acceptable range with an air car is reducing the power required to drive the car, so far as is practical. This pushes the design towards minimizing weight.

According to a report by the U.S. Government's National Highway Traffic Safety Administration, among 10 different classes of passenger vehicles, "very small cars" have the highest fatality rate per mile driven. For instance, a person driving 12,000 miles per year for 55 years would have a 1% chance of being involved in a fatal accident. This is twice the fatality rate of the safest vehicle class, a "large car". According to the data in this report, the number of fatal crashes per mile is only weakly correlated with the vehicle weight, having a correlationcoefficient of just (-0.45). A stronger correlation is seen with the vehicle size within its class; for example, "large" cars, pickups and SUVs, have lower fatality rates than "small" cars, pickups and SUVs. This is the case in 7 of the 10 classes, with the exception of mid-size vehicles, where minivans and mid-size cars are among the safest classes, while mid-size SUVs are the second most fatal after very small cars. Even though heavier vehicles sometimes are statistically safer, it is not necessarily the extra weight that causes them to be safer. The NHTSA report states: "Heavier vehicles have historically done a better job cushioning their occupants in crashes. Their longer hoods and extra space in the occupant compartment provide an opportunity for a more gradual deceleration of the vehicle, and of the occupant within the vehicle... While it is conceivable that light vehicles could be built with similarly long hoods and mild deceleration pulses, it would probably require major changes in materials and design and/or taking weight out of their engines, accessories, etc." [15]

Air cars may use low rolling resistance tires, which typically offer less grip than normal tires.[16][17] In addition, the weight (and price) of safety systems such as airbags, ABS and ESC may discourage manufacturers from including them.

Developers and manufacturers[edit]

Various companies are investing in the research, development and deployment ofCompressed air cars. Overoptimistic reports of impending production date back to at least May 1999. For instance, the MDI Air Car made its public debut in South Africa in 2002,[18] and was predicted to be in production "within six months" in January 2004.[19] As of January 2009, the air car never went into production in South Africa. Most of the cars under development also rely on using similar technology to low-energy vehicles in order to increase the range and performance of their cars. [clarification needed]]]

APUQ[edit]

APUQ (Association de Promotion des Usages de la Quasiturbine) has made the APUQ Air Car, a car powered by a Quasiturbine.[20]

MDI[edit]Main article: Motor Development International

MDI has proposed a range of vehicles made up of AirPod, OneFlowAir, CityFlowAir, MiniFlowAir and MultiFlowAir.[21] One of the main innovations of this company is its implementation of its "active chamber", which is a compartment which heats the air (through the use of a fuel) in order to double the energy output.[22] This 'innovation' was first used intorpedoes in 1904.

Tata Motors[edit]

As of January 2009 Tata Motors of India had planned to launch a car with an MDI compressed air engine in 2011.[23][24] In December 2009 Tata's vice president of engineering systems confirmed that the limited range and low engine temperatures were causing problems. [25] Tata Motors announced in May 2012[26] that they have assessed the design passing phase 1, the "proof of the technical concept" towards full production for the Indian market. Tata has moved onto phase 2, "completing detailed development of the compressed air engine into specific vehicle and stationary applications". [27]

Air Car Factories SA[edit]

Air Car Factories SA is proposing to develop and build a compressed air engine. [28] This Spanish based company was founded by Miguel Celades. Currently there is a bitter dispute between Motor Development International, another firm called Luis which developed compressed-air vehicles, and Mr. Celades, who was once associated with that firm.[29][30]

Energine[edit]

The Energine Corporation was a South Korean company that claimed to deliver fully assembled cars running on a hybrid compressed air and electric engine. These cars are more precisely named pneumatic-hybrid electric vehicles.[31] Engineers from this company made, starting from a Daewoo Matiz, a prototype of a hybrid electric/compressed-air engine (Pne-PHEV, pneumatic plug-in hybrid electric vehicle[citation needed]). The compressed-air engine is used to activate an alternator, which extends the autonomous operating capacity of the car.

The CEO of Energine was reportedly arrested for fraud.[32]

A similar concept using a pneumatic accumulator in a largely hydraulic system has been developed by U.S. government research laboratories and industry. It uses compressed air only for recovery of braking energy, and in 2007 was introduced for certain heavy vehicle applications such as refuse trucks.[33]

Kernelys[edit]

The "K'Airmobiles" project of Kernelys[34][35] aimed to produce commercial vehicles in France. The project was started in 2006-2007 by a small group of researchers. They said to be working on 2 types of vehicles; namely "VPA" (Vehicles with Pneumatic Assistance) and "VPP" (Vehicles with Pneumatic Propulsion) vehicles.[36] However, the project has in the end not been able to gather the necessary funds to go commercial.

People should note that, meantime, the team has recognized the physical impossibility to use on-board stored compressed air due to its poor energy capacity and the thermal losses resulting from the expansion of the gas.[37]

These days, using the patent pending 'K'Air Fluid Generator', converted to work as a compressed-gas motor, the company has reworked it's project in 2010 together with a North American group of investors, now intented for the purpose of developing a green energy power system. [38]

Engineair[edit]

Engineair is an Australian company which manufactures small industrial vehicles using an air engine of its own design.[39]

Honda[edit]

In 2010, Honda presented the Honda Air concept car at the LA Auto Show.[40]

Peugeot/Citroën[edit]

Peugeot and Citroën have announced that they too are building a car that uses compressed air as an energy source. However, the car they are designing uses a hybrid system which also uses a gasoline engine (which is used for propelling the car over 70 km/h, or when the compressed air tank has been depleted.[41][42]