Climatic tests are crucial to car manufacturers but represent a huge burden on financial and logistical resources as well as having a profound environmental impact. But offering automotive products on the global market means exhaustively validating them in global climatic conditions. Earlier this year href=”/oem-tracker/bmw-group”>BMW opened the doors of its Environmental Test Centre (ETC) for the first time. It was built at a cost of €130m on the same site as the (Forschung und Innovationszentrum) research and innovation centre in Munich and its aim, says ETC operations manager Jürgen Engelmann, is to “bring the whole world, with all its climate zones, into one building.”
With its new facility, BMW hopes to get closer to simulating its customers’ daily driving behaviour and drilling deeper into the kind of use its vehicles get in real world driving. The ETC is equipped to test all products from across the BMW Group including MINI, Rolls-Royce and Motorcycles.
There are five test cells grouped together under one roof. Three are designated ‘wind tunnels’ (due to the focus on aerodynamics) and simulate testing in extreme conditions of heat, cold, humidity, rain and snow. These are the environmental wind tunnel, climatic wind tunnel and thermal wind tunnel. In addition, there is the cold test chamber and altitude test chamber but these two are also effectively wind tunnels making five in all.
The test cells are thoroughly equipped and there’s some overlap of function to allow as much flexibility as possible. Cooling systems are modular with additional stages of cooling only being brought in to play as lower temperatures are required. This, of course, optimises energy consumption.
In cold weather, ambient air can be used to reduce the heat in test chambers in addition to artificially cooled air. The dynamometers and fans are equipped with regeneration systems, generating electricity as they slow down. Rotary and exhaust gas heat exchangers recover 75% of escaping heat.
Image processing is used to monitor and digitally record demisting performance, something that was previously laboriously done by hand with pens and paper
The centre is intelligently designed and cells heavily insulated to conserve energy. Two of the cells are used for extreme low temperatures and sharing a cooling circuit reduces the power consumption by 10mW. The water used in the test equipment is industrial grade ground water and not drinking water.
The wind tunnels are designed using a ‘vertical airflow’, which means the fans are positioned some 15m above the tunnel itself, with air entering and exiting the test chamber at each end. Entry nozzle sizes can be up to 8.4m² providing as uninterrupted an airflow as possible. There are four wheel-drive rolling roads in each cell and a steel belt drive in the environmental wind tunnel for motorcycles. Compared to rollers, the belt more accurately represents the surface of a road passing beneath the wheels.
Environmental wind tunnel
The Environmental wind tunnel provides a wide range of conditions without reaching the extremes of some of the others. The operating temperature range is between minus 20ºC and 55ºC, which is adequate enough to simulate Alaska, Scandinavia or the African deserts. The tunnel can generate rain and snow at various consistencies with snow variable between dry and wet.
Typical tests are for powered snow whipped up by vehicles in front which can block engine filters. A more subtle test is the aerodynamic performance of the A-pillar and how it influences water covering the side window.
HVAC systems can be tested in all conditions, especially air conditioning in hot countries and brake cooling. Air is driven by a 4.75m diameter fan with a motor power of 2060kW and air passes through a 14m x 10m plenum (like the fan, above the chamber). Maximum wind speed is 250km/h (at which rain can be simulated) and snow can be simulated at up to 160 km/h. The nozzle size (through which air enters the test chamber) is 3.5m x 2.4m or 8.16m².
Thermal wind tunnel
Whereas the environmental wind tunnel caters for hot and cold climates, the thermal wind tunnel is used to test vehicles’ ability to withstand sustained high loads in very hot conditions and the load change when the vehicle stops. For example, a vehicle towing in high temperatures which then stops places a sudden high load on its cooling system.
Essentially, the facility is mainly used to test cooling systems and thermal safety of vehicles. It can simulate higher speeds than the other tunnels (280km/h) and has a pit with a glass floor allowing thermographic tests of the chassis and suspension. The temperature range is minus 20ºC to 45ºC. A typical route profile would include 100km driving on a motorway to achieve steady thermal conditions, a cross-country route to increase powertrain temperatures, then a hill route to maximise temperatures and mechanical loads.
Climatic wind tunnel
The climatic tunnel shares the same control room, which is positioned between the two. The climatic tunnel is dimensionally identical to the thermal tunnel and is used for some thermal work but mainly for testing air conditioning systems, brake cooling and performing high speed tests.
There are several key differences with this tunnel though. Instead of aluminium used for the other fans, this one is made from carbon fibre to allow the fan (and therefore the airstream) to accelerate more quickly. Because of this it can easily match the acceleration rate of BMW’s highest performance cars, including the M5. This enables validation and simulation of the most arduous conditions, such as laps of the Nürburgring. Simulation of hot sun is more extreme in this tunnel as well. 24 heating elements generate 1200W/m², while at the opposite end of the scale temperatures can be reduced to minus 10ºC.
Altitude test chamber
One of the most sophisticated test cells in the complex, the altitude test chamber can simulate actual locations such as driving up Pike’s Peak or through Death Valley. This means it can reproduce pressure both at high alitutudes and below sea level.
The chamber is particularly useful for testing turbocharger engines because boost pressure must be varied at different altitudes. It is also used for development of engine control systems which have to continually adjust engine mixture settings with ambient air pressure. The chamber enables calibration to take into account evaporation of fuel at very high altitudes and develop systems to enable its closed loop return to the combustion system. A less obvious use of the chamber is to test the evaporative emissions system of the fuel tank on the ‘Denver Cycle’ at 1,620m above sea level.
It is estimated that a saving of 0.1gm/km across all the vehicles produced would be equivalent to 80% of the energy used for running the facility.
The pressure range is 4,200m above sea level and 200m below. One major challenge is analysing then extracting exhaust from the chamber without compromising intake and exhaust pressure and this is achieved through a complex series of valves. Temperature range in the chamber is minus 30ºC to 45ºC.
What is unusual about the altitude test chamber is the fact that it incorporates a wind tunnel at all - most do not. It’s smaller than the others, with a 2m² nozzle, but windspeeds of up to 250km/h are still possible.
Other parts of the wind tunnel system are also reduced in size, such as the plenum, which measures 12m x 6m and the fan diameter is 2,24m, its motor consuming 900kW. The solarium operates at between 400W/m² and 1200W/m² but like the others, it is also equipped with four wheel-drive rolling road dynamometer with a capacity of 750kW.
Cold test chamber
This is the smallest of the group and, although it incorporates a wind tunnel, it does not produce whole vehicle air flow; it produces just enough for cooling the engine. As a consequence, the entire chamber is much smaller.
Image processing is used to monitor and digitally record demisting performance, something that was previously laboriously done by hand with pens and paper. Vehicles are thermally preconditioned in one of eight basement soak rooms for all the test cells. The number of rooms means tests can be carried out in parallel, one or more being maintained while another is under test and this saves hours of waiting time.
Vehicles are brought to the cells in temperature controlled elevators. There are two smaller fans, each 1m in diameter and each powered by a 110kW motor. There’s a 1m² nozzle and wind speeds of up to 130km/h are possible. The four wheel-drive rolling road has a capacity of 180kW per axle.
In energy terms, the ETC should take care of its own environmental burden. It is estimated that a saving of 0.1gm/km across all the vehicles produced would be equivalent to 80% of the energy used for running the facility. One test in Sweden involves three days transporting test vehicles, backup vehicles and personnel. Even then the success of the test depends on the expected cold weather materialising. Multiply this by tests across the globe for all BMW brands and the environmental impact is significant. Although some location testing will still be necessary, the amount will be drastically reduced.