Your gasaholic friends may not believe you, but feel free to tell them that diesels will soon be cleaner than current gasoline engines. It's not a trick-they'll have to be that clean if manufacturers want to sell them in the USA.
Honda's new four-cylinder i-CTDI engine is possibly the most advanced diesel engine ever built. The 2.2L engine produces 138 hp and a hefty 250 lb-ft of torque, and it does it cleanly and quietly.
EPA Crackdown
By requiring all passenger diesels to meet Tier II Bin 5 emissions standards, the feds threw down the gauntlet and started a war on nitrogen oxides (NOX), hydrocarbons, and particulate (soot) emissions. As of January 1, 2007, all light-duty diesels sold in the U.S. have to emit 50 percent fewer hydrocarbons and NOX and 90-plus percent less particulate matter (compared with the rules instituted in 2004). That's a giant drop in emissions and probably caused a giant drop in the stomachs of engineers who needed to act quickly to ensure their engines would be ready in time or risk being locked out of the U.S. market for a model year or longer. Luckily, the government made the transition easier by requiring cleaner fuel for diesels.
Ultra-Low Sulfur Diesel
By now, all the on-road diesel being sold in the U.S. has a sulfur content of 15 parts per million. This ultra-low sulfur diesel (ULSD) is much cleaner than its predecessor, which was allowed to have up to 500 ppm of the nasty element.
Exhaust Gas Recirculation
EGR: Those may be three of the most hated letters among automotive enthusiasts. Reintroduction of exhaust fumes into the intake manifold has been blamed for strangling musclecar engines and reducing diesel performance for the sake of better emissions. Hate it or not, EGR is here to stay because it reduces NOX, and it's only getting more invasive. The new 6.7L Cummins, LMM Duramax, and 6.4L Ford Power Stroke are sucking up to 25 percent of their exhaust back into the engine. That's a lot of hot air, so each of the engines employs a large EGR cooler to chill the gases and sometimes even a catalyst to clean them before they are routed back into the engine. Not only is there less exhaust to spin the turbo(s), but up to a quarter of the intake charge will be dirty exhaust instead of fresh air-and weight has been added to the engine package. Let's just say that opinions about EGR probably won't be improving.
1) Honda DPF system during lean-burn operation, the NOX adsorbent in the lower layer of the catalyst adsorbs NOX from the exhaust gas.
2) As needed, the engine-management system adjusts the engine air/fuel ratio to rich-burn, where the nitrogen oxides in the NOX adsorption layer react with hydrogen obtained from the exhaust gas to produce ammonia (NH3). The adsorbent material in the upper layer temporarily adsorbs the NH3.
3) When the engine returns to lean-burn operation, NH3 adsorbed in the upper layer reacts with NOX in the exhaust gas and reduces it to harmless nitrogen.