An Introduction to Aftertreatment Systems

The main function of an aftertreatment system is to significantly reduce harmful emissions produced by diesel fuel powered equipment. It does so by targeting certain molecules present after diesel combustion and converting or processing them into less harmful byproducts. 

The targeted emissions include Particulate Matter (PM), Hydrocarbons (HC) and Nitrogen Oxides (NOx) present at different stages of the engine operation. Nowadays, in the US, it is mandatory that virtually all diesel engines are equipped with an aftertreatment system to meet government emissions requirements. 

Particulate Matter (PM):  

Particulate matter can be identified as the black soot that is exiting the exhaust pipes. It is the result of the partial combustion of hydrocarbons, engine oil and other additives present in fuel. Particulate matter is trapped in the Diesel Particulate Filter (DPF) by funneling the exhaust gases through a ceramic filter. As the equipment operates, PM accumulates in the DPF which requires cleaning. The cleaning, also called a regeneration cycle, is a process where the particulate matter is burned and transformed into ash.  

There are two types of regeneration cycles. The first is passive, which is where the engine, under normal operating conditions, produces enough heat to burn off the PM. The second is active or an induced regeneration. This is where the engine, under normal operating temperatures, does not produce enough heat to burn off the PM in the DPF. If this is the case, the engine will go into a regeneration cycle where it will put an artificial load on the engine to create higher exhaust gas temperatures. 

Hydrocarbons (HC): 

Hydrocarbons exiting the engine are unburned diesel fuel due to a cool engine or low in-cylinder combustion temperatures. Their presence will start to diminish as the engine warms up and in-cylinder temperatures increase.  

NOx:  

Finally, there is NOx, which is composed of Nitrogen Oxide (NO) and Nitrogen Dioxide (NO2). To reduce NOx, Diesel Exhaust Fluid (DEF) also known as AdBlue or Urea, is used in the aftertreatment system. DEF is composed of 32.5% urea (NH3) and demineralized water. DEF is sprayed and then spread into the exhaust gas via a mixer before entering the SCR catalyst.  

As DEF enters the system, it evaporates into ammonia (NH3) and water (H2O), the ammonia (NH3) sticks on the SCR catalyst and binds with the NO and NO2 (NOx) as they pass over the catalyst. Once bound, the NOx will combine with the NH3 to create a chemical reaction resulting in nitrogen 2N2 and water 3H20. 

(NO+NO2+2NH3 -> 2N2 + 3H2O) 

As the world starts to see the negative impacts of vehicle emissions, countries realize that there must be significant changes made to vehicles to protect planet earth so that we may survive. 

The USA implemented a phased plan for emissions regulations to give vehicle / engine manufacturers time to develop the technology to meet the regulation requirements. On-highway trucks were impacted by the first phase in 2008 and the second, more strict emissions regulations, in 2010. 

The US government also required emissions regulations for off-road vehicles. The timing of the requirements was slightly behind the on-road vehicle standards but followed similar emissions regulations. 

For off-road vehicles, the emissions standards are classified in “tiers”. Tier 1 being the least strict and Tier 4 being the strictest emissions regulations.  

Like on-road regulations, the EPA started with less strict emissions standards but increased the emissions reductions as years progressed.

KUS DEF products focus on NOx conversion. They include DEF sending units, DEF tanks, DEF nozzles, DEF pump housings, and other accessories. KUS being one of the most capable designers and manufacturers of SCR system components in the world, and understands that it is necessary to provide quality parts that are reliable and durable enough to survive the extreme operating conditions typically seen on our customer’s equipment. 

KUS DEF sending units feature an integrated design that include DEF level, temperature, and heating/thawing. KUS also manufactures and integrates into the DEF sending unit an ultrasonic DEF quality sensor that measures the concentration of the urea in the DEF. This will ensure that the DEF sprayed into your SCR system has the correct amount of urea to work with the aftertreatment system to reduce NOx emissions. 

KUS is in the unique position of being a total DEF tank assembly manufacturer. This means we can engineer, design, validate, and produce DEF tanks, DEF sending units, DEF caps, fill necks, and other DEF tank accessories. This makes KUS a one stop shop for providing a complete system for our customers. 

KUS engineering and design teams have more than 10 years of experience designing custom DEF tanks and tank assemblies for SCR system integrators, vehicle OEMs, and engine OEMs globally. KUS products can be found on many of the industry leaders in the power generation, off road equipment, and on highway vehicle markets. 

Tank Assemblies are engineered and designed for the SCR systems according to ISO 22241 standards, so rest assured that all products created by KUS are committed with the benefits of our customers, end-users and most importantly our planet.