The big emissions bogey for a diesel is NOx. There are two sources of NOx in any combustion device, fuel bound NOx and thermal NOx. Not much of an option for fuel bound NOx, whatever is in the fuel goes out the tailpipe, Thermal NOx is related to combustion temperature, Nitrogen in the combustion air starts to combine with oxygen as the flame temperature rises. The manufacturers are regulated on CO and NOx, one of the ways CO forms is the temps are too low so its a trade off, burn too cold to cut thermal NOx and CO rises, burn hot to cut CO and NOx rises. Diesel runs hotter than gas engines and will generate more atmospheric NOx. There are all sorts of tricks to try to reduce the flame temp like Exhaust Gas Recirculation (EGR) but that reduces the power output. The alternative is to install downstream CO and NOx catalysts and the NOx catalyst requires ammonia to remove the NOx. The engine can be tuned for a hotter flame and things that impact performance like EGR can be removed so the engine runs better. Urea is converted to ammonia in the emissions equipment and as noted it can be problematical to deal with. The nice thing about urea is that its relatively safe if its spilled when stored and transported compared to the alternatives which are aqueous ammonia or anhydrous ammonia.
I could guess that VW was using EGR on their diesels and the chip was bypassing EGR when the throttle was used aggressively. A lot of the old superchips did that trick. By the way most manufacturers design their cars around emissions, many smaller cars are set up so the part throttle performance is somewhat constrained by the emissions controls, when the throttle is applied aggressively into the higher revs than the test would require, the upper rev band is lot more powerful. Many standards have keep the throttle cranked up a bit after an aggressive shift in order to burn off excess emissions caused by the load change in the motor. My Fiesta currently has an emissions recall on my EGR system and I expect that the cure is they will reprogram the chip to have it applied more aggressively. I don't plan to have it done.
One major commercial diesel engine manufacturer bet their company on designing truck and stationary engines without NOx catalysts a few years ago and they lost the bet, it cost them millions as their engines couldn't pass emissions. Looks like VW may have done the same.
I deal with large stationary engines on occasion, some companies offer two versions, one version uses all the tricks to avoid a CO and NOx catalyst and the other version has a CO NOx catalyst, inevitably the one with the catalysts are higher efficiency and easier to tune. The state of Mass has some of the toughest limits for CO and NOx in the country and there are no companies selling non catalyst versions.
I could guess that VW was using EGR on their diesels and the chip was bypassing EGR when the throttle was used aggressively. A lot of the old superchips did that trick. By the way most manufacturers design their cars around emissions, many smaller cars are set up so the part throttle performance is somewhat constrained by the emissions controls, when the throttle is applied aggressively into the higher revs than the test would require, the upper rev band is lot more powerful. Many standards have keep the throttle cranked up a bit after an aggressive shift in order to burn off excess emissions caused by the load change in the motor. My Fiesta currently has an emissions recall on my EGR system and I expect that the cure is they will reprogram the chip to have it applied more aggressively. I don't plan to have it done.
One major commercial diesel engine manufacturer bet their company on designing truck and stationary engines without NOx catalysts a few years ago and they lost the bet, it cost them millions as their engines couldn't pass emissions. Looks like VW may have done the same.
I deal with large stationary engines on occasion, some companies offer two versions, one version uses all the tricks to avoid a CO and NOx catalyst and the other version has a CO NOx catalyst, inevitably the one with the catalysts are higher efficiency and easier to tune. The state of Mass has some of the toughest limits for CO and NOx in the country and there are no companies selling non catalyst versions.
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They are setting aside $7.2B to fix the software and regain public trust.
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