Black Smoke: Cause, Impact, and Prevention

Black Smoke: Cause, Impact, and Prevention

Oct 22, 2013

We have all seen clouds of black smoke emanating from the exhaust stacks of heavy duty diesel trucks especially when the truck is under high load or hard acceleration. The black smoke is composed primarily of elemental carbon from incomplete combustion of diesel fuel and traces of engine lubricant. The exhaust of a typical diesel engine contains elemental carbon (soot), semi-volatile organic hydrocarbons, sulfates (primarily sulfuric acid), and water vapor. Elemental carbon which is black is formed for a wide range of reasons when the diesel fuel charge in the combustion cylinder is incompletely combusted. Incomplete combustion occurs and soot is formed when there is an overabundance of fuel (both diesel fuel and lube oil), insufficient residence time in the combustion zone, and/or non-availability of sufficient oxidants.

Over-fueling is the primary cause of black smoke from the exhaust of a heavy duty diesel engine. Over-fueling can be caused by diesel fuel injector wear that enlarges the nozzle hole or erodes the injector needle and allows excess fuel to flow into the combustion chamber. In many cases the nozzle and needle wear is due to corrosion from contaminated or high sulfur diesel fuel. Diesel engines are not designed to efficiently burn excess fuel so much of the fuel is wasted and exits the engine only partially combusted. Nozzle and needle wear can increase particulate emissions (PM) by as much as 85%.

Dirty air-filters that do not allow sufficient air (oxidant) into the combustion chamber for complete combustion of the fuel charge contribute to black smoke. It is estimated that dirty air cleaners can increase PM by 40 to 50%.

Excessive oil consumption due to worn valves and valve stem seals, worn or stuck/sluggish rings from deposits, and worn cylinder liners contribute to black smoke. Engine wear and deposits can result from using the wrong oil for the application, excessive oil drain intervals, contaminated oil, and failing to maintain the proper oil levels in the engine. Performing regular maintenance with the recommended engine lubricant can minimize wear and deposits. Excessive oil consumption can increase PM by up to 85%.

Regular maintenance and the use of the right oil for the application can prevent premature engine wear and deposits that contribute to black smoke. Fuel injector nozzles may need to be cleaned or replaced. Air cleaners may need to be checked and cleaned or replaced as necessary. Regular preventive maintenance such as consistent oil changes and top-ups and using the recommended oil can prevent excessive valve train, ring, and cylinder wear. Using high performance diesel engine oils can control engine deposits that can cause stuck and sluggish rings. High performance diesel engine oils of the proper volatility can help control excessive oil consumption from volatility.

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