Effects of H₂ addition on the instability characteristics of CO/air and CH₄/air in a horizontal narrow channel

ABSTRACT

This paper investigates the instability characteristics of CO/H₂/air and CH₄/H₂/air mixtures in a narrow channel under standard temperature and pressure conditions. The CO/H₂ mixture exhibits a greater overpressure growth rate and maximum explosion overpressure as compared to the CH₄/H₂ mixture at the same hydrogen content. As the hydrogen content increases, the maximum explosion overpressure (P_max) value increases, while the corresponding time (θ) value gradually decreases. The maximum explosion overpressure of CH₄/H₂ and CO/H₂ mixtures is 28.27 kPa and 25.09 kPa, respectively. The flame wrinkles to form cells due to the Darius-Landau instability, and the interaction between the vortex tube and premixed flame affects the structure of turbulent premixed combustion. The oscillation frequency of the overpressure increases with increasing hydrogen content, and the oscillation belongs to the Helmholtz oscillation. The CO/H₂ mixtures exhibit greater flame thickness than CH₄/H₂ mixtures, resulting in lower Peclet numbers and therefore greater relative importance of heat losses. As the hydrogen content increases, the sensitivity coefficient of R99 (OH + CO <=> H + CO₂) in the CO/H₂ mixture gradually decreases, while the sensitivity coefficients of R38 (H + O₂ <=> O + OH) and R84 (OH + H₂ <=> H + H₂O) increase. The elementary reaction R38 plays a leading role in increasing the laminar burning velocity of the CH₄/H₂ mixture. The trend of R38 variation in the two mixtures is opposite with increasing hydrogen content.

KEYWORDS:

• Instability Characteristics
• Hydrogen content
• Overpressure growth rate
• Flame thickness
• Sensitivity coefficient

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Zhidong Guo

Zhidong Guo is a PhD student in the School of Resources and Safety Engineering, Chongqing University, PR China.

Fei Wu

Fei Wu is an associate professor in the School of Resources and Safety Engineering, Chongqing University, PR China.

Xiaoping Wen

Xiaoping Wen is a professor in the School of Mechanical and Power Engineering, Henan Polytechnic University, PR China.