Engine expert Prof. Thomas Koch, Director of the Institute for Reciprocating Engines at the Karlsruhe Institute of Technology, warns against blind actionism in pursuing possible diesel bans and explains technical issues concerning software updates that will help reduce nitrogen oxide emissions.
Professor Koch, diesel vehicles are popular and very common in Germany, but there is increasing skepticism. Politicians, environmental groups, and experts are all railing against diesel, there is talk of bans, and sales are falling. What impact does diesel actually have on the environment?
Prof. Thomas Koch: We have to differentiate between several types of emissions. First, there is carbon monoxide, of which there is a very low concentration in exhaust gas, typically less than in ambient air; it is therefore insignificant. Second, there are unburned hydrocarbons, which you can smell when driving behind classic cars with gasoline engines. In the case of diesel vehicles, their amounts in the exhaust is extremely low; due to engine exhaust aftertreatment, it is even lower than in city air. Third, particles including soot can escape. Their amounts are also insignificant. Here’s a comparison: a typical bicycle tire rim has a wear of four to five milligrams per kilometer due to abrasion, largely the result of braking. A diesel car emits only 0.2 to 0.5 milligrams per kilometer in the exhaust gas, when calculated without vehicle effects. The correlation between modern diesel engines and particulate matter is thus artificial. This whole debate is misguided. Finally, the fourth issue being focused on is that of nitrogen oxides, NO2 in particular. These emissions stem largely from diesel, affecting cars in the Euro 4 and Euro 5 emissions standard classes, as well as the first vehicles in the Euro 6 class.
In a joint declaration by the Scientific Association for Motor Vehicle and Engine Technology e.V. (WKM), you and 24 other leading engine experts warned against actionism with regard to bans on diesel vehicles. What was your intention with the declaration?
Prof. Thomas Koch: The association expressed its concern about the ongoing criticism of diesel. There is no justification for it. However, I have noticed that discussion on the matter has become more objective in the last few weeks. Criticism is certainly acceptable. But banning combustion engines, which includes diesel engines, is entirely out of the question. They are essential for long-term planning. I am convinced that we will still be using internal combustion engines in 50 years time, while also maintaining a mix of various propulsion systems.
Why do you believe the whole debate about diesel has become a “witch hunt”?
Prof. Thomas Koch: Volkswagen’s actions in the United States were clearly illegal. In Europe, the situation is entirely different. The EU Commission set the much-discussed nitrogen oxide limit value at 180 milligrams in 2007. It was clear to all experts in the field that the limit value could not be met last year with the technology available. You need only a little common sense to realize that this goal is unattainable in real-life operating conditions. This is why gray areas were deliberately left in the respective legislation. The engineers therefore faced the challenge of installing particle filters in Euro 5 engines that did not immediately become clogged with soot. There are several options. The filter can be heated to 600 degrees; however, this pushes the technical limits. As early as 2000, Peugeot developed a fuel additive which dissolves soot, but which contained cerin, which is slightly poisonous. A third option is to protect the particle filter with NO2. A high percentage of nitrogen oxide also prevents filter clogging, but results in a significantly higher concentration of NO2 in the exhaust as well. This compromise also came with a heavy price for manufacturers: a high amount of precious metals is needed in the oxidation catalyst to generate enough NO2.
Do you think that these understandable technical considerations made the industry go ahead with the production of vehicles with high nitrogen oxide emissions?
Prof. Thomas Koch: In the case of Euro 5, absolutely. The industry definitely lost sight of the limit value, partly in the conviction that it was not attainable in real-life operating conditions. Well aware of the existing gray areas, the industry believed that meeting the limit value during certification would be sufficient. That is why a razor-sharp distinction between the certification of an acceptable limit value and compliance with the limit value in real-life operating conditions must be made. The gray area was clearly abused in some cases with Euro 5 class vehicles due to the unattainability of 180 mg/km; it must be reiterated that this limit value was simply unattainable in real-life operating conditions.
How can this development be brought under control?
Prof. Thomas Koch: It is very complex because all particle filter models that receive a software update have to be redeveloped. Moreover, clean calibration along with adequate testing is not realizable within a half year. The situation with Euro 6 is different. The industry has not fully exploited the opportunities in this class, and has not prioritized the fuel consumption-relevant increase of exhaust temperature, which is necessary for CO2 reasons when AdBlue is added. However, I am very pleased that the SCR technology for Euro 6 is finally being introduced across Europe after the first field trials with a few US vehicles.
