In the mid 1970s as the first round of emissions regulations really started to bite hard in the US market, most car-makers struggled desperately to try and get the initial round of catalytic converters to work reliably. In those days - before electronic engine management systems and electronic fuel injection - car makers relied on those early catalyst systems, exhaust gas recirculation, and A.I.R. pumps. Most car-makers that is. Honda, was the exception. They had developed a stratified charge combustion chamber design, known as CVCC. It was good enough to allow Honda to avoid catalytic converters until the beginning of the 1980s. Later, Honda led the way with single cam multi-valve engines, bringing variable valve timing to inexpensive cars, and brought out the first production hybrid at virtually the same time as Toyota.
Honda has developed a new catalytic converter that, combined with new electronic engine controls, will apparently be able make their new diesel engine run as clean as a gas engine while still getting 30 percent better fuel efficiency. To overcome the nitrogen oxide emissions that can result from their lean-burn technology, the engine controls periodically switch from lean to rich fuel mixtures. The extra hydro-carbons that result from the rich mixture react in the new catalyst to produce ammonia. When the engine switches back to lean mode, the nitrogen oxides react with the ammonia to convert to nitrogen. The ammonia reaction is the same mechanism used by the urea injection in the Mercedes BlueTec diesels. The Honda mechanism is self-contained and produces it's own ammonia without driver intervention. The BlueTec system requires the driver to replenish the urea tank periodically.
Honda hasn't yet certified their new system with the EPA, but they have said that they are willing to license their system to other manufacturers. If anyone is able to make such a system it is likely to be Honda. They plan to have the system on the US market by 2009.
[Source: Automotive News - Subscription Required]