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Water mist system for engine compartment fire protection
Kim, A.; Crampton, G.
NRCC-47325
A version of this document is published in / Une version de ce document se trouve dans : Proceedings of 4th International Water Mist Conference, Rome, Italy,
Oct. 6-8, 2004, pp. 1-8
Water Mist System for Engine Compartment Fire Protection International Water Mist Conference 2004
October 6 – 8, 2004, Rome, Italy Andrew Kim and George Crampton
Fire Research Program,
National Research Council of Canada Ottawa, Ontario, Canada, K1A 0R6 Phone #: (613) 993-9555 Fax #: (613) 954-0483
E-mail: andrew.kim@nrc-cnrc.gc.ca
ABSTRACT
Typically, a water mist system is used for fire protection in a total flooding mode in an enclosed space. Use of water mist for fire protection in a local application is less common. This paper describes research work on the local application of water mist for engine compartment fire protection.
A water mist system was used to extinguish fires in the engine compartment of an armoured vehicle. An engine protection water mist system was installed in the engine compartment of an operational armoured vehicle. The system had a piping network distributed in the engine compartment of the tank, and many small water mist nozzles were attached to the piping.
Fire scenarios that simulate potential fires in the engine compartment were used in the tests. The engine fire scenarios consisted of a pan fire located between the cross members of the engine compartment floor and a spray fire located centrally on top of the engine pack. Two ventilation conditions (engine “ON” and engine “OFF”) were used in the tests.
The test results showed that the water mist system, once activated, extinguished the liquid fuel pool fire or spray fire in the engine compartment effectively. When the fire scenario was a combination of pan and spray fire, the water mist system had difficulty in extinguishing the fire in the engine compartment.
INTRODUCTION
In response to the phase-out of ozone-depleting halons by the Montreal Protocol, the Department of National Defence (DND) and the National Research Council (NRC) of Canada have been evaluating environmentally-safer alternatives to Halon 1301 for
potential DND applications.
Water mist technology is a relatively new development in the fire suppression area. A water mist system is environmentally-friendly and it does not have any negative impact on the environment or toxic by-products. Various research and testing
organizations, including NRC, have been studying the effectiveness of water mist systems for various fire protection applications. Previous studies have shown that water mist is effective in extinguishing enclosed fires, especially when fires are large.
However, water mist systems have some limitations: water mist does not behave like a gaseous system and its fire suppression is dependent on the water mist spray
characteristics and the location of the fire with respect to the spray nozzle location. It also has difficulty to extinguish small and shielded fires.
DND has various land vehicles whose engine compartments were protected against fires by halon systems. However, with the phase-out of halon, many vehicles, including Leopard tanks, are currently not protected against engine fires. DND is looking for an environmentally-friendly and effective system, such as a water mist system, for engine fire protection of armoured vehicles.
Recently, a company has developed a water mist system (WMS), which is designed to provide engine fire protection in military vehicles. This system consists of heat detectors, extinguishers and central control units. It incorporates several nozzles connected to a water reservoir through a small pump to produce water mist spray in the engine compartment. The system can provide several shots of short duration water spray depending on the successful extinguishment of engine fires.
This paper describes full-scale fire tests to determine the effectiveness of the WMS system against engine fires in the Leopard tank engine compartment, and provides the results.
TEST SET-UP
The tests were conducted at the NRC’s Centre for Surface Transportation Technology facility (U-91), which has the capability to lift the engine pack out of the Leopard tank engine compartment.
A WMS engine protection water mist system was installed in the engine
compartment of an operational Leopard tank by the manufacturer of the WMS system. This WMS system was specially designed for the Leopard tank engine compartment. The hardware consisted of a power pack (a 40 L fluid container and a high-pressure 24 volt pump), a relay, stainless steel piping, nozzles, sensors and a system control box.
The power pack, relay and the control box were installed in the crew
compartment of the tested tank. The system had a piping network distributed in the engine compartment of the tank. It had two layers of piping: one below the engine pack, close to the floor of the engine compartment, and one above the engine pack. These two layers of piping had many small water mist nozzles attached to the piping itself thus spraying water mist uniformly to the space between the bottom of the engine pack and
the engine compartment floor and to the space between the top of the engine pack and the engine compartment cover.
There were eight temperature sensors located at various points in the engine compartment measuring the temperatures. A microprocessor, with a company-developed software, evaluated the temperatures measured by the sensors to activate the water mist system.
