Fueling Internal Combustion Engines

Kim Taylor
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7.7

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There are many forms of transportation and many sources of energy that enable these forms of transportation to get where they are going.

How many forms of transportation can you name?

Different vehicles need different energy sources to get where they’re going. Most of them need some kind of fuel for their engines.

Fuel is a material that stores potential energy. Most fuels store potential energy in the bonds between their molecules. This is called chemical potential energy

How do you release the energy stored in fuel? This usually involves a chemical reaction called a combustion reaction. In other words, you need to burn the fuel. 

A combustion reaction involves fuel and oxygen. Most fuels are hydrocarbons or a mix of hydrocarbons. When they react with oxygen, they produce carbon dioxide (CO2) and water (H2O).

Combustion reactions release heat energy. Chemical reactions that produce heat are called exothermic reactions. Most vehicles use an engine to convert heat energy into mechanical energy. This energy gets transferred to the vehicle’s moving parts, like wheels and propellers. There, it takes the form of kinetic energy (energy of motion).

Fuels can be solid, liquid or gaseous.

  • Wood and coal are examples of solids used as fuels.

  • Gasoline, diesel and ethanol are examples of liquid used as fuels.

  • Propane, natural gas and hydrogen are examples of gases used as fuels. 

Fuels can be solids, liquids or gases
Fuels can be solids, liquids or gases (© 2019 Let’s Talk Science).

Today, most vehicles use liquid and gaseous fuels. But in the past, coal and wood were used to heat water and create steam. Steam engines in cars, trains and ships were used to turn wheels and propellers.

Today’s vehicles use two main types of fuels: 

  • Petroleum-based fuels
  • Biofuels

Fossil Fuels

Petroleum-based fuels are better known as fossil fuels. “Petroleum” can refer to either unprocessed crude oil or products made from refined crude oil

Liquid petroleum-based fuels include gasoline, petrodiesel, aviation gasoline, aviation jet fuel and marine fuel oil. 

Gaseous petroleum-based fuels include natural gas and propane. However, propane gas is stored in liquid form.

Automotive Gasoline (Mogas)

Gasoline is the most common type of vehicle fuel. It’s also called petrol in some English-speaking countries. 

Gasoline is a clear flammable fluid that ignites easily. It’s a blend of hydrocarbons refined from crude oil. It also contains additives like ethanol, which is a biofuel.  

Did you know?

Mogas is made up of hydrocarbon chains that have 7-11 carbon atoms.

Gasoline engines are spark-ignition engines. They ignite a mixture of fuel and air using spark plugs

Gasoline is used to fuel cars, pickup trucks, vans, SUVs, power boats, snowmobiles, scooters and motorcycles. In the past, automotive gasoline contained lead. Today, you can only buy unleaded gasoline for your car.

Petroleum Diesel (Diesel, Petrodiesel)

Diesel fuel is the second-most common type of vehicle fuel, after gasoline. Like gasoline, diesel is a liquid hydrocarbon refined from crude oil. 

Did you know?

Diesel fuel is made up of hydrocarbon chains that have 15-18 carbon atoms.

New types of diesel fuel are being developed. They include biodiesel, which is a biofuel. Petroleum-based is often called petrodiesel to distinguish it from plant- and animal-based varieties. 

Diesel engines are named after German inventor Rudolf Diesel. They use compressed air to ignite the fuel. Unlike gasoline engines, they don’t need a spark plug.

Diesel fuel is used in cars, pickup trucks, vans, SUVs, school buses, city buses, trains, power boats and ferries. 

Aviation Gasoline (Avgas)

Like automotive gasoline, avgas is a blend of liquid hydrocarbons. But unlike the gasoline used in cars, avgas contains tetraethyl lead (TEL). This toxic substance prevents ignition problems that can interfere with engine cycles. 

Did you know?

Avgas is made up of hydrocarbon chains that have 4-12 carbon atoms.

Dyes are often added to avgas. They make the fuel easy to see if there’s a spill. Aviation gasoline is used in small private and vintage piston-engined aircraft. These aircraft use spark-ignition engines. 

Aviation Jet Fuel (Aviation Turbine Fuel)

Aviation jet fuel is a liquid fuel similar to diesel. It can be used in either compression-ignition engines or turbine engines. A turbine engine is an internal combustion engine that turns a turbine. 

There are two types of aviation jet fuel:

  1. Unleaded kerosene (Jet A, JP-5, JP-8) 

  2. Blended naphtha-kerosene (Jet B, JP-4)

Both types contain short hydrocarbons (12-16 carbon atoms) refined from crude oil. However, the second type is only used in very cold temperatures. 

Researchers are working on developing plant-based jet biofuel. It would be made from sources like algae and Camelina.

Turboprops, jets and helicopters all use aviation jet fuel.

