In 2009 Honda plans to introduce passenger vehicles simultaneously in Japan and the United States that will employ a highly advanced diesel engine technology designed to fulfill U.S. Tier 2 Bin 5 emissions standards in all 50 states. Initially, a diesel Honda Accord will be offered, with the CR-V likely to be the second Honda vehicle to receive the engine. Future plans call for a diesel version of the Maxima, a planned cooperative venture with Renault. The stand-out feature of the Honda technology is that these engines, unlike products by competitors, do not require the addition of urea to function.

Honda first announced the diesel Accord at the Tokyo auto show in 2007. The vehicle features an aluminum 2.2-liter engine producing 150 horsepower with 260 lb. ft. of torque. Unlike similar diesels made by companies like Mercedes and Volkswagen, the Honda engines will not require replenishment with AdBlue urea liquid to ensure system function and efficient emissions control. The new engines have a NOx converter that, through a chemical reaction, produces its own ammonia while giving off nothing more than harmless nitrogen and water.

The NOx converter consists of two substrate layers on its honeycombed matrix. The outer layer functions to store the NOx while the secondary, lower layer, composed of platinum particles, principally reacts with the exhaust. It is this reaction that, during rich combustion, makes the ammonia. The ammonia, in turn, reacts with the stored NOx and results in the by-products nitrogen and water. According to statements by Honda, this technology was developed in-house and has a scalable capacity that will allow it to be used in a variety of vehicle configurations.

Since 2006, ultra-low sulfur diesel (ULSD) has been the standard in both Europe and North America with new, aggressively high emissions standards in place in the United States since the 2007 model year. The use of this cleaner burning variant of the diesel fuel has driven the development of innovative emissions control technologies that have in turn revived the diesel genre, once seen as the exclusive purview of smelly, dirty, heavy duty trucks. Diesel vehicles do have much higher levels of nitrogen oxide in their exhaust that have, until recently, made automakers wary of exploring such products as a way to meet higher fuel economy standards mandated by Congress.

The balance between meeting clean standards versus economy standards was, in the opinion of most car makers, too tricky and too expensive. Rapid advances in emissions technology, however, are changing the outcome of that equation. This new, urea-free technology from Honda clearly pushes the envelope in diesel emissions controls and serves to further drive the development of a whole spate of new diesels that will begin to appear on showroom floors late in 2008 and in 2009 from a variety of automakers.