The recall for diesel vehicles targets the six million cars equipped with engines of the Euro 5 standard, which was valid up until three years ago. The German government wants 90 percent of them to be sent to the auto repair shop in the next few months to have new engine software added. Will nitrogen oxide emissions decrease as a result?
Prof. Thomas Koch: I expect a reduction of about 20 to 30 percent on average. With some vehicles, no further improvement is possible, while others have greater potential. Yet I would advise caution. Now some people are trying to tinker with a number of parameters to get emissions from between 700 and 800 milligrams down to 500 milligrams, for example. There is intense interdependence of the factors affecting emissions, such as fuel efficiency, noise levels, durability, regeneration behavior, long-term stability, driveability, and so on. Success now depends on the configuration of each individual vehicle; with each new load, the particle filter becomes clogged with soot faster due to subsequently lower NO2 concentrations. Furthermore, the particle filter is a component that is important for safety and for vehicle operation.
One of your colleagues, Peter Mock, director of the ICCT Europe research institute, is concerned that the scheduled update reduces nitrogen oxide emissions while at the same time increasing diesel consumption. Are these assessments correct in your opinion?
Prof. Thomas Koch: I agree with Mr. Mock on that point. A moderate increase in fuel consumption can be expected for some models. With this technology, it’s like an apartment floor plan: If I want to have a bigger kitchen, the living room has to be smaller. I have to be honest. A particle filter that clogs up with soot more quickly leads to increased fuel consumption and the risk of increased oil dilution. Aging effects on the catalytic converter must also be taken into account. There are other challenges as well. In some Euro 5 vehicle series, over ten percent of exhaust gas recirculation valves have failed, which is definitely a safety concern. Imagine a case where the part fails at night on a road out in the country. Now Euro 5 needs to be adjusted again while pushing the limits of technology, increasing the role of NO2 within the bounds of what is possible.
What is your advice?
Prof. Thomas Koch: Speaking from a purely technical perspective, I went so far as to say that even the VW vehicles with illegal emissions-controlling software should be left as they are. Although I am not trying to sugarcoat a violation of the law, there are reasons why the cars were developed the way they were. A highly complex technical system that has been tested over several years should normally be left as is. Political pressure is now so high that a solution for NO2 emissions must be found. As a technician, I see huge challenges in accomplishing this. The engineers now benefit from at least ten more years of experience with particle filters, and calibration tools are also much better today.
Critics claim that a software update could lead to problems with exhaust gas recirculation, in particular for commuters who often drive short distances in the city. In addition, a drastic drop in engine performance may also result.
Prof. Thomas Koch: I do not see minor changes in engine performance as a critical issue. If there are any changes, they will be minimal. Diesel was never the best choice for purely short-distance travel. This certainly won’t change after the updates.
Can diesel bans for Euro 5 vehicles be prevented by the addition of AdBlue or electrically heated pre-cat systems like those offered by Twintec/Baumot, for example?
Prof. Thomas Koch: That is theoretically possible if enough installation space is available, if the vehicle has the necessary AdBlue equipment, and if the whole system has been proven to be reliable. However, it is not a plug-and play-solution. It also requires three to four years of intensive testing. This is a prototype which also heavily affects engine management by removing exhaust gases upstream of the turbine, in the exhaust gas turbocharger. Vehicle safety is also affected. All in all, the amount of work required to develop this is significant. In the end, an upgrade will cost far more than 2000 euros; to my knowledge, sufficient trials have not yet been carried out. By the time these solutions are installed (which is not possible for many vehicles), all emission measurements in Germany will be within the target range.
What are diesel engines of the latest generation capable of?
Prof. Thomas Koch: In terms of technology, the issue of nitrogen oxide emissions has been solved. The latest technology now being rolled out meets all limit values. Vehicles will emit between 20 to 40 milligrams, and in unfavorable conditions up to over 80 milligrams. The diesel engineers have done their homework. Now we need a little more patience until all measuring stations register levels within the permissible range. The levels improve significantly each year.