Clean Diesel: 8 Key Terms to Know
While the basics of diesel technology have remained fundamentally unchanged for more than 120 years, the advent of clean diesel has introduced car buyers, owners, dealers and mechanics to a host of new technologies and terms. Whether you’re doing research for an impending car purchase or talking to your favorite mechanic, here are eight acronyms to know:
- DEF (Diesel Exhaust Fluid). A mix of urea (ammonia) and water, DEF causes a chemical reaction that converts NOx pollutants into benign compounds such as nitrogen and water. A variety of brands exist, but most formulas are colored blue to match the blue cap used on the DEF storage tank.
- DPF (Diesel Particulate Filter). Since 2007, clean diesel vehicles have been outfitted with diesel particulate filters made of advanced ceramic materials. The filters are installed in the exhaust pipe where they strain up to 90% of from the exhaust stream any remaining soot and particulate matter.
- ECM (Engine Control Module). The engine control module is a compact computer system that monitors and adjusts engine performance to maintain fuel efficiency, maximize fuel burn and reduce emissions. To accomplish this, it controls a variety of systems including fuel injection timing and amounts, the EGR system and the diesel particulate filter and regeneration systems.
- EGR (Exhaust Gas Recirculation). Some carmakers use an enhanced exhaust gas recirculation system to reduce NOx emissions. The system returns exhaust gases to the engine, which lowers engine temperatures and reduces air volumes to minimize the formation of NOx pollutants.
- LNT (Lean NOx Trap). This device traps and holds NOx molecules contained in the exhaust stream of lean burning diesel engines to prevent the release of NOx pollutants. They can be used in conjunction with or in place of EGR and SCR systems.
- NOx (Nitrogen Oxides). In 2007, the EPA put more stringent rules in place to reduce nitrogen oxide pollutants created during diesel combustion. In addition to promoting smog formation and acid rain, NOx can damage airways and lung tissue, leading to ailments such as asthma, bronchitis, cardiovascular issues and emphysema.
- PM (Particulate Matter). This is a broad term used to describe soot and other particles that form when diesel fuel combusts. In the past, PM produced the characteristic black smoke associated with diesel engines, but with clean diesel most PM emissions are too fine to be seen by the human eye.
- SCR (Selective Catalytic Reduction). This term describes a specific process used to reduce NOx emissions. A urea-based diesel exhaust fluid is injected into the exhaust stream, where it causes a chemical reaction that converts NOx pollutants into neutral compounds such as nitrogen and water.