So if you run out while on the road, can you piss into it?
In all seriousness, this prompted me to do my compulsory Googling on this whole DEF crap. What a Rube Goldberg solution. WTF!?!?!?
Lean out the fuel/air mixture (Lean burn? ) to the point where the exhaust emits excessive NOx that then must be treated with piss and water that then shoots AMMONIA! out the pipes?
So some day CARB will ban ammonia emissions and they will have to add on some shitass cleanup system for that.
Why not just take the NOx and juice the engine in the first place?
Steve?
Well, its not quite that bad Stan! Gasoline engines are made to operate at what is called stoichiometric air fuel ratios which means only that there is just enough air to combine with the fuel to burn the mixture completely and this is regulated using oxygen sensors. Under these conditions, catalysts can continuously reduce nitrogen oxide emissions into the elements nitrogen and oxygen, which are harmless to the environment (nitrogen oxides combine with hydrocarbons in sunlight to create smog, which in places like Los Angeles have been a real problem in the past). Today's gasoline engine catalysts can continuously convert nitrogen oxides into the harmless nitrogen and oxygen with no need of an additive, but they must operate continuously at stoichiometric air fuel ratios or operating a little rich is OK too, but can never operate lean.
With diesels, they almost always run lean except at near wide open throttle (which also helps fuel economy). As most probably know, diesel engine speed/power is regulated by fuel flow, not by a throttle as in gasoline engines (it is the lack of a throttle that partly helps give diesel engines better efficiency than gasoline engines since there are no pumping losses due to a throttle, which makes a gasoline engine work like a vacuum pump to create a vacuum with the attendant energy losses to make that happen). Diesels also operate at very high compression ratios to also achieve greater efficiency compared to gasoline engines, but this also creates high nitrogen oxide emissions. So under lean conditions, nitrogen oxide catalysts will not work well. So diesels are very much harder to control for nitrogen oxide emissions. The best solution so far is for them to use a nitrogen oxide adsorber (not absorber) which means nitrogen oxide emissions are accumulated on the surface of the adsorber until the surface is full and then at regular intervals DEF is squirted into the exhaust stream ahead of the adsorber, and chemically reduces the accumulated nitrogen oxide emissions into ammonia and water. Early NOx adsorbers also had a catalyst after the adsorber to minimize ammonia emissions that are not a pollutant relative to smog, but of course can smell bad and irritate if the concentration is too high. But diesel engineers have learned how regulate carefully the amount of DEF dosing in conjunction with some temporary adjustments to diesel fuel injection at the same time to minimize ammonia emissions such that a clean up catalyst is often not needed anymore. CARB did consider setting limits on ammonia formation but decided to forego it in view of the improvements in the aftertreatment systems. And the required on-board diagnostic systems can detect when the upstream actions needed to minimize ammonia formation are not working correctly and set a fault code. The nitrogen oxide reduction part of the diesel aftertreatment systems is not so much the problem with diesels, it is properly operating the particulate filter such that is remains efficient over hundreds of thousands of miles without burning up or clogging due to run away regeneration or clogging up due to insufficient regeneration (regeneration mean setting off a fire inside the particulate filter to clean up the accumulated carbon so it can collect the particulate again). Doing this satisfactorily over many miles under so many different driving conditions and temperatures is where the real problems still exist in getting it right without destroying the filter or bringing the vehicle to a stop (or at least a big loss in power due to plugging).
The goal though, is to allow the engine to operate at its peak for power and fuel economy like the old diesels, but let the aftertreatment system clean up the exhaust almost completely, and not have to detune the engine like they have had to do in the past. In other words, operate just like the gasoline engines do now to maximize fuel economy/power and emit pretty close to zero emissions. Gasoline engines are so clean now that after about the first 20 seconds of startup, the tailpipe emissions are cleaner than the background air in such places as Los Angeles any more. Nice. The diesel guys just need more time to get it right and durable. Electric or fuel cell vehicles will not likely displace diesels for heavy duty trucks for a long time to come, so we need diesels still and they need to be clean. With light duty vehicles, the gasoline engine is on its way out.
Steve
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