OK...Phil asked so here goes!!
Up until now, engine makers have been dealing with emission challenges by modifying combustion in the cylinder to achieve the desired result. Basically they have 2 main issues to deal with, particulate matter (sooty black exhaust) and NOx (oxides of nitrogen). The earlier emission rules dealt primarily with particulates. The easiest way to clean them up was to have a more efficient combustion event and make the engine run lean (huge surplus of air vs. fuel). This was great as it got rid of the black exhaust and it made the engine more efficient. Anyone that had a 1995-98 Series 60 can attest to that, those engines were the most efficient engines to date as far as getting the most out of a drop of fuel. Problem was, when you had that "hot" of a burn in the cylinder you made a lot of NOx (the nitrogen in the air would actually burn or oxidize). NOx is a contributor to smog.
Starting with the 1998 emission rules, enigine makers had to cut down on the NOx emissions. Most did it by retarding the injection timing a bit, this cooled off the burn but it also hurt efficiency. Most noticed no difference as other truck technology had advanced enough to mask the difference and...the engine manufacturers found a way to "cheat" on the EPA test. All was OK until the EPA figured it out, then the s%#t hit the fan. The penalty the engine makers were given was that the emission rules that they needed to meed in 2004 now had to be met in Oct. of 2002 (we all remember how well that turned out
).
To meet the new rules the engine guys had to further "cool" the combustion event, this was done mainly with EGR. By shooting some exhaust back into the engine it diluted the burn enough to control NOx. Some engines (CAT) needed a catalytic converter of sorts as the "diluted" burn now caused a lot of particulates (sooty black smoke).
The 2007 rules called for even lower NOx, now the engine guys had to really ramp up the amount of EGR (exhaust) going back into the engine (almost double the 2002 rates). Now the engines were really great at NOx control but now the exhaust was really full of soot. This resulted in the DPF or soot trap systems you see on the newer trucks. If you took the DPF off of a new truck (and convinced the ECM it was still there) you would swear the turbo was blown, that's how dirty the exhaust is!
So now comes the 2010 rules, they are incredibly tough to meet. The engine guys know that if they meet the new rules with EGR only fuel mileage will suffer a lot and DPF life will be shortened (they would be burning off or regenerating a lot more often). The engine guys with European links (Detroit,Mercedes,Volvo etc.) decide to use a system they have had in Europe for a couple years called Selective Catalytic Reduction (SCR). This system does not rely on a "cool' burn in the cylinder to work, in other words, go make the engine efficient again and worry about cleaning up the exhaust after it leaves the engine!
SCR uses a weak urea (ammonia & water) soloution and injects it into the exhaust after the turbo. The urea partially reacts with the NOx in the exhaust and then passes through a catalytic converter that finishes the job. The new engines will still have a DPF soot filter on them (the rules for soot are really tight now) but it will not need to regenerate (burn off) nearly as often. This will save fuel as well as a regeneration uses anywhere between a quart to 2 gallons of fuel. So you get an engine that should give you anywhere from 5 to 10 percent better fuel mileage than what you have for 2007. Some European fleets have said the advantage is upwards of 15% but those results are not scientific.
So, what will you have on the new trucks? You will likely have a 20 or so gallon tank for the new fluid that you will need to fill probobly every second fuel stop depending on your set up. The engine will run without the fluid but will throw a code and de-rate to 50% horsepower. The tank will be heated to keep the fluid liquid while the engine is running, and the fluid will be available at pumping stations or in containers at truck dealerships. There will likely be a few hiccups at the start but it should be available widespread pretty quick. Now that Cummins has said this is how they are going to proceed that will make this even more universal.
Fear not, this time, the new rules will actually help us save fuel!!!!
Anyone want to know what time it is? I'll tell you how a watch works first
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