DEF is injected into diesel exhaust, enabling it to interact with a catalytic converter that removes NOx.
However, the liquid can freeze into a dome on a cold winter day, or the water can evaporate in the heat, Petti said. Therefore, sensors made by Wema are designed to heat the crystallized dome back into a liquid, and the company’s engineers have had to develop algorithms to compensate for temperature differences.
Petti said the Wema sensors are designed to last 15 years on a truck, even when submerged in liquid urea, and that sealing a system so DEF cannot invade it is very difficult.
Tenneco Automotive makes components for SCR systems for a variety of engine types, from cars to stationary power generators, but is also looking to develop alternative technologies, said company vice president Ben Patel.
“Liquid urea for SCR is here to stay. It is the proven, incumbent technology,” Patel said before launching into his descriptions of the alternatives.