Think Outside The Pump: Alternative Diesel Fuels

Alternate fuels_edited-2Diesel Fuel is one of the largest products of the petroleum-based fuels industry. It powers everything from container ships and locomotives, to pickup trucks and light aircraft. Mobile generators and industrial engines also benefit from the adaptability of this fuel. Diesel fuel, like any other petroleum derivative, has a finite source of raw material (crude oil) for the refinery process. We are all aware of the progressive push to aggressively pursue renewable, and sustainable fuel sources outside of oil. The threat of running out is of course an inevitability, but certainly not an imminent concern. It is more an idle threat to motivate the generations of today to lay the ground work for tomorrow.

Pursuit of alternative fuels to conventional diesel has a foothold on both the private hobbyist scale, and the global market. People are concocting french-fry oil fuel in their garages, while scientists are embroiled in complex hydrocarbon engineering from as little as water and air. The wide range of technology available means that whatever the budget, alternative fuels are just a creative stones throw away, existing nearly anywhere in the world. We would like to highlight some of the existing alternatives to fueling up at the pump … some of them you may be familiar with, and others may blow your mind.



Commercial biodiesel is a blend of petroleum based fuel, and soybean oil fuel.

Vegidiesel, fryer-fuel, greasel, fast-food fuel — whatever you call it, you are referring to biodiesel. Biodiesel is a fuel derived from recycled oils used mainly in the food service industry. Vegetable oil, soybean oil, and natural animal fats rendered down are the base for this diesel alternative. Regulated for commercial purposes by the American Society of Testing and Materials, ASTM D 6751 biodiesel is defined as “a fuel comprised of mono-alkyl esters of long-chain fatty acids derived from vegetable oils of animal fats, designated B100, and meeting the requirements of ASTM D 6751.

BiodieselWhen the concept of biodiesel first hit the consumer market, it was the new “free energy scheme,” or so it seemed. Home-brew kits flooded the market, and encouraged would-be fuel refiners to obtain free used cooking oil from local fast-food chains. Through a chemical process no more complicated than managing the additive in a swimming pool, the vegetable oil is converted to a burnable diesel substitute. According to,  “Biodiesel is made through a chemical process called transesterification whereby the glycerin is separated from the fat or vegetable oil. The process leaves behind two products — methyl ester (the chemical name for biodiesel) and glycerin …”

Biodiesel has it’s own benefits and drawbacks. The home refining of this fuel requires the transportation of raw cooking oil in large quantities, which requires a hazardous goods transportation permit because a spill will negatively affect road conditions. Start-up costs for a garage refinery will not pay for themselves in savings at the pump for quite a while, and the use of methanol in the blend puts your fuel system at risk if the mixture is incorrect.

The benefits include a cheaper source of fuel if you don’t mind giving up your weekends staring into vats and graduated cylinders. reports that “It is less toxic than table salt and biodegrades as fast as sugar. Produced domestically with natural resources, its use decreases our dependence on imported fuel and contributes to our own economy.”

Biomass Fuels (Algae)

All of the systems at the Green Crude Farm including the harvest system (pictured) will undergo a shakedown process that is designed to confirm the viability of the demonstration algae farm.

Algae is grown and harvested to produce green diesel. Photo courtesy of Sapphire Energy.

The next type of diesel fuel alternative is known as green diesel, renewable hydrocarbon fuels, or biomass fuels. Like biodiesel, that utilizes vegetable oil for a hydrocarbon source, green diesel is supplied with organic matter from algae. Yes, that green scum you try to keep out of the pool, or bathroom is being used to produce fuels for internal combustion engines. The U.S. Department of Energy Alternative Fuels Data Center describes the difference between biodiesel and green diesel as, “The two fuels are also produced through very different processes.


A vial of sample algae in the process of green diesel production. Photo courtesy of Sapphire Energy.

While biodiesel is produced via transesterification, renewable diesel is produced through various processes such as hydrotreating (isomerization), gasification, pyrolysis, and other thermochemical and biochemical means. Moreover, biodiesel is produced exclusively from lipids, whereas renewable diesel is produced from lipids and cellulosic biomass.”

Companies like San Diego-based Sapphire Energy are harnessing the power of algae, and refining it into “green crude,” an alternative to petroleum crude oil.


Fossil fuels extracted from the earth, such as propane, represents the era of man-made gaseous fuels being sourced from the by-products of refining processes. Propane powers everything from our barbecues to forklifts, and some conventional four-wheel vehicles. Propane as a diesel fuel has been a topic of debate for decades.


Popular in off-road applications, where liquid fuel in the float bowl of a carburetor may slosh on extreme inclinations, propane has a niche market for automotive enthusiasts. For diesel trucks propane was long used as an additive, a power adder to supplement conventional diesel fuel. Claims of more efficient burning, additional power, better mileage, and faster turbo spool had to be weighed against the hazard of transporting compressed liquid propane gas (LPG).

