Trucking is the dominant mode of freight transport around the globe, with a market size of approximately $430 billion annually for new heavy-duty (HD) vehicles. Diesel-fueled, compression-ignition (CI) engines, with their high efficiency and good torque and power characteristics, have been the backbone of HD transportation for decades. However, in a market projected to grow by 60% by the year 2030, uncertainty in petroleum prices and increasingly stringent emissions standards (requiring complex, expensive aftertreatment systems) are forcing major engine manufacturers to consider alternatives to traditional Diesel-fueled engines. In recent years, one of the emerging trends for HD engines has been the deployment of spark-ignited (SI), compressed natural gas (CNG) engines. These CNG SI engines are attractive due to their reduced fuel cost and simplified emissions system (only needing an inexpensive three-way catalyst). Unfortunately, the port fuel injection and reduced compression ratio inherent in all SI engines lowers both their power density and efficiency, as compared to the standard CI engines. As such, there is a need in the HD transportation market for a better alternative.
ClearFlame Engines proposes a program to continue development of an innovative approach to HD engine operation that has the potential to significantly outperform current engine technologies. ClearFlame’s technology leverages low-carbon liquid fuels in HD engines to produce up to 30% more engine power, at higher efficiency, and with significantly cleaner exhaust emissions. This engine technology further benefits from the use of a simple and inexpensive aftertreatment system (a three-way catalyst), unlike current Diesel engines. Our approach would outperform current Diesel-fueled technologies, while achieving the emissions and fuel-flexibility of natural-gas-fueled alternatives, but without the associated drawbacks.
ClearFlame’s engine technology centers on the development of a combustion system that integrates compression-ignition of a direct-injected, low-sooting fuel (such as ethanol or methanol) in a thermally insulated combustion chamber. Direct-injected CI operation ensures high power density, and allows for a high compression ratio, increasing efficiency. At the same time, due to the minimal soot production afforded by alcohol fuels, the engine maintains stoichiometric conditions, further increasing power and enabling three-way catalysis. Load variation, while maintaining stoichiometric conditions, can be achieved with exhaust gas dilution at moderate loads and mode switch to SI operation at very low loads.
This program would build upon research conducted at Stanford University that confirmed the viability of CI combustion and load variation of ethanol in an insulated, single-cylinder research engine. The experiments demonstrated a 30% increase in power from traditional Diesel operation. At the same time, measured particulate emissions remained under the EPA regulation limit at stoichiometric without aftertreatment, obviating the need for a particulate filter and ensuring that a three-way catalyst could handle all other emissions. Meanwhile, modeling showed not only that this concept would be more efficient than current Diesel engines (46% vs 43%) in its basic configuration, but also that future work could enable efficiencies of near 50% with adequate mechanical regeneration, and over 60% with thermal exhaust regeneration.
The goal of the proposed program would be to demonstrate the technology on a multi-cylinder production engine, to enable subsequent commercialization. A stock Diesel engine (e.g. a Cummins ISX 15) would be modified with the following: thermal barrier coatings; high-pressure alcohol-tolerant direct injection; variable valve actuation; uncooled turbocharging; and three-way catalysis for exhaust aftertreatment. This would provide a suitable test bed for a proof-of-concept demonstration of the complete engine technology—showing higher efficiency, increased power, and simplified emissions—and serve as a prototype for future production.