Engineers at Mercedes Benz in Germany have developed lean-burn engines that can improve mileage by 5 to 10% and reduce emissions. They would like to use them in cars slated for the U.S. market to meet future CAFÉ standards. Unfortunately, the technology won’t work with gasoline currently refined and sold in the U.S. because its sulfur content, at 95 ppm, is much too high. The technology also won’t work in Africa or Asia, which also significant sulfur in their gasoline. The sulfur level has to be below 50 ppm before lean-burn engines will work. The problem is that the sulfur overwhelms and ruins a trap that pulls nitrogen oxides from the exhaust before it goes through a catalytic converter. The trap is necessary because lean-burn technology generates too much NOx for conventional three-way catalytic converters to work. The trap captures and stores excess NOx so that it can be burned off later
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