|Universität Bielefeld > Department of Chemistry > Research Groups > Physical Chemistry I > PC I - Projekte > PC1 - Projekte - SFB686|
Model-based control of homogenized low-temperature combustion
In the forseeable future, economically and ecologically feasible energy scenarios will include the use of fossil fuels in efficient practical combustion systems. In conventional combustion, stabilization is achieved with a mixture gradient between air and fuel. This leads to a conflict, however, between the emission of soot and oxides of nitrogen (NOx), which cannot be reduced simultaneously with conventional approaches. An important step forward is the development of techniques leading to homogenized low-temperature combustion.
Figure 1. Left: Schematic representation of a novel preheatable low-temperature burner. Fuel, oxidizer and inert diluent are fed separately (via a two-chamber system) through holes and tubes in the matrix. Right: top view of the burner matrix with 91 tubes and 306 holes.
By homogenization and low peak temperatures, significant reductions in soot and NOx emissions can be achieved simultaneously; in addition, the efficiency is increased. With this approach, however, instabilities may result. These are caused by convergence of the relevant time scales for mixing (shorter because of homogenization) and chemical reaction (longer because of lower temperatures). The goal of the large-scale cooperation project SFB 686 is to achieve stabilization of homogenized low-temperature combustion systems by suitable active control. A prerequisite for dedicated control mechanisms for these combustion systems is a detailed physical and chemical analysis of the underlying fundamental processes.
In the first project period, PCI participation includes project B3 which is devoted to investigation and improvement of the necessary reaction mechanisms for the homogenized low-temperature combustion regime for the entire SFB team; these mechanisms are then a starting point for reduction as a basis for control.
Experimental data for combustion model development are provided e.g., by a special low-temperature burner developed within the SFB (see Fig. 1), which makes temperatures below about 1500 K accessible for detailed analysis. The experimental investigations rely on a combination of molecular-beam mass spectrometry and laser diagnostics permitting detection of major and intermediate species under low-temperature combustion conditions (see Fig.2).
In the second project period, the successful experiments in B3 from the first period are now being validated and reduced. In continuation of this approach, experiments with further fuels are planned including dimethyl ether, ethanol and n-heptane; also, the pressure range will be extended. A second project C5 contributed by the PCI group is now devoted to the adaptation of chemiluminescence to active control of low-temperature combustion processes.
Further information is available under: http://www.sfb686.rwth-aachen.de/