Zeldovich mechanism
Zel'dovich mechanism is a chemical mechanism that describes the oxidation of nitrogen and NOx formation, first proposed by the Russian physicist Yakov Borisovich Zel'dovich in 1946.[1][2][3][4] The reaction mechanisms read as
![{\displaystyle {\ce {{N2}+ O <->[k_1] {NO}+ {N}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/db330a69b225a4de48c833f5a080c16dac3012b4)
![{\displaystyle {\ce {{N}+ O2 <->[k_2] {NO}+ {O}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/9532dac50fbf62d3ea427b7c204361a574798a66)
where and are the reaction rate constants in Arrhenius law. The overall global reaction is given by
![{\displaystyle {\ce {{N2}+ {O2}<->[k] 2NO}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/bdfdb2701971bfab2f8a9b87aa4e00ed2a618451)
The overall reaction rate is mostly governed by the first reaction (i.e., rate-determining reaction), since the second reaction is much faster than the first reaction and occurs immediately following the first reaction. At fuel-rich conditions, due to lack of oxygen, reaction 2 becomes weak, hence, a third reaction is included in the mechanism, also known as extended Zel'dovich mechanism (with all three reactions),[5][6]
![{\displaystyle {\ce {{N}+ {OH}<->[k_3] {NO}+ {H}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/44eaa5bf736ce62b3b9c4397cbd1d92fcda0aaf9)
Assuming the initial concentration of NO is low and the reverse reactions can therefore be ignored, the forward rate constants of the reactions are given by[7]
where the pre-exponential factor is measured in units of cm, mol, s and K (these units are incorrect), temperature in kelvins, and the activation energy in cal/mol; R is the universal gas constant.
NO formation
[edit]The rate of NO concentration increase is given by
![{\displaystyle {\frac {d[\mathrm {NO} ]}{dt}}=k_{1f}[\mathrm {N} _{2}][\mathrm {O} ]+k_{2f}[\mathrm {N} ][\mathrm {O} _{2}]+k_{3f}[\mathrm {N} ][\mathrm {OH} ]-k_{1b}[\mathrm {NO} ][\mathrm {N} ]-k_{2b}[\mathrm {NO} ][\mathrm {O} ]-k_{3b}[\mathrm {NO} ][\mathrm {H} ]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/021d3cc40b85d98e2d4a7c5e02bfe82fda4a6dd8)
N formation
[edit]Similarly, the rate of N concentration increase is
![{\displaystyle {\frac {d[\mathrm {N} ]}{dt}}=k_{1f}[\mathrm {N} _{2}][\mathrm {O} ]-k_{2f}[\mathrm {N} ][\mathrm {O} _{2}]-k_{3f}[\mathrm {N} ][\mathrm {OH} ]-k_{1b}[\mathrm {NO} ][\mathrm {N} ]+k_{2b}[\mathrm {NO} ][\mathrm {O} ]+k_{3b}[\mathrm {NO} ][\mathrm {H} ]}](https://wikimedia.org/api/rest_v1/media/math/render/svg/c08b9a0fe01f258c6373e93e56382db91fc0f333)
See also
[edit]References
[edit]- ^ Y.B. Zel'dovich (1946). "The Oxidation of Nitrogen in Combustion Explosions". Acta Physicochimica U.S.S.R. 21: 577–628
- ^ Zeldovich, Y. A., D. Frank-Kamenetskii, and P. Sadovnikov. Oxidation of nitrogen in combustion. Publishing House of the Acad of Sciences of USSR, 1947.
- ^ Williams, Forman A. "Combustion theory". (1985).
- ^ Zeldovich, I. A., Barenblatt, G. I., Librovich, V. B., Makhviladze, G. M. (1985). Mathematical theory of combustion and explosions.
- ^ Lavoie, G. A., Heywood, J. B., Keck, J. C. (1970). Experimental and theoretical study of nitric oxide formation in internal combustion engines. Combustion science and technology, 1(4), 313–326.
- ^ Hanson, R. K., Salimian, S. (1984). Survey of rate constants in the N/H/O system. In Combustion chemistry (pp. 361–421). Springer, New York, NY.
- ^ "San Diego Mechanism".