Emission Control Systems in Diesel Engines

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Click for the Glossary of Terms relevant to Emission Control Systems

Scania Urea System

The Scania Urea System The image shows Scania's Urea system.
This system was OK upto and including Euro IIIB emission control regulations - I'm sure it now serves as the base for later standards when a particulate filter was added.

The basis of this SCR system is to convert
NOx (nitrogen oxides) and NH₃
(ammonia produced by the urea catalyst) into N (Nitrogen) and H₂O (water vapour)

AdBlue System

Selective Catalytic Reduction (SCR) technology by AdBlue

Used, interalia, by Detroit Diesel, Mercedes and MTU

Components of the AdBlue SCR system are:
SCR catalyst
AdBlue Fluid injection unit
AdBlue tank
AdBlue injection control unit

Cummins Catalytic converters

Particulate Filter - Removes PM and is the first element in an SCR system.

There are two stages in a particulate filter, stage one is a diesel oxidation catalyst,
and stage two is the filter to trap carbon particles.

In stage one Nitric Oxide (NO) is converted into Nitrogen Dioxide (NO₂) by the catalyst
Then the (NO₂) flows to stage 2, where the carbon particles react with it to
to form Carbon Dioxide (CO₂).

Elements in a catalytic system:
the exhaust gasses will pass through the following elements before exiting to the air:

Particulate Filter
- Nitric Oxide is converted into Nitrogen Dioxide by the catalyst
- Then the (NO₂) flows to stage 2 of the particulate filter, where the carbon particles react with it to form Carbon Dioxide (CO₂)
Decomposition Reactor
Changes nitric oxide into ammonia
SCR Catalyst Unit
Changes ammonia into water and nitrogen

Detroit Diesel DD13 engine achieved Zero N₂o emissions

Oshkosh Choose Detroit Diesel
For their fire and rescue vehicles

The DD13 engine has selective catalytic reduction (SCR) technology, with this technology Detroit Diesel has effectively achieved Zero N₂O emissions. (N₂O - Nitrous Oxide - is that smog producing, climate warming emission, hated worldwide.) At the same time the DD13 has reduced fuel consumption by power used - when compared to competitor's engines.

.We want to provide fire departments the option of achieving the most stringent emissions targets while maximizing engine performance and reducing fuel consumption,. said Wilson Jones, Oshkosh Corporation executive vice president and Fire & Emergency president. (quote from Oshkosh.Com's site)

Glossary - related to Emission Control and Fuel Systems

ACERT - Advanced Combustion and Emissions Reduction Technology

AdBlue - trade name of a DEF - It is a reagent that changes NO_x into ammonia (NH₃) and carbon dioxide (CO₂)
when heated by exhaust gasses in the process of combustion.
AdBlue is a registered trade name and is now available at thousands of fuel service
stations worldwide.
New computer controlled engines are programmed to stall if the AdBlue component
is short or if it's delivery system fails, thus forcing owners and operators to
stay within the emission control laws.

CRDI - Common Rail Direct Injection

Decomposition Reactor - The second element in an SCR system.
Carbon Dioxide and other exhaust gasses(CO₂) from the Particulate Filter pass into this reactor
which is laced with DEF

DEF - Diesel Exhaust Fluid, AdBlue - is the trade name of a DEF.
It is a reagent that changes (NO₂) into ammonia (NH₃) and carbon dioxide (CO₂)
when heated by exhaust gasses in the process of combustion.

EGR - Exhaust Gas Recycling
Emission control by recycling a portion of the exhaust gasses back to the engine intake. It lowers oxide emissions by starving the engine of unnecessary oxygen.
EGR works with ignition and is contrasted to SCR which cleans post ignition.
The logical future of emission control technologies is to combine EGR technology with SCR technology in the same engine. Detroit Diesel does this with their DD series engines.

EPA - United States Environmental Protection Agency

HPDI - High Pressure Direct Injectors

HPI-TP - High Pressure Injection - Time Pressure

NO_x or NOx - A generic term for all the nitrogen oxides
emitted in the process of combustion. If allowed into the atmosphere NO_x reacts with other
air pollutants from the process of combustion and from other sources, like factories
and indeed by sweet nature herself, to form acid rain and smog.

Particulate Filter - Removes PM and is the first element in an SCR system.
There are two stages in a particulate filter, stage one is a diesel oxidation catalyst,
and stage two is the filter to trap carbon particles.

In stage one Nitric Oxide (NO) is converted into Nitrogen Dioxide (NO₂) by the catalyst
Then the (NO₂) flows to stage 2, where the carbon particles react with it to
to form Carbon Dioxide (CO₂).

PM - Particulate Matter
Fine particles emitted after combustion that include hydrocarbons, gases, acids and unburned
fuel. In the atmosphere they become suspended and mix with dust and other pollutants.
They are considered carcinogenic, especially particles smaller than 2.5 microns that
appear as a haze, fine mist or smoke.

SCR Catalyst - The third element in an SCR system.
The SCR Catalyst - Changes remaining NOx and NH₃ (ammonia) into N (Nitrogen) and H₂O (water vapour)

SCR - Selective Catalytic Reduction technology.
"SCR" is the name of a post-combustion technology treatment for diesel vehicles,
that allows them to reduce emissions of PM particulate matter
and NOx (nitrogen oxides).
There are various manufacturers of SCR technologies who employ a DEF (Diesel Exhaust Fluid) as part of their system.

Urea - Really just another term for a DEF Diesel Exhaust Fluid.