Experimental Study On Fire Suppression Of Water Mist With Additives In Ship Cabin Confined Space

The high-pressure water mist fire extinguishing system replaces the traditional fire extinguishing agent such as halogenated alkane,and is widely used in the fire fighting and control of ship fires.However,the ship fire is mainly oil pool fire,and the high-pressure conventional water mist will strengthen the flame combustion and cause the flame to spread.At the same time,its features such as large space for arrangement,poor performance of oil fire suppression and high installation cost reduce the effectiveness of ship fire control to a certain extent.To further improve the applicability of water mist in ship fire-fighting,in view of shortcomings of high-pressure water mist system,this paper studies the performance of water mist containing KCl,NaCl and CaCl₂ to suppress oil pool fire with low pressure water mist,which has reference significance for low pressure water mist fire protection application.Based on a 1.5m?L?×1.5m?B?×1.0m?H?closed cabin platform,using n-heptane as a fire source,an experimental study on the oil pool fire suppression by low-pressure water mist with different additives?NaCl,KCl,CaCl₂?,different mass fraction solutions?5%,10%,15%,20%?and different nozzle pressures?0.2MPa,0.4MPa,0.6MPa?was conducted,which used a 20 cm diameter oil pool and a nozzle with the atomizing cone angle of 80°.The purpose was to compare the performance of oil pool fire suppression by water mist under different conditions in the ship confined cabin,so as to obtain the best suppression ratio scheme.By measuring the flame combustion state and cabin environmental parameters,analyzing the parameters of heptane combustion flame height,heptane mass loss rate,flame temperature,ambient temperature and flame morphology,the research results show that:?1?Low-pressure pure water mist can strengthen the oil pool fire combustion,and its fuel mass loss rate,flame height and flame temperature are much higher than that of heptane free combustion.The highest values of the data are:2.0g/s,75cm,550?.?2?The low mass fraction?5%?solution has a poor inhibition of fuel loss rate.The average mass loss rate of KCl solution decreases linearly with the increase of pressure or solution mass fraction.The NaCl and CaCl₂ water mist increase with the solution mass fraction,and the average mass loss rate decreases first and then increases?10%curve value is the lowest?.The optimal pressure to suppress the average mass loss rate of heptane by water mist containing KCl,NaCl and CaCl₂ is 0.6MPa,and the optimal mass fraction are 20%,10%and 10%,respectively,and the corresponding minimum values are 0.147g/s,0.159g/s,0.123g/s,which are 35%,29%,and 45%lower than the free combustion value?0.227g/s?of heptane.?3?KCl and NaCl have a good restraining effect on flame temperature,while CaCl₂ has weak effect on flame temperature.KCl and NaCl have the best temperature suppression effect at 0.6MPa nozzle pressure,and the temperature curve can be reduced by 36%to 350?from550?.Among the three additives,all experimental minimum temperature curves were arranged from small to large:NaCl<CaCl₂<KCl,and the corresponding proportion?nozzle pressure-mass fraction?are 0.6 MPa-10%,0.2 MPa-10%,0.6 MPa-20%,which the highest value are 350?,380?and 450?,respectively.When the mass fraction is 5%or 10%,NaCl has the best temperature inhibition effect,and the temperature curve is below 350?.When the mass fraction is more than 10%,KCl has the best temperature suppression effect and the temperature is below 450?.From the economic view and the effect of temperature suppression,NaCl has the best effect,followed by KCl.?4?The nozzle pressure affects the flame combustion process.When the nozzle pressure rises,the experimental time is shortened,and the flame height enters the boiling combustion or decay phase in advance,causing the flame to quickly extinguish.The mass fraction of the solution affects the flame falling rate and the overall height.The change trend of the overall flame height with the mass fraction under the three additives is:decrease?KCl?,rise?NaCl?,decrease?CaCl₂?.?5?Water mist containing additives can effectively reduce the indoor temperature of the cabin.When the mass fraction of KCl is 20%,the peak value of wall temperature curve is the lowest,which is 65??0.2MPa?,63??0.4MPa?and 53??0.6MPa?respectively.When the mass fraction of NaCl is 10%,the peak value of curve is the lowest?40??.The 20%curve is the highest?70??;the same CaCl₂ mass fraction is 10%curve peak is the lowest?50??.?6?NaCl has the most obvious influence on the flame morphology.The time when the flame begins to decay with pressure is 120s?0.2MPa?,110s?0.4MPa?,40s?0.6MPa?,followed by KCl:120s?0.2MPa?,90s?0.4MPa?,60s?0.6MPa?,while the change of CaCl₂flame morphology is less affected by pressure.?7?The variation trend of the overall flame height with the improvement of mass fraction in the three additives is as follows:decrease?KCl?,increase?NaCl?,and decrease?CaCl₂?.KCl,NaCl and CaCl₂ solutions all reaches the minimum flame height at the pressure of0.6MPa,and their suppression ratios are 20%?KCl?,10%?NaCl?and 20%?CaCl₂?,respectively.Experiments show that KCl has the best effect on flame height suppression,and the flame fluctuates between 25-35cm and extinguishes quickly.?8?20%mass fraction KCl solution has the best extinguishing effect under 0.6 MPa nozzle pressure.