Propane carries the chemical formula of C3H8, a hydrocarbon chain comprised of three carbon atoms, and eight hydrogen atoms. Along with natural gas, propane is naturally odorless. In order to better detect leaks, and warn of an impending safety risk, the gas fuels are odorized with an intentionally off-putting smell.

Natural Gas Odorant

According to the National Propane Gas Association, “On Friday, July 31, 2015, President Obama signed into law a bill making it easier for all Americans to use propane autogas. Included in the extension of the highway bill, the excise tax equalization provision permanently reduces the tax rate on propane autos and levels the playing field for all alternative fuels.”

Natural Gas


Natural gas is a product of decomposing organic matter like plants, and animals that became trapped under millennia of sedimentary layers of earth. Natural gas has been used to fuel compression ignition engines in a multitude of vehicles for ages. Buses, trams, fleet vehicles, and even some experimental aircraft are being produced to run on natural gas. 

These hydrocarbon laced gases are locked in the earth and are a source to be tapped similarly to conventional petroleum oil. Natural gas is liberated from the ground by drilling, similarly to oil field drilling. A controversial means of extracting natural gas is called fracking. Fracking is a mining technique whereby large sheets of buried rock are fractured hydraulically using water pressure, thus freeing the trapped natural gas which can then be collected.


The United States and Eastern Europe hold most of the world’s natural gas resources.

The controversy surrounding his practice is due to possible seismic side-effects, and public health risks as natural gas is released in a less than controlled manner. Natural gas remains in gaseous form at normal atmospheric pressure but is stored as a liquid for industrial applications. LNG is a fuel that can be substituted in both gasoline and diesel engines. Better suited to gasoline than diesel, LNG has an octane rating of over 120, making this fuel very stable and difficult to ignite in a compression ignition engine.

Some manufactures of diesel engines, like Cummins, have started to produce dual-fuel systems to hybridize the use of natural gas alongside diesel fuel. Cummins Dual Fuel Engines are marketed by Cummins with their statement that, “For operators of high-horsepower oil and gas equipment, where power density is critical and large quantities of fuel are burned, Cummins Dual Fuel provides and opportunity for impressive reductions in total fuel costs by using a technology that substitutes natural gas for diesel fuel in the engine combustion process.”

Blue Crude


The last alternative fuel we will cover is the most exciting, ambitious, and fascinating development in renewable fuel technology — blue crude.  Also known as E-Diesel, blue crude is the product of an engineering endeavor by Audi, working together with a company called Sunfire. Incredibly, only two raw ingredients are needed to produce this diesel substitute. Carbon dioxide (CO2) and water (H2O). These ingredients supply the building blocks to produce a hydrocarbon fuel to feasibly runs a diesel engine. By only using renewable resources, and only producing byproducts safe to living things, Audi may have an answer for fuels of the future.

To produce blue crude out of water and carbon dioxide, first the water is split into its individual atomic particles. Known as “cracking,” pure hydrogen and oxygen are generated through an aggressive electrolysis process involving high heat and electrical current. Don’t think you’ve spotted the fault yet, thinking the source of that power is some coal or nuclear source. Nope. Audi and Sunfire harness wind and solar power to catalyze this crucial reaction.

NREL_FT_diesel_vs_conventional_diesel_photoWith the hydrogen stripped of its oxygen atoms it is mixed with the carbon dioxide. Through a reactor process known as a reverse water gas shift, the CO2 becomes carbon monoxide (CO), creating a byproduct of water. In the third and final stage to producing blue crude, the hydrogen and carbon monoxide are introduced via the Fischer-Tropsch Process. This process takes the gaseous hydrogen and carbon monoxide and converts them to a liquid hydrocarbon comparable to petroleum crude oil. The resulting crude can be refined into diesel fuel, and on the surface seems to be a clean alternative.

The proving of this fuels’ potential has been demonstrated by the the German Federal Minister of Education and Research. Dr. Johanna Wanka ran the first five liters of fuel produced in her Audi A8 TDI.Audi 2


Diesel fuels are not limited to the fossil fuels we get at the local pump. There are a constant stream of developments as companies and governments pursue renewable energy sources. Exciting breakthroughs may spawn other products like additives, and dependence on oil companies may fade. We hope you appreciated the diversity of fuel sources diesel vehicles can use, and think about what other options exist.

If you have home-brewed fuel for your diesel we want to hear from you! Leave us a note.

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About the author

Trevor Anderson

Trevor Anderson comes from an eclectic background of technical and creative disciplines. His first racing love can be found in the deserts of Baja California. In 2012 he won the SCORE Baja 1000 driving solo from Ensenada to La Paz in an aircooled VW. Trevor is engaged with hands-on skill sets such as fabrication and engine building, but also the theoretical discussion of design and technology. Trevor has a private pilot's license and is pursuing an MFA in fine art - specifically researching the aesthetics of machines, high performance materials and their social importance to enthusiast culture.
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