This content is not included in your SAE MOBILUS subscription, or you are not logged in.
Skeletal Mechanism for NOx Chemistry in Diesel Engines
ISSN: 0148-7191, e-ISSN: 2688-3627
Published May 04, 1998 by SAE International in United States
Annotation ability available
Most computational schemes and kinetic models for engine-out NOx emissions from Diesels are based on the Zeldovich or extended Zeldovich mechanism. However, at pressures typical of both the premixed and diffusion portions of the combustion process, the third-body reaction leading to the formation of N2O (O + N2 + M) becomes faster than the leading reaction in the Zeldovich mechanism (O + N2). As in gas turbines, particularly those involving lean-premixed combustor designs, NO formation in Diesels through the N2O mechanism can thus proceed more efficiently than through the traditional route. Decomposition of NO in the combustion products during the power stroke can also occur by both the reverse Zeldovich reactions and the second order step that produces N2O (2NO ® N2O + O).
Based on these observations, a skeletal mechanism consisting of seven elementary reactions is used to develop a two-zone model for NOx emissions from direct injection (DI) Diesel engines. To evaluate the chemistry in the first zone where NO forms, the stoichiometric flame temperature and corresponding equilibrium burned gas conditions are computed at start of combustion conditions. The second zone is that in which the NO formed in zone 1 decomposes and is characterized with the equilibrium composition and flame temperature at the end of combustion, based on a fuel/air dual cycle analysis.
Characteristic chemical times for NO formation in zone 1 and NO decomposition in zone 2 are formulated from the law of mass action applied separately to each zone. The ratio of the value for decomposition to that for formation is easily computed from equilibrium analyses at the stoichiometric and overall equivalence ratios. The utility of using this ratio to evaluate the influence of decomposition upon exhaust emissions is examined. A general chart is presented, in which the logarithm of this kinetic time ratio is graphed versus reciprocal end-of-combustion flame temperature. Lines of constant pressure at start of combustion (representing turbocharger boost ratio, engine compression ratio, and injection timing) and constant peak engine pressure allow approximate positioning for any engine on the chart as a function of load once preliminary design is completed. In general, the chart suggests that decomposition of NO becomes increasingly significant as engine load (end-of-combustion flame temperature) is increased. Finally, the kinetic time ratios are computed for operating conditions typical of one light-duty and three heavy-duty turbocharged engines and found entirely consistent with results deduced from the general chart.
CitationMellor, A., Mello, J., Duffy, K., Easley, W. et al., "Skeletal Mechanism for NOx Chemistry in Diesel Engines," SAE Technical Paper 981450, 1998, https://doi.org/10.4271/981450.
New Techniques in SI and Diesel Engine Modeling
Number: SP-1366; Published: 1998-05-04
Number: SP-1366; Published: 1998-05-04
SAE 1998 Transactions - Journal of Fuels and Lubricants
Number: V107-4; Published: 1999-09-15
Number: V107-4; Published: 1999-09-15
- Walsh, M. “Global trends in Diesel particulate control - a 1995 update,” SAE Paper 950149 1995
- Lavoie, G. A. Heywood, J.B. Keck, J.C. “Experimental and theoretical investigation of nitric oxide formation in internal combustion engines,” Combust. Sci. Tech. 1 313 326 1970
- Ahmad, T. Plee, S.L. “Application of flame temperature correlations to emissions from a direct injection Diesel engine,” SAE Paper 831734 1983
