Moreover, the introduction of the Euro VI emission norm in 2012 will require diesel engines to run even hotter, with engine-out exhaust gas temperatures in the region of 850deg C and surface temperatures upwards of 200deg C on exhaust system components. In the tight confines of the engine compartment these temperatures cause fuel and hydraulic lines and connectors of plastic or rubber to age and deteriorate faster.
This increases the risk of leaks, which are often difficult to discover, and constitutes a sure-shot fire hazard, because a fuel spray or vapour in such high temperature conditions will almost certainly ignite. To avoid this, the engine components must be thermally insulated so that any fuel spray is kept away from hot surfaces, and fuel and hydraulic lines laid out so that mechanical wear is minimised.
But even the best precautions cannot eliminate the possibility of a fire entirely, and then the difficulty of access for maintenance in engine compartments of rear-engined city buses and coaches can result in a potential fire hazard being overlooked. This is why fire extinguishers are mandated for buses. AIS-052 too specifies that buses must carry two fire extinguishers.
However, manually operated extinguishers are of limited utility when a fire starts in the engine compartment — by the time the driver is able to stop the vehicle, get hold of the device, and activate it, the fire is often already impossible to control as the temperature can shoot up to 900deg C levels in less than five seconds. Moreover the extinguishant often causes additional damage to the engine components and, in the case of powder-type extinguishers, requires a major effort to clean up after the fire has been put out.
The most effective solution to extinguishing engine compartment fires is to use a fixed, fully automatic system that both detects and suppresses the fire before it rages out of control. Fogmaker International AB of Sweden produces a system using water mist that works independently of the vehicle’s power supply, is environmentally harmless, and causes little damage to the engine and subsystems, resulting in low repair costs.
According to MD Andréas Svensson, water mist is up to three times more effective than powder or gas-based extinguishers,. The fast-acting Fogmaker uses water pressurised at 100 bar in a piston accumulator to generate, via a system of patented nozzles, a fine mist with an average droplet size of 50 microns (8,000 droplets are equal to one drop with a diameter of 1mm) that extinguishes the fire completely and brings the temperature down by 750deg C in just 10 seconds.
This innovative extinguisher uses three mechanisms to attack the three essential elements of the fire — heat, oxygen, and fuel. First, by evaporating, the water mist cools the burnt gases and hot parts in the engine compartment. As against one calorie required to warm one gram of water by 1deg C, 540 times more is needed to evaporate the same quantity from 0deg C to vapour. This contributes to the rapid extinguishment and reduces the risk of reignition.
Second, the mist droplets evaporate instantaneously, expanding to 1640 times their volume. The vapour increases the water content of the air and thus prevents supply of oxygen to the fire. And finally, the water mist also includes a film-forming foam that covers any inflammable pool of oil products that may have formed in the engine compartment or below it.
The Fogmaker had its genesis in the motor racing industry, and its inventor Kennerth Samuelsson was an active Formula 3 and sportscar driver till the early 1990s. At that time, the FIA (the international motorsports federation) had decided to ban halon-based extinguishers, and Samuelsson set to work developing a water mist extinguisher that would operate irrespective of its position in the car.
In the Fogmaker the extinguishant is pressurised by nitrogen gas, and the unique construction of the cylinder ensures that it will always be completely emptied irrespective of the installation angle or position when released. This permits horizontal installation in cramped compartments and saves space. This is also a decisive safety factor in vehicles that run the risk of falling on their sides.
For a standard two-axle bus the system consists of a tough extruded aluminium cylinder of 6.5 or 8 litres, which can be installed either in the engine compartment or outside, for example in the luggage hold. The cylinder, hard-anodised for extreme corrosion-resistance, is connected via high-temperature-resistant tubing to six or seven nozzles. Svenssson said the system acts for a full minute and 20 seconds, compared for only 12 seconds for a 6kg portable powder extinguisher.
Owing to the high pressure of the water mist, the Fogmaker does not require thick sprinkler pipes, which makes for simpler installation. Detection and activation of the system take place hydropneumatically — a pressurised detector hose bursts in the event of a fire and the pressure drop activates the valve on the cylinder. A pressure switch on the detector cylinder gives sound and light alarms to the driver.
Fogmaker International was established in Växjö, Sweden in 1995, and entered the bus market in 2001. Kennerth Samuelsson was active in the company until last year, when Svensson, who had joined in 2000, acquired the business with a friend in a management buyout. To date it has installed systems in over 35,000 vehicles — mostly buses, but also underground machines and boats.
The product is available as an OEM-fitted option from EvoBus (Mercedes-Benz and Setra), Volvo, Irisbus Iveco, MAN and Neoplan, Van Hool, and VDL. According to Svensson leading bus and coach operators in Sweden, Norway, Denmark, Finland, France, Spain, Italy, and the UK require their vehicles to be standard-fitted with the Fogmaker.
Transport for London requires all its new buses to have the system, and has also undertaken a retrofit of its Trident double-deckers. The company recently won an order to retrofit 2,400 buses in the Bus Eirann and Dublin Bus fleets in Ireland, and last year supplied 250 units for engine and AC fire protection on Mercedes-Benz, Volvo, Solaris, and VDL buses for the Dubai transport authority.
For its bus installations so far the cost of the system has been “less than one percent” of the purchase price of the bus, which Svensson described as “cheap insurance”. He
told Autocar Professional the system is equally suitable for front-engined buses that constitute the bulk of the Indian bus market, but given that
these buses all sell for less than Rs 30 lakh, will Fogmaker be able to supply a system at the equivalent of 540 euros?
Svensson is hopeful. “A new BRT bus will probably cost more than 50,000 euros (Rs 30 lakh),” he said, adding that some coach operators besides would appreciate the safety of a fire-protected engine compartment. But offering the Fogmaker at a competitive price will only be possible with local assembly, and Svensson was in India last month scouting around for a partner.
Swiss company Gorba AG, a major supplier of intelligent transportation systems and displays that operates in India through a joint venture with Integra Holding AG, also of Switzerland, would be an obvious prospect. Though, according to Svensson, a partnership with Gorba Integra is still an open issue