Volkswagen has not one problem, but two. The first, is how to salvage its reputation after we all found out about the firm’s use of defeat software to cheat US EPA emission control tests.
The second problem is in some ways much tougher: the company has to figure out what to do about it.
It goes without saying that the reason for cheating on the test is that there is no way to achieve legal emission levels at the power and efficiency delivered by the EA189 engine. But why only this engine? To understand that, we have to consider what’s going on inside the combustion chamber.
Fuel combines with oxygen in the air to produce carbon monoxide, carbon dioxide, water vapor and of course heat.
Carbon monoxide is a deadly killer, so catalytic converter technology was developed to convert it into yet more CO2. Note that while CO2 is a greenhouse gas, it is not a pollutant. Oxygen is only 21 percent of the air we breathe. 78 percent is nitrogen and at the elevated temperatures and pressures of automotive combustion chambers, the oxygen reacts with nitrogen to produce an assortment of oxides of nitrogen, or NOx.
NOx is a problem because it’s a major contributor to photochemical smog and the very attributes that make diesel engines so efficient also make them potent producers of NOx. There is no free lunch.
One strategy to extract the NOx is exhaust gas recirculation (EGR). This is widely and erroneously believed to be a “re-burning” of exhaust gases, but in fact it acts like an inert filler in the combustion chamber air fuel charge – reducing combustion chamber temperatures and thus lowering NOx levels.
That’s great for the environment, but terrible for power, economy and drivability.
Modern EGR is mapped and computer-controlled to maintain just the right amount to keep NOx levels in check without making the vehicle undrivable. But if it’s power and economy you’re after, you might be out of luck.
VW engineers neatly created an algorithm that detected when the car was undergoing emissions tests. It would drastically increase the amount of exhaust gas recirculation to produce very clean emissions. In every other operating mode, EGR was reduced dramatically to result in greater power and economy.
One possible fix for VW is to remap the engine control algorithm to add more EGR, but the result will show in lowered fuel mileage and reduced power – something its customers won’t take lying down.
But there is another way.
It’s called selective catalytic reduction (SCR). The chemistry is complex, but to put it simply: a special counter-converter converts the NOx back to nitrogen gas and CO2, neatly resolving the problem.
Remember though, there’s no free lunch here either. SCR needs a steady stream of urea, or diesel exhaust fluid, in the exhaust stream to make the system work.
VW’s logical solution at this point is to add urea injection to the affected engines. Unfortunately, the under-hood area in these vehicles is already packed, making adding anything difficult. The revamped exhaust system and plumbing may also prove ruinously expensive to develop, manufacture and retrofit in the field.
After that, it will be necessary to convince owners to have the retrofit installed, then carry diesel exhaust fluid with them and replenish the tank periodically.
Fortunately, a little goes a long way and the fluid can usually be topped off during scheduled maintenance. Chevrolet’s excellent Cruze Diesel, a competitive model to VW’s Golf and Jetta lines, uses this technology successfully, as do many other light-duty diesels.
Look for a crash program at VW to engineer a retrofit of urea injection systems. It will be expensive, very expensive, but unless Volkswagen can cut some sort of deal with legislators, it may be the only technical solution for millions of VW diesel owners.