Three Filters Needed to Reduce Emissions for Your Fleet


How DOC, DPF and SCR Filters Help Diesel Engines Perform

Emission standards have led to the need for technology that reduces emissions in large engines. Equally important is the need for these standards to be met while maintaining the power and performance of diesel engines. In order to accomplish this, more than one filter is required. To be more specific, three filters are required.

So, what are the differences between Diesel Oxidation Catalysts (DOC), Diesel Particulate Filters (DPF) and Selective Catalytic Reduction (SCR) catalysts? The most significant difference between these filters is each one’s purpose in the removal of particulates and harmful gases.

The DOC is the first filter in the diesel exhaust after-treatment system and is a flow through filter containing precious metals that begin to oxidate hydrocarbons, carbon monoxide and unburned fuel and oil. It, like the DPF, is a honeycomb ceramic filter. The DOC differs from the DPF in that the DPF is a wall-flow filter that traps remaining soot that the DOC could not oxidize. The soot remains in the DPF until is regenerated either through passive or active regeneration.

Back pressure will return to normal when soot is gone. Ash, however, doesn’t burn or oxidize and will remain until removed. Ash consists of metals, minerals and other trace elements from the breakdown of additives, lubricants and engine wear. While ash will build at a much slower rate than soot, it will cause major problems—increased back pressure, fuel consumption and DPF failure-if ignored. It also will increase the number of active regenerations. This can lead to extremely high temperatures and poor fuel economy. Plus, constant back pressure can negatively impact the turbo charger. Finally, the longer that ash is left in the DPF, the more likely it is to harden and close off part of the filter. Shorter intervals between regenerations is an indication that ash build up is occurring and that the DPF should be cleaned.

The final component in the after-treatment system is the flow through SCR catalyst. The SCR introduces diesel emissions fluid. This fluid contributes to the further break down of nitrogen oxides that pass through to the SCR filter.

All of these filters are in different locations, but each can become congested. Blockages in any of the systems can cause significant and costly issues including damage to the exhaust system and particulate matter entering the environment.

As a CrownSource customer, you have access to deep discounts on the parts you need – like DPFs, DOCs, and SCR filters –  to keep your fleet running smoothly. Login to our eProcurement Platform, CrownConnect, to see all our aftermarket parts that meet OEM specs. Not a customer? Schedule a demo now.

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