California Construction Trucking Association (CCTA)

By Mark Studevant, Los Angeles Freightliner

It is important that truckers understand the process needed in purchasing a diesel particulate filter (DPF) to meet the new CARB On-Road Truck and Bus Rule.  It is a very costly proposition, so do your homework.  Not every truck can be retrofitted. 

Engine maintenance, engine condition, and engine duty-cycle play big roles in retrofitting diagnosis and assessment.  These factors as well as exhaust temperatures, vehicle speed, load, idling, geography, ambient temperatures and driver tendencies play a role in whether the truck can be retrofitted and with a particular filter. 

Knowing the exhaust temperature profile before applying a DPF muffler is important so that you don’t make a costly mistake. Insufficient temperatures may lead to premature DPF plugging and increased maintenance to keep the filter clean and allow the engine to run properly.

Below: Image is a screen capture of a data-logger software as it
records the exhaust temperature during engine operation.

A data-logger is a device used to record the exhaust temperature during engine operation.  The data logger is installed by an authorized dealer.  It is a fairly simple operation that typically costs around $300 and takes just a few minutes by an experienced mechanic to install.  Once the data logger is installed the recorder is operated for several days under normal operating conditions to provide a minimum of 24 hours of recorded time.

This time is critical to get a CARB approved snapshot of the exhaust temperature profile. Engine duty-cycle plays a major role in exhaust temperatures, and as stated earlier it’s influenced by factors such as vehicle speed, load, idling, geography, ambient temperatures and driver tendencies.  Once the 24 hours of engine run time is achieved the data logger is removed and the data is downloaded into a sophisticated software program that looks at tens of thousands of readings and results in a histogram.  It is with the histogram that the retrofit manufacturers and installers determine the right filter for the trucker and truck.
 All diesel particulate filters use the engine temperature to create DPF regeneration. Regeneration is the process of removing the accumulated soot from the filter. This is done either passively (from the engine’s exhaust heat in normal operation or by adding a catalyst to the filter) or actively introducing very high heat into the exhaust system. On-board active filter management can use a variety of strategies:

1. Engine management to increase exhaust temperature through late fuel injection or injection during the exhaust stroke
2. Use of a fuel borne catalyst to reduce soot burn-out temperature
3. A fuel burner after the turbo to increase the exhaust temperature
4. A catalytic oxidizer to increase the exhaust temperature, with after injection (HC-Doser)
5. Resistive heating coils to increase the exhaust temperature

Many on-board active systems use extra fuel, whether through burning to heat the DPF, or providing extra power to the DPF’s electrical system, although the use of a fuel borne catalyst reduces the energy required very significantly. Typically a computer monitors one or more sensors that measure back pressure and/or temperature, and based on pre-programmed set points the computer makes decisions on when to activate the regeneration cycle.

The additional fuel can be supplied by a metering pump. Running the cycle too often while keeping the back pressure in the exhaust system low will result in high fuel consumption. Not running the regeneration cycle soon enough increases the risk of engine damage and/or uncontrolled regeneration thermal runaway and possible DPF failure.

Only through proper data logging and vehicle assessment by a reputable DPF installer can the proper use and installation of a verified diesel particulate filter be achieved.  Using out-of-state or non-professional installers is a major risk.  If the data logging is not done correctly, as well as the filter installation, fines of up to $10,000 per day can be and have been assessed to the truck owner and retrofit installer by CARB.  

In many instances it makes no sense to install a diesel particulate filter on an older truck that has not been well maintained.  Especially since a DPF can cost anywhere between $12,000 to $23,000 when installed on high HP engines.  Realistically the trucker would be better off to buy a newer compliant vehicle and retire their old vehicle completely.