Extinction of the counterflow diffusion flame in high pressures has been studied experimentally up to the ambient pressure of 10 MPa. Oxidizer was air and fuels were methane, ethane. carbon monoxide, carbon monoxide/hydrogen mixtures. Experimental results have shown that the critical stagnation velocity gradients for the methane and ethane are about constant for pressures up to about 2 MPa and 1 MPa,respectively, beyond which they decrease with the increase of pressure. For the carbon monoxide, the critical stagnation velocity gradient increases with pressure, reaches a maximum at about 1 MPa, and decreases. The increase of the hydrogen content in the carbon monoxide/hydrogen mixture results in increase of the critical stagnation velocity gradient for a certain value of pressure below 1 MPa, beyond which it does not affect when the hydrogen is below about 0.7. The apparent pressure exponent of the overall reaction in the flame were obtained from the flame extinction data. For the methane and ethane,the apparent pressure exponents are one at pressures below about 2 MPa for methane and 1 MPa for ethane, beyond which they decrease. For the carbon monoxide, the apparent pressure exponent is two at pressure below about 1 MPa, beyond which it decreases. When the hydrogen content is less than about 0.7, the increase of the hydrogen content results in decrease of the apparent pressure exponent under the pressure below about 1 MPa. When the pressure is larger than 1 MPa, the hydrogen conlent below 0.7 dose not affect the overall chemical reaction rate of carbon monoxide and air.
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