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Energy Systems Division

Combustion Modeling with Detailed Chemistry

Developing high-fidelity reduced mechanisms for use of biodiesel fuel in combustion systems

It is well known that the optimization of engines burning liquid and gaseous fuels through repeated experiments is a routine but rather expensive and time-consuming process. Predictive numerical simulations with realistic chemistry is a promising option in reducing overall cost, particularly if the detailed mechanisms can be substantially reduced without significant loss of accuracy. In the past, detailed chemical kinetic mechanisms included only a few species (3-10) and handful of reactions (20-50). Due to the advent of faster and cheaper computational resources, detailed simulations with 40-60 species and 150-200 reactions have become rather routine in industry and academia. However, these mechanisms in the past have been plagued by inadequate validation and limited operation range.

Argonne researchers, in collaboration with University of Connecticut (UConn) and Lawrence Livermore National Laboratory (LLNL), have developed high-fidelity reduced mechanisms for biodiesel fuel. These reduced mechanisms are extensively validated against idealized combustion systems such as shock tube, rapid compression machine, jet stirred reactor, constant volume turbulent spray-combustion chambers, metal-engine and other data. These mechanisms can better predict experimental data compared to other chemical kinetic models available in the literature. These well-validated mechanisms will be shared here at a later stage.

Biodiesel Surrogates for Engine Modeling

The desired reduced biodiesel mechanism should:

  • Be small in mechanism size (about 100-125 species),
  • Represent real biodiesel properties well,
  • Include low and high temperature chemistry, and
  • Require no tuning of rate parameters to match specific data-sets.

The surrogates’ range of operation consists of a pressure of 1-100 atm; an equivalence ratio of 0.5-2.0; and an initial temperature of 700-1800 degrees K .

Mechanism reduction is performed using directed relation graph (DRG), isomer lumping, DRG aided with sensitivity analysis, and error cancellation techniques at UConn. The original mechanism was obtained from LLNL, consisting of 3329 species and 10806 reactions. These reduced mechanisms are extensively validated at Argonne, against idealized combustion systems before implementation in an engine modeling code. Some sample validations are presented for biodiesel fuel.

The tertiary component mixture of Methyl Decanoate (MD), Methyl-9-Decenoate (MD9D), and n-heptane (NHPT) is used as a surrogate for soy-derived biodiesel. The reduced mechanism consisted of 89 species and 364 reactions. Simulations were performed to mimic the constant volume combustion chamber at Sandia National Laboratories. Turbulence spray-combustion data obtained such as lift-off length, ignition delay, species concentrations and others were used for further validation of the reduced mechanism.

The mechanism is clearly able to predict flame lift-off length (Figure 1) and ignition delay accurately. The average equivalence ratio at lift-off length is also well predicted by the chemical kinetic model. In addition, the OH distribution is also well predicted.

In general, the soot characteristics are well predicted by the model (Figure 2), including locations of high soot and low soot. For simulations, C2H2 is used as a soot precursor. Simulation results are presented in terms of mass-fractions, whereas experimental data is in volume fraction. Since reliable density information is not available, it was difficult to convert the soot mass-fraction into volume fraction.

After this extensive validation, researchers will implement the reduced mechanism for full-cycle engine simulations.

The simulations ran for 85 hours to completion on an 8 core machine (1 node) with the enhanced spray models and refined computational grids (0.25mm min. grid size). Considerable speed up was also observed by using a larger number of computational nodes.

All the simulations were performed at the fusion cluster at Argonne National Laboratory. The authors gratefully acknowledge a grant of computing resources at the Laboratory Computing Resource Center at Argonne National Laboratory. Collaborators in this work were the University of Connecticut and Lawrence Livermore National Laboratory.

Reduced Reaction Mechanisms for CFD

  • 115 species, 460 reactions mechanism using methyl decanoate, methyl 9-decenoate, and n-heptane as surrogates for biodiesel fuel (mech.dat and therm.dat). Reference: Z. Luo, M. Plomer, T. Lu, S. Som, D.E. Longman, S.M. Sarathy, W.J. Pitz, Development and Robust validation of a reduced mechanism for biodiesel surrogates for compression ignition engine applications,” Fuel 99: 143-153, 2012.
  • 103 species, 370 reactions mechanism using n-dodecane as a surrogate component for diesel fuel (mech.dat and therm.dat). This mechanism has been used extensively in the 2012 Engine Combustion Network (ECN) workshop. Reference: S. Som, D.E. Longman, Z. Luo, M. Plomer, T. Lu, Three Dimensional simulations of diesel sprays using n-dodecane as a surrogate,” Eastern States Section of the Combustion Institute Fall Technical Meeting, Storrs, October 2011.
  • 145 species, 869 reactions mechanism using methyl butanoate and n-heptane as surrogates for biodiesel fuel (mech.dat and therm.dat). Reference: W. Liu, R. Sivaramakrishnan, M.J. Davis, S. Som, D.E. Longman, T. Lu, Development of a reduced biodiesel surrogate model for compression ignition engine modeling,” 34th Proceedings of the Combustion Institute, Poland, 2012. http://​dx​.doi​.org/​10​.​1016​/​j​.​p​r​o​c​i​.​2012​.​05.090
  • 117 species, 472 reactions mechanism using n-heptane as a surrogate for diesel fuel (mech.dat and therm.dat). Reference: M. Raju, M. Wang, P.K. Senecal, S. Som, D.E. Longman, A reduced diesel surrogate mechanism for compression ignition engine applications,” ICEF2012-92045, ASME Internal Combustion Engine Division Fall Technical Conference, Vancouver, Canada, September 2012.

