What are biofuels and flex fuels?

The first combustion engines ran on gasoline and diesel. Today, the options available to power a vehicle are more varied than ever – along with electric propulsion, combustion power can be fuelled by a variety of alternative fuels. Some of the most popular alt-fuels worldwide are biofuels and flex fuels.

With such a diverse selection available, it can be easy to get lost in the different fuel terminology. In this article, we explore these two common terms, breaking down what biofuels are, what flex fuels are, and what the difference is between the two.

What are biofuels?

In short, biofuels are fuels made from organic material, typically plants such as sugarcane and rapeseed grown specifically to be processed into fuel – however, it is also possible to create biofuels via waste products from food or cooking. 

These organic materials are either fermented or processed to create fuels that have similar properties to gasoline or diesel, allowing them to be used as alternative fuel sources for engines. 

In many cases, these biofuel blends are mixed with gasoline or diesel for sale at the fuel pump. At small concentrations, biofuels mixes do not change the behavior of the overall fuel blend, and are labelled as conventional fuels. At large concentrations, biofuel mixes do change the behavior of the overall fuel blend, and are labelled as flex fuels.

Read more about alternative fuels with Brazil's technology neutral policies.

How are biofuels made?

There are two common types of biofuels: bioethanol and biodiesel. 

Bioethanol is created by fermenting a sugar‑ or starch‑based crop, much like producing an alcoholic spirit. A range of alcohols are produced by fermentation, although ethanol is the most abundant alcohol and is what is usually used for fuel. With further treatment, the methane waste gas produced by this process can also be processed into biomethanol to be used alongside bioethanol.

Biodiesel is produced from vegetable oils or animal fats using a process called transesterification, wherein they are mixed with alcoholic catalysts such as ethanol or methanol. The resulting fatty acid esters are true diesel fuels, capable of ignition in a diesel engine solely through compression without the use of a spark. 

Globally, Brazil is one of the largest producers of bioethanol, while the EU is a major producer of biodiesel.

The process of creating biofuels starts with agriculture

Read more about why India is adopting bioethanol.

What are flex fuels?

Mixing biofuels into conventional fuels is an easy way to reduce the lifecycle emissions of a nation’s vehicle parc. At small concentrations, biofuels do not significantly change the behavior of fuel in an engine, and are simply sold as conventional fuels at the pump. 

Biofuel mixtures are usually labelled with a letter and a number – the letter signalling the biofuel type, and the number signalling its share of the fuel blend. Conventional fuel blends that use biofuels include:

• Bioethanol-gasoline at E5 or E10, with some regions using E15 mixes
• Biodiesel-diesel at B5 or B7, with some fleets and heavy vehicles using B20 mixes

By contrast, flex fuels are conventional-biofuel mixes where the biofuel makes up a much larger share. These allow a fuel system to take advantage of the affordability and fuel security afforded by fossil fuels, while still making use of the net-zero emissions offered by biofuels. Most flex fuel blends are bioethanol-gasoline mixtures, with the most common mixes being E85, E75, and E70.

Vehicles that use flex fuels must be designed to do so, since biofuels have different properties to their fossil fuel equivalents. However, many modern flex‑fuel vehicles are not limited to one ratio and can run on varying ethanol–gasoline concentrations, adjusting automatically as needed.

Read more about alternative fuels and why hybrids will stay central to global mobility.

What is the difference between biofuels and flex fuels?

Biofuels and flex fuels are related but distinct concepts. 

Biofuels fit into a broad group of fuels derived from biological sources, such as ethanol, biodiesel, and biogas, and they may be used either in pure form or blended with conventional fuels. 

Flex fuels, by contrast, are standardized high-biofuel blends. Typically, these are high bioethanol-gasoline blends designed for use in flex-fuel vehicles capable of operating on a wide range of ethanol–gasoline mixtures. 

While flex fuels are chemically defined by their composition rather than the origin of the ethanol, in practice the ethanol component is almost always bioethanol, as flex-fuel systems are primarily intended to increase the use of renewable fuels rather than synthetic or fossil-derived alcohols.

Flex fuels have become a common sight at fuel pumps across parts of the world in recent years

Read more about alternative fuels and why the EU must adopt a technology-neutral approach.

What are the use cases for flex fuels and biofuels?

One of the main benefits of biofuels is that they are produced from renewable sources. Crops can be grown, consumed, and replanted, with each new crop recapturing the carbon released from a combustion cycle. In this way, the tailpipe emissions of biofuel vehicles will be offset by the production of further fuel.

Flex fuels, with their combination of bioethanol and gasoline, offer a compromise. The biofuel content helps reduce emissions, while the gasoline component increases efficiency and offsets some challenges facing ethanol – in particular, its difficulty as a fuel in colder climates. Ethanol has a lower vapor pressure, meaning that a predominantly ethanol‑based mix can struggle to ignite in low temperatures if not blended with gasoline.

These fuels also offer economic benefits. As petroleum and gasoline prices fluctuate and remain finite resources, biofuels provide a renewable alternative that can often be cheaper and more locally produced - though crop growth is not possible in all regions.

Read more about alternative fuels and how hybrids can speed up decarbonization.

The state of flex fuels and biofuels

Today, flex fuels are used to power either large commercial fleets that are particularly emissions-intensive, or the fuel systems of regions with strong bioethanol supplies – usually, markets with large crop surpluses.

The latter makes bioethanol particularly attractive for developing or middle income economies located near the equator, such as Brazil or India. As a result, data from the OECD shows that biofuel adoption is increasing at an average of 3% every year.

At Horse Powertrain, we develop engine technologies that use many of these fuel types to power low-emission mobility. To find out more about the engines we produce that leverage biofuels and flex fuel blends, take a look at our products.

To learn about our products, read more here: spotlight solutions.