DPFs for Industrial Engines made simple
This Tech Tip was designed to answer many of the questions we have received from customers about DPFs when used in industrial applications on Perkins, Deutz, and Deere industrial engines.
What is a DPF?
A diesel particulate filter is designed to reduce particulate matter emissions from a diesel engine. Essentially it is a soot trap. In fact some manufacturers such as DCL have even labeled their DPFs as “soot filters” and registered the trademark.
Does it improve air quality?
Yes, a DPF improves the quality of the air by removing particulate matter. It does not make it safe to breathe though. Only a diesel oxide catalyst (DOC) by removing CO does that.
Do DPFs have a DOC component?
Most of those designed for use in off road applications in closed spaces do also have a DOC. On road trucks tend not to use a DOC with their DPF system especially in a line haul operation with high exhaust temperatures.
How Does a DPF work?
A DPF uses a honeycomb ceramic structure with a series of alternate tubes or channels. The tubes are plugged at opposite ends and the diesel exhaust gas enters through the open end of each tube. The plugged end of each channel forces the soot particles against the porous walls of the channels. The soot is burned off there and the gases such as steam and CO 2 pass through the adjacent exit tube.
What is passive regeneration?
Under high load conditions the exhaust gas temperatures are high enough to quickly bake off most soot or PM in the DPF. In other words, the exhaust gas temperatures clean the DPF of excess soot.
What is active regeneration?
Under conditions of low load such as excessive idling the diesel exhaust gas temperature is not high enough to burn off the soot so it accumulates in the DPF. This can create blockages. Some active systems including those made by Huss and Rypos Inc. use an electronic charge to clean the DPF. Other systems, notably those used in over the road trucks inject fuel into the exhaust system.
Cleaning a DPF
To ensure adequate performance a DPF should be cleaned at regular intervals. Mineral particulate and heavy metals from engine bearings and cylinder liners that get trapped in the lube oil will build up in the DPF substrate. This material is known in the aggregate as ash and will clog the space in the channels meant for the soot. Unlike soot, ash is inert and un-burnable. If left to accumulate it can damage the DPF. As a result it must be periodically removed from the DPF.
How does ash damage a DPF?
If the ash is not periodically removed from the DPF it will become hardened in the filter and hard to remove. Because ash is cooler than the other material in the DPF it can cause the brittle substrate in the DPF to crack. Once the ceramic in a DPF begins to crack, it will crumble, break up and blow out the exhaust stack. The expensive DPF can quickly become no longer serviceable and must be replaced.
How Do You Clean a DPF?
When DPFs first became common it was standard practice to simply blow them out with compressed air. Later, people used sand blast machines and thermal cleaning ovens to bake them clean. As the population of DPFs has increased manufacturers such as OTC Tools have developed dedicated cleaning systems. These systems are superior because the soot is not blown all over the shop floor and the oven cleaning temperatures are controlled to avoid damaging an expensive DPF.