Study On The Flammability Limit Of Single-component Gas Fuel At O₂/CO₂ Atmosphere

O2/CO2 combustion technology is one of the effective means to reduce greenhouse gases.If O2/CO2 combustion technology is adopted,CO2 enrichment can be realized and the cost of capture can be reduced.Due to the high CO2 concentration,the combustion characteristics of gaseous fuel in O2/CO2 atmosphere are different from those under air-assisted combustion conditions.To master the combustion characteristics of gaseous fuel in O2/CO2 atmosphere is an important prerequisite for the application of O2/CO2 combustion technology.The flammability limit in the combustion characteristic is one of the important bases to determine the mixture safety and combustion stability.The topic will focus on the flammability limit of gaseous fuels in O2/CO2 atmosphere.The flammability limits of seven gases including C2H6,C2H4,C2H2,C3H8,C3H6,C4H10,and C4H8 were measured.The results show that with the increase of CO2 concentration,the flammability lower limit of fuel shows a linear increase in a small range.The upper limit of flammability decreases in the form of single arch ellipse.CHEMKIN software was used to quantitatively compare the enthalpy change rates of fuels in O2/CO2 atmosphere and O2/FCO2 atmosphere.The influence of CO2 directly involved in chemical reaction on the combustion process at the flammability limit was analyzed.It was found that with the increase of CO2 concentration,the chemical reactivity of CO2 had little influence on the lower flammable limit and gradually increased.The influence on the upper limit of combustibility increases first and then decreases.Based on the principle of energy balance,the influence of the radiation characteristics and thermal physics of CO2 on the combustion process at the flammability limit is analyzed.Temperature is the main factor affecting the radiation heat transfer of CO2.At the upper limit of combustibility,the fuel concentration is higher,and the combustion releases more heat,resulting in higher flame temperature.Therefore,the radiation characteristics of CO2 have a strong influence on the upper limit of combustibility.When CO2 concentration is high,the thermal physics of the mixture plays a leading role in the flammability limit,which is due to the large specific heat capacity and strong heat absorption capacity of CO2.With the increase of CO2 concentration,the influence of its thermal physical properties on the flammability limit cannot be ignored.Based on the thermal theory,the calculation model for the flammability limit of hydrocarbon fuel in O2/CO2 atmosphere is deduced.By comparing the experimental value with the theoretical value,the maximum absolute deviation of the model is less than 1%when calculating the lower flammable limit.When calculating the upper limit of combustibility,the maximum absolute deviation is around 3%.The model is simple and the results are reliable,and it has a good reference value for predicting the flammability limit in industry.