- 1
- 2
- next
- | single page
Given all the talk about electric cars, clean diesel, ethanol and more, it can be confusing to know how fuels work and their advantages and disadvantages. Here's a guide.
Gasoline
Atomically, the gas we pour into our tanks is a mix of hundreds of hydrocarbons, derived from crude oil. It's distilled in refineries to create motor and jet fuels, diesel, lubricants and other products. In fact, only 19 to 20 gallons of each 42-gallon barrel of oil becomes gasoline.
Gasoline is ignited by a spark in an engine cylinder. As it expands, it pushes down pistons to make your engine run. The burned gas, ejected through the engine's tailpipe, contains carbon monoxide, nitrogen oxides and hydrocarbons, all of which are noxious air pollutants.
Each gallon of gas represents about 124,000 British thermal units, which is roughly equal to the amount of electrical energy the average U.S. family consumes in a day. Only an average of 15 percent of that energy is actually used to move your car -- engine and drivetrain inefficiencies eat up the rest.
Gas at the pump is rated by its octane grade, which denotes a gas mixture's ability to prevent engine knocking. It works out like this:
Regular has octane ratings of 85 to 87, the lowest anti-knocking ability
Midgrade is rated 88 to 90
Premium is 90 and above and mostly needed for high-compression engines
Ethanol
Praised and vilified in equal measure, ethanol (and, to a lesser extent, methanol) is a biofuel additive that stretches supplies of gasoline. It's an alcohol derived from corn primarily as well as sugar cane and other plant materials, and it was first popularized by an oil-starved Nazi Germany. Today, ethanol comprises only about 3 percent of the total gasoline stores in the United States.
Generally speaking, regular unleaded gas in the U.S. contains no more than 10 percent ethanol (designated at pumps as E10). Beyond that ratio, engine modifications are required to keep exhaust pollution at acceptable levels. Specially modified engines in flexible-fuel vehicles can burn E85, which is 85 percent ethanol. Engines that run E85 are specially manufactured to deal with the high alcohol content in the fuel.
At best, ethanol can produce less pollution than gasoline, and at worst, it can be dirtier than gasoline. Much depends on the entire life cycle of ethanol production, going all the way back to farm tractors putting seeds in the ground. A lot of oil can be burned to create a gallon of ethanol that will extend fuel supplies and potentially burn cleaner than gas.
Of course, ethanol is a renewable energy source, which wins over many environmentalists as well as people who don't want to import oil. The downside is that redirecting edible biomass -- particularly corn -- toward fuel production can inadvertently jack up the cost of food.
Diesel
Like gas, diesel is distilled from crude oil and comprised of hundreds of hydrocarbons, including the carcinogen benzene. But diesel differs from gas in significant ways.
Diesel doesn't need a spark to explode in an engine's cylinders the way gas does. Compressing diesel and air alone is enough to ignite the mixture and power the engine. With more potential energy (139,000 Btu per gallon), diesel pushes a vehicle 20 percent to 40 percent farther than gas. Diesel creates more greenhouse gases than gasoline, but its greater efficiency means it produces 10 percent to 20 percent less of the pollutants per gallon than gas.
Its exhaust differs from gasoline's, too. There are more particles in diesel's exhaust, which can be seen as soot on tailpipes and adjacent bumpers. Fine and ultra-fine particulates have been linked to increases in asthma and lung cancer. Diesel fuel also has comparatively high sulfur content. Sulfur combines with trace metal alloys to act as a lubricant in engines, but it creates acid rain when burned.
Governments in North America and Europe have been restricting the amount of sulfur in diesel for about 20 years. Ceilings in the United States fell from 5,000 parts per million to 500 ppm (low-sulfur diesel) in 1993. All retail pumps in the country are required to dispense ultra-low-sulfur diesel, spewing just 15 ppm, by Dec. 1. Some engine modifications are needed in order to run on ultra-low-sulfur diesel.
Gasoline
Atomically, the gas we pour into our tanks is a mix of hundreds of hydrocarbons, derived from crude oil. It's distilled in refineries to create motor and jet fuels, diesel, lubricants and other products. In fact, only 19 to 20 gallons of each 42-gallon barrel of oil becomes gasoline.
Gasoline is ignited by a spark in an engine cylinder. As it expands, it pushes down pistons to make your engine run. The burned gas, ejected through the engine's tailpipe, contains carbon monoxide, nitrogen oxides and hydrocarbons, all of which are noxious air pollutants.
Each gallon of gas represents about 124,000 British thermal units, which is roughly equal to the amount of electrical energy the average U.S. family consumes in a day. Only an average of 15 percent of that energy is actually used to move your car -- engine and drivetrain inefficiencies eat up the rest.
Gas at the pump is rated by its octane grade, which denotes a gas mixture's ability to prevent engine knocking. It works out like this:
Ethanol
Praised and vilified in equal measure, ethanol (and, to a lesser extent, methanol) is a biofuel additive that stretches supplies of gasoline. It's an alcohol derived from corn primarily as well as sugar cane and other plant materials, and it was first popularized by an oil-starved Nazi Germany. Today, ethanol comprises only about 3 percent of the total gasoline stores in the United States.
Generally speaking, regular unleaded gas in the U.S. contains no more than 10 percent ethanol (designated at pumps as E10). Beyond that ratio, engine modifications are required to keep exhaust pollution at acceptable levels. Specially modified engines in flexible-fuel vehicles can burn E85, which is 85 percent ethanol. Engines that run E85 are specially manufactured to deal with the high alcohol content in the fuel.
At best, ethanol can produce less pollution than gasoline, and at worst, it can be dirtier than gasoline. Much depends on the entire life cycle of ethanol production, going all the way back to farm tractors putting seeds in the ground. A lot of oil can be burned to create a gallon of ethanol that will extend fuel supplies and potentially burn cleaner than gas.
Of course, ethanol is a renewable energy source, which wins over many environmentalists as well as people who don't want to import oil. The downside is that redirecting edible biomass -- particularly corn -- toward fuel production can inadvertently jack up the cost of food.
Diesel
Like gas, diesel is distilled from crude oil and comprised of hundreds of hydrocarbons, including the carcinogen benzene. But diesel differs from gas in significant ways.
Diesel doesn't need a spark to explode in an engine's cylinders the way gas does. Compressing diesel and air alone is enough to ignite the mixture and power the engine. With more potential energy (139,000 Btu per gallon), diesel pushes a vehicle 20 percent to 40 percent farther than gas. Diesel creates more greenhouse gases than gasoline, but its greater efficiency means it produces 10 percent to 20 percent less of the pollutants per gallon than gas.
Its exhaust differs from gasoline's, too. There are more particles in diesel's exhaust, which can be seen as soot on tailpipes and adjacent bumpers. Fine and ultra-fine particulates have been linked to increases in asthma and lung cancer. Diesel fuel also has comparatively high sulfur content. Sulfur combines with trace metal alloys to act as a lubricant in engines, but it creates acid rain when burned.
Governments in North America and Europe have been restricting the amount of sulfur in diesel for about 20 years. Ceilings in the United States fell from 5,000 parts per million to 500 ppm (low-sulfur diesel) in 1993. All retail pumps in the country are required to dispense ultra-low-sulfur diesel, spewing just 15 ppm, by Dec. 1. Some engine modifications are needed in order to run on ultra-low-sulfur diesel.
