Combustion Characteristics of Alternative Fuels: Butanol

Combustion Characteristics of Alternative Fuels: Butanol

Shamel S. Merchant,^1,* Everton Fernando Zanoelo,² Nils Hansen,³ Kevin M. Van Geem⁴ and William H. Green Jr.¹

¹  Department of Chemical Engineering, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA

²  Federal University of Paraná (UFPR), Curitiba, PR, Brazil

³ Combustion Research Facility, Sandia National Laboratories, Livermore, CA, USA

⁴ Laboratory of Chemical Technology, Univ. Ghent, Ghent, Belgium

*  Corresponding author:  shamel@mit.edu

In the last few years, spurred by growing concerns of depletion of fossil fuels and global warming, researchers have actively tried to find alternative fuel candidates. This has led to identification of a large number of candidate molecules available naturally or synthesized using bioengineering. The next question is identification of a suitable alternative fuel for commercialization, which often is an arduous task involving rather extensive (and expensive) experimentation to assess the performance of any proposed fuel. Moreover even if a potential alternative fuel is identified the engine experiments provide no mechanistic insights into how the combustion occurs, this makes it often difficult to predict combustion characteristics of fuel under nonstandard test conditions i.e. blend of fuels, modified or new engine concepts. It would be much more convenient if we could just predict each proposed fuel's performance on the computer, based in large part on first-principles calculations, and limit our experimental work to the most promising options

Automated mechanism generation makes it feasible to quickly construct these predictive models, but often their accuracy of prediction is of question. In current investigation we present a comprehensive mechanism for all butanol isomers (n-, iso-, sec- and tert-butanol). The kinetic mechanism is generated using the open source software package Reaction Mechanism Generator (RMG)[1] and include pressure-dependent kinetics. The accuracy of the predictive mechanism is tested by comparing against a large number of available datasets in literature – pyrolysis product profiles in plug flow reactor[2] and shock tube, jet-stirred reactor mole fraction profiles[3], opposed flow diffusion flame mole fraction profiles[4], laminar flame speeds at different pressures[5] and autoignition delays in rapid-compression machine[6].Overall we see that for many performance parameters the model predictions are about as accurate as the experiments, while the prediction errors are significantly larger for other types of performance measures. A flux and sensitivity analysis is performed to identify important parameters in the mechanism. The success of butanol test case has validated the automatic mechanism generation paradigm for fuel chemistry and has opened doors to quick screening of vast number of fuel candidates (i.e iso-pentanol).

References

1.         Green, W.H. et al.  Reaction Mechanism Generator (RMG).  2012; Available from: http://github.com/GreenGroup/RMG-Java.

2.         Van Geem, K.M., et al., Accurate High-Temperature Reaction Networks for Alternative Fuels: Butanol Isomers. Industrial & Engineering Chemistry Research, 2010. 49(21): p. 10399-10420.

3.         Togbex, C., A. Mzex-Ahmed, and P. Dagaut, Kinetics of Oxidation of 2-Butanol and Isobutanol in a Jet-Stirred Reactor: Experimental Study and Modeling Investigation. Energy & Fuels, 2010. 24(9): p. 5244-5256.

4.         Oßwald, P., et al., Combustion of butanol isomers – A detailed molecular beam mass spectrometry investigation of their flame chemistry. Combustion and Flame, 2011. 158(1): p. 2-15.

5.         Veloo, P.S. and F.N. Egolfopoulos, Flame propagation of butanol isomers/air mixtures. Proceedings of the Combustion Institute, 2011. 33(1): p. 987-993.

6.         Weber, B. and C.-J. Sung, A Rapid Compression Study of the Butanol Isomers at Elevated Pressure. 7th US National Meeting of the Combustion Institute, 2011