Diesel fuel is often considered a dirty fuel because it involves burning crude oil, a fossil fuel with a high carbon footprint and a host of negative environmental side effects. But diesel fuel also includes biodiesel, which experts have touted as an environmentally friendly substitution for traditional diesel with a lower carbon footprint. So, we had to ask: What is diesel fuel really, and how can it help mitigate climate change?

Diesel fuel is a combustible liquid used as fuel in compression-ignition (diesel) engines. Diesel produces between 2.6 and 10kg of emissions per gallon of fuel burned. Depending on the type of diesel, it can contribute to or help mitigate climate change.

Keep reading to find out all about what diesel fuel is, its global capacity, its carbon footprint, its environmental benefits and drawbacks, and how it can mitigate climate change.

The Big Picture of Diesel Fuel

Diesel fuel encompasses both traditional (petroleum) diesel and biodiesel, both of which are commonly used as transportation fuels. Diesel fuel can either be classified as a nonrenewable or renewable resource, depending on the type, and it has varying effects on the environment.

How Is Diesel Fuel Defined

Diesel fuel (diesel), also known as diesel oil, is a combustible liquid used as fuel in diesel engines.

“Diesel: a liquid obtained from petroleum, used as fuel in car engines, etc.”

Oxford Dictionary

Diesel fuel is combustible, meaning that it uses compressed air in a cylinder to ignite the fuel. When compared to gasoline, it produces more energy upon combustion, has a better fuel economy, and has fewer refining steps; however, it also produces greater quantities of certain air pollutants (sulfur, solid carbon particulates) and emits more CO₂ per unit than gasoline does. 

What Are the Different Types of Diesel Fuel 

The two main types of diesel fuel currently include petroleum diesel (diesel oil) and biodiesel.

Petroleum diesel is a transportation fuel produced via the distillation of crude oil (petroleum). It is the most common form of diesel fuel used in the modern transportation industry. 

“Diesel oil: a fuel obtained from petroleum distillation that is used in diesel engines. It has a relatively low ignition temperature (540°C) and is ignited by the heat of compression”

Collins Dictionary

There are subcategories of petroleum diesel (e.g., diesel #1, diesel #2, and off-road diesel) that differ in the refinement process. One gallon of petroleum diesel produces roughly 10.1kg of CO₂ upon combustion. 

Biodiesel is an alternative, cleaner-burning fuel than petroleum diesel. It is a subset of biofuels (ethanol and biodiesel) which is made from biomass. Biomass is renewable organic material from plants and animals that can be used to produce a wide range of products, including fuel.

“Biodiesel: a type of fuel made from plant or animal material and used in diesel engines”

Oxford Dictionary

Biodiesel is created via the transesterification of vegetable oil, animal fat, and grease found in biomass sources. One gallon of biodiesel produces 70% less emissions than petroleum diesel.

How Does Diesel Fuel Work

Diesel fuel is produced via the distillation of either crude oil (petroleum diesel) or biomass sources (biodiesel). Both petroleum diesel and biodiesel are used in diesel engines, which use compressed air in a cylinder to ignite the fuel and produce energy.

How Does Diesel Fuel Actually Produce Energy

Generating energy from diesel fuel begins with either extracting crude oil (for petroleum diesel) or gathering biomass sources (for biodiesel). Following processing and refinement, the fuels can be used in diesel engines to power vehicles.

How Does Petroleum Diesel Fuel Actually Produce Energy

Oil and natural gas are often found within the same reservoir, so they are often extracted in the same manner. Drilling or fracking exposes oil reservoirs for extraction. 

Once the crude oil is extracted, it is transported via pipeline to refineries where it is broken down into various components and reconfigured into new products. One of these new products includes petroleum diesel.

To produce diesel from crude oil, it must be distilled. In this process, crude oil is heated until it becomes a vapor. The vapor is lifted upwards in a distilling column and collects at different levels in trays, separating the liquids. Lighter products (butane) rise to the top of the column whereas gasoline, naphtha, kerosene, diesel, and heavy gas oil collect in trays going from top to bottom in the column. The heavier diesel at the bottom of the column is refined in later processes.

