Effects of nitrogen and carbon monoxide on the detonation of hydrogen-air gaseous mixtures

Abstract

Nitrogen inhibition is considered as a mitigation measure against chemically sensitive mixtures in industry and carbon monoxide is possibly generated during molten corium concrete interaction in a severe accident of nuclear power plants. To study the effects of the N2 and CO on the detonation of H2-air mixtures, a detonation facility of 78 mm inner diameter and 10 m length is set up. Key measured parameters includes detonation cell size, flame velocity, lean and rich detonation limits. All the measured detonation parameters are theoretically predicted by CJ theory or one-dimensional ZND model. Detailed chemical kinetics mechanism for H2-air and H2-CO-air mixtures is coupled with reactive Euler equations. Experiments and theoretically analysis has been performed mostly at 0.101 MPa and 293 K. Results shows that N2 increases the detonation cell size and narrows down the detonable range significantly. Especially when N2 concentration is more than 43%, all mixtures are unable to detonate. Moreover, when the added N2 concentration is larger than 20%, detonation velocity does not increase with hydrogen concentration for rich mixtures. The above effects of N2 is explained by the replacement of O2 with N2 and by the weak chemical reaction of N2. CO significantly decreases the cell size of lean H2-air mixtures and increased the cell size for rich H2-air mixtures. For lean H2-air mixtures, the added CO linearly decreases the lean detonation limit, thus increasing the possibility of detonation to occur in the severe accidents. Therefore, the contribution of CO must be carefully considered in the safety assessment. Results also shows that pure CO is difficult to detonate in the air, while small quantity of hydrogen can significantly enhance the rate of CO oxidation reactions.