NONCATALYZED DPFs
Occupational diesel engines with highway certification that are operated for extended periods of time at low engine load must have noncatalyzed diesel particulate filters (NC-DPFs). This kind of application is unique in that exhaust temperatures seldom increase to a point where DPF passive regeneration cycles or the appropriate operation of oxidation catalysts are possible. This section’s unit is an example of a standard Mack Trucks unit that is utilized in a waste packer. All regeneration cycles are active in this type of vocational vehicle due to the lower exhaust temperatures, and they can be started in the following ways:
- Automated or system-initiated. requires a vehicle to be traveling at a speed greater than 10 mph (16 km/h).
- Software or a driver-initiated EST.
Controls for NC-DPF
A specialized electronic control unit (ECU) called a thermal control unit oversees NC-DPFs (TCU). Although a specific message identification (MID) address is allowed on the J1939 data bus, the engine ECU manages the first Mack Trucks NC-DPF via a special bus connection. The versions released after 2010 make use of a J1939-networked aftertreatment module.
Components for NC-DPF
An NC-DPF aftertreatment canister can be broken into three portions as shown below and is typically fixed vertically to a stanchion behind the vehicle cab.
1 . Combustion chamber section. Engine exhaust downstream from the turbocharger is piped into the base of the combustion chamber. The key components in or mounted close to the combustion chamber section of the NC-DPF are:
- A check valve and a combustion air valve (ported from the intake manifold)
- Additional air valve (ported from the pneumatic system: supplies atomization module)
- Fuel shutdown valve, atomization module, and fuel pump
- Coil and ignition module
- Lighters (pair of spark plugs)
- nozzle for fuel injection
- A temperature probe for the inlet air (A1: exhaust temperature pyrometer)
Temperature gauge for the flame (A2: flame temperature pyrometer)
- Sensor for Delta Pressure (upstream probe)
- DPF section. The particle filter is located in this area, which is the middle region of the aftertreatment canister. It serves as a conduit for the combustion chamber’s exhaust gas before it is vented into the canister’s muffler portion. The important parts in the DPF section or mounted nearby are:
- Core DPF filter
- Additional air valve (ported from the pneumatic system: supplies atomization module)
- DPF
- Temperature sensor type A3 (DPF upstream pyrometer)
- The exhaust portion. The muffler part of the aftertreatment canister receives exhaust gas leaving the DPF section. The following essential parts are located in or close to the muffler portion of the NC-DPF:
- Mufflers with resonators
- Temperature sensor for A4 (pyrometer monitors temperatures downstream from the DPF prior to exiting the stack)
- The delta pressure sensor’s downstream probe (reports the differential pressure to signal pressure drop across the DPF section)
- NOx detector (data is broadcast to the engine ECM via a proprietary bus [pre-2010] or the J1939 data bus)
Operating Principle for NC-DPF
When it is not regenerating, the NC-DPF serves as a particle trap. Active regeneration is necessary when the DPF starts to become restricted by entrapped soot. A driver or EST may start an active regeneration cycle; alternatively, it may be automated. Normal requirements must be satisfied in order for the regeneration to be automated, including a minimum road speed, a minimum engine temperature, and others. The TCU, which is typically located on the exhaust stack stanchion, controls the regeneration after it has begun. The combustion chamber portion receives air from the intake manifold while diesel fuel (from the fuel subsystem) is atomized with the aid of system air pressure and injected across two ignitors (spark plugs). A flame that is strong enough to oxidize soot particles trapped in the DPF is created as a result.