Reducing Diesel Soot by Using Late-Cycle Oxygen Enrichment

Meeting stricter emission regulations without compromising fuel economy in diesel engines presents a real challenge. New technologies are being developed for use before, during, and after the in-cylinder fuel combustion stage in the engine.

The trick is to reduce soot emissions in heavy-duty and light-duty diesel engines without increasing the formation of nitrogen oxides (NOx), a precursor to ozone that contributes significantly to smog. Argonne's approach is late-cycle auxiliary gas injection (AGI), which adds air or oxygen-enriched air. A high-velocity air stream from the air injector provides turbulent mixing of the combustion by-products. Increasing the oxygen concentration further enhances soot oxidation and helps burn up the soot particles as they form. Because NOx is formed early in the combustion cycle, adding air or oxygen-enriched air late in the cycle does not increase NOx.

Argonne's work focuses on modifying the in-cylinder air composition by adding oxygen-enriched air directly into the combustion chamber during the late stages of the combustion cycle. Specific projects include

• Developing KIVA-3 computer simulations to help optimize the AGI and fuel parameters
• Setting up a single-cycle diesel engine test stand and conducting late-cycle oxygen enrichment experiments

A test matrix for computer simulations was developed, and parametric test results were obtained by using a central gas injector location. Simulation results indicate the following:

• AGI is effective in reducing soot.
• The duration of the AGI has little effect on soot formation.
• Late-cycle AGI does not significantly alter the amount of NOx emissions.
• Varying the AGI composition has little effect on soot oxidation, which suggests the mixing caused by AGI is the dominant mechanism that affects engine-out soot emissions.

Future simulations will include a side gas injector location, and the model will be extended to a small-bore, high-speed, compression ignition, direct injection engine.

A test stand was designed and constructed with state-of-the-art instruments to measure gas and particulate (soot) emissions. Researchers will obtain baseline performance, combustion, and emissions characteristics. The engine will then be modified for late-cycle oxygen enrichment air injection (with a side injector) for additional experiments.

Research Partners

U.S. Department of Energy
Caterpillar, Inc.
University of Wisconsin - Madison, Engine Research Center

August 26, 2004