"Chemical Filter" Cleans Up Diesels

Diesel engines are the most efficient internal combustion engines, but the smoke and particulate emissions they generate have prevented them from being considered a "clean" technology.

Researchers have known since the 1970s that when oxygen-rich air is fed into an engine, the higher oxygen ratio allows fuel to burn more completely, which reduces emissions of the incomplete combustion products and increases power. But, until recently, the reduction in particulates was accompanied by an increase in oxides of nitrogen (NOx) emissions because of the higher combustion temperatures. Lack of a compact onboard oxygen source also prevented the use of oxygen enrichment for practical applications. With this breakthrough, Argonne seems to have overcome both challenges.

To address the second challenge, lack of a compact onboard oxygen source, Argonne and Compact Membrane Systems (a company that custom-makes prototype air separation membranes) developed a low-cost permeable membrane to separate ambient air into oxygen- and nitrogen-rich air before it enters the engine. The membrane works by a process called solution diffusion, in which pressurized ambient air is passed across tubes coated with a special polymer that separates the air into two streams: one rich in oxygen and the other in nitrogen. The oxygen-rich air is directed to the engine to optimize combustion. Argonne is working to minimize the size and power requirements for the membrane. The current version of the membrane is 10 times shorter and uses 60% less power than its predecessors. The goal is to develop a membrane about the size of an air filter.

This new strategy is a major step in addressing air pollution caused by diesel engines. The first beneficiaries will be railroads and people who live and work near them. Ultimately, the technology will be applied to truck and automobiles.

August 26, 2004