HEALTH & SAFETY
Valve used for control of coolant in DEF multi-function head unit
COOLANT CONTROL
Chad VanRens from TLX Technologies explores the use of coolant control valves for off-road vehicle SCR thermal management systems
I
n the 1970s, countries across the globe began a decades-long process of implementing mandates intended to improve air quality.
Reducing emissions from power plants, industrial facilities, vehicles and heavy equipment have played a crucial role. This includes reducing nitric oxide and nitrogen dioxide (Nox) emissions, a key contributor to smog and linked to cardiovascular and respiratory disease.
REDUCING NOX Increasing pressure to meet targets for reducing NOx emissions drove manufacturers of diesel vehicles to adopt selective catalyst reduction (SCR) systems. First developed in the 1950s, SCR technology proved effective at reducing NOx and saw its first application in power plants. Now these systems are the standard means of reducing NOx in diesel vehicles. SCR systems can reduce NOx by
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as much as 90%. In diesel engine applications, urea, also known as diesel exhaust fluid (DEF), is sprayed into the exhaust stream where it breaks down into ammonia. The ammonia and NOx then flow into a catalyst composed of base metals where they chemically react, reducing NOx to nitrogen and water vapour.
THERMAL MANAGEMENT MATTERS DEF freezes at temperatures below -11ºC and degrades if it gets hotter than 30ºC. Depending on the specific vehicle, SCR systems may use different thermal management systems for heating and cooling DEF to keep it within its optimal temperature range, between 12ºC and 30ºC. For certain applications, engine
coolant is used for both heating and cooling DEF. Depending on the
DEF multi-function head unit. Includes coolant valve, heat exchanger and sensors
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