Automatic fire suppression and extinguishing system design for a wheeled military vehicle

Ground military vehicles have always been known with their superior weapon systems. Eliminating enemy targets is always the most important aspect. Throughout history, military professionals sought to have good attacking properties while procuring ground military vehicles. Things are changing in recent years. Nowadays, evaluting ground vehicles are not only based on a vehicle's attacking abilities. Protecting a mission requires also the protection of the vehicle as well as the personnel. Ballistic systems are very important for the defence properties of a vehicle. On the other hand, suppression systems are constantly under development in order to protect the personnel and military vehicle as well. Automatic Fire Suppression and Extinguishing System handles the fire situations without human intervention. Fire remains among the greatest threats in a military vehicle which requires the designers pay more attention for it. Fire protection is an important area of concern during the design, development and deployment phases for all modern wheeled ground vehicles. There are definitely manual modes for redundancy and emergency but the main purpose is to be able to suppress or extinguish a fire to prevent damage to either personnel or equipment. Preventing fire in the early stages dramatically reduce the possibility of personnel death. This system possess the same importance when compared with the ballistics protection of the vehicle. In this study, a system technologically advanced is presented but the main concern was to provide a practical, lightweight and effective solution to an already known problem. Explosion protection of the personnel in crew compartment in ground military vehicles is a unique and difficult application with sophisticated requirements that must balance suppression characteristics with safety limits. There are two types of components in the system: Suppressors and Detectors. As for the detectors, there are two possible alternatives. They can either sense the thermal energy or can detect the ultraviolet and infrared range of light caused by fire. Light sensitive optical detectors have very quick response and can detect fire in 2-4 miliseconds. It is obvious that their response time is at its highest. Main trick in this technology is to be able to respond any kind of fire within miliseconds. Unfortunately using only infrared or ultraviolet sensors might lead to errors in slowly developing fire conditions. That is why, new type of optical detectors use both of these sensors to be able to identify different types of fire more effectively. Thermal wire is another type of detector which uses the heat energy to detect the fire. These are traditionally used in non-human environments and are slow to respond because it takes some time for the fire to build up heat energy sufficient to activate the thermal wires and send detection signal to control box. For military vehicles, this is a designer's decision to use either optical detectors or thermal wire. As for the suppressors, there are couple of alternatives at hand. In the past, Halon was being used most of the time to suppress fire. However, it is hazardous to human health although it can record quite fast suppression time. FM200 is Halon's replacement in the industry. It has slower suppression time but the mixture can be made in a way that can enable the suppression of fire and do not harm human health at the same time. Novec and aerosol are also evaluated for their suppression performances as well. Aerosol is mostly used for low volume areas and was not useful for this application. On the other hand, usage of Novec was performance-wise was a good solution but it was not preferred. Free volume in the crew compartment determines the amount of extinguishing agent that needs to be used in the system as well as number of extinguishing cylinders. Decision for the number of optical detectors came from analysis in 3D environment, sampling is applied to verify the results. Detection of fire is not only needed for suppressing fire but to do it in a safe manner so that crew was not affected. Sensors can differentiate the real fire conditions with other hydrocarbon signatures coming from other non-threatening sources. A set of optimization took place during the development phase to overcome false alarm situations especially for peace conditions. As for the distribution agent, the valve system below the cylinders plays the most critical role. This system that was used is quick to respond and releases the extinguishing agent effectively. Deflectors are used to enhance the capability to reach almost everywhere. This is a product that can be modified based on the layout of the vehicle so that dead spots and areas which might deter the performance can be eliminated. For powerpack compartment, defining the risky areas has utmost importance. In order to have a better suppression characteristic and faster suppression time, instead of using thermal wire, optical detectors are preferred. Distribution of the agent is performed with well-placed nozzles. In order to prevent problems in harsh and sandy conditions, these nozzles have caps as well. Fuel lines are also the most critical areas in terms of possible fire condtions. These lines if placed closely to the electric lines may pose as a sparkling point for a fire condition. Control unit is the heart of the system and provides the necessary feedback to user so that any type of malfunction can be detected before the operation. Microprocessor used helps reducing the response time and a well-designed cover for protection provides the user with a robust experience. Although this agent is completely harmless to human beings, concentration after releasing it for fire protection plays a vital role. High concentration for better suppression characteristics could lead to problems in the field if the air ventilation system is not working properly. In order to avoid this problem, concentration level after releasing the agent is set to around %10-12 initially and verified with the test results. Configuration and layout depends on the vehicle volume and component layout. Usually there are 2 main compartments: Powertrain compartment and personnel compartment. Detectors shall be placed so that they cover almost any volume in the vehicle to be able to provide best level of protection. There should not be any obstacles within the line of sight of the optical detectors. Although they are very sensitive to fire, obstacles within their sight might reduce the possibility to suppress the fire in 250 miliseconds. Testing of a fire suppression system is the last step to verify and validate the system's performance. Cup burner test is the most common method to see the results of system design characteristics. In this study, this test process is conducted to be able to see and observe the placement of the suppressors and detectors of the system. This test is combined with a gas concentration test to check several areas in the vehicle. It is important to note that since there are some development areas for better performance. Other than the prohibited Halon which needs to be replaced in older vehicles as well, FM200 is the most commonly used agent which can be used as a suppression agent for portable extinguishers as well. However, this aspect of the system still needs additional research for better suppression and distribution properties. Optical detectors have been developed to be able to reduce false alarm rates and better fire detection capabilities. In this study, UV-IR optical detectors are used however there are different types of optical detectors developed for better fire detection characteristics. Using smoke detectors in combination with optical detectors may be evaluated as well for different areas within the vehicle. These detectors still require further development to reduce false alarm rates and better protection of the powerpack compartment but especially crew compartment. Automatic Fire Suppression System demand in the military industry can be considered as a starting point for future local content development strategies. In this respect, localization of this system can be realized by establishing local opportunities in the market.