Following refinement, the finished petroleum diesel fuel can be used in compression-ignition diesel engines, whereby the engine uses compressed air in a cylinder to ignite the fuel rather than a spark (flammable).

How Does Biodiesel Fuel Actually Produce Energy

Biomass sources are extracted and converted to biodiesel via chemical conversion, a process whereby transesterification is used to convert vegetable oil, animal fat, and grease into fatty acid methyl esters.

Just like petroleum diesel, biodiesel can be used in compression-ignition (diesel) engines to produce energy. It can be blended with petroleum diesel (in any percentage). For example, B100 is pure biodiesel, and B20 is a blend of 20% biodiesel and 80% petroleum diesel. 

What Is the Global Capacity of Diesel Fuel

Oil, including petroleum diesel fuel, is the world’s largest source of energy and our primary fuel for transportation. The US and China alone account for over one-third of global oil consumption, with India, Russia, and Japan rounding out the top 5 countries. 

The top 10 largest oil producers in the world account for 72% (67 million barrels per day (mb/d)) of global oil production, which is approximately 94 mb/d total. The US, Saudi Arabia, and Russia are the top producers of oil worldwide.

Biodiesel is one of the two most common biofuels. Global biofuel demand has increased by roughly 6% per year since 2016. In 2022, biofuels accounted for roughly 3.5% of the global transportation energy demand. But we still have a ways to go to meet the 9% target laid out in the Net Zero by 2030 Scenario. 

The US, Brazil, Indonesia, China, and Germany are the five largest biofuel-producing countries in the world, accounting for roughly 75% (900 TWh) of global biofuel production (1,187 TWh).

What Is the Carbon Footprint of Diesel Fuel

The carbon footprint is one of the ways we measure the effects of human-induced global climate change. It primarily focuses on the GHG emissions associated with consumption, but also includes other emissions such as methane (CH₄), nitrous oxide, and chlorofluorocarbons.

“Carbon footprint: the amount of greenhouse gasses and specifically carbon dioxide emitted by something (such as a person’s activities or a product’s manufacture and transport) during a given period”

Merriam Webster

Basically, it is the amount of carbon emitted by an activity or an organization. This includes GHG emissions from fuel that we burn directly (e.g., heating a home or driving a car) and GHG emissions from manufacturing the products that we use (e.g., power plants, factories, and landfills).

One gallon of petroleum diesel fuel emits approximately 10.1kg (10,100g) of CO₂ when combusted. One gallon of biodiesel produces approximately 2.6kg (2,600g) of CO₂ when combusted, 74% less than petroleum diesel.

The total carbon footprint of diesel fuel would equal the carbon footprint from building + the carbon footprint from extracting and refining + the carbon footprint from transportation + the carbon footprint from building back. 

Because petroleum diesel is a major global fuel source for transportation and biodiesel is a possible substitute, it is important to understand what diesel’s carbon footprint is and how its carbon emissions affect the global climate change process.

How Environmentally Friendly Is Diesel Fuel

Diesel fuel is one of our most important energy sources for transportation. Depending on the type of diesel, it can either contribute significantly to climate change or work to mitigate it. 

“Environmentally friendly: (of products) not harming the environment.”

Cambridge Dictionary

Petroleum diesel fuel is not environmentally friendly, and although there are ways to minimize its environmental impact, it does not benefit the environment. Biodiesel is more environmentally friendly than petroleum diesel, but it is still only as beneficial as the methods used to produce it. 

What Are The Environmental Benefits of Diesel Fuel

Petroleum diesel is considered to be a dirty fuel source because of its high rate of CO₂, SO₂, and NO_x emissions as well as other chemicals that contribute to and exacerbate global climate change. For these reasons, it does not benefit the environment.