The WMS system was designed to use 50% potassium lactate water solution. Fire scenarios that simulate potential fire in the engine compartment were used in the tests. The Leopard tank has two fuel tanks located inside the engine compartment. Three reinforcing beams are on the bottom of the engine compartment and naturally divide the bottom into four big "pans". If fuel leaks from the fuel tank fittings or connections, it may accumulate in these "pans" underneath the engine. Cracked fuel tanks, broken fuel lines feeding the fuel injectors or ruptured hydraulic fluid lines may result in fuel spray and form fuel pools. They can be ignited by potential ignition sources, such as hot metal surfaces in the exhaust, brake and transmission assemblies.
To simulate these potential fires, a pool fire and a spray fire were used in the tests. The engine fire scenarios consisted of a pan fire located between the cross members of the engine compartment floor and a spray fire located centrally on top of the engine pack. The pan, measuring 280 mm by 440 mm, was fitted with a resistive coil of 20 gauge Nichrome wire on the side of the pan for ignition, and a thermocouple was attached to monitor the ignition and extinguishment of the fire. The flame under the engine was also monitored using a photodiode flame sensor mounted near the fuel tank.
Heptane was used as fuel in the pan. The heat release rate of this pan fire was estimated to be approximately 70 kW.
Fuels in the compartment may be re-ignited by a hot engine surface after fire extinguishment. To simulate this, re-ignition attempts were made in the tests by having the hot ignition element powered for the whole duration of the tests.
The spray fire consisted of a 18.5 ml/s spray nozzle located on top of the engine near an access portal. Heptane fuel was supplied through a 10 mm copper tube from a pressure canister at 100 psi. Ignition was similar to the pan ignition.
Two ventilation conditions of engine “ON” and engine “OFF” were used in the tests.
TEST RESULTS
A total of seven tests were conducted in this study. Test results are summarized in Table 1.
Test #1 was conducted with a pan fire in the engine compartment. Heptane was poured into the pan, and it was ignited using an electric igniter. The engine was off during the test.
The WMS system had temperature sensors that would activate the water mist spray once they reached a pre-determined critical temperature. The temperature sensors were set at 150°C. However, during the test, the temperature sensors were reading a slow rise of temperatures in the engine compartment, probably due to the slow speed of the sensors or improper locations of the sensors with respect to the fire growth of the pan fire in the bottom of the engine compartment. Ideally, the sensors should pick up the fire ignition and the water spray should be activated within 20 s of the ignition. Since the WMS system did not activate, and a fire was visible and growing in the engine compartment, water spray was activated manually at approximately 80 s after the fire ignition to reduce the fire damage in the engine compartment. At the time of the water mist spray, the maximum temperature recorded by the WMS sensors was only 45°C.
The pan fire in the engine compartment was extinguished soon after the water spray was activated.
The test showed that the WMS system, once activated, extinguishes a liquid fuel pool fire in the engine compartment effectively, however, the sensors need to be re-examined for their effectiveness.
Test #2 was conducted under the same condition as in Test #1.
Since the WMS sensors were slow in activating the water spray, the test
procedure was changed to manually activate the water spray if the WMS system did not activate automatically within 20 s of the fire ignition, to minimize damage to the engine.
In the test, the WMS system did not activate automatically, so it was activated manually at 29 s after the fire ignition. The water spray lasted for approximately 12 s, and the fire was extinguished during the water mist spray.
Test #3 was also conducted with a pan fire in the engine compartment, however, in this test, the engine was on during the test.
The WMS system was activated manually at 24 s after the fire ignition, because it did not activate automatically. The water spray lasted for approximately 16 s, and the fire was extinguished during the water mist spray.
The test showed that the WMS system, once activated, can extinguish a liquid fuel pool fire in the engine compartment, and whether the engine is on or off (thus different ventilation conditions in the engine compartment) does not make much difference in the effectiveness of the WMS system.
Test #4 was conducted with a fuel spray fire in the top portion of the engine compartment.
In this test, the engine was off during the test. The WMS system was activated automatically at approximately 10 s after the ignition of the spray fire. The spray fire was extinguished soon after the water mist spray activation.
Test #5 was also conducted with a fuel spray fire in the top portion of the engine compartment, however, in this test, the engine was running during the test.
The WMS system was activated automatically at approximately 15 s after the ignition of the spray fire. The spray fire was extinguished soon after the water mist spray activation.
