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Musings about the environment and all it touches, from education to city planning

Say it ain’t so, Herbie!

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Greenpeace-France: "I am your air!"

Greenpeace-France: “I am your air!”

A car isn’t just a means to get places. It’s a social signifier. Some cars send messages louder than others, and not always good ones. Think of the symbolism associated with a brand such as Hummer (insecure sociopath), a Cadillac (pimp), a Corvette (bad in bed, must compensate somehow), a Buick (dignified senility – except in China, where they are hugely popular). There are many others like that, though some cars are just meh.

But Volkswagen? The cool car? The love bug? The rebellious, hippie, birkenstock granola car? Say it ain’t so! The sense of betrayal is palpable out there – just look at Greenpeace France’s view of it, above. Volkswagen’s counter-culture image was forged in the sixties, and we’ve been saddled with it since. But the company now is the establishment: the biggest car maker in the world, with a stable that includes Bentleys and Audis. Still, what transpired this week comes as a shock.  Especially from a company with a strong, public environmental commitment.

So what exactly happened? An environmental NGO, ICCT, decided to test a few Diesel imports (a Passat and a Jetta, both VW models, and a BMW X5) under real-life conditions. When the emissions of the pollutant NOx were found to be much, much higher than expected, they alerted the EPA. The American agency confirmed the results, threatened to withdraw the import permit of diesel VWs, and the company fessed up: their cars are equipped with a software that alerts the engine controls that it is undergoing a test, and adjusts the engine so as to reduce the emissions. Indeed, the engine can run without producing significant emissions, but that means that the car is less peppy, and also uses more fuel. Basically, they cheated.

By now, the issue has been all over the world news (here in the German papers, it managed to displace the refugee crisis as issue number one). So I won’t add to the collective indignation, but I want to point out one conundrum, all too common when tackling climate change.

In a diesel engine, NOx are produced when the engine runs optimally. Controlling NOx takes away some energy from the engine. So, it’s not just engine peppiness; it’s the amount of greenhouse gases that it emits. I doubt that Volkswagen folks will try to use this as an excuse, but the fact remains: trying to remove a pollutant that is toxic (NOx) adds to the emissions of a climate change pollutant (CO2).

Why is that? It has to do with the type of NOx control used on VW smaller models. There are three strategies to control the pollutant. NOx are formed when the oxygen in the air reacts with the nitrogen in the air. This reaction only happens at high temperatures, which is why diesel engines, which run hotter than gasoline engines, emit more NOx. So, strategy number one consists of lowering the combustion temperature or letting in less oxygen in the combustion chamber. This is usually done by mixing a bit of exhaust gas to the intake air. But then the result is less efficiency, so higher fuel consumption, so more greenhouse gases.

The other two strategies remove the NOx after the fact. One injects urea into the exhaust over a special catalyst; this produces a reaction that removes the NOx. It adds to the complexity of the controls, requires a special tank of urea, and as a result this strategy is more common in heavier, luxury vehicles. (Yes, urea as in what’s in urine; it’s marketed as Diesel Exhaust Fluid, or DEF, for polite society.)

The final approach uses what’s called a Lean NOx Trap, LNT for short. It uses a set of metal compounds that can adsorb the NOx like a sponge. When the sponge is full, a squirt of fuel is added; the adsorpbent metals also act like a catalyst, causing NOx to react with the fuel and turn into innocuous nitrogen gas. The other products of the reaction are water and, you guessed it, the greenhouse gas CO2. This is the system that Volkswagen uses in its smaller models, because it is simpler and lighter.

And, apparently, it can easily be rigged to work only when you’re at a testing station. Clever! But no, not cool, not when NOx is linked to asthma, heart attacks, you name it.

Oh yeah, what about that Beamer that passed the test? Apparently it uses the urea system. So it’s all good, is it? Well, maybe not. Just a few days before the VW scandal exploded, a European ENGO (Transport and Environment) speculated that many manufacturers may have installed so-called “defeat software”, since their own tests showed a huge discrepancy. In their tests, Audi and Opel came out much worse than Volkswagen, and even BMW didn’t look too good. Go figure, but something does stink there.


Written by enviropaul

September 23, 2015 at 10:42 am

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