Studies On Fire Smoke Characteristics And CO Distribution Law Of An Aircraft Cargo Compartment

It is important to detect an inflight fire as early as possible to prevent catastrophic casualties and property loss.To provide theoretical basic on the design of multi-sensor fire detection systems for aircraft cargo compartment,it is practically worthwhile to study the fire smoke characteristics in ceiling jet zone including smoke characteristics and gas concentrations beneath the ceiling.The lag time of a fire plume was measured and analyzed in a simulated aircraft cargo compartment at four atmospheric pressures?100kPa,90kPa,80kPa,70kPa?.Results showed that the heat release rate is the major factor in the determination of the lag time,while the ambient pressure can also have a slight effect on it.Based on Alpert's theory and our experiments,a new correlation predicting the lag time of a fire plume has been developed in an air craft cargo compartment.Numerical simulations based on experiments were conducted by FDS to investigate the influence of reduced pressure on CO concentration spread and decay profile of a ceiling jet.CO concentration profile is found to be divided into two phases,where CO concentration fluctuates wildly in phase one of 0.5?r/H?2 close to plume impingement region,and then CO concentration decays smoothly and slowly in phase two of 0.5?r/H?2.Accordingly empirical correlations are proposed to describe CO concentration decay profile.Through comparison of CO concentration clouds at different pressures versus time,CO concentration spread velocity is obtained to show that CO spreads faster at reduced pressure.Based on the measured CO concentration and ceiling temperature,the entrainment properties of a ceiling jet at reduced pressures were analyzed.Considering the low pressure effect on entrainment,the air entrainment ratio C_?is introduced into the correlation of the ratio of mass flow rate coefficient?_r??₀ to predict the ceiling mass flow rate.Further,the entrainment coefficient of a ceiling jet at reduced ambient pressures is calculated and presented compared with the plume.