The test showed that the WMS system can extinguish a liquid fuel spray fire in the engine compartment, and whether the engine is on or off (thus different ventilation conditions in the engine compartment) does not make much difference in the
effectiveness of the WMS system.
Test #6 was conducted with a combination of a pan fire on the bottom and a fuel spray fire in the top portion of the engine compartment. In this test, the engine was off during the test.
The WMS system was activated automatically at approximately 16 s after the ignition of the pan and spray fires. The initial water spray lasted for approximately 14 s, but the fire was not extinguished. After 19 s, the WMS system activated again for a second cycle. The second cycle lasted for approximately 55 s. The fire was not
extinguished during the second cycle. After 21 s, the WMS system was activated again, but this time manually, and continued to spray. The fire did not seem to be suppressed by the water spray, so the fuel spray was discontinued. With the spray fire cut off,
continuous water spray extinguished the pan fire and the remaining flames in the engine compartment.
Test #7 was again conducted with a combination of a pan fire on the bottom and a fuel spray fire in the top portion of the engine compartment, but in this test, the engine was running during the test.
There was a problem with the central unit of the WMS system, so it was not possible for the system to be activated automatically.
The WMS system was activated manually, and followed the water spray cycle of Test #6. The result was similar to Test #6. The fire was not extinguished during the two cycles of water spray. The WMS system was activated manually for the third cycle, and continued to spray. The fire did not seem to be suppressed by the water spray, so the fuel spray was discontinued. With the spray fire cut off, continuous water spray extinguished the pan fire and the remaining flames in the engine compartment. Figure 1 shows
temperatures in the engine compartment during the test, which indicates that the temperatures in the engine compartment remained high, despite several cycles of water mist spray because the fire was not extinguished in the engine compartment.
The tests showed that the WMS system could not extinguish a combined fire scenario of pan and spray fires in the engine compartment. The tests also showed vulnerability of the sensors and central unit of the WMS system.
CONCLUSION
A WMS engine protection water mist system was installed in the engine
compartment of an operational Leopard tank. Fire scenarios that simulate potential fire in the engine compartment were used in the tests. The engine fire scenarios consisted of a pan fire located between the cross members of the engine compartment floor and a spray fire located centrally on top of the engine pack. Two ventilation conditions of engine “ON” and engine “OFF” were used in the tests.
The test results showed that the WMS system, once activated, extinguishes a liquid fuel pool fire in the engine compartment effectively, however, the performance of the sensors was not consistent and the sensors need to be re-examined for their
effectiveness. In spray fire tests, the WMS system activated automatically and
extinguished the spray fire. The results showed that whether the engine was on or off (thus different ventilation conditions in the engine compartment) did not make much difference in the effectiveness of the WMS system in suppressing the pool fire or the spray fire.
When the fire scenario was a combination of pan and spray fire, the WMS system had a difficulty in extinguishing the fire in the engine compartment. The tests also again showed vulnerability of the sensors and the central unit of the WMS system.
ACKNOWLEDGEMENTS
The authors would like to acknowledge the assistance of Mr. Michael Ryan in setting up and instrumenting the test compartment. Financial assistance for the study by DAVPM, DND is greatly appreciated. Special appreciation goes to Mr. Wolfang Aistleitner and Mr. Adrien Van Kessel for their assistance during the experiments.
Table 1 Summary of Test Results
Test # 1 2 3 4 5 6 7
Fire Type Pan fire Pan fire Pan fire Spray fire Spray fire Pan/Spray fire combination
Pan/Spray fire combination
Engine ON/OFF Off Off On Off On Off On
WMS System Activation
Manual Manual Manual Automatic Automatic Automatic/Manua l Manual System Activation Time (s) 81 29 24 10 15 16 / 49 / 125 18 / 48 / 71 Number of Spray Cycle 1 1 1 1 1 3 3 Water Spray Duration (s) 25 12 16 59 51 14 / 55 / 66 15 / 16 / 47 Fire Extinguishement ?
Yes Yes Yes Yes Yes No No
Time (s) 0 20 40 60 80 100 120 140 Temperat ure (C) 0 200 400 600 800
Left side (from turret) Right side (from turret) Top Centre Engine Pan Flame Spray fire Extinguisher Timing extinguisher on 18 s after spray ignition off 33 s on 48 s off 64 s on 71 s
