Abstract
In response to the limited resources of fossil fuels as well as to their combustion contributing to global warming through CO2 emissions, it is currently discussed to which extent future energy demands can be satisfied by using biomass and biogenic by-products, e.g., by cofiring. However, new concepts and new unconventional fuels for electric power generation require a re-investigation of at least the gas turbine burner if not the gas turbine itself to ensure a safe operation and a maximum range in tolerating fuel variations and combustion conditions. Within this context, alcohols, in particular, ethanol, are of high interest as alternative fuel. Presently, the use of ethanol for power generation—in decentralized (microgas turbines) or centralized gas turbine units, neat, or cofired with gaseous fuels like natural gas (NG) and biogas—is discussed. Chemical kinetic modeling has become an important tool for interpreting and understanding the combustion phenomena observed, for example, focusing on heat release (burning velocities) and reactivity (ignition delay times). Furthermore, a chemical kinetic reaction model validated by relevant experiments performed within a large parameter range allows a more sophisticated computer assisted design of burners as well as of combustion chambers, when used within computational fluid dynamics (CFD) codes. Therefore, a detailed experimental and modeling study of ethanol cofiring to NG will be presented focusing on two major combustion properties within a relevant parameter range: (i) ignition delay times measured in a shock tube device, at ambient (p = 1 bar) and elevated (p = 4 bar) pressures, for lean (φ = 0.5) and stoichiometric fuel–air mixtures, and (ii) laminar flame speed data at several preheat temperatures, also for ambient and elevated pressure, gathered from literature. Chemical kinetic modeling will be used for an in-depth characterization of ignition delays and flame speeds at technical relevant conditions. An extensive database will be presented identifying the characteristic differences of the combustion properties of NG, ethanol, and ethanol cofired to NG.
Highlights
The largest part of our energy used - electric power generation, heating, transportation, and aviation - is based on fossil fuels
We focus on two major combustion properties - ignition delay time and burning velocity – for temperature, pressure and fuel air regimes typical for so called “micro gas turbine combustors”
Ethanol mixtures The reaction model of the present work (DLR-RG) is describing very well the ignition and the heat release of the ethanol-air mixtures studied in the present work
Summary
The largest part of our energy used - electric power generation, heating, transportation, and aviation - is based on fossil fuels. Alternative and renewable energy resources became increasingly important, mainly to combat greenhouse emissions, and to ensure security of supply and a lower increase of costs for energy by reducing fuel import dependency. Sustainability in energy supplies requires new concepts with respect to feedstock, production, and the final product. Improvements in overall-efficiency of the technical process are desirable as this will directly lead to lower emissions of CO2, besides NOx, unburned hydrocarbons, and soot particles, contributing towards an environmental friendly energy production. An increase in efficiency and at the same time a reduction of CO2 and pollutants is required. Small to large-scale gas turbines - stand alone, process integrated or in combined cycles - will be needed
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