On the other hand, biodiesel offers many environmental benefits if it is made from waste materials or used cooking oil and operated on a small scale. These benefits include:

• Improving air quality: Biodiesel produces 1.0%, 8.3%, and 13% of the agricultural nitrogen, phosphorus, and pesticide pollutants, respectively, per net energy gain. It can decrease GHG emissions between 56-96%, the equivalent of planting 1.9 billion trees. It can also cut global warming pollution by 80-90% when compared to petroleum diesel. 

• Increasing engine efficiency: Biodiesel can yield 93% more energy than the energy used in its production. 

• Reducing wastewater: Biodiesel production, compared to petroleum diesel production, can reduce wastewater by up to 79%.

• Reducing hazardous waste: Biodiesel is nontoxic, biodegradable, and can reduce hazardous waste by up to 96%. It will degrade quicker in the case of an oil spill, and it will not cause as many environmental problems compared to petroleum diesel. It also degrades when it comes into contact with water.

Depending on the source material and scale of the operation, biodiesel can be an environmentally friendly alternative to petroleum diesel.

What Are The Environmental Drawbacks of Diesel Fuel

Because petroleum diesel is a product of crude oil refinement, it comes with some of the same drawbacks as oil, including:

• Oil spills: Small oil spills occur when refueling a ship, and large oil spills occur when pipelines break, oil tankers sink, or drilling operations go wrong. Oil spills cause serious environmental harm by contaminating water and soil, causing explosions and fires, harming wildlife, and contaminating seafood. Because diesel evaporates less easily than gasoline, it is more difficult and expensive to remediate. Diesel oil slicks on roads or oil spills in the water can also persist longer in the environment, causing extensive environmental harm.

• Air pollution: Diesel combustion releases sulfur dioxide (SO₂), nitrogen oxides (NO_x), particulate matter (PM), unburned hydrocarbons, volatile organic compounds (VOCs), and CO₂ into the environment which can cause respiratory problems and even premature death. VOCs are a group of chemicals that lead to the formation of ground-level ozone (smog). SO₂ and NO_x combine in our atmosphere to form sulfuric and nitric acids. These then mix with water to form acid rain which can harm flora and fauna.

The easiest way to mitigate the environmental impact of petroleum diesel fuel is to simply not rely on it in the first place. Although some refer to biodiesel as an environmentally friendly alternative to petroleum diesel, it can still have environmental drawbacks depending on how it is produced.

If made from unused cooking oil (canola, soybean, palm oil), biodiesel can come with environmental drawbacks. In some parts of the world, large swaths of forests have been cleared and burned to plant soybeans and palm trees. Dedicating land for the sole purpose of biofuel production leads to deforestation, a phenomenon that occurs at roughly 10 million hectares (~ 25 million acres) per year. Deforestation expedites global climate change because it reduces the amount of trees that can capture our CO₂ emissions. 

What Are Ways to Make Diesel Fuel Less Environmentally Detrimental 

The most effective way to reduce petroleum diesel’s negative environmental effects is to use an alternative fuel source. These alternative fuel sources can include:

• Electricity: Vehicles using electricity as fuel do not release CO₂, but the power plants that produce the electricity may still be responsible for some emissions.
  
• Hydrogen: An electric motor is powered by a hydrogen fuel cell, where hydrogen reacts with oxygen across an electrochemical cell similar to that of a battery to produce electricity, water, and small amounts of heat.

• Natural gas (NG): NG in the form of compressed natural gas (CNG) or liquefied natural gas (LNG) can be used as fuel in cars. Large-scale manufacturing of NG vehicles is not currently available, but diesel vehicles can be retrofitted for CNG.

• Propane: Liquefied petroleum gas (LPG) is used in fleet operations including buses, shuttles, and police vehicles. 

• Alcohols (ethanol, methanol, and butanol): Certain alcohols can be used as vehicle fuel because they have physical and combustion properties that are similar to gasoline.

• Vegetable and waste-derived oils: Vegetable oils, yellow grease, used cooking oils, or animal fats are converted into biodiesel via the process of transesterification.

The most effective way to reduce biodiesel’s negative environmental effects is to avoid sources such as unused cooking oils and instead use sources such as waste products and used cooking oils. The scale of biodiesel production is also important to consider because the land needed to produce biodiesel is also often needed for food and carbon storage.

