Fuel Consumption versus Polution Abatement.

[waross]

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 NO^x?
Doesn't higher combustion chamber temperature mean more NO^x?
How do we get rig of NO^x?
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 NO^x 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

 

[RodRico]

waross,

I hadn't heard of injecting propane or natural gas into diesel intakes, but this article from Engine Professional magazine says it does in fact reduce particulartes (soot):

http://www.dieselperformanceproducts.com/images/news/engineprofesionalmagazinearticle.PDF

. That being said, I'm pretty sure wide adoption of this strategy would still require large changes to infrastructure.

Another possibility to improve diesel involves use of dimethyl ether which, I believe, is compatible with existing infrastructure. See

https://en.wikipedia.org/wiki/Dimethyl_ether#Fuel

. Also see the great overview of alternative fuels at

http://www.energy.gov/downloads/chapter-7-advancing-systems-and-technologies-produce-cleaner-fuels

I'm not 100% positive, but I think the culprit in particulate (soot) emissions is the rich blend at the boundary between the fuel spray and hot air, not the load. This view is supported by the chart below (from

http://www.dieselnet.com/tech/emissions_idle.php)

indicating 20 grams of particulates from 11.6 kg of fuel at idle (1.7 grams of particulates per kg of fuel) versus 197 grams of particulates from 197 kg of fuel while cruising (2 grams of particulates per kg of fuel). I have seen data indicating particulates jump during transient conditions, but I suspect that's due more to a fuel injection strategy (overly rich to maximize power during acceleration) than the inherent process.

Rod

 

[waross]

Is it feasible to allow higher combustion temperatures and more compensate with SCR or are we hitting the point of diminishing returns?

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

 

[waross]

Anecdotally; back in the late 70s there was a surge in installations of propane systems and some natural gas systems.
Compressed natural gas systems were available but went nowhere. I saw a demonstration vehicle with high pressure natural gas storage tanks filling the trunk that had the equivalent capacity of about 3 gallons of gasoline.
There were a few niches for LNG.
My neighbour worked for the gas utility and drove a 3/4 ton van with an LNG conversion.
It worked well as long as he was using it but the LNG systems used the evaporation of the fuel as it was drawn off to keep the remainder cold enough to stay liquid.
If the vehicle was parked for a time, the temp in the tank would rise and the gas would start to vaporize and escape slowly through the pressure relief valve.
It was a slow process, it took about a week to lose all your liquid.
Another niche was occupied by Greyhound lines.
Back then a large part of Greyhounds business model was parcel express. It was reported that on many runs the express revenue paid the bills and passenger revenue was a bonus.
Due to the volume of parcel express moving between Vancouver BC Canada and Seattle Washington, about 150 miles, the parcel express was transported on semi trailer trucks.
They were reported to be using LNG for economy. The "Use it or Lose it" aspect was not an issue on the relatively short and easily planned haul.
Does anyone see any issues with adding propane to existing engines and using the dual fuel option.
Will a dual fuel system satisfy the EPA?
Will there be any mechanical issues with adding propane to a modern engine?



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

 

[RodRico]

waross.

If the major engine manufacturers thought they could get higher efficiencies by simply improving SCR, I imagine they would have done so already. I'm of the opinion there aren't any easy opportunities to improve emissions or efficiency remaining within the current paradigm. After DFI and/or HCCI, the only areas remaining are in new fuels (which is where study is now turning), and those may be slow in coming due (due to infrastructure costs and economies of production scale).

Rod

 

[CWB1]

Does anyone see any issues with adding propane to existing engines and using the dual fuel option.
Will a dual fuel system satisfy the EPA?
Will there be any mechanical issues with adding propane to a modern engine?

Like anything else, properly engineered systems work great and are offered by any number of companies, poorly engineered solutions OTOH can cause all manner of issues. From a technical standpoint there a number of considerations that need to be kept in mind regarding existing (assuming you meant stock) engines. At higher blend ratios you have diesel/gasoline/kero/etc flow rates so low that many stock injectors may struggle to control. Intake manifolds, ducting, turbo/SC/boost systems for direct injection engines usually aren't optimized for the necessary equal cylinder-cylinder fuel distribution when running higher blend ratios. Onroad gaseous fuel system design whether it be CNG, LNG, or propane is an entire series of challenges unto themselves, not overly complex but involving a ton of tribal knowledge developed through experience and testing. Calibration is much the same, there's a ton of tribal knowledge involved with tuning two complete fuel systems that need to interact while acting independently. One good example of this is that compression-ignition engines will actually knock at higher blend ratios and may suffer preignition problems as well.

Regarding onroad non-blended CNG/LNG/other gaseous systems, there are a number of manufacturers building certified engine systems and/or complete vehicles and I'm sure a few certified kits as well. I lived in this world for an OE for a number of years in the recent past but never paid much attention to the kit builders as many of them at the time were rather homeshop'ey. In a nutshell, onroad gaseous systems are pretty mainstream today. In rural Indiana I regularly saw CNG semis hauling milk as I see them hauling cars and parts here in Detroit today. CNG stations are fairly commonplace here in the Midwest and LNG occasionally found in denser city populations. Personally I don't have the desire to own a gaseous fueled vehicle but have had colleagues who have without too much fuss.

Edit: I forgot to address the question regarding the EPA and blended/dual fuel engines. Yes, these engines are held to the diesel standard by the EPA.

