Principles of Operation
To meet EPA guidelines, engines that are compliant with EPA10 and newer regulations use an aftertreatment system (ATS) with an aftertreatment device (ATD) and Selective Catalytic Reduction (SCR) technology to reduce NOx downstream of the engine.
Notice: Follow these guidelines for engines that comply with EPA10 or newer regulations, or damage may occur to the ATD and the warranty may be compromised.
-
Use ultralow-sulfur diesel with 15 ppm sulfur content or less.
-
Do not use fuel blended with used engine lube oil or kerosene.
-
Engine lube oil must have a sulfated ash level less than 1.0 wt %; currently referred to as CK-4 oil.
-
Use only certified diesel exhaust fluid (DEF) in the DEF tank.
Notice: FA-4 engine lube oil is available, but is not compatible with all engines. See the engine manufacturer's operation manual to determine if FA-4 oil can be used in your vehicle's engine. Failure to do so could lead to engine damage and is not warrantable.
Important: Using non-specification fuels or oils can lead to shortened diesel particulate filter (DPF) cleaning or replacement intervals. For example, using CK-4+ oil with 1.3% sulfated ash (30% more ash content) may result in the need for DPF cleaning or replacement 20 to 30% sooner than would normally be required.
Important: See the engine manufacturer's operation manual for complete details and operation of the ATS.
After exhaust gasses leave the engine, they flow into the ATS. First they flow into a two-part ATD, comprised of a diesel oxidation catalyst (DOC), and a diesel particulate filter (DPF). The DPF traps soot particles, then exhaust heat converts the soot to ash in the DPF, in a process called regeneration (regen). The harder an engine works, the better it disposes of soot. When the engine is running under load and regen occurs without input, it is called passive regen. If the engine isn't running hot enough, the electronic controls may initiate an active regen, whereby extra fuel is injected into the exhaust stream before the diesel particulate filter, to superheat the soot trapped in the filter and burn it to ash. Both types of regen occur without driver input.
Warning: Active regeneration can occur automatically anytime the vehicle is moving. The exhaust gas temperature could reach 1500°F (816°C), which is hot enough to cause a fire, heat damage to objects or materials, or personal injury to persons near the exhaust outlet. See Regen-Inhibit Switch later in this chapter for instructions on preventing automatic regen if necessary.
The exhaust temperature can remain high even after the vehicle has stopped. When stopping the vehicle shortly after an automatic regen, ensure the exhaust outlets are directed away from structures, vegetation, flammable materials, and anything else that may be harmed by exposure to high heat.
Operating at reduced engine load will allow soot to accumulate in the DPF. When this occurs, the DPF lamp illuminates, indicating that a regen must be performed, and the driver must either bring the vehicle up to highway speed to increase the load, or park the vehicle and initiate a parked regen. See Parked Regen, later in this chapter for instructions.
Note: Beginning September 2, 2014 some chassis are equipped with an option that allows a regen to occur at 0 or 1 mph (0 or 2 km/h), instead of the standard 5 mph (8 km/h) threshold. Based on the engine programming parameter, if a regen occurs and vehicle speed is reduced to either 0 or 1 mph (0 or 2 km/h), the regen process will not be cancelled.
If the vehicle is programmed for the 0 mph (0 km/h) parameter, vehicle speed can be reduced to 0 mph (0 km/h) and the regen will continue. Vehicles with this option are equipped with a regen inhibit switch to cancel the regen if needed.
If the vehicle is programmed for the 1 mph (2 km/h) parameter, vehicle speed can be reduced to 1 mph (2 km/h) and the regen will continue. If vehicle speed is less than 1 mph (2 km/h), the regen will be cancelled.
After the exhaust stream passes through the ATD, it flows through another canister housing the SCR device. A controlled quantity of DEF is injected into the exhaust stream, where heat converts it to ammonia ( NH3) gas. This mixture flows through the SCR device, where the ammonia gas reacts with the NOx in the exhaust, to produce harmless nitrogen ( N2) and water vapor ( H2O), which then exits out of the tailpipe.