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Old 04-22-2018, 01:20 PM   #1
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Pet Peeve: Diesel Emissions Terminology

Why do most people refer to modern diesel emission systems as DEF system? DEF is just one component of a diesel's emission system and I personally think the most reliable and trouble free component as compared to the diesel particulate filter (DPF).

Typical diesel emission components:

EGR (exhaust gas recirculation): Exhaust gas is bypassed and re-routed into the intake and usually cooled first in an air to air or air to liquid cooler to bring intake temps down. Having exhaust gas which is high in inert gas reduces nitrogen oxide emissions. DRAWBACK: This exhaust contains carbon particulates (diesel exhaust soot) which acts as an abrasive, ends up in oil, clogs intake manifold assemblies, and is just bad for an engine. Modern diesels with SCR now have lower EGR duty cycles which is a good thing.

Diesel Oxidation Catalyst (DOC) The diesel oxidation catalyst, or DOC, is essentially the diesel equivalent of a gasoline engine's catalytic converter. As exhaust gases flow through the catalyst, residual hydrocarbons and carbon monoxide gas is converted into carbon dioxide gas and water vapor by means of an oxidation reaction.

Diesel Particulate Filter (DPF) The diesel particulate filter, or DPF, filters particulate matter (soot) from the exhaust stream. Diesel particulate filters can capture up to 100% or particulate emissions, and are responsible for the absence of dingy black buildup on the tailpipes of modern diesel engines .The engine's computer system constantly monitors DPF loading, or the quantity of particulates captured in the filter. When the DPF is "full", the the filter is cleaned by a process known as regeneration. Under ideal conditions, removal of the DPF for manual cleaning should never be required.

Regeneration Process (Regen, Reburn) Regeneration is the process in which accumulated particulate matter is burned off in the DPF. Since diesel soot is comprised of partially combusted hydrocarbons they can be further combusted, at which point the resulting gases are expelled through the tailpipe and into the atmosphere. In order for regeneration to occur, the exhaust gas temperature must be increased to the point that particulates in the filter combust. This temperature is typically between 950° and 1050° F. The three regeneration strategies are passive, active, and manual. By nature of the process, regeneration may also be referred to as "reburn", or just simply "regen".

Passive regeneration is the naturally occurring regen strategy, requiring input from neither the driver nor engine control module. Passive regeneration occurs when operating conditions, most notably exhaust gas temperature, reach or exceed the minimum range in which regeneration can occur. Passive regen often occurs under relatively high loads at constant speed; long periods of highway driving while towing, for example. Passive regeneration rarely occurs with adequate incidence to completely unload a DPF, although it may reduce the frequency of initiated active regeneration cycles.

Active regeneration is the process by which the control module initiates a regeneration cycle. During this period, fuel is introduced into the exhaust stream where it combusts, raising exhaust gas temperatures such that the burning of particulate matter in the filter is facilitated. Most, but not all engines, use a post-injection technique to introduce fuel into the exhaust stream. This strategy injects diesel fuel late during the exhaust stroke where it is expelled with the outgoing exhaust gases. This method is somewhat controversial in contrast to the "9th injector" technique, as it contributes to cylinder washing and fuel dilution of the engine oil. The frequency in which active regen is initialed will depend on driving patterns - lengthy periods of idling and stop-and-go driving will require more frequent cleaning, while consistent highway driving will reduce DPF loading and negate the need for frequent active regeneration cycles. By nature of injecting raw diesel fuel into the exhaust stream instead of combusting it for means of propulsion, the active regeneration process significantly impacts fuel economy.

Manual or static regeneration is a regen strategy that can be initiated by a technician through the vehicle's on-board diagnostic system. Some vehicles allow a manual stationary regeneration.

