The largest source of US greenhouse gas emissions is transportation.

Graph from EPA

In order to seriously address climate change there will need to be major changes in the US transportation sector because it is 29% of our total US greenhouse gas emissions. If the grid used to charge electric cars and SUVs is dramatically shifted towards renewable energy sources such as wind or solar, the change will be climate-friendly.

The diesel engines that play many important roles in modern society are not a good solution to replace. They power trucks, trains, boats and barges, many public and school buses, heavy farm and construction equipment, military vehicles, and generators for making backup electricity. Diesel engines' high Torque makes them powerful enough for heavy loads while their high efficiency makes them good for long routes or long tasks. Diesel engines have air pollution issues.

Powerful blue day cab big rig semi truck with dry van semi trailer driving on the wide road at twilight time

Diesel powered big rig trucks are important in modern society.


The diesel sector is important to the climate change challenge. The US Energy Information Agency says that the US diesel use in the 2020 transport sector was 44.6 billion gallons,constituting 16% of total US petroleum consumption and generating 26% of the fossil CO 2 emissions of the transportation sector. The sector would expand the use of plant and animal-based fats in the production of biodiesel. There is a possibility to use bioethanol made from plant-based carbohydrates. There are pros and cons for each option.

The global market value of biodiesel is estimated to reach US$ 25.9 billion by the end of the year. It is usually blended with diesel at 20% and sold as B20. The US has a production capacity of over 2 billion gallons per year, which is 5% of the diesel use. Animal fat from rendering facilities and used restaurant frying oil are used to make biodiesel.

B20 is the most common blend on the market today with 20% and 80% of diesel. It can be used for almost any diesel engine. Diesel engines that use an 80% biodiesel blend can also use it, but the fuel efficiency begins to decline and there are storage issues under cold temperatures. To achieve a significant carbon footprint reduction for the diesel engine sector, the production of biodiesel needs to be substantially expanded, but it would be minimally disruptive to the mechanical and distribution aspects of the segment.

The modification of existing diesel engines would be the novel option. The technology is being pursued by a company called ClearFlame Engine Technologies, and the status of the technology will be discussed below.

Ethanol plant, Milton, Wisconsin

The plant is in Wisconsin. The images were taken by Education Images/Universal Images Group.

Universal Images Group via Getty Images

The automotive sector is supplied with 10-15% blends of bioethanol. The global market in 2020 was worth US$ 33.7 billion and is expected to grow to US$64.8 billion by the year 2025. Corn or sugarcane is the main source of production. The US has a production capacity of 17.4 billion gallons per year. The ClearFlame technology needs to be used to eliminate the climate change profile of the US diesel engine sector in order for it to work, but the production of bioethanol needs to be increased.

A comparison of energy profiles.

The CO2 released by burning fuels is classified as biogenic, meaning that it was captured by plants as opposed to fossil carbon, which was released by burning fuel. The fossil-based energy involved in making a biofuel still has a fossil carbon footprint. The amount of energy in the final product is divided by the production energy requirements. As the production systems have matured, the carbon efficiency of both biodiesel and bioethanol has improved. In 1998 the biodiesel efficiency was 3.2 and in 2011 it was 5.52. The average bioethanol efficiency is 2.1 in one study, but it can be as high as 4.0 in some production facilities according to another USDA study. Adding carbon capture capability during production could improve the profile of bioethanol, as well as the farming part of the footprint could be reduced by using electrified nitrogen fertilization.

ClearFlame is a start-up company that wants to overcome the limitation of diesel engines by using bio-based fuels. Their goal is to modify existing engines so that they are fuel efficient.

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Julie and B.J. Johnson founded ClearFlame.

Photo from ClearFlame

Two mechanical engineering graduate students met in 2009. The students were inspired by one of their professors to look to technology as a way to pursue societal values. Changing to electric vehicles was an important solution for some markets, but billions of people in the world would need a different sustainable solution. The students went on to receive their degrees. The goal of the company was to retrofit existing diesel vehicles and equipment with fuel engines that could use any low carbon footprint fuel.

They have been taken seriously by the venture investment community and key elements of the industries they hope to serve. They raised $3 million with an impressive list of grant partners, followed by securing $17 million in Series A Financing in 2021.

ClearFlame's engine modification involves a higher-temperature combustion process, which combines small plumbing changes with a different fuel injection system to enable the use of any low carbon fuel. Almost any engine manufactured since 2010 is expected to be compatible with this modification. According to a study by Gladstein, Neandross and Associates, the total cost of ownership of a Clear-Flame-equipped truck was expected to be less than diesel, natural gas, electric, and hydrogen-based platforms. ClearFlame wants the technology to pay for itself within the first two years. The engines would generate less smog and less soot because of the fuel change. Inter-state shippers would benefit from a cleaner profile with individual states setting fuel and emissions standards. In countries with carbon taxes, the advantage of the biofuel is attractive. This change could help companies that have their own distribution fleets to meet their own goals while also lowering their costs.

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A truck is ready for a road test.

ClearFlame Technologies

The next critical stage for this technology is now underway as industry players get to kick the tires to see if the modified engines have the performance and staying power needed for these demanding uses. The first ClearFlame modified trucks began road testing. Prototype farm equipment is being evaluated by John Deere. The power generators are being tested.

The next challenge is to consider fuel distribution issues if the results meet expectations. It would be easy to fuel agricultural machinery with full strength bioethanol, which is made close to the fermentation facilities at which it is made. It is delivered to fuel terminals with 98% concentration for blend for something like automobile fuel. If bigger pumps were in place for quickly filling their tanks, regional trucking fleets could tap into those supplies. A future use for long-distance trucking would require some infrastructure adjustments at the truck stop level, but still use the existing liquid distribution terminals.

Many parties in the vehicle and equipment sectors are interested in this technology. It is important to the agricultural community. A member of the Iowa Corn Association is on the ClearFlame Board. From an energy independence point of view, the idea of shifting the diesel engine sector further towards biofuels is attractive. The hope is that this solution will fit the ecomodernist vision.