 

[waross]

Rod;
"If the major engine manufacturers thought they could get higher efficiencies by simply improving SCR, I imagine they would have done so already. " Makes a lot of sense.
CWB1 Thanks for the heads up.

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

 

[gruntguru]

If the fuel rate is not increased, the addition of a turbocharger or an increase in boost will reduce combustion temperatures. The extra mass shares the same heat input.

CNG is not very good as a supplementary fuel (fumigation). CNG/Air ratios much above about 1.3 (lambda) do not support a consistent flame front. Its Octane rating is very high so it can often work quite well as a primary fuel with about 5% pilot injection of diesel fuel for ignition. A reduction in boost is needed to maintain pre-conversion power levels and throttling to maintain part load mixtures below 1.3

je suis charlie

 

[SomptingGuy]

SCR isn't customer-friendly. It feels like having to add 2-stroke oil to your tank. (Car) manufacturers hoped that the alternative (highly complex) systems not requiring any user-intervention might be viable. They weren't. This experiment died when VW were caught out. Now that SCR is effectively required for all diesel cars, the systems might get better. As will the aftermarket options to delete them without detection. We still don't have anything purely passive for diesel NOx, like the (massively fortuitous) TWC that's standard on all gasoline vehicles.

Steve

 

[romke]

spark ignition engines are per definition easier to clean up them compression ignition engines. a modern spark ignition engine runs on a fixed air/fuel ratio and the pollutants can be controlled by a TWC and eventually a additional filter for very small dust particles.

getting a diesel clean is much more difficult, given the fact that it runs on a varying air/fuel ratio and that given a specific combustion temperature you may end up with either high HC or high NOx. thus you are dealing with a lot more variables. to control the output you need rather complicated equipment that in itself, although cleaning up certain unwanted exhaust gas components, also can have a negative influence on specific fuel consumption.

apart from cleaning up exhaust gases comes the requirement to reduce CO2 emissions. that can only be achieved by burning less fuel - either through a lower power output and reduced speed or by making lighter vehicles. the latter is not that easy because we also want all kinds of comfort gadgets, airbags, crass protection structures etc. in fact the weight has come up quite a bit in a lot of vehicle types over the last 20 or so years....

for heavy vehicles it will be hard to stop using diesel engines, because in terms of mileage diesel still is superior. in terms of the optimal fuel in terms of cost and cleanliness there is the added problem that taxation of the various fuels is not equal and also varies tremendously from country to country. the end user probably decides on the basis of cost per km. it would be a good idea to tax the various fuels on the basis of actual pollution - where the taxation thus is in line with the contribution of the vehicle to pollution of the environment. unfortunately we are still a long way away from taxing the polluter for the dangers he causes to the health of all mankind.....

 

[gruntguru]

apart from cleaning up exhaust gases comes the requirement to reduce CO2 emissions. that can only be achieved by burning less fuel

Or fuel with lower carbon content eg methane or hydrogen.

je suis charlie

 

[Mongrel]

Quote: it would be a good idea to tax the various fuels on the basis of actual pollution - where the taxation thus is in line with the contribution of the vehicle to pollution of the environment. unfortunately we are still a long way away from taxing the polluter for the dangers he causes to the health of all mankind..... /quote

Okay then, shall we park every truck in the world, and you can farm your own food? Make your own clothes and items?
It's not such a simple problem.

 

[waross]

We are now paying a carbon tax. Both fuels and natural gas are taxed. Wait for it.

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

 

[dgallup]

China has instituted price controls aimed at keeping natural gas prices permanently below diesel on an equivalent gallon basis. They are also banning diesel trucks inside a lot of the most polluted cities. We are tripling our sales of natural gas fuel injectors in China despite USA tariffs on steels we are buying from Europe and Chinese tariffs on the injectors causing large price increases.

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[CWB1]

it would be a good idea to tax the various fuels on the basis of actual pollution

It's not such a simple problem.

Not the least of which is the fact that "scientists" cant seem to agree on which exhaust compounds are the most harmful to nature, nvm the extent to which they are harmful. China's regulation creating an artificial demand for natural gas to the detriment of diesel assumes that excess methane emissions are preferable to excess soot, yet many folks argue otherwise. Stateside the EPA has done similar to a lesser extent, yet modern diesels are in many cases actually removing more manmade compounds from urban areas than they are emitting.

 

[RodRico]

I understand the fact that the Chinese have developed a liking for beef is producing a *lot* of methane (it turns out Ronald Reagan was right when he commented on "bovine flatulence" even though he took a lot of flack for it at the time). China is the elephant in the room when it comes to emissions; the western economies are mature and their emissions are in decline while China is responsible for most emissions and isn't even close to full economic maturity. On the plus side, they are the only ones moving forward with some of the more modern nuclear reactor designs; they have a high temperature gas-cooled reactor (HTGR) comin on line soon (see

http://www.energy.sc.gov/files/gnac/NGNP_HTGR_Technology.pdf

for details).

 

[3DDave]

Methane is invisible to people; twilight-noon from soot isn't. Neither are brown horizons from NOx concentrations. I recall flying back from Los Angeles, CA, and looking down at the vast city as the plane headed East. When the terrain went from flat to foothills it was eerie to see a brown stain leaking in the shallow valleys towards the desert and realize that all of LA was hundreds of feet deep in that.

 

[dgallup]

Methane is given a CO2 equivalence of 25. Way too much methane is released while drilling and fracking. The Obama admin EPA was about to put in tighter controls on oil field methane emissions but of course the tRump EPA nixed it.

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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.