Energy Fuels 2009, 23, 4900–4907 Published on Web 08/27/2009
: DOI:10.1021/ef900378s
Measurements of Laminar Burning Velocities and Markstein Lengths of n-Butanol-Air Premixed Mixtures at Elevated Temperatures and Pressures Xiaolei Gu, Zuohua Huang,* Qianqian Li, and Chenglong Tang State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, Xi’an, People’s Republic China Received April 29, 2009. Revised Manuscript Received August 5, 2009
Measurements of laminar burning velocities and Markstein lengths of n-butanol-air premixed mixtures was made over a wide range of equivalence ratios at initial temperatures of 413, 443, and 473 K and initial pressures of 0.1 and 0.25 MPa using the high-speed schlieren photography and outwardly propagating flame. Effects of laminar flame thickness, thermal expansion ratio, and flame Lewis number on flame stability response were studied. Schlieren photos of flame propagation are recorded. The results show that laminar burning velocities of n-butanol-air premixed mixtures are increased with the increase of initial temperature, and they decrease with the increase of initial pressure. Markstein lengths are decreased with the increase of the equivalence ratio, and they decrease with the increase of initial temperature, and all these indicate that the flame instability is increased with the increase of equivalence ratio, the decrease of initial pressure, and the increase of initial temperature. Rice et al.5 and Yacoub et al.6 have studied engine emissions and knock characteristics of the butanol-gasoline blends. Liao at al.7 measured the laminar burning velocities for ethanol-air mixtures experimentally over a wide range of equivalence ratios in a constant volume combustion bomb, and the effect of flame stretch at the flame front was discussed. Alasfour8 experimentally investigated the availability analysis of a sparkignition engine using butanol-gasoline blends. The results showed that maximum power is greater when using the butanol-gasoline blend compared to that of pure gasoline. Dagaut et al.9 have recently investigated the oxidation of blends of n-butanol-gasoline surrogate mixtures (85-15 vol %) using a jet-stirred reactor (temperatures range from 770 to 1220 K at 10 bar). Yang et al.10 studied combustion intermediates in premixed, low-pressure (30 torr, 1 torr = 7.5 kPa), laminar, n-butanol-oxygen flames, for all four isomers, by using photoionization mass spectrometry. McEnally et al.11 studied methane-air flames doped with four isomers of butanol and two isomers of butane. The major species, the decomposition kinetics of the butanol dopants, and the emissions of toxic byproducts were measured. Oehlschlaeger et al.1 experimentally studied the autoignition of four isomers of butanol at high temperatures in a shock tube, and a kinetic mechanism for description of their high-temperature oxidation was developed. Sarathy et al.12
1. Introduction The energy crisis and air pollution created an incentive to study and evaluate alcohols as alternative fuels or fuel additives in spark-ignition engines. Ethanol is proposed as a replacement because it is biodegradable and less detrimental to groundwater with the positive impact of emissions reduction and octane improvement. Unfortunately, ethanol is classified as a solvent and is fully miscible in water, preventing it from being transported via pipeline like pure gasoline. n-Butanol has several advantages over ethanol as a transportation fuel. It has a higher energy density than ethanol. The volumetric energy density of n-butanol is only 9% lower than that of gasoline1 while ethanol has 30% less energy per unit volume compared with gasoline, which has been shown to negatively impact vehicle fuel economy, especially at higher blend ratios. n-Butanol also has a much lower vapor pressure than ethanol, reducing the evaporative emissions and chance of explosion. n-Butanol is much less hygroscopic compared to ethanol, preventing it from water contamination. n-Butanol has also shown to be less corrosive to materials in automotive fuel systems and existing pipelines than ethanol and is very close in octane rating to gasoline. In fact, n-butanol has physical properties similar to gasoline and can be used as a direct replacement for gasoline in spark-ignition engines with few or no modifications.2 The fuel properties of the base fuels are summarized in Table 1.3
(7) Liao, S. Y.; Jiang, D. M.; Huang, Z. H.; Zeng, K.; Cheng, Q. Determination of the laminar burning velocities for mixtures of ethanol and air at elevated temperatures. Appl. Therm. Eng. 2007, 27 (2), 374– 380. (8) Alasfour, F. N. Butanol- A single-cylinder engine study: availability analysis. Appl. Therm. Eng. 1997, 17 (6), 537–549. (9) Dagaut, P.; Togbe, C. Oxidation kinetics of butanol-gasoline surrogate mixtures in a jet-stirred reactor: Experimental and modeling study. Fuel 2008, 87, 3313–3321. (10) Yang, B.; Osswald, P.; Li, Y.; Wang, J.; Wei, L.; Tian, Z.; Qi, F.; Kohse-Hoinghaus, K. Identification of combustion intermediates in isomeric fuel-rich premixed butanol-oxygen flames at low pressure. Combust. Flame 2007, 148 (4), 198–209. (11) McEnally, C. S.; Pfefferle, L. D. Fuel decomposition and hydrocarbon growth processes for oxygenated hydrocarbons: butyl alcohols. Proc. Combust. Inst. 2005, 30 (1), 1363–1370. (12) Sarathy, S. M.; Thomson, M. J.; Togbe, C.; Dagaut, P.; Halter, F.; Mounaim-Rousselle, C. An experimental and kinetic modeling study of n-butanol combustion. Combust. Flame 2009, 156 (4), 852–864.
*Corresponding author. Tel.: þ0086 29 82665075. Fax: þ0086 29 82668789. E-mail address:
[email protected]. (1) Moss, J. T.; Berkowitz, A. M.; Oehlschlaeger, M. A. An experimental and kinetic modeling Study of the oxidation of the four isomers of butanol. J. Phys. Chem. A 2008, 112 (43), 10843–10855. (2) ButylFuel LLC. www.butanol.com (accessed October 2008). (3) Wallner, T.; Miers, S. A. A comparison of ethanol and butanol as oxygenates using a direct-injection, spark-ignition engine. ASME J. Eng. Gas Turbines Powers 2009, 131, 032802-1–032802-9. (4) Hara, T.; Tanoue, K. Laminar flame speed of ethanol, n-heptane, Iso-octane air mixtures; JSAE Paper No. 20068518, Society of Automotive Engineers of Japan: Tokyo, 2006. (5) Rice, R. W.; Sanyal, A. K.; Elrod, A. C.; Bata, R. M. J. Eng. Gas Turbines Power 1991, 113, 377–381. (6) Yacoub, Y.; Bata, R.; Gautam, M. Proc. Inst. Mech. E Part A: J. Power Energy 1998, 212, 363–379. r 2009 American Chemical Society
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pubs.acs.org/EF
Energy Fuels 2009, 23, 4900–4907
: DOI:10.1021/ef900378s
Gu et al.
Table 1. Typical Properties of Base Fuels3 gasoline
ethanol
chemical formula composition (C, H, O) (mass%)
C4-C12 C2H5OH 86, 14, 0 52, 13, 35
lower heating value (MJ/kg) density (kg/m3) octane number (R þ M)/2 boiling temperature (°C) latent heat of vaporization (kJ/kg) self-ignition temperature (°C) stoichiometric air/fuel ratio laminar flame speed (cm/s)a,b,4 mixture calorific value (MJ/kg)b ignition limits in air (vol %) solubility in water at 20 °C (mL/100 mL H2O)
42.7 715-765 90 25-215 380-500 ∼300 14.7 ∼33 3.75 0.6