- Duffy, K.P. Nicols, J.T. Mellor, A.M. Plee, S.L. “Flame temperature correlations for effects of EGR in high speed direct injection Diesel engines,” Proceedings of the 1996 Technical Meeting Central States Section/The Combustion Institute 1996
- Arcoumanis, C. Nagwaney, A. Hentschel, W. Ropke, S. “Effect of EGR on spray development and emissions in a 1.9L direct injection Diesel engine” SAE Paper 952356 1995
- Kaufman, F. Kelso, J. “Thermal decomposition of nitric oxide,” J. Chem. Phys. 23 1702 1707 1955
- Kaufman, F. Kelso, J. “Reactions of atomic oxygen and atomic nitrogen with oxides of nitrogen,” Seventh Symposium (International) on Combustion The Combustion Institute Pittsburgh 53 56 1959
- Kaufman, F. Decker, J. “Effect of oxygen on thermal decomposition of nitric oxide at high temperatures,” Seventh Symposium (International) on Combustion The Combustion Institute Pittsburgh 57 60 1959
- Aiman, W. “A critical test for models of the nitric oxide formation process in spark-ignition engines,” Fourteenth Symposium (International) on Combustion The Combustion Institute Pittsburgh 861 868 1973
- Plee, S. Ahmad, T. Myers, J. Siegla, D. “Effects of flame temperature and air/fuel mixing on emission of particulate carbon from a divided chamber Diesel engine” Particulate Carbon: Formation During Combustion Plenum Press New York 423 483 1980
- Fenimore, C.P. “Formation of nitric oxide in premixed hydrocarbon flames,” Thirteenth Symposium (International) on Combustion The Combustion Institute Pittsburgh 373 380 1971
- Malte, P.C. Pratt, D. T. “The role of energy-releasing kinetics in NO x formation: fuel lean, jet-stirred CO-air combustion,” Combust. Sci. Tech. 9 221 231 1974
- Glassman, I. Combustion Academic Press New York 1996
- Polifke, W. Döbbeling, K. Sattelmayer, T. Nicol, D.G. Malte, P.C. “A NO x prediction scheme for lean-premixed gas turbine combustion based on detailed chemical kinetics,” ASME Paper No. 95-GT-108 1995
- Mikus, T. Heywood, J.B. Hicks, R.E. “Nitric oxide formation in gas turbine engines: a theoretical and experimental study,” NASA CR 2977 1978
- Miller, R. Davis, G. Lavoie, G. Newman, C. Gardner, T. “A super-extended Zel'dovich mechanism for NO x modeling and engine calibration,” SAE Paper No. 980781 1998
- Nicol, D. Malte, P.C. Lai, J. Marinov, N.N. Pratt, D.T. “NO x sensitivities for gas turbine engines operated on lean-premixed combustion and conventional diffusion flames,” ASME Paper No. 92-GT-115 1992
- Nicol, D.G. Steele, R.C. Marinov, N.M. Malte, P.C. “The importance of the nitrous oxide pathway to NO x in lean-premixed combustion,” ASME Paper No. 93-GT-342 1993
- Nicol, D.G. Malte, P.C. Steele, R.C. “Simplified models for NO x production rates in lean-premixed combustion,” ASME Paper No. 94-GT-432 1994
- Magruder, T.D. McDonald, J.P. Mellor, A.M. Tonouchi, J. Nicol, D.G. Malte, P.C. “Engineering analysis for lean premixed combustor design,” AIAA Paper No. 95-3136 1995
- Tomeczek, J. Gradon, B. “The role of nitrous oxide in the mechanism of thermal nitric oxide formation within flame temperature range,” Combust. Sci. Tech. 125 159 180 1997
- Dec, J.E. “A conceptual model of DI Diesel combustion based on laser-sheet imaging,” SAE Paper 970873 1997
- Bowman, C.T. Hanson, R.K. Davidson, D.F. Gardiner, W.C. Lissianski, V. Smith, G.P. Golden, D.M. Frenklach, M. Goldenberg, M. 1995 http://www.me.berkeley.edu/gri_mech/
- Reynolds, W.C. 1987 Dept. of Mech. Eng., Stanford Univ.
- Tuttle, J.H. Colket, M.B. Bilger, R.W. Mellor, A.M. “Characteristic times for combustion and pollutant formation in spray combustion,” Sixteenth Symposium (International) on Combustion The Combustion Institute Pittsburgh 209 219 1977
- Sawyer, R.F. Cernansky, N.P. Oppenheim, A.K. “Factors controlling pollutant emissions from gas turbine engines,” Atmospheric Pollution by Aircraft Engines 1973