Reactivity Controlled Compression Ignition Engines: A Dual-Fuel Breakthrough in Clean Combustion

Reactivity Controlled Compression Ignition (RCCI) is an advanced internal combustion technology that uses two fuels of different reactivity to achieve ultra-low emissions and high thermal efficiency. Developed at the University of Wisconsin–Madison’s Engine Research Center under the leadership of Wisconsin Distinguished Professor Rolf Reitz, RCCI represents a significant advancement in clean diesel engine technology.

How RCCI Works

The RCCI process begins with the introduction of a low-reactivity fuel—such as gasoline or ethanol—into the intake port during the intake stroke. This creates a well-mixed charge of low-reactivity fuel, air, and recirculated exhaust gases. As the piston moves toward top dead center, a high-reactivity fuel—typically diesel—is injected directly into the cylinder under high pressure. This injection triggers ignition of the premixed low-reactivity charge, resulting in a controlled combustion process that occurs near top dead center.

By stratifying fuel reactivity within the combustion chamber and carefully controlling injection timing, RCCI enables precise management of combustion phasing, duration, and magnitude. This approach avoids the need for a throttle, similar to conventional diesel engines, while significantly reducing harmful emissions.

Key Benefits of RCCI Technology

Research has demonstrated that RCCI engines deliver multiple advantages over conventional diesel combustion:

• Ultra-low nitrogen oxide (NOx) and particulate matter (PM) emissions
• Higher thermal efficiency due to reduced heat transfer losses
• Elimination of the need for costly after-treatment systems
• Compliance with stringent EPA 2010 emissions guidelines without exhaust after-treatment
• Improved fuel efficiency, with brake thermal efficiency increasing from 29.1% to 33.5% in experimental studies, and further enhancements possible with oxygen enrichment

These benefits are achieved through the dual-fuel strategy, which allows for simultaneous reduction of NOx and soot—traditionally a trade-off in diesel engine design.

Fuel Flexibility and Applications

RCCI is compatible with a variety of fuel pairings, enhancing its potential for real-world application. Examples include:

• Gasoline and diesel
• Ethanol and diesel
• Gasoline blended with cetane-number boosters such as di-tert-butyl peroxide (DTBP)

The technology has been shown to effectively burn biofuels in diesel engines, offering improved performance and reduced smoke emissions. Alcohols serve well as low-reactivity fuels due to their low cetane number, high self-ignition temperature, low viscosity, and good vaporization. Vegetable oils and other oxygenated fuels with higher cetane numbers can function as high-reactivity fuels.

Development and Intellectual Property

RCCI was pioneered by the research group of Rolf Reitz at the University of Wisconsin–Madison. The underlying patents are managed by the Wisconsin Alumni Research Foundation (WARF). Derivative concepts have also been explored by major engine manufacturers, including Caterpillar.

Conclusion

Reactivity Controlled Compression Ignition represents a promising path toward high-efficiency, clean combustion in internal combustion engines. By leveraging dual-fuel stratification and precise injection control, RCCI overcomes many limitations of conventional diesel and gasoline engines. As research continues and the technology matures, RCCI could play a key role in reducing the environmental impact of transportation and power generation while maintaining or improving fuel efficiency.