DIESEL EMISSIONS


Diesel Engine Regeneration Types and Failures


THE DIESEL ENGINE HAS SEEN MANY CHANGES over the last 20+ years. One of the most significant changes was to the diesel emissions system in 2007 which was necessary to meet new Environmental Protection Agency mandates for diesel exhaust. When the EPA mandated these new lower levels of pollutants in the exhaust, engine manufacturers had to develop emissions systems that would meet the new criteria. Previous advancements in turbos, charge air cooling, common rail fuel injection and Exhaust gas recirculation helped to pave the way in creating more efficient cleaner operating diesel engines.


Today, a large portion of the class 6, 7 and 8 trucks on the road have a diesel exhaust filtering system that captures the majority of particulate matter and dangerous nitrogen oxides (NOx). In the last issue of The Cooling Journal, we published an article detailing how certain components of a diesel engine can affect the exhaust and eventually impact the filters that are designed to filter the emissions produced by a diesel engine. A significant contributor to extending the diesel particulate filter’s life is the regeneration a diesel engine produces to help clean the Diesel Oxidation Catalyst (DOC) and the Diesel Particulate Filter (DPF).


When I was a young man, we had exhaust systems on our cars that consisted of two hooker headers and two cherry bomb mufflers with some steel tubing plumbed out the sides of the car. Fuel loaded, filthy exhaust produced by a 650 double pumper Holley carb dumping raw fuel into the engine, which half of it came out the exhaust barely burnt. The cars were almost as bad as the old trucks going down the road billowing black smoke out of the dual chrome exhaust pipes on either side of the cab. Those days are long gone, auto and diesel exhaust today is almost as clean as the air we breathe.


Different Types


There are three types of regeneration that any DPF service and sales personnel should be aware of:


• Passive regeneration • Active regeneration • Manual regeneration


By: Mark Taylor


NARSA/IDEA Executive Director mtaylor@narsa.org


Any regeneration is performed by a process created by the diesel engine and engine controls. The ways in which they can occur are different.


Passive regeneration is achieved when a diesel engine produces an exhaust temperature of 350 degrees Celsius or 662 degrees Fahrenheit. Just by the exhaust reaching, this temperature soot trapped in the diesel particulate filter will be burned off. A problem can occur in vehicles who operate at a lower temperature for extended periods of time due to operating conditions or a component malfunction.


Active regeneration occurs when the DPF becomes loaded with soot. Pressure differential sensors located before and after the DPF are responsible for detecting this condition and alert the engine ECU the filter is filling up with soot and needs to be cleaned. The ECU sends a command to the HC (hydrocarbon) dosing valve located before the DOC and DPF. The HC Dosing valve opens allowing diesel fuel to enter the exhaust stream and elevate the temperature of the exhaust to facilitate the burning of the soot collected in the DPF. The Active Regeneration process happens automatically as the vehicle is in operation. There may be a light on the dash that will alert the driver this process is underway.


Manual regeneration is initiated by the operator of the vehicle and only occurs when the vehicle is stationary. The check engine light, MIL, or light similar to a check engine light will illuminate notifying the driver a regeneration needs to be initiated. The vehicle’s operator must set the parking brake and activate the regeneration switch. This manual regeneration process is very similar to Active regeneration as diesel fuel is injected into the exhaust pipe before the DOC and DPF. The only differences between Active and Manual is operator initiated and the vehicle is stationary.


Now that the different types of on vehicle DPF regenerations have been explained, let’s find out what conditions could affect the regeneration process. If regeneration does not occur for whatever reason, the diesel particulate filter will fill up with soot which will cause the engine to derate and or completely shut down. Either way, this is not an ideal situation and will need immediate attention to remedy the problem. It is imperative vehicle operators pay attention to the instrument cluster and any MILs that light up.


22 | THE COOLING JOURNAL | January/February 2022


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