Manufacturers who have invested in diesel engine production are faced with a dilemma. The exhaust gas measurement, which was previously compliant with the law, is being scrutinized and will no longer exist. Ultimately, pollutant detoxification is only possible with complex technical processes. As an additional consumable, AdBlue has been an effective medium for detoxifying pollutants in trucks for years, but it has a greater impact on passenger cars as a cost factor and calls into question the profitability of diesel cars.
As a last resort to reduce the high nitrogen oxide emissions in practice, the manufacturers rely on a chemical process in which harmful nitrogen oxides are converted into nitrogen and water vapor with the help of ammonia. For this purpose, a storage catalytic converter is integrated, which can store the nitrogen oxides for a short time. This elaborate process currently offers the best level of efficiency in pollutant detoxification and must even be used in small cars with diesel engines. In addition to the technology, you need an additive in a separate tank with the brand name AdBlue: a mixture of 67,5% water and 32,5% urea. AdBlue is injected into the exhaust gas flow from the additional tank and chemically decomposed by the catalytic converter. This forms ammonia, which reacts with the nitrogen oxides and converts them mainly into nitrogen and water vapor. With this method, nitrogen oxides react selectively. This is why this process is also called Selective Catalytic Reduction (SCR) in technical terms.
Elaborate cleaning process
Technically, the complex process only works with the help of pressure, temperature and exhaust gas sensors. And technically, the emission reduction efficiency of more than 80% can only be achieved if the added amount of AdBlue is continuously 40–60 milliliters per liter of diesel fuel consumed. With continuous cleaning without shut-off devices, this results in another 100–4 liters of AdBlue for 6 liters of diesel. The additional costs then run through like a red thread: starting with the higher purchase price, through the additional costs for AdBlue consumption, to the maintenance of the system in the event of errors in the exhaust gas cleaning. Since AdBlue freezes at –11,5 ° C, the tank for the additive can be heated in all cars. At Mercedes it gets to the point and AdBlue is defined as a regular fuel.
Easily accessible tanks that can be refilled with AdBlue at the filling station using a tap are currently only available on a few models. Otherwise the irritating and corrosive solution must be refilled manually. And that is quite time-consuming because the tank is often housed in the trunk. There is little interest on the part of the manufacturer in larger tanks that improve service-friendliness, because then weight and fuel consumption increase and thus the classification in higher weight classes with stricter specifications for the exhaust gas values.
The distance that must be covered each year for a diesel to pay off economically is achieved in reality, for example, by sales representatives. The higher costs do not pay off for private users. While the share of new registrations of diesel cars in 2015 was 48% of new registrations, the share for October 2016 has already fallen to 44,2%. If the pressure of the approval authorities increases and nitrogen oxide emissions can only be measured under real conditions, it is likely that only diesel vehicles with SCR technology will be approved. The farewell to the diesel car continues slowly.
Cover picture: Copyright © Jürgen Fälchle @ fotolia.com
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