Definition of node. 1a : a pathological swelling or enlargement (as of a rheumatic joint)b : a discrete mass of one kind of tissue enclosed in tissue of a different kind.
Diesel exhaust fluid (DEF) from a separate tank is injected into the exhaust pipeline, where the aqueous urea vaporizes and decomposes to form ammonia and carbon dioxide. Within the SCR catalyst, the NO. x are catalytically reduced by the ammonia (NH. 3) into water ( H2O) and nitrogen (N.
ADVERTISEMENT. DEF is a necessity to make this happen. Kept in a separate reservoir tank from the diesel fuel, itâs a solution of 32.5% high-purity urea mixed with very high-purity water. Urea is an organic nitrogen-containing compound commonly used in agriculture as a fertilizer.owever, you canât just buy fertilizer and make your own DEF. The urea used to make DEF is known as automotive grade or environmental grade, a higher grade than the kind used for fertilizer. Although it meant a new technology and a new fluid to deal with, the good news was, SCR meant fuel savings.