Return to Cummins Diesel Specs.
6.7L Cummins Emissions System
The 6.7L Cummins, introduced midway through the 2007 model year, was designed to meet strict emissions requirements for diesel engines, as outlined by the EPA. Sophisticated tuning and a complex system of components maintain acceptable levels of CO2, NOx, and new for 2007, particulate emissions. An advanced exhaust gas recirculation (EGR), diesel oxidation catalyst (DOC), and diesel particulate filter (DPF) completed the emissions system on 2007 to 2012 model year trucks. Selective catalytic reduction (SCR) became standard in 2013, when Ram/Cummins launched more powerful versions of the 6.7L Cummins (up to 385 horsepower and 850 lb-ft). The SCR system requires the use of diesel exhaust fluid (DEF), a urea based substance, to further cut nitrous oxide emissions (NOx).
Diesel Oxidation Catalyst (DOC)
Essentially a catalytic converter for diesels, the DOC is employed to carbon monoxide, hydrocarbons, and other harmful gases into water and carbon dioxide. Palladium and platinum are used as catalysts during the oxidation process.
Diesel Particulate Filter (DPF)
The DPF captures particulate matter (soot) from the exhaust stream via a honeycomb shaped element. It is said to reduce diesel particulate and unburned hydrocarbon emissions by up to 90 percent. Two regeneration modes clean the filter when it is "full"; passive and active regeneration. Passive regeneration occurs naturally anytime the exhaust gas temperature reaches the required threshold to burn the collected particulates from the filter. Since the conditions that allow for passive regeneration do not occur frequently, the engine relies on active regeneration to burn off particulates that have accumulated in the filter. Active regeneration relies on various sensors to tell the control module when the filter needs to be cleaned. During active regeneration, commonly referred to as "reburn" or "regen", the engine's idle is increased and diesel fuel is introduced into the exhaust stream to reach the required temperatures. Temperatures inside the DPF can exceed 1,000 degrees F when diesel fuel is burned in the exhaust. The disadvantages of this exhaust aftertreatment is that the DPF can clog (many 6.7L Cummins owners repeatedly have this issue) and fuel economy is greatly diminished.
Exhaust Gas Recirculation (EGR)
Exhaust gas recirculation, also known as EGR, is a technology that is not specifc to the diesel industry. EGR systems have been used for years in both diesel and gasoline powered vehicles. In a diesel, the primary function of the EGR system is to lower the amount of nitrous oxides (NOx) produced by the combustion of diesel fuel. A portion of the engines exhaust gas is recirculated into the engine and combusted again. This reduces the amount of oxygen introduced into the combustion chamber, as well as lowers peak combustion temperatures. NOx is primarily formed when nitrogen and oxygen are subjected to high temperatures, and the formation occurs much faster as temperatures rise.
Selective Catalytic Reduction (SCR)
Ford's Power Stroke and GM's Duramax diesels have been using selective catalytic reduction since 2010. Cummins new high output engines (350 hp for manual trans, 370 - 385 hp for automatic trans) launched during 2013 have SCR systems that require the use of diesel exhaust fluid. DEF is steadily injected into the exhaust stream where it mixes with exhaust gases before entering a catalyst that transforms harmful nitrous oxides into harmless water and nitrogen gas. The DEF level must be maintained or the engine will cease to function normally. While the SCR system seems like a hassle for owners, it actually improves fuel economy by reducing the frequency of DPF regenerations and allowing the engine to run leaner under light load. Ideally, a tank of DEF should last between oil change intervals, though towing and stop-and-go driving may require more frequent fill ups.