Research on environmentally friendly fire suppression systems for aircraft cargo.

Abstract

It is widely known in the aviation community that the use of Halon1301 as fire suppression agent has been banned as it presents high ozone depleting potential. This fact dictates that there is a necessity for fire suppression systems replacement on all existing aircraft within a limited timeframe. So far, Nitrogen (IG-100) was proven to be the most promising replacement agent for future aviation. The present research project attempts to assess the handling, performance and installation of a Nitrogen (IG-100) fire suppression system on aircraft cargo in order to accelerate the transition to Halon-free systems. The research has been conducted under the umbrella of the EU Clean Sky 2 (CS2) “Environmentally Friendly Fire Suppression System for Cargo using Innovative Green Technology” (EFFICIENT) project. The methods used to achieve the project targets are based on analytical and numerical 3D-CFD modelling as well as both in-house and public domain experimental information of respective cargo fire suppression systems. Additionally, they are aligned with FAA requirements and follow the Minimum Performance Standard (MPS) required for testing and certification. The Nitrogen (IG-100) system design space exploration focused on the examination of exchange rates between parameters such as the number and location of discharge nozzles and ventilation ports with the system effectiveness, operability and safety. The resulted fire suppression system design was also used for the development of the detailed design and operation strategy of the Cranfield in- house test rig as well as the experimental testing and procedures, the risk assessment and installation cost estimation. The outcomes of CFD simulations presented satisfactory agreement with the theoretically expected analytical calculations. Additionally, they were validated against the experimental data coming from the above mentioned Cranfield based test rig. The data regarded No-Fire and Open Surface Liquid Fire tests using Jet- A fuel. Both CFD and experiments showed that system achieved the desired average Oxygen concentration within 60 seconds discharge, while maintaining it below 16% for more than 45 minutes, satisfying the FAA MPS. Additionally, the average overpressure level inside the compartment remains within limits both during and after agent discharge. Finally, based on their comparison, numerical model adaptations and calibration are suggested in order to improve modelling fidelity and simulation accuracy. The proposed Nitrogen based design suggests minimum modifications to the already existing Halon1301 based systems in order to accelerate the replacement process. Furthermore, the system provides ease in handling and operation with capabilities of minimising Nitrogen wastage by varying the agent mass used based on the level of the cargo load and the nature of its content. Finally, recommendations for future improvements regarding the system response time, the fire protection time, the weight and complexity are included.