Combustion Chemistry

Fire fascinates humankind since early history – both because of its destructive potential and of its many benign applications. Using fire, techniques such as lighting and heating, cooking and baking have become established. Combustion was involved early on in processing metals, clay and glass as well as in preparing medicines and spirits. Since the industrial age, combustion in furnaces and engines has become the major source of energy for transportation, heat and power generation. Top industries such as car, ship, aircraft and power plant production, steel- and glassmaking rely on combustion energy, typically produced using fossil fuels today. Especially in the transportation sector, energy density – the energy stored in the mass and volume of the fuel – must be considered, since this determines range and efficiency. Petroleum-based hydrocarbon fuels, well-established for this purpose, are not easily outperformed. Concerns about global climate change, air quality and human health as a consequence of carbon dioxide and other pollutant emissions from combustion of fossil fuels has led to increasing research activities regarding potential alternatives. Biofuels and biomass are being advocated as one solution. Chemically, these fuels often contain further elements than the presently used hydrocarbons constituted from carbon and hydrogen. Chemical functions present, for example, in oxygenated alternative fuels such as alcohols, ethers, esters and furans lead to different classes of combustion reactions, often hitherto unexplored, and may generate novel undesired emissions. Strategies for classification of the combustion behavior of alternative fuels with respect to pollutant formation follow a dual approach: on the one side, computer models for the complex reaction networks are being established to predict the combustion reaction under conditions relevant for the specific process, and on the other, cutting-edge experimental methods are being applied to test, validate and refine such models in controlled environments. Multiple scales must be spanned in this research from the molecular level to the size of practical combustors, and simultaneous information on the flow and many chemical compounds is necessary, posing extreme challenges to both experiment and simulation. Chemistry is thus becoming increasingly important to evaluate the complete sequence from fuel preparation to emission control and abatement. Recent examples will be discussed in the presentation.