There are four core components to Ford’s Power Stroke, GM’s Duramax, and RAM’s Cummins diesel engine aftertreatment systems; namely the Exhaust Gas Recirculation (EGR), the Diesel Oxidation Catalyst (DOC), the Diesel Particulate Filter (DPF), and the Selective Catalytic Reduction (SCR). The diesel engines in Ford, GMC, Chevrolet, and RAM pickups, all utilize these four components.
EGR (EXHAUST GAS RECIRCULATION)
The ERG is an emission control technology that reduces NOx emissions from diesel engines.
How it works:
The EGR lowers the cylinder temperatures during the combustion process and thereby lowers the amount of NOx created. The EGR removes a portion of the oxygen and replaces it with inert gases which lower the cylinder temperatures. An EGR cooler lowers exhaust temperature before it flows back into the intake manifold.
DIESEL OXIDATION CATALYST (DOC)
The purpose in the design of the DOC is the conversion of carbon monoxide and hydrocarbons into carbon dioxide and water. The DOC breaks down the diesel engine’s exhaust pollutants in the exhaust system, thereby reducing particulate matter.
How it works:
The exhaust passes through the DOC with minimal restriction. As a method of preparing the exhaust for treatment in the Diesel Particulate Filter, the aftertreatment system executes a hydrocarbon dosing system where fuel is dosed at a specific temperature. The fuel is thereby converted into a vapor and the vapor initiates a chemical reaction which produces heat. The truck’s control module regulates this heat, maintaining it at a certain temperature that is optimal for the DPF.
DIESEL PARTICULATE FILTER (DPF)
The DPF is an exhaust device that traps particulate matter, commonly known as soot or ash.
How it works:
Different from the flow-through design of the DOC, the DPF’s design is that of a wall-flow. The exhaust flows into, rather than through, the DPF where it is collected on the walls of the filter in the form of soot, and eventually as ash. The two purposes of the DPF are to catch soot and store ash.
SELECTIVE CATALYST REDUCTION (SCR)
The SCR is the emissions control system that injects Diesel Exhaust Fluid (DEF), a liquid reducing agent, through a special catalyst into the exhaust stream of the diesel engine.
How it works:
The SCR further reduces NOx, and it is capable of reducing NOx at the tailpipe outlet to nearly zero NOx emissions. The SCR is a flow-through technology a lot like the DOC. The SCR injects diesel exhaust fluid which is 67.5% water and 32.5% urea. The water will evaporate, and when it does the remaining urea converts to ammonia and the ammonia reacts with the NOx, converting it into nitrogen and water.
Regularly Scheduled Maintenance Is Vital To Optimal Aftertreatment System Performance
These four core components which, comprise the diesel engine aftertreatment system, work in tandem to substantially reduce NOx emissions.
A common mistake which diesel pickup owners make is failing to service the aftertreatment system as regularly as it needs it. DPFs require regular cleaning, and the rest of the system requires regular inspections. Upstream leaks in the system can often times be the cause of downstream failures. The technicians at Cummins Automotive & Diesel Service can diagnose your diesel truck’s aftertreatment problems and perform the correct repair by looking at all four of the core components which make up the aftertreatment system, rather than potentially missing the full scope of the system’s status by assuming, at the outset, that the fault is with just one of the components.
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