Selective Catalytic Reduction (SCR) The selective catalytic reduction (SCR) process employs the use of a diesel exhaust fluid (DEF) in order to convert NOx emissions into harmless nitrogen gas and water vapor through a reduction reaction. The system is highly efficient and the use of SCR systems on DPF equipped vehicles greatly reduces active regeneration frequency and therefore positively impacts fuel economy. DEF is a solution comprised of urea (~32%), distilled water, and additives which increase its shelf life. It is highly corrosive and spills should be immediately cleaned from paint.

DEF is constantly injected into the exhaust stream through the dosing nozzle located at the front of the SCR device. There, the DEF is mixed with the exhaust stream by means of a spiral mixer. The homogeneous mixture then flows through the catalyst itself, there the reduction reaction occurs.

It is necessary to maintain the DEF fluid level and quality, i.e. you cannot put anything but DEF in the tank. The system is smart and will recognize, for example, if pure water were to be used in place of DEF. If the DEF level is depleted, speed will be limited, and eventually the engine will enter "idle-only" mode. Normal operation will resume once the DEF tank has been refilled. These penalties are required by the United States Environmental Protection Agency (EPA) and are standard operating procedures for all SCR equipped pickups regardless of make.

Thanks for reading and please quit calling the emissions system DEF as DEF is only one of main components. Most folks have problems with their DPF not DEF system though Ford seems to have problems with their DEF pumps and DEF heaters failing prematurely.

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Old 04-23-2018, 08:10 AM   #2
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Never hurts to be educated about the equipment we use!


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Old 04-23-2018, 08:16 AM   #3
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Fortunately for me, I've sold my DEF diesel, oops-diesel engine, so I will never utter those letters again!
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Old 04-23-2018, 09:27 AM   #4
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Pet Peeve: Diesel Emissions Terminology

While not an engineer, most refer to the system as DEF because that’s all, they hear and it’s the fluid they have to buy. I could care less what they call the system because I know what they are referring to.
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Old 04-23-2018, 09:32 AM   #5
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I like the DEF system in my diesel truck. If that’s all I need to do to eliminate the black smoke, smell and emissions, I think it’s worth it.
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Old 04-23-2018, 09:49 AM   #6
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Dpf. Junk. Why do you think it's the first thing people remove from there new trucks?
It's useless piece of government over reach.
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Old 04-23-2018, 10:08 AM   #7
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Glad my 2006 duramax doesn't have all that
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Old 04-23-2018, 10:09 AM   #8
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Originally Posted by vmax View Post
Dpf. Junk. Why do you think it's the first thing people remove from there new trucks?
It's useless piece of government over reach.
Without the DPF there would be no new diesels on the road. Overreach? I used to think they were overkill, but I'm a fan of this rock we're on and will live with the DPF in order to have my diesel and help reduce pollution.

Just a quick note on the DPF, they do have a finite life. Regen doesn't remove any of the soot-turned-to-ash from the DPF and over time it will reach a point where it will need to be replaced because it is full. This is where some people will try to clean it out themselves or do the deletes rather than pay for a new DPF, which will run at least $1500 or so for an aftermarket one.
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Old 04-23-2018, 10:18 AM   #9
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DEF or DPF systems are an environmentalist lie.

What is better, Saving 10% in fuel emissions with it or a 60% increase in mileage without it?

I have a grand Cherokee diesel that gets very good mileage at 25mpg but another person who has removed his gets 42mpg.

It's not a just an internet claim as I have actually been with him when he drove over 200 miles. Same vehicle and same year as mine.

When he filled up it showed 996 mile range compared to my 600.

I am planning on removing mine soon.
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Old 04-23-2018, 10:23 AM   #10
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You clearly don’t understand how these systems reduce emissions/pollution so it makes sense that you would call them a lie.

Fuel economy doesn’t correlate directly to emissions. Please take the time to learn about the pollutants that these emissions systems reduce. Doesn’t matter that you get better fuel economy without them, you end up emitting far more pollutants without them as well regardless of how much better your fuel economy is.

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