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Fuel Consumption versus Polution Abatement.

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waross

waross

Electrical
Jan 7, 2006
27,204
The following thoughts are always present whenever I am driving my truck taking my young cowboy to summer rodeos, at about $0.60 per mile for fuel.
Gee, I have a fairly new truck with an almost state of the art diesel engine.
I have dual sequential turbo chargers to improve efficiency.
But don't those turbos work be extracting heat from the exhaust gasses?
Don't those BTUs extracted from the exhaust then show up as higher temperatures in the combustion chamber.
Good for efficiency, right.
But what about NOx?
Doesn't higher combustion chamber temperature mean more NOx?
How do we get rig of NOx?
Lower the temperature in the combustion chamber, right?
We can do that by introducing exhaust gasses that will not support combustion.
It seems that even after losing some heat in the turbo, the exhaust gasses may still be too hot.
Well we can cool the exhaust before introducing it into the combustion chamber.
Have we just lost some of the efficiency gained by the operation of the turbo? I don't know, I'm asking.
Now the other side of the compromise.
Is it correct that lower combustion chamber temperatures promote the production of more soot in the exhaust?
No problem, we can use a Diesel Particulate Filter to trap the soot. Hot exhaust can promote the combustion of the carbon in the DPF.
Great idea. Wait, didn't the twin sequential turbos just cool the exhaust by extracting as much energy and BTUs as possible in the quest for efficiency?
Dang, the exhaust isn't hot enough to effectively burn the soot/carbon out of the filter. It will soon plug up.
There must be a solution.
Hey let's make the exhaust hotter. Great idea. How can we do that? We can add fuel to the exhaust to promote burning in the filter. That will keep the filter burned clean.
Considering the load that I am pulling and compared to older engines, I may be dumping as much fuel into the exhaust as I am burning to pull the load down the highway.

I understand the need for cleaner air in the cities, but is it feasible to allow a little higher levels of polutants out on the highways away from population centers? Not really a suggestion, more a question.

Is it time to move away from diesel power to lighter fuels such as LNGs?
How much pollution could be avoided by using propane instead of diesel?
Can NOx in a propane powered engine be reduced economically by using larger displacements per HP and less EGR rather than having an EGR system working against the turbo system?
Given the very great ratio between the first cost of an engine and the cost of fuel over the lifetime of the engine, I am not much concerned about a heavier, larger more expensive engine block.
Can anyone fill in some actual numbers here?


Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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"...dual sequential turbo chargers..."

Are those stock? Or added afterwards?
 
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No names, no pack drill, that has been implemented in the past and when the regulators found out they were rather annoyed. What happens if you have a freeway or interstate that goes through a built up area?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376
 
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Maybe I should have said just "sequential turbo chargers". Dual may imply two sets for a total of four.
No.
Just one set of two turbos.
Stock.
6.4 Power Strokes and later Maxxforce 7s.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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It seems to be a practice in the service industry to have a blank spacer fitted into the EGR to get better fuel economy and stop the cloging


A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare
 
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Turbocharging shouldn't really bump peak combustion temperature much once you consider intercooling.

The peak combustion temperature is right next to the surface of each individual droplet, right in the diffusion zone between rich (at the droplet surface) and lean (in the bulk of the chamber). EGR adds dilution right there. It has some effect on thermal efficiency but applied within reason, not much. Maybe a percent or two.

Keeping the exhaust hot enough for the emission control systems to operate does indeed kill efficiency during light load puttering around and idling. The most modern diesel engines (which the 6.4 is not) have the emission control components attached directly to the engine with the shortest possible path between the cylinder and the DPF, and the DPF and SCR are one and the same part (by coating the DPF internal matrix with the SCR catalyst and putting the AdBlue injector ahead of it). In fact the most modern designs have the oxidizing catalyst followed directly by the SCR injector and the DPF/SCR catalyst in one housing (it can be a bolt together or clamp together assembly) attached directly to the turbocharger outlet.

The best designs are addressing the EGR clogging by using low pressure EGR with the exhaust taken from after the DPF so that there's no particulates in it. This also means the recirculated exhaust is going through the intercooler, and the best designs nowadays use liquid cooling so that the temperature in the intercooler doesn't drop below freezing. Volkswagen learned that one the hard way.

Yes, this is complicated. And this is why, after years of driving VW diesels, I have gone back to modern spark ignition engines, no turbo, no direct injection, no EGR, but with variable valve timing and with modern high compression combustion chambers. The efficiency still does not match that of a diesel but there is a whole lot less Rube Goldberg involved.

