Researchers at the University of Wisconsin led by Dr. Rolf Reitz are developing a dual-fuel compression engine combustion strategy called reactivity controlled compression ignition (RCCI) to simultaneously reduce fuel consumption and regulated emissions of NOx and PM. (Earlier post.)
The Wisconsin Alumni Research Foundation (WARF) is seeking commercial partners interested in developing the process, and the University has applied for a US patent on the technique. Members of the Wisconsin team—as well as partners at Oak Ridge National Laboratory—will deliver a set of papers on RCCI at the upcoming SAE Powertrains, Fuels and Lubricants Meeting in San Diego in October.
Numerous technologies have been developed to address the need for diesel engines with reduced emissions. However, measures which reduce engine-out NOx production typically increase PM production, and vice-versa (the “soot-NOx tradeoff”). Current technologies and combustion strategies developed to reduce both NOx and soot generation are difficult to implement and control and many still require expensive after-treatment measures.
The RCCI process uses in-cylinder fuel blending with at least two fuels of different reactivity and multiple injections to control in-cylinder fuel reactivity to optimize combustion phasing, duration and magnitude. The process involves introduction of a low reactivity fuel into the cylinder to create a well-mixed charge of low reactivity fuel, air and recirculated exhaust gases.
Examples of fuel pairings for RCCI are gasoline and diesel mixtures, ethanol and diesel, and gasoline and gasoline with small additions of a cetane-number booster (di-tert-butyl peroxide (DTBP).
The level of recirculated exhaust gas and the closure of the intake valve are controlled such that a high reactivity fuel is injected before ignition of the premixed fuel occurs. The high reactivity fuel is injected using single or multiple injections directly into the combustion chamber.
Multiple injections of fuels at different reactivities allow optimization of Premixed Controlled Compression Ignition (PCCI) type combustion in engines, reducing emissions without the need for after-treatment methods. By appropriately choosing the reactivities of the fuel charges, their relative amounts, timing and combustion can be tailored to achieve optimal power output (fuel efficiency), at controlled temperatures (controlling NOx) with controlled equivalence ratios (controlling soot), the researchers say.
Key benefits cited of the strategy include:
- Lowered NOx and PM emissions
- Reduced heat transfer losses
- Increased fuel efficiency
- Eliminates need for costly after-treatment systems
- Complies with EPA 2010 emissions guidelines without exhaust after treatment
Derek Splitter, Reed Hanson, Rolf Reitz. High Efficiency, Low Emissions RCCI Combustion by Use of a Fuel Additive (SAE 010-01-2167)
Scott Curran, Vitaly Prikhodko, Robert Wagner, Kukwon Cho, Charles Sluder, Sage Kokjohn, Rolf Reitz. In-Cylinder Fuel Blending of Gasoline/Diesel for Improved Efficiency and Lowest Possible Emissions on a Multi-Cylinder Engine (SAE 2010-01-2206)
Dual-fuel lab engines achieve high efficiencies, low emissions (Automotive Engineering)
Wenmiao Chen, Shijin Shuai and Jianxin Wang (2010) Effect of the Cetane Number on the Combustion and Emissions of Diesel Engines by Chemical Kinetics Modeling. Energy Fuels, 24 (2), pp 856–862 doi: 10.1021/ef900993g