Experimental Investigation of Flame Structure and Combustion Limit During Premixed Methane/Air Jet Flame and Sidewall Interaction

The effects of inlet gas parameters and sloping sidewall angle on the flame structure and combustion limit with and without sidewall were experimentally investigated.Flame height and impact angle were obtained by chemiluminescence intensity analysis of CH*distribution.First,the combustion characteristics of flame with and without sidewall at different equivalence ratios were explored;then,the influence of Reynolds number and inlet gas temperature on flame structure and combustion limit of v-shaped flame with sidewall were analyzed,and the results with sidewall were compared with those without sidewall.Finally,the variation trend of flame parameters with different sloping sidewall angles was analyzed.The experimental results show that the existence of sidewall makes flame shape change from“M-shaped”to“inverted N-shaped”,and conical shape to trapezoidal shape.The inhibition effect of sidewall on flame stretching downstream is strengthened with the increase in Reynolds number;but as the temperature of the inlet gas increases,the inhibitory effect is obviously weakened.When sloping sidewall angle decreases from 90°to 55°at 5°intervals,flame height and impact angle of v-shaped flame reach the extreme value whenβ=80°.Compared with the case without sidewall,the range of v-shaped flame with sidewall has no obvious trend of broadening or shrinking when inlet gas temperature is increased;however,as sloping sidewall angle decreases,the range of the v-shaped flame shrinks obviously and flammability limit increases significantly.

Study on fire extinguishing performance of ultrafine water mist in a cup burner

Two simplified models for predicting minimum extinguishing concentration(MEC) of ultrafine water mist(UFM)(<10 m) were developed based on limiting oxygen concentration(LOC) and combustion limit temperature(CLT),respectively.Experiment was conducted using a modified cup burner which can reduce the surface adsorption of UFM.Two typical liquid fuels,n-heptane and ethanol,were used in the experiment.Tests using the same scenario were repeated 20 times or 10 times according to the variance of extinguishing time.The average and the standard deviations of extinguishing time were used to evaluate the fire extinguishing performance of UFM.Experimental results agree well with the model based on LOC,and disagree with the model based on CLT.The disagreements were explained by analyzing flow behavior of UFM.It was concluded that the primary mechanism of fire extinguishment with UFM was oxygen dilution.

Experimental Investigation on Plasma-assisted Combustion Characteristics of Premixed Propane/Air Mixture

A detailed study on the plasma-assisted combustion(PAC) characteristics of premixed propane/air mixture is presented. The PAC is measured electrically, as well as optically with a multichannel spectrometer. The characteristics are demonstrated by stable combustion temperature and combustion stability limits, and the results are compared with conventional combustion(CC). Stable combustion temperature measurements show that the introduction of PAC into combustion system can increase the stable combustion temperature, and the increment is more notable with an increase of discharge voltage. Besides, the rich and weak limits of combustion stability are both enlarged when plasma is applied into the combustion process and the increase of discharge voltage results in the expansion of combustion stability limits as well. The measurements of temperature head and emission spectrum illustrate that the kinetic enhancement caused by reactive species in plasma is the main enhancement pathway for current combustion system.