Research

Stability of combustion systems

For example, the wall can directly influence the reaction process via catalytic effects. Already at a low chemical activity, catalytic processes can be highly relevant for effects such as pollutant formation or flame stability via radical adsorption on the wall. This becomes obvious by the fact that walls of different qualities can have decisive influence on the stability of combustion systems. The reaction-diffusion system of the gas phase becomes more complex due to the high gradients at the wall. Furthermore, a number of pollutants, especially unburned hydrocarbons, carbon monoxide and soot are formed largely in regions close to the wall.

Efficient exhaust gas purification

The aftertreatment of pollutants in the exhaust train always happens on surfaces that often represent partition walls of honeycomb structures (monoliths). Those monoliths can be coated with a catalytic material on which the rate of the purifying chemical reaction is increased, or they are designed as filters to absorb soot particles, nitrogen oxides or ammonia. Walls in the exhaust train, such as exhaust pipes or mixers also play an important role during the provision of additives used in emission control, such as ammonia. Aqueous ammonia is used as precursor and can form undesirable films and solid deposits at theses walls. In all those cases chemically reacting turbulent flows interact with solid walls.

High temperature gradients

Combustion and exhaust systems are characterized by low temperatures in close proximity to the wall as well as by high temperature gradients. This leads to special conditions during heat transfer. The fluid-wall heat transfer processes are of central significance and have to be understood in the context of transient processes to analyze near-wall reaction processes.