ClearFlame Engine Technologies, a startup developing net-zero engine technology (earlier post), announced the publication of an independent study that finds ClearFlame’s technology could help fleet owners and other heavy-duty truck operators lower total costs while meeting sustainability goals sooner than currently available alternatives.

The study was conducted by Gladstein, Neandross & Associates (GNA) and commissioned by ClearFlame, whose investors include Bill Gates-founded Breakthrough Energy Ventures, John Deere, Mercuria, and Clean Energy Ventures.

ClearFlame has developed a technology that allows a heavy-duty engine to continue to operate using MCCI-based combustion when fueled on a wider range of fuels, including ethanol. 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%.

Because this technology allows the engine to continue to operate on an MCCI diesel-like cycle, the engine maintains the high thermal efficiency and torque of traditional diesel engines.

ClearFlame-based engine technology uses MCCI to maintain diesel engine cycle efficiency and torque

Ethanol’s shorter hydrocarbon chains (two-carbon atoms vs diesel’s twelve- carbon atoms) reduce or eliminate soot formation under typical engine conditions. The inherently lower soot forming propensity of ethanol compared to diesel fuel would allow ClearFlame to operate the engine closer to stoichiometric conditions, enabling the use of three-way catalyst (TWC) aftertreatment systems to control NO_x emissions.

TWC systems are lighter and less expensive than SCR systems, and do not require the use of diesel emission fluid (DEF), resulting in lower capital, operating, and maintenance costs for the aftertreatment system.

The ClearFlame system is currently being demonstrated on the Cummins X15 diesel platform through a retrofit strategy that entails the modification of some EGR and intake air components, as well as fuel injectors and other fuel system components.

EGR and air flow component modifications

An analysis of the expected emissions performance and total cost of ownership for the ClearFlame business model versus diesel, CNG, BEV, and FCV options in the over-the-road heavy-duty truck market presented in this paper indicates that:

• The TCO of ClearFlame-based trucks could be, on average, $0.08 per mile lower than diesel trucks in over-the-road applications.

• ClearFlame’s cost per mile in this application is expected to be substantially lower than BEV and FCV platforms, primarily due to the high purchase costs of these platforms.

• ClearFlame’s technology has the potential to reduce well-to-wheels GHGs and tailpipe emissions relative to traditional diesel fuel significantly. ClearFlame is estimated to provide a 42% lifecycle carbon reduction compared with diesel, as well as approximately 22% lower GHG than battery electric vehicles based on the national average grid mix.

• The cost per mile for battery-electric and fuel-cell technologies in long-haul trucking is currently high, making technologies like ClearFlame important options to immediately provide cost-effective GHG and tailpipe emissions reductions.

The TCO analysis was conducted when diesel fuel’s national average was $3.48 per gallon in October 2021 and found that ClearFlame-enabled trucks would have a lower TCO than diesel by $0.08 per mile, lower than natural gas by $0.09 per mile, lower than electric by $0.97 per mile, and lower than hydrogen platforms by $0.61 per mile.

The report also highlights the potential for even greater GHG reductions using other feed sources developed by the ethanol industry with lower carbon intensities. For instance, further improvement to ethanol production processes—such as utilizing more corn fiber and stover, or adding carbon capture to production facilities—would result in GHG emissions reductions of 69-83% compared with diesel, depending on the region.

The report further highlights that ClearFlame can significantly reduce tailpipe PM_2.5 by 99%, DPM by 100%, and SO_x by 95% relative to traditional diesel fuel. While ClearFlame’s technology is expected to meet all the same emissions regulations for modern diesel engines, it is also fully expected to meet the stricter standards being enacted by California’s Low NOx Heavy-Duty Omnibus Regulation and proposed by the US EPA, without the additional cost and complexity facing diesel engines.

This study clearly shows that ClearFlame’s technology can provide significant and cost-effective GHG and tailpipe emissions reductions in the immediate future. While most of the discussion around sustainable fuels today focuses on compressed natural gas, battery-electric, and hydrogen fuel cell vehicles, alcohol fuels have the potential to play a valuable role in sustainable transportation. ClearFlame’s engine technology and ethanol fuel supply model could address the historic barriers to the adoption of ethanol fuels in the heavy-duty market.

—Patrick Couch,, GNA study author

The independent study was commissioned by ClearFlame Technologies and conducted by GNA Clean Transportation & Energy Consultants. ClearFlame was allowed to comment on the study protocol and was provided with a report of the results. The study results were not impacted apart from suggestions for clarification.

The model evaluates various platforms in Class 8 over-the-road applications, a market that is assumed to be well suited to the ClearFlame technology as vehicle range, weight, fuel costs, fuel availability, and fueling time are key concerns in this application.

The TCO model evaluates the following cost components for each technology: Vehicle Purchase Cost, Federal Excise Tax, State Sales Tax, Vehicle Maintenance, Vehicle Insurance, Fuel Costs, Depreciation Tax Benefits, Incentives (RFS and Low Carbon Fuel Standard), Residual Value.

The net cash flow over the useful life of the truck (8 years) is used to calculate the average cost per mile (CPM) for each of the technologies. The average annual mileage for this analysis is 101,000 miles, based on the US EPA MOVES model default value for Class 8 long-haul semi-tractors.