Emission Systems Explained

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EMISSION SYSTEMS EXPLAINED

Emission Systems Australia
Emissions Control System
Nitrous Oxides
Carbon Monoxide
Carbon Dioxide
Diesel Particulate Matter
Exhaust Gas Recirculation (EGR)
Selective Catalytic Reduction (SCR)
Diesel Exhaust Fluid (DEF)
Diesel Oxidation Catalyst (DOC)
Diesel Particulate Filter (DPF)
Driving Range Between Refills Of A Vehicle’s DEF Tank
Maintenance Of DEF Levels
Purchasing DEF
Filling DEF
Storing DEF
Electronic On-board Warning System
Adding DEF To A Low Or Empty Tank
Maintaining DEF Quality
Warranty Concerns
Emissions Control System

Both the 6.6L Duramax diesel and 6.7L Power Stroke diesel engines meet all Federally mandated emissions regulations using a complex network of emission control devices, including:

  • A diesel particulate filter (DPF)
  • A diesel oxidation catalyst (DOC)
  • An exhaust gas recirculation system (EGR)
  • Various sensors to monitor and manage the emission control system
  • A selective catalytic reduction process (SCR)

The SCR system works by using diesel exhaust fluid (DEF), which is a urea-based solution used to reduce NOx emissions via a reduction reaction.

Nitrous Oxides

Unlike the nitrous oxide (N2O) commonly known as laughing gas, nitrous oxides (NOx) are the compounds of nitric acid and nitrogen dioxide that play a part in the development of smog and acid rain.

They are produced when combustion happens in the presence of nitrogen—like what happens when fuel combusts in a diesel engine and comes into contact with the naturally occurring nitrogen in the air.

Aside from causing pollution, these compounds are also known to worsen medical conditions such as bronchitis and asthma. 

Carbon Monoxide

This compound is a highly toxic colourless and odourless gas produced during combustion.

Carbon Dioxide

Formed when various hydrocarbon compounds—such as those that petroleum-based fuels are made up of—combust, carbon dioxide is considered a greenhouse gas and believed to be one of the main contributors to global warming.

Diesel Particulate Matter

Commonly abbreviated to DPM, diesel particulate matter is the soot that comes from the combustion of diesel fuel. It is classified as carcinogenic by the World Health Organisation (WHO) and is known to cause other health issues such as difficulty breathing.

Exhaust Gas Recirculation (EGR)

This is a technique used to minimise NOx emissions in various forms of combustion engines. It works by recirculating part of the vehicle’s exhaust gases through the air intake and mixing it with the inbound air charge, resulting in significantly lower NOx emissions, thanks to:

  1. Minimised oxygen levels in the combustion chamber
  2. Reduced combustion temperatures

An EGR valve controls how much of the exhaust gases flow into the recirculation circuit based on parameters such as speed, manifold pressure, and load.

The exhaust gases are cooled by an EGR cooler using engine coolant before being recirculated.

Selective Catalytic Reduction (SCR)

Engineered to treat the vehicle’s exhaust post combustion, an SCR system uses DEF to minimise the amount of NOx released into the atmosphere.

The process is as follows:

  1. The system injects DEF into the exhaust while the vehicle’s engine is running
  2. The heat coming from the exhaust, in turn, turns the DEF into ammonia
  3. One the ammonia mixes with the other exhaust gases and reaches the SCR catalyst, it facilitates the breakdown of NOx emissions
  4. The DPF then catches the resulting particulate matter and incinerates it during each regeneration cycle
  5. Reduced emissions, along with water vapor and nitrogen, are released via the vehicle’s exhaust system
Diesel Exhaust Fluid (DEF)

A non-flammable fluid, DEF is made up of 67% purified water and 33% ammonia-based urea. It is used by diesel engine exhaust systems to cut emissions by converting NOx into water vapour and nitrogen.

Diesel Oxidation Catalyst (DOC)

Practically the diesel counterpart of the catalytic converter of a gasoline engine, a DOC converts residual carbon monoxide and hydrocarbons in exhaust gases into water vapour and carbon dioxide via an oxidation reaction.

Diesel Particulate Filter (DPF)

Designed to filter soot and other particulates from the vehicle’s exhaust stream, DPFs can capture as much as 100% of particulate emissions. They are what keep soot from building up on tailpipes of virtually all modern vehicles equipped with diesel engines.

The vehicle’s powertrain control module (PCM) is in charge of monitoring DPF loading. Every time the DPF becomes full, it is cleaned via a process called regeneration.

As long as this system works at peak capacity, there’s no need to remove and manually clean the vehicle’s DPF.

Driving Range Between Refills Of A Vehicle’s DEF Tank

In most cases, SCR systems use DEF at a rate between 1 and 1.25% of the total fuel usage of the vehicle. This means that one refill of DEF should provide about 8,000 kilometres of driving range.

Of course, this is just an estimate since, again, DEF usage is directly associated with fuel consumption. So, the actual values would ultimately depend on driving conditions.

Maintenance Of DEF Levels

An on-board electronic warning system should alert the driver whenever the vehicle’s DEF levels dip to about 1,000 km worth of driving range, and then a couple more times between 300 and 0 km.