How Does Diesel Fuel Contribute To And Combat Climate Change

Diesel fuel’s role in either contributing to or combatting climate change depends on if we are talking about petroleum diesel (that contributes to climate change) or biodiesel (that helps combat climate change). 

Climate change is arguably the most severe, long-term, global impact of fossil fuel combustion. Every year, approximately 36 billion tons (bt) of CO₂ are emitted from burning fossil fuels, with the carbon found in petroleum diesel fuel reacting with oxygen in the air to produce CO₂ and warming the earth by acting as a heating blanket.

“Climate Change: changes in the world’s weather, in particular the fact that it is believed to be getting warmer as a result of human activity increasing the level of carbon dioxide in the atmosphere:”

Cambridge Dictionary

CO₂ emissions from petroleum diesel combustion contribute to climate change in the following ways:

• Increasing temperatures: Earth’s atmosphere has warmed 1.5°C since 1880. This may not seem like a lot, but these degrees create regional and seasonal temperature extremes, reduce sea ice, intensify rainfall and drought severity, and change habitat ranges for plants and animals.

• Rising sea levels: Global sea levels have increased approximately 8-9 inches since 1880, displacing people living along coastlines and destroying coastal habitats. Roads, bridges, subways, water supplies, oil and gas wells, power plants, sewage treatment plants, and landfills remain at risk if sea level rise goes unchecked. 

• Melting of sea ice: Since 1979, arctic sea ice has declined by 30%. Sea ice plays a major role in regulating the earth’s climate by reflecting sunlight into space and providing habitat for animal species. If all of the glaciers on Earth melted, sea levels would rise by approximately 70 feet, effectively flooding out every coastal city on the planet. 

• Changing precipitation patterns: Extreme weather events (e.g., hurricanes, floods, droughts) are becoming more common and more intense. Storm-affected areas will experience increased precipitation and flooding whereas areas located further from storm tracks will experience decreased precipitation and droughts.

• Ocean acidification: The ocean absorbs 30% of the CO₂ released into the atmosphere, which decreases the pH (increases the acidity) of the ocean. In the past 200 years, the pH of oceans has decreased by 0.1 pH units, which translates to a 30% increase in acidity. Aquatic life unable to adjust to this rapid acidification will die off. A prime example of this is coral bleaching, where coral expels the algae (zooxanthellae) living in their tissues as a result of changes in temperature, light, or nutrients. 

To help keep global temperature rise below 1.5°C, as outlined in the Paris Agreement, we must shift at least 80% of our electricity generation to low-carbon sources. Over 140 countries have stated a net-zero target, covering roughly 88% of the world’s emissions. However, under current conditions, global emissions are projected to increase by 9% by 2030 instead of the 45% reduction in emissions that is needed.

Reduced CO₂ emissions associated with using biodiesel, rather than petroleum diesel, combat climate change. 

• B20, the most widely used form of biodiesel, can reduce emissions from carbon monoxide (CO) by 12.6%, hydrocarbons by 11%, particulates by 18%, and air toxics by 12-20%. 
• Biodiesel can play a crucial role in meeting emission reduction targets as laid out in the Paris Agreement, if it is sourced responsibly.

Final Thoughts

Diesel fuel is a combustible liquid used as fuel in compression-ignition (diesel) engines. The two most common types of diesel fuel include fossil fuel-derived petroleum diesel and biomass-derived biodiesel. Biodiesel produces roughly 70% less harmful emissions than petroleum diesel when combusted.

Petroleum diesel plays an important role in our economy because it is one of our most important energy sources for transportation. But biodiesel has seen an increase in recent years as more emphasis is put on mitigating the climate crisis. 

Petroleum diesel contributes significantly to climate change via air pollution and oil spills, whereas biodiesel works to mitigate climate change with its lower carbon footprint. The most effective way to mitigate negative environmental effects associated with diesel fuel is to switch from petroleum diesel to biodiesel.

Stay impactful,

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