Variable Oxygen- or Nitrogen-Enriched Air System for Combustion Engines

Cold-starting a gasoline engine results in significant emissions of hydrocarbon, carbon monoxide, and air toxics. Other types of engines are not necessarily cleaner or more efficient. For example, diesel engines release particulates and smoke, and natural gas engines reduce emissions but have lower power density. And engines that burn alcohol fuels produce air toxic emissions over time.

These problems can be solved, to some degree, through variable air composition. Researchers have demonstrated that nitrogen oxide (NOx) emissions can be reduced by exhaust recirculation in both gasoline and diesel engines. However, only a limited amount of exhaust can be recirculated without reducing power output and fuel economy. Recirculated soot particles may also cause wear in diesel engines.

Argonne is developing a simple process that uses low-cost permeable membranes to separate ambient air into oxygen- and nitrogen-rich streams. The membrane, which is about the size of an air filter, supplies an oxygen-rich stream to improve combustion or a nitrogen-rich stream for exhaust post-treatment.Since Argonne began working to apply this technology to engines in the early 1990s, membranes have become more compact and less expensive.

Increasing the oxygen flow to the engine offers the following benefits:

In diesel engines, reduces particulate emissions and increases engine power output
In gasoline engines, reduces emissions during cold starts to meet the U.S. Environmental Protection Agency's (EPA's) Tier II emissions standards (year 2004)
Increases the power density of vehicles powered by natural gas and reduces emissions from alcohol fuel vehicles to meet Ultra-Low-Emission Vehicle (ULEV) standards for formaldehyde and NOx emissions
Allows the use of lower-grade fuels in diesel engines

Increasing the nitrogen flow to the engine offers other advantages:

In diesel-fueled vehicles, potentially reduces NOx emissions without the problems caused by exhaust gas recirculation (engine wear, oil contamination)
Eliminates the need for a heat exchanger to cool exhaust gases before recirculation
Can be used to generate monatomic nitrogen plasma that chemically reduces nitrogen oxide and nitrogen dioxide from both gasoline- and diesel-powered engines.

Air can be enriched in oxygen or nitrogen by selective permeation through nonporous polymer membranes, the "solution diffusion" mechanism. The process is technically simple, and the equipment compact and modular. A single air separator membrane provides both oxygen- and nitrogen-rich streams so that the nitrogen-to-oxygen ratio can be varied for either combustion or exhaust treatment applications.

Argonne has filed for, or is in the process of filing for, the following patents:

Method and Apparatus for Reducing Cold-Phase Emissions from Gasoline-Powered, Light-Duty Passenger Vehicles (ANL-IN-95-070)
NOx Reduction Method (ANL-IN-92-066)
Nitrogen Spark De-NOx-er (ANL-IN-94-133)
Method and Apparatus for Providing Variable Oxygen-to-Nitrogen Ratio in the Air for Combustion Engine Applications (ANL-IN-95-152)

Argonne has concluded a cooperative research and development agreement (CRADA) with the U.S. Department of Energy and the Association of American Railroads to study the application of oxygen enrichment for locomotive diesel engines. Subsequently, on the recommendation of an external expert panel, Argonne has initiated a new CRADA with Mack Trucks to focus on nitrogen enrichment with membranes and applying the nitrogen-rich combustion air to reduce NOx emissions from on-highway, heavy-duty trucks. The tests at Mack Trucks are pending.

Argonne has also been involved in a project with Caterpillar, Inc., to investigate the effectiveness of monatomic nitrogen for reducing NOx in diesel exhaust. Argonne has provided Caterpillar with the data generated by the laboratory evaluation to help Caterpillar guide its decision to commercialize this technology.

In another study, Argonne is installing a prototype membrane on a light-duty, flexible-fuel vehicle to provide oxygen-enriched air for emissions testing during the EPA's Federal Test Procedure driving cycle.

August 26, 2004