What is a propane vehicle?

Propane, also known as liquefied petroleum gas (LPG), has been used in vehicles since the 1920s. It is considered an alternative fuel under the Energy Policy Act of 1992 and qualifies for alternative fuel vehicle tax incentives.

Today, most propane vehicles are conversions from gasoline vehicles. Dedicated propane vehicles are designed to run only on propane; bi-fuel propane vehicles have two separate fueling systems that enable the vehicle to use either propane or gasoline.

Propane vehicle power, acceleration, and cruising speed are similar to those of gasoline-powered vehicles. The driving range for bi-fuel vehicles is comparable to that of gasoline vehicles. The range of dedicated gas-injection propane vehicles is generally less than gasoline vehicles because of the 25% lower energy content of propane and lower efficiency of gas-injection propane fuel systems. Extra storage tanks can increase range, but the additional weight displaces payload capacity. Liquid Propane Injection engines, introduced in 2006, promise to deliver fuel economy more comparable to gasoline systems.

Lower maintenance costs are a prime reason behind propane's popularity for use in delivery trucks, taxis, and buses. Propane's high octane rating (104 to 112 compared with 87 to 92 for gasoline) and low carbon and oil contamination characteristics have resulted in documented engine life of up to two times that of gasoline engines. Because the fuel mixture (propane and air) is completely gaseous, cold start problems associated with liquid fuel are eliminated.

Compared with vehicles fueled with conventional diesel and gasoline, propane vehicles can produce significantly lower amounts of harmful emissions. Another benefit of propane vehicles is increasing U.S. energy security.

B20 and B100: Alternative Fuels

The interest in biodiesel as an alternative transportation fuel stems mainly from its renewable, domestic production; its safe, clean-burning properties; and its compatibility with existing diesel engines.

Biodiesel can be legally blended with petroleum diesel in any percentage. The percentages are designated as B20 for a blend containing 20% biodiesel and 80% petroleum diesel, B100 for 100% biodiesel, and so forth. B100 and blends of B20 or higher qualify for alternative fuel credits under the Energy Policy Act of 1992.

B20

Twenty percent biodiesel and 80% petroleum diesel—B20—is the most common biodiesel blend in the United States. Using B20 provides substantial benefits but avoids many of the cold-weather performance and material compatibility concerns associated with B100.

B20 can be used in nearly all diesel equipment and is compatible with most storage and distribution equipment. B20 and lower-level blends generally do not require engine modifications. Not all diesel engine manufacturers cover biodiesel use in their warranties, however. See the National Biodiesel Board's Standards and Warranties page to learn more about engine warranties. Because diesel engines are expensive, users should consult their vehicle and engine warranty statements before using biodiesel. It is similarly important to use biodiesel that meets prescribed quality standards—ASTM D6751-07b (see Biodiesel Production for more information on this standard).

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. 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 and so forth. Low-level biodiesel blends also provide benefits.

B100

B100 or other high-level biodiesel blends can be used in some engines built since 1994 with biodiesel-compatible material for parts such as hoses and gaskets. However, as biodiesel blend levels increase significantly beyond B20, a number of concerns come into play. Users must be aware of lower energy content per gallon and potential issues with impact on engine warranties, low-temperature gelling, solvency/cleaning effect if regular diesel was previously used, and microbial contamination.

B100 use could also increase nitrogen oxides emissions, although it greatly reduces other toxic emissions. All these issues can be handled, but currently B100 use might be best for professional fleets with maintenance departments prepared to deal with this fuel.

What is Natural Gas?

Natural gas is a mixture of hydrocarbons, predominantly methane (CH4). As delivered through the pipeline system, it also contains hydrocarbons such as ethane and propane and other gases such as nitrogen, helium, carbon dioxide, hydrogen sulfide, and water vapor. See the AFDC Fuel Properties database for more details.

Natural gas has a high octane rating and excellent properties for spark-ignited internal combustion engines. It is non-toxic, non-corrosive, and non-carcinogenic. It presents no threat to soil, surface water, or groundwater.

Most natural gas is extracted from gas and oil wells. Much smaller amounts are derived from supplemental sources such as synthetic gas, landfill gas and other biogas resources, and coal-derived gas.

Natural gas accounts for approximately one quarter of the energy used in the United States. Of this, about one third goes to residential and commercial uses, one third to industrial uses, and one third to electric power production. Only about one tenth of one percent is currently used for transportation fuel.

