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techdirections - March 2017

Diesel Exhaust Aftertreatment Maintenance

Curt Ward 2017-03-04 00:55:45

The modern diesel vehicle is very different from its predecessors. One of the major differences is in the exhaust system. This is as of a result of the changes to the tailpipe emission rules that were phased in during 2007-2012. The reduction in the allowed level of particulate matter and oxides of nitrogen (NOx) emissions has resulted in changes to the exhaust aftertreatment system. Did you know that the proper maintenance of the vehicle will help ensure the aftertreatment system operates as designed? Much like a gasoline engine-equipped vehicle, the various components of the diesel exhaust aftertreatment system are designed to reduce the level of hydrocarbons, carbon monoxide, and oxides of nitrogen. Additionally, it is designed to reduce the level of particulate matter. In order for the exhaust system to operate as designed, it is imperative that vehicle maintenance be performed according to the manufacturers’ recommendations. In this article we are going to focus on the following customer maintenance items: Diesel fuel Bio-diesel Motor oil Diesel exhaust fluid Diesel engine maintenance habits Customer driving habits The use of quality diesel fuel is critical to the longevity of the diesel particulate filter (DPF). Poor fuel quality will result in a larger volume of diesel particulate matter, which will shorten service intervals of the DPF. One of the critical measures of the fuel is the cetane level. The higher the cetane level, the lower the point of auto-ignition and the more complete combustion of the air fuel mixture. The more complete the combustion, the smaller the volume of particulate in the exhaust stream. The cetane level in the local fuel was measured by a local laboratory and found it to be 39, which is well below the desired level of 41-43. To improve the cetane number, the fuel was conditioned with a cetane booster. Subsequent testing of the fuel found the cetane level improved to 41. The result was increased combustion efficiency and a 2 mpg increase in fuel economy, as well as a smaller volume of particulate matter. What about bio-diesel, can I use it in my vehicle? The stock answer is to check the manufacturer specific information. For example, a 2012 Ford F250 pickup truck with a 6.7 liter PowerStroke engine is OK to run up to a blend of 20% bio-diesel without any modifications to the truck. A 2012 Volkswagen TDI, by comparison, does not recommend the use of any bio-diesel fuel. The exhaust aftertreatment system will not suffer any ill effects as long as the blend of bio-diesel is within the manufacturers recommendations. The use of the proper diesel motor oil is critical to the longevity of the exhaust aftertreatment. Modern diesel engines require engine oil that meets the CJ-4 SAE specifications. This is low ash motor oil that has been in use since late 2006. The use of this oil meets all the current lubrication requirements and does not have a negative effect on the diesel particulate filter. Note that in late 2016 the CJ-4 oil specification was replaced by the CK-4 oil specification as the industry meets the requirements of the 2017 and beyond engines. It should also be noted that the CK-4 oil will be backwards compatible. The use of engine oil other than what is recommended by the manufacturer may result in an increased level of particulate in the exhaust stream. Diesel exhaust fluid (DEF) is required in vehicles equipped with a selective catalyst reduction system. Not all diesel vehicles are equipped with this system. The catalyst, in conjunction with the DEF, reduces the level of NOx in the exhaust stream. It is important to monitor the level of the diesel exhaust fluid and refill the reservoir when it gets low. Most vehicles are designed to hold enough DEF that it can be refilled at the time of a normal oil service without risk of running out. The vehicles are designed with a series of warning lights to alert the driver when the system gets low. If the system is allowed to run empty or a fluid other than DEF is used to refill the reservoir, the vehicle may default to a depowered mode of operation. When refilling the DEF system, make sure to use quality fluid that has been stored properly. Regular diesel engine maintenance is critical to the operation of the exhaust aftertreatment system. This would include replacing the diesel fuel filters, air filter, and servicing the cooling system with quality replacement parts as required by the manufacturer. Failure to follow these recommendations may result in premature wear in the engine or the high pressure fuel system. Unwanted oil, coolant, or diesel fuel in the aftertreatment system are leading causes of exhaust system component failures. Customer driving habits will have a significant effect on the diesel exhaust aftertreatment system performance. The modern diesel engine is designed to driven under a load. Short trip driving, or long stretches of idle time, will diminish the effectiveness of the exhaust aftertreatment system. These maintenance items are not difficult to perform, however, they may differ from a similar vehicle equipped with a gasoline engine. By following the manufacturers’ service recommendations, the exhaust aftertreatment system will operate as designed and will provide miles of trouble-free service. Curt Ward is an automotive professor, Joliet (IL)Junior College and serves as a visiting automotive instructor, Southern Illinois University, Carbondale. He holds five ASE certifications. Reprinted from NACAT News, Fall 2016.

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