Research Of Characteristics In Bus Fire Based On Numerical Simulation

It is very important to conduct fire investigation research since bus fire,especially closure air conditioning bus,cost more and more casualties.At present,analysis methods level of these fire investigation are still low,most investigators don't have enough experience,which make it difficult to reach a conclusion correctly.At the same time,both lessons of major accident and improvements of legal awareness ask for greater improvement of the fire investigation.It is important for bus fire investigation to improve technology and precision and carry out work optimally.To improve errors of CO and temperature prediction in numerical simulation of under-ventilated fire,extending mixture fraction combustion model based on two-step reaction mechanism is used,two-step reaction mechanism and single-step reaction mechanism were compared theoretically. Source codes and two-step reaction mechanism were compiled.The ISO 9705 reduced scale enclosure model was used for numerical simulation validation.effect in production of CO and CO₂ was analyzed,inside temperature data was also analyzed and compared with NIST experiment results.It is demonstrated that two-step reaction mechanism is much more suitable for under-ventilated fire,which can improve predicting precision of CO production,decrease error of prediction of inside temperature.Two-step reaction model validated is applied to research of combustion charactistics in reduced scale simplified model of ordinary bus.The third chapter conducts effect research under different outside velocity,fire power and opening condition.the changes of temperature and velocity data under different external factors are analyzed.The results show that simplified model can be divided into three parts in length based different fatalness,25%,58% and 17%,respectively.The most dangerous area under different opening is identified,vcritical values of fire power are obtained.when fire power is below 100 kW,Similar linear relations between inside temperature and wind speed,inside velocity and wind speed are obtained,also the max velocity and wind speed in front area,all of which can provide referential guidance for investigation of bus fire.The fourth chapter conducted a numerical reconstruction of an actual air conditioning bus fire in virtue of combustion model validated in second chapter and conclusion reached in third chapter.The possibilities of causes resulting in casualties were analyzed. By using numerical simulation method,a fire process reconstruction is conducted,lots of scientific data are obtained.Temperature,visibility and gas species concentration of critical detectors and slices are researched,FID exponent also is analyzed.It is proved that numerical reconstruction can recur fire process by comparing the simulation results and testimony of witness.The feasibility of a improvement program is validated.Numerical reconstruction can improve fire investigation reports and provide guidance for fire prevention,rescuing plans improvement and law-making.