Engineering Explained: What's All The Hype About VW And Emissions Cheating?

The situation with Volkswagen and cheating emissions in the US market is very serious. Let’s attempt to focus on facts, answering the following six questions:

1. What is Volkswagen accused of doing?
2. How do diesel emissions work? (Very basic overview)
3. What is a defeat device?
4. Why does it matter?
5. How can you digitally alter emissions?
6. Should everyone panic?

1. What is Volkswagen accused of doing?

The US Environmental Protection Agency (EPA) has issued Volkswagen a Notice of Violation (NOV) for failing to comply with the Clean Air Act. It’s claimed that VW has installed ‘defeat devices’ which alter the emissions of the vehicle. When the vehicle is being tested for emissions, the vehicle operates in a different mode which allows it to pass the test. When the vehicle is operating normally, the defeat device works to reduce the amount of influence on emissions control. It’s not yet clear how the vehicle knows when it is being tested for emissions. To put it very plainly, VW is cheating US emissions with certain 2009-2015 model year diesel vehicles with 2.0-litre engines.

2. How do diesel emissions work?

Modern diesel engines have several stages of emissions control that the exhaust gas undergoes as it leaves the tailpipe.

• Diesel particulate Filters (DPF) are used to remove soot from the exhaust.
• Diesel oxidation catalysts (DOC) are used to react with the exhaust gases so that the byproducts leaving the exhaust pipe are primarily CO2 and H20.
• Selective catalytic reduction (SCR) is a way of reducing nitrogen oxide (NOx) emissions by injecting diesel exhaust fluid (DEF) into the exhaust gas before it enters the catalyst. The same goal is shared here: start with NOx but end with nitrogen (N2) and water (H2O) on the other side. You may hear of DEF commonly referred to as AdBlue.

3. What is a defeat device?

A defeat device is a system with the goal of allowing an engine to pass emissions, even though the true emissions would not pass. This isn’t exactly something new. In 2007 the EPA shut down Casper’s Electronics’ sales of O2 simulators which trick the car into thinking the emissions systems are fully functional when they are not (you could even remove the catalytic converter completely).

In the case of VW, the defeat device is purely digital; it’s a matter of coding which according to the EPA allows the car to “bypass, defeat, or render inoperative elements of the vehicles’ emissions control system that exist to comply with CAA emissions standards.” According to the EPA NOV, the defeat device knows whether or not to activate based on various inputs including the steering wheel position, vehicle speed, duration of engine operation, and barometric pressure. A “dyno calibration” is run under emissions testing, and a “road calibration” is used during normal operation.

4. Why does it matter?

NOx emissions are poisonous gases which can cause a vast array of environmental problems. This gas can cause respiratory illnesses, reacts with air to form nitric acid and toxic organic nitrates, and reacts with the atmosphere to produce ground level ozone formation (smog). It’s a poison to the air, and it’s incredibly important that levels are kept low. The EPA is claiming NOx levels from VW as high as 40 times above EPA requirements. To put this into perspective, the EPA found that with the Casper O2 sims, emissions were as much as 50 times above EPA requirements, and this could be with the catalytic converter completely removed!

5. How can you digitally alter emissions?

Let me be clear that it isn’t known what Volkswagen is altering in order to pass the test at this time. While speculating what it might be doing is fascinating, it’s important to know that all of the facts aren’t out yet. For the purposes of better understanding emissions, the following points are some of the ways that you could decrease emissions through digital tuning.

Exhaust Gas Recirculation

The way this works is fairly straight forward. Exhaust gas is recirculated into the intake manifold. This gas is added to the air fuel mixture, but is not capable of combustion as it is depleted of oxygen. The added gas acts as a buffer (absorbs some heat, and reduces the volumetric efficiency of the engine) and overall reduces the peak temperatures reached in combustion. With lower temperatures, oxygen (O2) and nitrogen (N2) molecules do not split to then recombine and form harmful nitrogen oxides. The more EGR you have, the less performance you’ll have, but it will result in fewer NOx emissions.

Variable Valve Timing

A modern way of controlling exhaust gas recirculation is by using variable valve timing (rather than an EGR valve). When the engine is on the exhaust stroke, the exhaust valve can close prematurely, keeping a specific portion of inert gas behind to use in the next power stroke. To reduce NOx emissions, you can close the exhaust valve sooner on the exhaust stroke. To increase performance, you would do the opposite.

Increase AdBlue/DEF Injection

The reaction of the SCR will be less efficient if less AdBlue is injected. Though this may not have a huge impact on performance, the less AdBlue that’s injected, the less frequently you’ll have to fill it, meaning a reduction in maintenance.

Air/Fuel Ratio

Diesel engines have a far larger range of air/fuel mixtures under which they can operate versus gasoline (ratios of 70:1 are not unheard of). If the engine is running fairly lean, O2 will be left over after the reaction, and this O2 is used to react with the nitrogen at high temperatures to form NOx. By altering the air/fuel ratio you can change the emissions.

6. Should everyone panic?

Only if you’ve just recently invested your entire portfolio into VW stocks (gotta remember to diversify!) need you panic. Regardless of what happens here, it’s undeniable that VW makes phenomenally efficient vehicles. So far, the Jetta TDI is the most fuel efficient vehicle I’ve tested, and it commonly achieved greater than 50mpg when I drove it (peaking at 62 mpg for a brief highway trip).

Volkswagen has a problem and they will address it, and current VW TDI customers will be notified of the recall. It will be a bumpy ride for the execs at VW. Fix the problem, obey the law, and move on.

Shout out to The Humble Mechanic, who works for a VW dealer, for providing insight on the subject. He offers his perspective here.