NOx emissions from diesel engine

Patent Pending SCR (selective catalytic reduction) injects a water and urea mix, known as diesel exhaust fluid (DEF), into the exhaust of a diesel engine to change nitrogen oxide into nitrogen and water. SCR can reduce 90% of the NOx in the exhaust system. SCR systems do not need a PM (particulate matter) filter, but when the SCR and PM filters are combined the engine is 3% to 5% more fuel efficient. One disadvantage of the SCR system is the need to refill the DEF tank, which varies with the miles driven, load factors, and the hours used.[18] The SCR system is not as efficient at higher revolutions per minute. SCR is being optimized to have higher efficiency with broader temperatures, be more durable and more precise in its application