Diesel exhaust fluid AKA DEF

[topgut]

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Hi All,
I found a pretty good site that has info about how the BlueTech/SCR systems work. Its basic and does not go into TOO much detail.

It has basic info on how the SCR system works and I found it interesting since its rumored that the Mahindra trucks will use an SCR system to control NOx.

Read and learn...........John

Mansfield Oil Company : Local Service, Nationwide

[Joe Callimachus]

I've read about SCR on a couple of sites and there's one question that I still can't wrap my mind around.

It says on the Mansfield site that "SCR is expected to improve overall fuel economy by approximately 5%."

Can someone explain to me how something that occurs after the fuel is burned and has left the engine can improve MPG?

[ack]

Originally Posted by Joe Callimachus

I've read about SCR on a couple of sites and there's one question that I still can't wrap my mind around.

It says on the Mansfield site that "SCR is expected to improve overall fuel economy by approximately 5%."

Can someone explain to me how something that occurs after the fuel is burned and has left the engine can improve MPG?

I suspect that this savings is expressed in relational terms:

1. The mileage of the test vehicle not using any form of NOx treatment isn't considered. This is a key point. The reality is that you HAVE to use a NOx suppression system on Diesel engines to reduce NOx pollutants!

2. Each approved system type is compared to it's "competitor" system on the same vehicle in various operating parameters.

3. Based on the same vehicle/different NOx system comparisons, performance parameters are measured and compared.

The result is that, among other things, an SCR system provided 5 percent more fuel economy in comparison to other NOx-reducing systems. Conversely, other NOx systems reduced fuel economy by 5 percent when compared to the same vehicle equipped with an SCR NOx system.

In summation, SCR NOx systems do not reduce mileage by up to 5 percent compared to other NOx systems. Either description is factually correct, but saying "SCR is expected to improve overall fuel economy by approximately 5%." sounds better to the Mansfield Marketing Department.

Remember, NOx reduction is REQUIRED so this means that the comparison of mileage is between all NOx systems. If you compared SCR NOx to the same vehicle that is not equipped with a NOx suppressant system, the mileage most likely would be almost the same!

Any system that does not reduce mileage is - to me - a good thing.

[gandrimp]

It COULD be as simple as higher exhaust temps flow easier.

[blue7.3]

I suspect it is also due to reduced EGR use, which dilutes the fuel-air mixture to lower combustion temps, reducing NOx. That also reduces combustion efficiency and hence, fuel mileage. EGR systems are more difficult to deal w/ on a diesel where internal temps and pressures are higher. In fact the EGR system on the Ford 6.0 diesels is one of the systems that is blamed for their horrific service records. (7.3's don't have EGR.)

Thanks for the article top!

-pete

[Joe Callimachus]

Ok I got it now. Thanks, guys,

[topgut]

There was a post on this site that I read and linked to 'the truth about SCR'.

If you search that you will find all kinds of info on the SCR vs EGR philosophy.

OK, now that I have your attention I will talk about the EGR system on my early vw TDI engine in my 97 Passat. Generally, the reason EGR is used is it controls the combustion temperature of the engine which reduces NOx. What this does to the engine over time is it plugs up the intake manifold with soot and eventually requires the intake manifold removal and cleaning. Not the best system but the vehicle gets about 45 MPG. There are ways to avoid the intake manifold plugging up but that is outside the dealers options when setting up the ECU of the car. It requires changing settings in the ECU of the car essentially turning off the EGR or setting it to minimum which avoids the plugged manifold. What suffers? The air quality. But its still way cleaner than what I saw in the 70's.

Now to SCR. From what I have read, the advantage of SCR over EGR is that SCR minimizes EGR which should plug less intake manifolds. The disadvantages are more equipment on the vehicle adding to the cost of the vehicle and the vehicle operator has to add the DEF to the tank. The advantages are much reduced NOx by as much as 90% or more and less plugged manifolds.

Looking back at the EGR and Particulate trap systems I think that SCR will render the EGR systems obsolete over time.

About the 5% better fuel efficiency; well the EGR / PT systems inject fuel into the exhaust cycle of the engine to burn off the particlates in the trap. I've been told that is why the recent diesel engines in pick ups have less fuel economy than the trucks of about 10 years ago. But, the engines run cleaner.

So, what is better? If you are the EPA, the system that emits the least toxins is better. If you are a consumer, the vehicle that gives the most MPG for the least cost and hassle is better. So, it looks like the SCR is the balance weight on the scale. Less PT regeneration and less plugged intake manifolds works for me and apparently the big MFGR's too.

Hope this is informative and ++ to Navistar for their 'different' Technology as well.

If I need to be corrected please do so I can learn more.

Good luck.........John

[dadtdave]

Great read John. Thanks. Dave

[DickIsGone]

Christ...
More spam.

Andy, please start killing these turds at the gate.

[blue7.3]

Originally Posted by Dick

Christ...
More spam.

Andy, please start killing these turds at the gate.

Spammer obliterated!

I don't know if Andy can filter these guys out up front, but flag the posts when you see them and we'll take 'em out. They get tagged so they can't just turn around and come back...

-pete