Study on the Laminar Characteristics of Ethanol, n-Butanol and n-Pentanol Flames 2015-01-1933

Due to serious energy crisis and pollution problem, interest in research of the alternative fuels is increasing over the world. Alcohol fuels are always considered to be promising alternative fuels. Lower alcohols owning high octane number is good octane enhancer for SI (Spark ignition) engine, however is difficult to be used in CI (Compression Ignition) engines. Higher alcohols like pentanol with higher energy content, poor water solubility and higher cetane number are good choice for the CI engines. In this study, laminar flame behaviors of ethanol-air, n-butanol-air and n-pentanol-air mixtures at 393 K and 0.1 MPa are compared and analyzed with the spherical propagating flames. Comparison of the laminar flame speeds measured in the previous studies (Li et al.) show that laminar flame speed of ethanol is the fastest with slower flame speed of n-butanol and n-pentanol at lean mixture. At rich mixture, three alcohols present very close values. The effective Lewis number of n-pentanol is the biggest, and then n-butanol and ethanol. The difference among the three fuels is decreasing with the increase of equivalence ratio. However, all the values are bigger than one and indicating diffusively stable flame front. Flame thicknesses of three alcohol fuels are very close, while the wave number decreases in the order of n-pentanol, n-butanol and ethanol and shows the hydrodynamic instability is enhanced with the carbon number increasing. Combining with the schlieren pictures, it is seen that ethanol has the more stable flame front at very rich mixture, which indicates hydrodynamic instability plays the dominant role at the rich condition.