A Simulative Study On The Interaction Between Diffusion Flames And Water Mist With Additives

As one of Halon potential alternatives, water mist has been widely investigated around the world because of its high suppression effectiveness, non-toxicity, environmental friendliness and competitively price. However water mist is still considered as a physical method of fire suppression. The efficacy of water mist is lower than chemical agents such as Halon 1301, and has limited application in special fire scenarios. In order to further improve the fire extinguishing effectiveness of water mist, there is recently a consideration of adding additives into water mist, through amending the physical or chemical properties of water. Moreover, the effectiveness of a water mist system is dependent on spray characteristics with respect to the fire scenario. Other factors, such as the enclosure effect and dynamics mixing created by the discharge of water mist, also affect the performance of water mist. Therefore, there still is no generalized "first principles" approach to design of water mist systems. Design criteria for each manufacture's equipment are determined through full-scale fire testing according to internationally recognized test protocols. However, these tests are much more expensive and only limited fire scenarios may be involved. As the performance-based code design has become popular, there is a stringent requirement to develop a quantitative approach to estimate and predict the performance of water mist systems under various fire scenarios.The key answers to the above questions are the mechanisms of interaction between diffusion flames and water mist with additives. With the review of the current research status in mind, the thesis proceeds in three purposes. First, we establish a small-scale experimental apparatus to investigate the fundamental mechanisms of gaseous diffusion flames suppressed by water mist with additives. Secondly, we try to study the factors affecting the fire suppression effectiveness of water mist in the open environment through full-scale fire testing. Thirdly, we attempt to establish the fire suppression model of water mist.The first part: study on the interaction between a small-scale diffusion flame and water mist with additives. In this part, simple flame apparatuses widely used in the combustion research were firstly reviewed. The cup burner apparatus was finally selected considering its flame structure comparability. Experiments and numerical simulation were conducted to explore the CH₄/air flame characteristics in the cup burner, which provided the base for further experiments. Interaction of CH₄/air...