Document Type

Thesis

Date of Award

10-30-1990

Degree Name

Master of Science in Chemical Engineering - (M.S.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Joseph W. Bozzelli

Second Advisor

Dana E. Knox

Third Advisor

Robert Benedict Barat

Abstract

A detailed reaction mechanism based upon fundamental thermochemical kinetic principles has been developed to describe the concentration profiles of OH, CH, NH, CN, and NO including prompt NO radicals in laminar flow, fuel rich methane flames as well as flames doped with 700 ppm ammonia. A one dimensional laminar flat flame code which incorporated diffusion, and the detailed reaction mechanism was used to predict the radical concentration profiles from the model. These calculated values are compared to experimental data of Dean (1984).

The model consist of two reaction subsets, hydrocarbon oxidation set and an ammonia oxidation set. The reactions most important for coupling the two subset are :

CH + N2 <----> HCN + N (1)

CH2 + N2 <----> HCN + NH (2)

CH3 + NO <----> HCN + H2O (3)

The mechanism shows good agreement (within experimental error) with experimental concentration as function of distance above the burner, except for NO. The mechanism predicts that reaction (1) is mainly responsible for nitrogen fixation in the fuel rich flame studied. The contribution to the nitrogen fixation by reaction (2) and the Zeldovich (1948) mechanism are negligible.

A rate constant for reaction (1) (from QRRK) consistent with the shock tube data of Bowman (1990) results in under prediction of the NO concentration by a order of magnitude. A higher value corresponding to a barrier of 10 Kcal for reaction (1) increases the NO peak by a factor of 4.5. Inclusion of the following reaction :

CH3 + N2 < > HCN + NH2 (4)

improves the NO profile by a factor of six.

NO decomposition in the flames studied takes place mainly through reaction (3).

A higher value for rate constant for reaction 2 relative to the shock tube data of Bowman and Dean (1990) and an nitrogen fixation reaction in the form of (4) is needed to properly account for the observed nitrogen fixation.A higher value for rate constant for reaction 2 relative to the shock tube data of Bowman and Dean (1990) and an nitrogen fixation reaction in the form of (4) is needed to properly account for the observed nitrogen fixation.

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