Zeldovich mechanism

The Zeldovich mechanism (after the Soviet physicist Jakow Borissowitsch Seldowitsch , also thermal N O mechanism) is the oxidation of atmospheric nitrogen .

O + N 2	->	NO + N
N + O 2	->	NO + O

The first step of the reaction requires an activation energy of 315 kJ / mol , the reaction therefore only takes place at high temperatures, for example in the hot areas of a flame , or when a missile re-enters the earth's atmosphere. It is therefore also used to analyze combustion processes. The rate of formation of NO increases exponentially at temperatures above the range from 1200 ° C to 1400 ° C (converted about 1500 to 1700 Kelvin ). This mechanism was later extended by Lavoie, Heywood and Keck (1970):

O + N 2	<->	NO + N (1)
N + O 2	<->	NO + O (2)
N + OH	<->	NO + H (3)

The reaction rates result in

${\displaystyle k_{1,\mathrm {vorw} }=7{,}6\times 10^{13}\times \exp \left(-{38370 \over T}\right)\mathrm {m^{3} \over kmol\cdot s} }$

${\displaystyle k_{1,\mathrm {r{\ddot {u}}ck} }=1{,}6\times 10^{13}\qquad \qquad \qquad \qquad \mathrm {m^{3} \over kmol\cdot s} }$

${\displaystyle k_{2,\mathrm {vorw} }=T*6{,}4\times 10^{9}\times \exp \left(-{3139 \over T}\right)\mathrm {m^{3} \over kmol\cdot s} }$

${\displaystyle k_{2,\mathrm {r{\ddot {u}}ck} }=T*1{,}5\times 10^{9}\times \exp \left(-{19500 \over T}\right)\mathrm {m^{3} \over kmol\cdot s} }$

${\displaystyle k_{3}=2{,}8\times 10^{10}\qquad \qquad \qquad \qquad \ \ \ \quad \mathrm {m^{3} \over kmol\cdot s} }$

relevance

The Zeldovich reaction is important, among other things, in the engine combustion process. In engine combustion, the chemical equilibrium is not reached while the flame front passes through the combustion chamber. NO is only formed behind the flame front in the burnt. Despite the high temperature, the reactions take place so slowly that no equilibrium can be achieved. The formation of nitrogen oxides is favored by high combustion chamber temperatures above approx. 2200 Kelvin (K) and the presence of a sufficient oxygen concentration in the mixture above λ = 1. During the expansion (one work cycle in a 4-stroke internal combustion engine ) there is initially a slight NO regression, but this quickly subsides because the reactions freeze when the temperature falls below 2200 K.

Individual evidence

1. ^ Fritz Baum: Air pollution control in practice . Oldenbourg Wissenschaftsverlag , Munich 1988, ISBN 3-486-26256-4 , p. 86 .
2. ^ F. Pischinger: Internal combustion engines. Lecture reprint. Volume II, RWTH Aachen, 1989, OCLC 1067705266 .

swell

• GP Merker, G. Stiesch: Technical combustion. Engine combustion . BG Teubner Verlag, Stuttgart 1999, ISBN 3-519-06381-6 .
• JB Heywood: Internal Combustion Engine Fundamentals . McGraw-Hill, New York 2002, ISBN 0-07-028637-X .
• YB Zeldovich: The Oxidation of Nitrogen in Combustion and Explosions. In: Acta Physicochimica USSR Volume 21, 1946, pp. 577-628.
• GA Lavoie, JB Heywood, JC Keck: Experimental and Theoretical Study of Nitric Oxide Formation in Internal Combustion Engines. In: Combust. Sci. Tech. Volume 1, No. 4, 1970, pp. 313-326.