Analysis of fire spread and fire extinguishing agent distribution in nacelle of helicopter under no-ventilation condition

Nacelle fire is seen as one of the most difficult to put out. To clarify the characteristics of fire spread in nacelle and determine the minimum usage of fire extinguishing agent, a numerical study is conducted to investigate fire activity in helicopter nacelle by analyzing the distribution of heat release rate, velocity vector field, temperature field and the distribution of fire extinguishing agent concentration with FDS (Fire Dynamics Simulator). Full scale experiment is implemented and three fire sources are set in the nacelle away from front fire wall of 1/4 position, 1/2 position and 3/4 position, respectively. Fire extinguishing system is designed by the results of fire spread. The distribution of fire extinguishing agent concentration is investigated from 6 s to 10 s. Ten scenarios are studied, which are established by changing mass flow rate or injection time. The results indicate that the fire spread in nacelle is affected by the position of inlet and fire source significantly under no ventilation condition. More attention should be paid on 1/4 position which locates at the opposite face of inlet. In order to improve the dependability of helicopter and reduce the waste of fire extinguishing agent, minimum usage of agent is obtained. Decreasing agent mass flow rate is propitious to improve reliability of fire extinguishing system when meets fire suppression requirement.