In the trucking industry, I don't think natural gas or propane would be viable for long haul. Lots of city buses and short run trucks around here use natural gas, so it's already in use. Control of nitrogen oxides in a nat gas engine is the same as for a gasoline engine ... throttled stoichiometric operation, regulated with a lambda sensor, and a 3 way catalyst. Thermal efficiency is still no match for a diesel on account of the throttled operation, but the fuel is cheaper and particulate emissions are way down, no need for a particulate filter.

Minor tweaks such as fiddling with engine size etc don't make enough difference in engine out emissions to get the job done. You need the catalyst, and once you have that, the upstream fiddling (which is what screws up thermal efficiency) doesn't matter as much.
 
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Thank you for the explanation Brian. I was thinking of propane more than natural gas.
LNG may be more viable for some uses if you can live with the "Use it or Lose it." factor.

Brian said:
Thermal efficiency is still no match for a diesel on account of the throttled operation, but the fuel is cheaper and particulate emissions are way down, no need for a particulate filter.
Click to expand...
If you add in the fuel that is dumped into the DPF the overall efficiency numbers may change.
Is there anything that can be legally done to help a 6.4 short of a trade in?
EGR and DPF deletes are still legal in Canada. I should have said Alberta. Many of the other provinces have apparently stepped up enforcement. They must be installed new but there was a loophole in the enforcement or lack of it.
That is due to change in January. Rumour has it that the enforcers will be checking emissions and non-compliant vehicles may be towed. Seeing your living quarters and three horses on the hook is something to avoid.




Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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I'm with Brian. My most recent drive was chosen by selecting from the VVT NA gasoline vehicles in my size and price range. Diesel tech for today's emissions legislation is just too complex and unreliable - nowhere near mature.

Steve
 
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I have been hearing good things about the new GM Duramax.
I am starting to think more about a suggestion made in another thread.
Trade the truck off.
Running around 20,000 lb. GVW, how do the GM gas engines compare to the GM diesel engine for miles per dollar?

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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I may be dumping as much fuel into the exhaust as I am burning to pull the load down the highway.
Click to expand...


So your new truck is getting 1/2 the mileage of the old truck when pulling the same trailer?

Fuel efficiency data for diesel trucks over the years would say your continued arguments about burning 2X the fuel because so much is being dumped into the exhaust are wrong.

 
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waross said:
I understand the need for cleaner air in the cities, but is it feasible to allow a little higher levels of polutants out on the highways away from population centers? Not really a suggestion, more a question.
Click to expand...

That's been done more than once and the EPA has taken the offending parties to court. A good friend of mine spent the last couple of years of his career providing expert testimony against the EPA. A big factor in his taking early retirement. The HD trucking industry had algorithms that detected interstate driving based on steady speeds and lack of shifting. It would advance the injection timing to improve fuel economy. During city driving and of course, the EPA emissions cycle, it would retard the timing and meet all the requirements. Not that different from VW dieselgate but I think those would exceed emissions in city driving too.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
 
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Hi Lionel; Fuel efficiency data may be based on a hard working engine.
Most of my driving is at the legal limit on flat roads on cruise control.
My engine seldom works hard.
It doesn't work hard enough to keep the DPF up to temperature.
It is often in regen (dumping fuel) while cruising under my normal driving conditions.
Beware of applying overall averages to specific cases.
A google search brings up the following data on A comparable truck:
GMC Sierra 3500HD – The average fuel economy was determined to be 13.6 miles per gallon. You can get up to 19.3 miles per gallon on the interstate.
That agrees with figures that I have heard from mechanics.
I'm getting about 8.33 Miles per US gallon.
The truck was recently serviced by a dealer including a cylinder drop test and found to be in good shape.
Maybe it's time to trade.
All it takes is money.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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You're averaging ~8 MPG all the time?

Or is that 8 MPG during regen (which should happen roughly once every tank of fuel unless your truck spends a lot of time idling or in traffic)

Or is that 8 MPG while towing a trailer, in which case why are we even talking about it?
 
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You have very well described the idiocy of it all in your first post.
 
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Now you're saying that because of the lighter duty use the fuel economy is worse compared to working the engine harder all the time?

