High-Pressure Laminar Burning Velocity Measurements of Ethanol - A Co-Optima Fuel Candidate 2020-01-0332
Co-Optimization of Fuels and Engines initiative (Co-Optima) of the U.S Department of Energy started investigations on several candidates of biofuels and blends for internal combustion engines. At this stage, only a few biomass-derived fuel blendstocks (including ethanol) for advanced spark-ignition engines have been selected using enhanced screening criteria, which included boiling point, toxicity, research octane number, octane sensitivity, and economical distribution system, etc. Ethanol, of which this paper is focused on, is also an important fuel because of its high-octane number which in turn promotes advance ignition timing and higher thermal efficiencies in reciprocating engines. Measurements of laminar burning velocity (LBV) is a key metric to understand fuel performance and applicability in engines. Furthermore, in order to quantify more complicated, and practical, burning regimes such as turbulent combustion much of the underlying theory requires knowledge of LBV. While there exist many studies for ethanol LBV under atmospheric conditions, there are only few studies on combustion characteristics at high pressures that are relevant to engines. Here measurements of ethanol LBVs at two initial pressures of 2 atm and 10 atm and two initial temperatures of 373 K and 428 K are presented. Equivalence ratio was varied in a wide range from 0.7 to 1.5 to examine the effects on laminar burning velocity. It has been noticed that a cellular structure formed during combustion at 10 atm with synthetic air. To restrain occurrence a cellular flame during combustion, a mixture of helium and nitrogen in synthetic air was employed. The results presented are also compared with the predictions of some of the available detailed kinetic mechanisms as part of their validation process and found to be in good agreement with simulations. Current effort provides a comprehensive investigation of ethanol LBVs which can be used in the development of detailed and reduced kinetic mechanisms in the future.