A sample of bunker fuel. Notice how thick and black it is.
A sample of bunker fuel. Notice how thick and black it is (Source: Glasbruch2007 [CC BY-SA 3.0] via Wikimedia Commons).

Heavy Fuel Oil (Bunker Fuel)

Heavy fuel oil is a thick, dark liquid made up of long hydrocarbon chains. It contains two types of fuel: 

  • Distillate fuel consists of hydrocarbons that get boiled and condensed during fractional distillation.
  • Residual fuel consists of hydrocarbons that are too heavy for distillation and end up as residue

Residual fuel is very thick. So distillates are added to lower its viscosity and allow it to flow. 

Heavy fuel oil needs to be heated before you can burn it. This requires special equipment that would take up too much room on smaller vehicles. That’s why heavy fuel oil is only used on very large ships. 

Heavy fuel oil is also called bunker fuel. This name comes from the containers where the oil is stored on ships and in ports.

Compressed Natural Gas (CNG)

Natural gas is a naturally occurring mixture of hydrocarbons. It’s found in underground deposits called natural gas fields. It’s also found near oil fields. 

Did you know?

Natural gas mostly consists of methane. Methane is a hydrocarbon with one carbon atom.

Compressed natural gas (CNG) is made by compressing natural gas to less than 1% of the volume it would occupy at standard atmospheric pressure. CNG can be stored in cylinders. It’s used in vehicles in much the same way as gasoline. 

Natural gas is primarily used in buses as a substitute for gasoline, diesel fuel and propane. 

A propane truck
A propane truck (Source: kozmoat98 via iStockphoto).

Propane (Liquified Natural Gas, Auto Propane)

Propane is a short gaseous hydrocarbon (C3H8). It’s a by-product of natural gas processing and crude oil refining. When stored under pressure in a tank, propane turns into a colourless, odourless liquid. 

Did you know?

For safety reasons, a bad-smelling additive is put into propane. Otherwise, you wouldn’t be able to smell a leak!

When the pressure is released, liquid propane evaporates into a gas used for combustion. Like gasoline engines, propane engines use a spark to ignite the fuel. 

Many people use propane to fuel their BBQs. But it’s also used in fleet vehicles like police cars and taxis. Some vehicles run only on propane. Others can run on both propane and gasoline. Most propane vehicles are actually converted gasoline vehicles.

Biofuels

Ethanol

Ethanol is a biofuel. It’s a type of alcohol made from plants. 

Did you know?

Ethanol is an alcohol with two carbon atoms (C2H5OH).

In Canada, ethanol mainly comes from corn and wheat. Researchers are also looking at using cellulose from plant waste. Ethanol and other alcohols are often added to gasoline. Burning alcohol produces less carbon monoxide and soot than burning gasoline. 

Since 2010, gasoline sold in Canada must have an average of 5% renewable content. This normally comes in the form of ethanol. 

All gasoline vehicles made since the early 1980s can use gasoline that contains some ethanol. Today, all major vehicle makers allow the use of gasoline with up to 10% ethanol. Gasoline that contains 5% ethanol is called E5. Gasoline that contains 10% ethanol is called E10. Flex Fuel Vehicles (FFVs) can run on any combination of gasoline and ethanol up to 85% ethanol (E85). 

Biodiesel

Biodiesel is another biofuel. It’s a type of diesel fuel made through a chemical reaction between fat and alcohol. The fat can be either plant- or animal-based.

Did you know?

BIodiesel is made up of esters with 8-20 carbon atoms.

B100 made from soybeans
B100 made from soybeans (Source: Leandro Maranghetti Lourenço [CC BY-SA 3.0] via Wikimedia Commons).

Most biodiesel comes from canola. But it can also be made using other raw materials. Plant sources include soybeans, jatropha, algae and waste vegetable oil. Animal sources include beef and chicken fat. 

Any diesel engine can run on 100% biodiesel. However, it typically makes up between 2% and 20% of diesel fuel. Most diesel engine warranties allow owners to use blends from B5 (5% biodiesel) to B20 (20% biodiesel). 

Today, biodiesel is used in cars, trucks, buses and trains. Scientists are even testing biodiesel in aircraft. Since 2011, diesel fuel sold in Canada must have an average of 2% renewable content. In other words, it has to contain 2% biodiesel.

As you can see, there are many types of fuel. Think of all the different types of vehicles you have seen in the past week. What types of fuel do you think they use?

References

Brain, M. (2000, April 1). How diesel engines work. HowStuffWorks.

Brain, M. (2002, February 6). How gasoline works. HowStuffWorks.

Government of Canada. (2019, July 16). Renewable fuels regulations.

U.S. Department of Energy. (n.d.). Alternative fuels data center.

Wise Geek. (n.d.). What is bunker fuel?

Kim Taylor

Thanks to Nick MacCallum, P.Eng for helping in the review of this backgrounder.

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