What is ultra-low sulfur diesel?

Ultra-low sulfur diesel (ULSD) is diesel fuel with 15 parts per million (ppm) or lower sulfur content. The U.S. Environmental Protection Agency requires 80% of the highway diesel fuel refined in or imported into the United States (100% in California) to be ULSD as of 2006. One hundred percent must be ULSD nationwide by 2010. Different requirements apply to non-highway diesel.

Currently, the vast majority of ULSD is produced from petroleum. However, biodiesel; biomass-to-liquids, coal-to-liquids, and gas-to-liquids diesel; and hydrogenation-derived renewable diesel are inherently ultra-low sulfur fuels and could help meet ULSD requirements in the future. Petroleum-based ULSD is not considered an alternative fuel under the Energy Policy Act of 1992 (EPAct), but most ULSD fuels produced from non-petroleum and renewable sources are considered EPAct alternative fuels.

Ultra-Low Sulfur Diesel as a Vehicle Fuel

Ultra-low sulfur content in diesel fuel is beneficial because it enables use of advanced emission control technologies on light-duty and heavy-duty diesel vehicles. The combination of ULSD with advanced emission control technologies is sometimes called Clean Diesel.

Nitrogen oxides (NOx) and particulate matter (PM) are the two most harmful diesel pollutant emissions. These emissions can be controlled with the use of catalytic converters (for NOx) and particulate traps (for PM). However, sulfur—in amounts that used to be allowable in diesel fuel—deactivates these devices and nullifies their emissions control benefits. Using ULSD enables these devices to work properly.

In general, ULSD should cause no noticeable impact on vehicle performance, although fuel economy might be slightly reduced because the process that produces ULSD can also reduce the fuel's energy content. Removing sulfur from diesel reduces lubricity. This issue can be resolved by the addition of additives prior to retail sale that increase lubricity. In addition, blending biodiesel with ULSD also increases lubricity.

Using ULSD in older diesel vehicles might affect fuel system components or loosen deposits in fuel tanks. These vehicles should be monitored closely for fuel system problems and premature fuel filter plugging during the transition to ULSD. New vehicles designed to use ULSD must never be fueled with a higher-sulfur fuel. If kerosene is blended with ULSD for improved cold-weather performance, it must be ultra-low sulfur (15 ppm or lower) kerosene. New engine oils have been developed for use with new diesel vehicles fueled with ULSD.

What is hydrogen?

Hydrogen is the simplest and most abundant element in the universe—it is number 1 on the periodic table of elements (this link takes you to Los Alamos National Laboratory's site). At Earth surface temperatures and pressures, it is a colorless, odorless gas (H2). However, hydrogen is rarely found alone in nature. It is usually bonded with other elements. See the AFDC Fuel Properties database for more details.

Very little hydrogen gas is present in Earth's atmosphere. 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 about 95% of the hydrogen produced in the United States. Almost all of the approximately 9 million tons of hydrogen produced here each year are used for refining petroleum, treating metals, producing fertilizer, and processing foods. Hydrogen has been used for space flight since the 1950s; learn more on the NASA Web site.

Hydrogen also can be used to fuel internal combustion engines and fuel cells, both of which can power low- or zero-emissions vehicles such as fuel cell vehicles. Major research and development efforts are aimed at making hydrogen vehicles practical for widespread use.

Diesel Vehicles

Diesel vehicles may be making a comeback. Diesel engines are more powerful and fuel-efficient than similar-sized gasoline engines (about 30-35% more fuel efficient). Plus, today's diesel vehicles are much improved over diesels of the past.

Better Performance

Improved fuel injection and electronic engine control technologies have

• Increased power
• Improved acceleration
• Increased efficiency

New engine designs, along with noise- and vibration-damping technologies, have made them quieter and smoother. Cold-weather starting has been improved also.

Cleaner

Today's diesels must meet the same emissions standards as gasoline vehicles, and advances in engine technologies, ultra-low sulfur diesel fuel, and improved exhaust treatment have made this possible.

Although emissions of particulates and smog-forming nitrogen oxides (NOx) are still relatively high, new "clean" diesel fuels, such as ultra-low sulfur diesel and biodiesel, and advances in emission control technologies will reduce these pollutants also.