Funding

This work is supported by the U.S. Department of Energy’s Vehicle Technologies Program under Gurpreet Singh and Kevin Stork.

Publications

  • S. Som, D.E. Longman, Z. Luo, M. Plomer, T. Lu, P.K. Senecal, E. Pomraning, Simulating flame lift-off characteristics of diesel and biodiesel fuels using detailed chemical-kinetic mechanisms,” Journal of Energy Resources Technology 134 (3), 2012.
  • W. Liu, R. Sivaramakrishnan, M.J. Davis, S. Som, D.E. Longman, T. Lu, Development of a reduced biodiesel surrogate model for compression ignition engine modeling,” 34th Proceedings of the Combustion Institute, Poland, 2012. http://​dx​.doi​.org/​10​.​1016​/​j​.​p​r​o​c​i​.​2012​.​05.090
  • Z. Luo, M. Plomer, T. Lu, S. Som, D.E. Longman, S.M. Sarathy, W.J. Pitz, Development and Robust validation of a reduced mechanism for biodiesel surrogates for compression ignition engine applications,” Fuel 99: 143-153, 2012.
  • Z. Luo, M. Plomer, T. Lu, S. Som, D.E. Longman, A reduced mechanism for biodiesel surrogates with low temperature chemistry for compression ignition engine applications,” Combustion Theory and Modeling 16(2): 369-385, 2012.
  • M. Raju, M. Wang, P.K. Senecal, S. Som, D.E. Longman, A reduced diesel surrogate mechanism for compression ignition engine applications,” ICEF2012-92045, ASME Internal Combustion Engine Division Fall Technical Conference, Vancouver, Canada, September 2012.
  • A.I. Ramirez, S. Som, T.P. Rutter, D.E. Longman, S.K. Aggarwal, Investigation of the Effects of Rate of Injection on Combustion Phasing and Emission Characteristics: Experimental and Numerical Study”, Spring Technical Meeting of the Central States Section of the Combustion Institute, Dayton, April 2012.
  • Z. Wang, K.K. Srinivasan, S.R. Krishnan, S. Som, A computational investigation of diesel and biodiesel combustion and NOx formation in a light-duty compression ignition engine”, Spring Technical Meeting of the Central States Section of the Combustion Institute, Dayton, April 2012.
  • S. Som, D.E. Longman, Z. Luo, M. Plomer, T. Lu, P.K. Senecal, E. Pomraning, Simulating flame lift-off characteristics of diesel and biodiesel fuels using detailed chemical-kinetic mechanisms and LES turbulence model,” ICEF2011-60051, ASME Internal Combustion Engine Division Fall Technical Conference, Morgantown, USA, October 2011.
  • S. Som, D.E. Longman, Z. Luo, M. Plomer, T. Lu, Three Dimensional simulations of diesel sprays using n-dodecane as a surrogate,” Eastern States Section of the Combustion Institute Fall Technical Meeting, Storrs, October 2011.
  • T. Lu, M. Plomer, Z. Luo, S.M. Sarathy, W.J. Pitz, S. Som, D.E. Longman, Directed Relation Graph with Expert Knowledge for Skeletal Mechanism Reduction,” 7th US National Combustion Institute Meeting, Atlanta, March 2011. (pdf)
  • S. Som, D.E. Longman, Numerical study comparing the combustion and emission characteristics of biodiesel to petrodiesel,” Energy and Fuels 25: 1373-1386, 2011
  • Z. Luo, T. Lu, M.J. Maciaszek, S. Som, D.E. Longman, A reduced mechanism for high temperature oxidation of biodiesel surrogates,” Energy and Fuels 24: 6283-6293, 2010.
  • Z. Luo, M. Plomer, T. Lu, S. Som, D.E. Longman, A Reduced Mechanism for Biodiesel Surrogates with Low Temperature Chemistry,” 7th US National Combustion Institute Meeting, Atlanta, March 2011. (pdf)