More carbon monoxide due to smaller displacement
The trend among carmakers toward smaller engines is leading to the increased occurrence of carbon monoxide on the walls of cylinder chambers, as researchers at Darmstadt Technical University have determined. Their simulated processes of combustion engines and resulting studies are relevant for both the automotive industry and engine designers.
Carbon monoxide is produced by incomplete combustion of the fuel and should be avoided not only because of its harmful effect on health. Because engine manufacturers are increasingly tending to build smaller engines, more toxic gas is released. According to researchers from the Department of Mechanical Engineering at Darmstadt Technical University, this downsizing leads back to an increased occurrence of carbon monoxide.
"It is cooler there than inside the cylinder, so coupled reaction-transport processes run differently on the walls. However, we did not expect such a high carbon monoxide concentration near the walls," says Sebastian Bürkle, managing director of the Collaborative Research Center Transregio 150.
Computer simulations important
Since flame-wall interactions are more pronounced in smaller engines, the problem is more serious at the walls than in machines with larger displacement. If nothing else, the phenomenon has uncovered the cause of the high carbon monoxide levels using computer simulation. "Our calculations show that the carbon monoxide is not generated near the walls, but accumulates there due to the flow," says co-author Guido Künne.
The results are not only relevant for carmakers, but also for aircraft engine designers. A new technique known as lean-burn combustion does reduce nitrogen oxide emissions from aviation. But because the flame burns closer to the wall in the process, the carbon monoxide concentration increases.
The amount of pollutants could be reduced, for example, by a different geometry of the combustion chamber or a higher wall temperature.
