研究結果有主要三點。第一，正丁醇/空氣和第三丁醇/空氣混合物的層流火焰速度(SL)隨著壓力的增加而下降，相反地，在一相同的u條件下，紊流火焰燃燒速度(ST)隨著壓力增加而上升。ST的增加歸因於，壓力與運動黏滯係數的倒數成反比( -1 p-1)，故壓力增加，雷諾數也會增加。第二，在相同條件下，正丁醇/空氣的SL和ST較第三丁醇/空氣混合物高，此一差異歸因於正丁醇和第三丁醇之件的化學反應路徑，且一般認知的直鏈燃料火焰速度較支鏈燃料快也適用於醇類。第三，本研究使用文獻常用的四個火焰速度一般通式，來觀察正丁醇/空氣和第三丁醇/空氣混合物的SL和ST之預測和其自我相似性。 ;Greenhouse gas emissions, uncertainties related to fuel prices, and seeking different options for renewable energy with low emissions are the main goals for many researchers to venture into biofuel research. Alcohol-based biofuels are widely accepted as alternative fuel sources to partly or fully consume for spark-ignition engines or other combustion applications thereby reducing global warming emissions. Butanol isomers are interesting alcohol-based biofuels due to their advantages of low lubricity, low corrosion, and fewer ignition problems in cold weather. This study investigates experimentally the laminar and turbulent burning velocities (SL and ST) of n-butanol/air and tert-butanol/air mixtures at a constant high-temperature T = 373 K over a range of pressure p = 1-5 atm and r.m.s turbulent fluctuation velocity u = 0 – 4.2 m/s. Experiments were performed in a dual-chamber fan-stirred cruciform burner capable of generating near-isotropic turbulence with negligible mean velocities. A high-speed camera is used to record the time evolutions of flame radii <R(t)> within the experimental domain 25 mm ≤ <R(t)> ≤ 45 mm so that SL and ST can be determined. For turbulent burning velocity data convert using Bradley’s mean progress variable to ST,c̅=0.5 because it shows a better representative regardless of the flame geometries with ST,c̅=0.5 = ST(<R>c̅=0.1/<R>c̅=0.5)2 = ST(1.4)2.
Results show three main points. First, the value of the SL of n-butanol and tert-butanol mixtures decreases with increasing pressure. It indicates that n-butanol/air and tert-butanol/air mixture present the same instability behavior with the fact that the density of the unburned mixture (u) increases in proportion to the increase of pressure but the mass burning capability of laminar premixed flame has its limitation. In contrast, the value of ST increases with increasing pressure at any given u. The increase of Reynolds number plays a role in this situation because the pressure is inversely from kinematic viscosity, -1 p-1. In addition, the laminar and turbulent burning velocities of the n-butanol/air mixture are generally faster than those of the tert-butanol/air mixture under the same conditions. The main reason for the difference value in the laminar and turbulent burning velocity between n-butanol and tert-butanol is chemical kinetics.. Moreover, normalization analysis of these measured ST/SL data of n-butanol/air and tert-butanol/air mixtures are made by using four selected general correlations from the literature to observe their predication merits and drawbacks.
