LML Duramax Emissions

Related Topics:

6.6L Duramax LB7

6.6L Durmax LBZ

6.6L Duramax LLY

6.6L Duramax LMM

6.6L Duramax LML















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6.6L Duramax LML Emissions System



6.6L Duramax LML emissions system diagram



HCI - Hydrocarbon Injector

The HCI is located in the turbocharger downpipe. It is simply a fuel injector, used to inject diesel fuel into the exhaust stream during active regeneration (cleaning of the diesel particulate filter). This active regeneration strategy is unique to the LML, as the previous LMM allowed fuel to be injected into the cylinder during the exhaust stroke instead of utilizing a seperate injector. However, GM found that cylinder washing was a problem, as the fuel injected during the exhaust stroke would "wash" the oil from the cylinder. By injecting fuel directly into the exhaust stream, cylinder washing is not a concern.


DOC - Diesel Oxidation Catalyst

The diesel oxidation catalyst, or DOC, converts hydrocarbons and carbon monoxide into water and carbon dioxide through an oxidization reaction. For all intents and purposes, the DOC is the diesel equivalent of a gasoline engine's catalytic converter.


DEF Injector

DEF (diesel exhaust fluid) is injected downstream of the DOC. DEF is composed of 32.5% urea, its active ingredient, distilled water, and a very small amount of additives. Because of its urea content, some people call the process "urea injection". DEF is required for the selective catalytic reduction process to occur. The heat of the exhaust converts the DEF into carbon dioxide and ammonia.


SCR - Selective Catalytic Reduction

Once DEF is added to the exhaust, it travels through the SCR catalyst. Here, nitrous oxides (NOx) are converted to nitrogen gas (N2) and water (H2O) by means of a reduction reaction. Reducing NOx emissions is the purpose of the SCR system.


DPF - Diesel Particulate Filter

Once the exhaust stream has been treated by the DOC and SCR, it travels through the diesel particulate filter, where particulate matter (soot) is trapped and stored. The DPF is cleaned through a process known as regeneration, which is divided into two strategies. Passive regeneration occurs at anytime the vehicle is being operated and the exhaust gas temperature is high enough to burn the particulate matter trapped by the filter. It is a naturally occuring process, meaning that it occurs whenever the conditions are met under normal operation. Active regeneration occurs when the engine senses that the DPF needs to be cleaned as it is approaching maximum capacity. When active regeneration occurs, fuel is injected into the exhaust stream via the HCI to increase the exhaust gas temperature so that the particulate matter can be burned off. Active regeneration dramatically reduces fuel economy since fuel is being used for purposes other than moving the vehicle. The exhaust system features a specifically designed air cooled exhaust tip to reduce the heat of the exhaust gases as they are expelled.


EGR - Exhaust Gas Recirculation

Exhaust gas recirculation is used to reduce NOx emissions. Since nitrous oxides form in oxygen rich, high temperature environments, introducing exhaust gases back into the intake air charge reduces the amount of these harmful compounds that form. Exhaust gas recirculation is not a new technology and has been regularly used on diesel engines for many years. (Note - the EGR system is integrated into the engine, not the exhaust system).