The developers of diesel engines stand for a conflict of interest: many measures that reduce nitrogen oxide emissions provide a clear increase in fuel consumption. At the autumn meeting of the Forschungsvereinigung Verbrennungskraftmaschinen e.V. (FVV) in Würzburg, researchers presented new approaches to meet the objectives of achieving a clean diesel engine.
In order to improve the harmful emissions of diesel engines, not only the exhaust gas after-treatment system should function properly. The engine developer wants to reduce the emission of the engine already in the base. In addition to constructive measures, the control of the engine plays an important role in this. It is necessary that the various variable systems are controlled in such a way that the legal exhaust gas limits are reliably observed, while at the same time the engine uses as little fuel as possible.Three of the most important variables, which are not independent of each other and specifically for the passenger diesel, the injection start, the amount of returned exhaust gases to the cylinder and the eddies of the air in the cylinder. The latter can for example be influenced by turning an intake channel on or off.
Towards clean diesel engine
Researchers at the ETH Zurich published the results of a project, with which the regulation of these quantities in the future will be considerably more flexible. can be performed. The researchers calculate the course of the combustion in the engine on the basis of the heat curve and control the engine using the results of this calculation.The current engines are dependent on the data of the physical emission sensors, such as those for the determination of the NOx percentage in the exhaust gas. The calculation model would not require such sensors.
Virtual sensor network
The researchers do not want to replace the physical sensors, but supplement them with a virtual sensor network. Together with control technicians from the ETH Zurich, it was investigated to what extent the calculation corresponds with reality. The result: even for dynamic test cycles such as the World Light-Duty Test Cycle (WLTC), which was discussed at the introduction, the calculated values correspond cumulatively with the actual emission values.A faster engine arrangement would also be a different one in the future. Problem of modern diesel engines can solve: the combustion process is very dynamic. It is important that the vehicle responds immediately if the driver presses the accelerator pedalPhysical sensors that record the basic emission values always react with a delay of up to 2 seconds to the change in the operating state of the engine. In addition, the delay of exhaust gas aftertreatment systems is added. This results in higher emissions for a short time. The researchers are convinced that with modern control methods they can roughly halve this delay time.
Research in Japan
In Japan, too, intensive research is being done into methods to further reduce the emission values of diesel engines. At Waseda University in Tokyo, scientists are looking for ways to more accurately control the regeneration of particle filters. Because extra fuel is injected for each regeneration, the exact knowledge of the actual operating condition during the entire lifetime of the vehicle can lead to significant savings in consumption.For both oxidation and SCR catalysts the concepts were studied, which temperatures function. This is important in order to reduce the ever-increasing emission values after a cold start.Another approach is to reduce deposits arising in the engine through exhaust gas recirculation. This would make it possible to continuously work with larger quantities of exhaust gas recirculation. The resulting drop in temperature causes less NOx formation inside the engine.That both Germany and Japan carry out intensive research into the diesel engine, reflects the potential that is still present with this combustion principle. Further research will make it possible to reduce the emissions in real street traffic as well.