Abstract
Experimental characterization of the burning behavior of gaseous mixtures has been carried out, analyzing spherical expanding flames. Tests were performed in the Device for Hydrogen-Air Reaction Mode Analysis (DHARMA) laboratory of Istituto Motori—CNR. Based on a high-pressure, constant-volume bomb, the activity is aimed at populating a systematic database on the burning properties of CH4, H2 and other species of interest, in conditions typical of internal combustion (i.c.) engines and gas turbines. High-speed shadowgraph is used to record the flame growth, allowing to infer the laminar burning parameters and the flame stability properties. Mixtures of CH4, H2 and air have been analyzed at initial temperature 293÷305 K, initial pressure 3÷18 bar and equivalence ratio = 1.0. The amount of H2 in the mixture was 0%, 20% and 30% (vol.). The effect of the initial pressure and of the Hydrogen content on the laminar burning velocity and the Markstein length has been evaluated: the relative weight and mutual interaction has been assessed of the two controlling parameters. Analysis has been carried out of the flame instability, expressed in terms of the critical radius for the onset of cellularity, as a function of the operating conditions.
Highlights
No matter the claim and the quest for new answers to the needs of an energy-thirstier society, thermal conversion systems will play a key role in the energy supply chain
Markstein length has been evaluated: the relative weight and mutual interaction has been assessed of the two controlling parameters
CH4 has been used with heat engines for a long time, even if with the status of a “niche” solution: as a fuel for internal combustion (i.c.) engines, it offers some advantages over gasoline, having wider flammable limits and better anti-knock characteristics, at the cost of a lower flame speed
Summary
No matter the claim and the quest for new answers to the needs of an energy-thirstier society, thermal conversion systems will play a key role in the energy supply chain This awareness, along with the urgent need of CO2 reduction (currently the main driver of technology advance), has at least two direct consequences: the introduction in the energy cycle of CO2-neutral fuels (biomass-derived) and the design/development of more efficient conversion systems. Sometimes placed in the category of “alternative” fuels, methane (CH4) is a hydrocarbon, sporting the peculiarity of the lowest C/H ratio, if compared to other fuels: by trivial reasoning, the less the carbon, the less the CO2 This feature has boosted a renewed attention to CH4, which represents the main constituent of natural gas. The overall effect is to extend the stable operation map to extreme conditions (e.g., high EGR)
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