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ClearFlame Engine Technologies partners with Alto Ingredients to demo ethanol-fueled MCCI in heavy-duty diesels; high efficiency, low emissions

Startup ClearFlame Engine Technologies announced a partnership with Alto Ingredients, a leading producer of specialty alcohols and essential ingredients, to conduct pilot demonstrations of ClearFlame’s solution for diesel engines using low-cost ethanol in Class 8 trucks.

ClearFlame will provide Alto with a Class VIII truck retrofitted with a 500hp heavy-duty demonstration engine, which can match diesel torque and efficiency by achieving true diesel-style combustion (MCCI, mixing-controlled compression ignition) of any decarbonized fuel.

In turn, Alto will provide fuel and fleet support, which will enable real-world testing on the road. ClearFlame anticipates its engine running on ethanol can reduce GHG vehicle emissions by more than 45% and offer an estimated 15-30% TCO savings when compared with a diesel-fueled solution.

ClearFlame’s engine technology enables low-carbon and carbon-negative fuels to be easily integrated into existing diesel engine platforms, offering a more sustainable and cost-effective solution than diesel fuel while utilizing existing liquid fuel infrastructure.

It provides the same performance, efficiency, and rugged practicality associated with diesel engines, while eliminating the need for complex aftertreatment solutions.

By replacing 100% of the petroleum fuel used with decarbonized fuels such as ethanol, ClearFlame’s engine technology significantly reduces greenhouse gas emissions, particulate matter and smog, helping to meet stringent emissions regulations while reducing overall engine cost. ClearFlame-enabled trucks will begin driving in late 2021, for fleet testing to begin in the first quarter of 2022.

The ClearFlame solution leverages diesel-style mixing-controlled compression ignition (MCCI). Historically, clean-burning fuels, and those that are easy to make from waste CO2 streams or syngas, have failed to ignite using MCCI.

ClearFlame’s solution, grounded in technology developed during doctoral studies at Stanford University and validated using more than $3 million in grant funding, addresses this problem by elevating combustion temperatures in order to enable use of non-traditional fuels without sacrificing performance. In fact, it increases power by 25%.


In a high-temperature environment, any fuel will behave like diesel fuel, having short ignition delay and burning as it is injected in a mixing fuel plume. Low-sooting fuels allow for the elimination of diesel particulate filtration (DPF). Use of soot-free “Clear” Exhaust Gas Recirculation (EGR) can allow for lower NOx emissions without the competing soot constraint, meeting next-generation emissions standards without added aftertreatment complexity.

Without soot from diesel fuels, compression ignition engines are not limited to lean operation and can instead use the stoichiometric air-fuel ratio. ClearFlame uses soot-free “Clear” Exhaust Gas Recirculation (EGR) to maintain this ratio under varying load conditions.

Stoichiometric operation substantially increases power density and leaves an exhaust composition suitable for three-way catalysis (TWC) instead of Selective Catalytic Reduction (SCR) using urea/ammonia (DEF). Simplifying the engine’s aftertreatment system improves its reliability and reduces its cost by about 75%. It also improves its NOx reduction capability to near-zero levels. Using soot-free fuels eliminates the need for a Diesel Particulate Filter (DPF).

In its development work, ClearFlame used both computational modeling and single-cylinder engine experiments to optimize combustion chamber geometry to leverage the advantages of these clean-burning fuels, allowing this concept to achieve efficiencies that are comparable to the baseline diesel engine but with much lower emissions.

The team then implemented the results on a heavy-duty production engine provided by Cummins.


  • Blumreiter, J., Johnson, B., Zhou, A., Magnotti, G. et al. (2019) “Mixing-Limited Combustion of Alcohol Fuels in a Diesel Engine,” SAE Technical Paper 2019-01-0552, doi: 10.4271/2019-01-0552.


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