If the DEF tank is left empty, the maximum speed of the vehicle will first drop to 88 km/h and then to 6 km/h when it is next started as required by federal and state law.

Purchasing DEF

Also known as AdBlue, DEF is available at most truck servicing outlets, truck stops, and select auto parts shops in 10- or 20-litre containers.

Filling DEF

Ford’s F-series trucks all have their DEF filler points next to their fuel filler points. They’re easily identifiable by their blue filler cap.

GMC and Chevrolet trucks, on the other hand, have their DEF filler points under the bonnet behind the engine bay on the driver’s side. They also have blue caps.

In most cases, it’s not necessary for the driver to refill the vehicle’s DEF tank themselves. DEF refills are part of Performax Perth’s periodic maintenance services. But in the event that the fluid runs out before the next maintenance schedule, here are two tips to make the process easier:

  1. When refilling directly from a bottle, use a step and a long-neck funnel.
  2. Only use 10-litre containers because they’re easier to handle.
Storing DEF

As a general rule, it is best to store DEF out of direct sunlight because higher temperatures shorten its shelf life. See diagram below:

<temp-to-shelf-life diagram>

DEF that has exceeded its shelf life should be thrown away because it can cause issues in a vehicle’s emission system if used—which, in turn, could cause the vehicle to go into limp mode. 

Problems caused by contaminated, expired, or incorrect DEF are not covered by Performax International’s warranty. This is why it is best to do DEF refills in truck stops or auto stores that keep the fluid refrigerated. It also helps if these stores have a sizeable customer base of diesel truck drivers as well. These two things should ensure you are getting good quality product.

If you plan to not drive your car for an extended period of time, be sure to leave a small amount of DEF in it and do a refill once you decide to use it again.

Electronic On-board Warning System

This system is designed to take the guesswork out of maintaining correct DEF levels in a vehicle. It alerts the driver—via the driver information center (DIC)—whenever the vehicle’s DEF levels dip too low, the DEF quality in its tank is compromised, or there are other related concerns.

Check your owner’s manual for a more detailed description of your vehicle’s electronic on-board warning system.

Adding DEF To A Low Or Empty Tank

To prevent a vehicle’s on-board speed limiter from kicking in, there should always be at least four litres of DEF in its tank. The recommended refill amount, though, is about 13 litres.

Refills reset the vehicle’s system and eliminates the need for a service visit. But keep in mind that it could take at least half a minute for the DEF level warning to go away after a successful refill.

Maintaining DEF Quality

Again, poor-quality or contaminated DEF can negatively impact the vehicle’s performance. So, it is important to prevent any from getting into the tank.

In the event that they do, however, the vehicle’s electronic on-board warning system will alert the driver so they can make the necessary adjustments.

If the poor-quality or contaminated DEF is not changed within 300 kilometres, the vehicle’s on-board speed limiter will kick in, reducing its maximum speed to 88 km/h the next time it is started. If the fluid is still not replaced, the vehicle’s maximum speed will drop to 6 km/h.

Warranty Concerns

Problems caused by poor-quality or contaminated DEF are not covered by warranty. In addition, tampering, modification, and/or removal of components from the vehicle’s exhaust system—particularly in the section between the engine and DPF—not only voids the vehicle’s warranty, but is also subject to substantial government fines.

Understanding The Regeneration Process

Also known as “regen” or “burn”, regeneration refers to the process where particulate matter collected in the DPF is incinerated as the vehicle’s exhaust gas is heated to around 950° to 1050° F.

It works because diesel soot is made up of hydrocarbons that are only partially combusted, making it possible for them to be incinerated some more before the resulting exhaust gases go out of the vehicle’s tailpipe.

There are three types of regeneration:

  1. Passive
  2. Active
  3. Manual
Passive Regeneration
Active Regeneration
Manual Regeneration
Passive Regeneration

As the name suggests, passive regeneration happens without any input from the driver or the vehicle’s engine control unit (ECU). It occurs automatically whenever the temperature of the vehicle’s exhaust gases go high enough to incinerate particulates in the DPF.

This typically happens when the vehicle is required to work hard while running at a constant speed (like when you’re towing a boat on a highway), provided there is not enough incidence of active regeneration to completely clear out the DPF.

Too much passive regeneration, though, can reduce the occurence of active regeneration. But that shouldn’t be a problem since they both accomplish the same thing.

Active Regeneration

Unlike passive regeneration, active regeneration is initiated by the vehicle’s ECU. It triggers the process by introducing fuel into the exhaust stream to cause it to combust and raise the temperature of the exhaust gases. This, in turn, facilitates the incineration and clearing out of the particulates collected in the DPF.

The initialisation of active regeneration cycles depend on driving conditions. Stop-and-go driving and extended periods of idling would cause it to go off more often, while constant speeds would cause it to occur less frequently.

Of course, since active regeneration uses fuel, it can negatively impact a vehicle’s fuel economy.

Manual Regeneration

Also known as static regeneration, this process is initiated by a technician using the vehicle’s built-in diagnostic system. It is usually done to fix an issue with active regeneration that keeps it from firing off when needed.

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