Volks Wagon AG recently admitted that engine management computers on its Audi and VW diesel motors were programmed to run a different calibration when the car was hooked up to an emissions testing dynometer and when the cars were regularly driven on the road. This allowed the car to "pass emissions" by reducing the amount of nitrious oxide (NOx) emissions during testing compared to normal operation. This is being described as terrible thing to do. But is it really?
NOx is one component in urban smog. It is a result of excessive combustion temperatures. Excessive combustion temps are the result of more efficient combustion. Which also results in a massive reduction in other pollutants such as co1, unburned hydro carbons and diesel particulates (black smoke), and excessive fuel consumption. So the trade off was an increase in NOx against much better fuel economy, and much cleaner overall emissions. It results in a net co2 emissions reduction.
Nox has always been a difficult problem. Improving efficiency increases combustion temps. With gasoline, and some diesel, engines since the 1970s; have used EGR. EGR is Exhaust Gas Recirculation. By introducing some of the spent exhaust gasses at the cylinder intake the combustion temperatures are decreased. But the efficiency is also reduced. Therefore the resultant incomplete combustion must be completed by other means, such as catalytic converters and air injected into the exhaust system.
Another well known way to improve combustion efficiency, but it increases combustion temps, is to start the fuel burn earlier in the crankshaft cycle. With gasoline engines this is done by "advancing the spark." With diesels this is done by "advancing the injector timing." This is done all the time. The results are a significant improvement in fuel economy and also power production. I suspect this all the VW engineers did. They simply maximized power production and maximized fuel efficiency (which also yields much cleaner overall emissions) when the car was cruising down the highway as mandated since 2011 by US Gov agencies.
This is probably a case of conflicting rules and regulations.
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.