Comparing your mileage to a Duramax didn't address the point I posted. You're claiming that fuel efficiency has drastically dropped due to the emissions equipment. I don't believe it's true or that you have any data which supports that claim. I do agree that it was found the fuel economy did drop in the first years the newer filter systems were installed, but it wasn't by around 1/2 or drastically ("I may be dumping as much fuel into the exhaust as I am burning to pull the load down the highway.") and the manufacturers have figured out how to get it back and then some since that time.

It's often in regen towing a trailer? As jgKRI pointed out, there should only be a regen cycle around every tank of fuel for a truck that is towing or working and on the highway. Certainly not often or most of the time.

 
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Or is that 8 MPG during regen (which should happen roughly once every tank of fuel unless your truck spends a lot of time idling or in traffic)
Click to expand...
I wish. I only get an indication that the pig is in regen when I pull off for a coffee and the hot exhaust warning comes on as I take it out of gear.
It goes into regen many times during normal highway driving.
My driving is normally at the legal limit here,100 kph (62.5 MPH) on flat roads with little traffic. Typically a couple of hundred miles per trip with almost no idling and few stop signs. That's part of the problem. The engine may not be working hard enough to burn off the DPF.
Yes, pulling a trailer but similar trucks pulling similar loads are getting 60% to 80% better mileage.
Thank you everyone for your input.
I think that the consensus is that there is really nothing that can be done to improve this truck.
Thanks for your information in regards to EGR and regen, Brian.
Thanks also for the engine priorities.
My choice is between the Cummins and the Duramax. To many serious issues with past Powerstrokes to trust Ford for a few years.
I have always preferred GM over Dodge for truck quality, but the new GM 4500HDs will be built by Navistar with GM engines. I am presently driving a Navistar product am not impressed with the tinny body nor with the flakey Body Control Computer.
Too many glitches and false warnings.
I guess that I will be looking at both Cummins and Duramax.
Time to trade.
Thanks for the informative discussion. friends.


Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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Now you're saying that because of the lighter duty use the fuel economy is worse compared to working the engine harder all the time?
Click to expand...
Not quite. But at lighter loads the efficiency drops because of more regen cycles.
At heavier loads, I expect that the truck will burn more fuel, but a greater percentage of the fuel will be pushing the truck down the road and a smaller percentage will be dumped in the exhaust.
the manufacturers have figured out how to get it back and then some since that time.
Click to expand...
Maybe so, but that doesn't help those of us with older trucks.
And the improvements that have been made point out the poor performance and poor mileage of earlier systems.



Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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Waross,

The increased heat from turbochargers is reduced by use of intercoolers. In the end, the improved volumetric efficiency resulting from recovery of work from exhaust is positive, particularly in throttled engines.

EGR gasses are often cooled reduce their impact on intake temperature (
Low Temperature Combustion (LTC) using Homogeneous Charge Compression Ignition (HCCI) is a well known (if not yet mature) strategy to clean up soot and NOx. You can get a sense of how much work is being done in this area by entering "HCCI LTC site: (sans quotes) into Google.

Here's a chart showing the relations between equivalency (a value of one indicates stoichiometric). Note that NOx results from high temperature while soot results from running rich (which is unavoidable when fuel is injected into hot air).
Capture_ytrcah.jpg


I agree with others here that the current system of contraptions used to improve efficiency and reduce emissions is too complex. I've spent a good deal of time working to devise a simple form of HCCI LTC. It's not yet clear if I have been successful.


As for alternate fuels, I think the front runner in the race to save internal combustion has to be those that employ existing delivery infrastructure such as higher ethanol and biodiesel blends. Anything else requires a huge rebuild of infrastructure, and if a huge investment in infrastructure is required, we may as well go all-electic IMHO.

Rod
 
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Thank you everyone for your explanations and for the contributions to my continuing education.
Is it safe to say that the EPA DOES not believe in the effects of carbon dioxide on possible global warming?
I have often wondered about the economics of a system using renewable energy to supply both the energy to upgrade heavier fuels to propane and to extract hydrogen from water.
This would have the effect of adding hydrogen rather than dropping out carbon. This will result in more fuel out than fuel in.
The byproduct will be O2
This would also have the effect of working towards making renewable energy portable.

As far as HCCI, I understand that diesel engines have been run successfully on propane or natural gas by the simple expedient of introducing the gaseous fuel into the intake manifold. A small charge of diesel fuel was injected to ignite the charge.
Is this a step on the way to a poor man's HCCI? Not the best but an improvement. Possibly a step in a proof of concept project to combine LTC with gaseous fuels.
Rod; When a diesel engine is operated with a light load does that tend to produce even more soot?
Thanks

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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