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Why test drive systems and materials in extreme cold?
Patrolmen in our areas are often much busier once the winter really kicks in and temperatures drop. Engines and other car components really suffer in low temperatures and sometimes end up breaking down. Although this is peanuts compared with what machinery and vehicles are faced with in extreme climates. How do people deal with this?
In countries such as Finland, Sweden, Norway, Canada, China, Mongolia and Russia, where the temperatures regularly fall below 0°C, sometimes even to extreme levels of -40°C or -50°C, much more attention must be paid to such conditions and so the design of the machinery must always be optimised in order to continue operating. Therefore the drive systems and materials used on the machinery must be able to operate properly in such extreme conditions. It is therefore necessary to carry out tests at the same extreme conditions in order to determine the levels of reliability and robustness of the machinery in similar circumstances.
Vehicles and other machines must be able to start up and remain running at extremely low temperatures. Continued operations in these extremes of temperature (from -30°C to even -60°C at some locations), can only be guaranteed if this is taken into account early on in the design stage and also at the end of the production development cycle. This is done by carrying out thorough validation tests. This is why sectors such as mining and quarrying and the off-highway industry always have their products tested under extreme conditions in climatic test chambers. The typical tests carried out on such machinery include the cold start tests, testing the heating and cooling systems in a variety of climatic conditions, testing the functioning of hydraulic systems in extreme cold, testing the functionality of the windscreen de-icing systems (ice testing) and making inspections for breaks and leakages in joints and seals that focuses on preventing leakages.
Engines, drive systems, after-treatment systems and cold starting
Engines and drive systems must generally be able to start up and do their work in all circumstances. The search for reduced fuel consumption has resulted in modern engines running more smoothly at higher compression ratios, with the combustion occurring at higher temperatures. This has resulted in relatively low CO and HC emissions, but higher emissions of NOx. In order to deal with the higher NOx emissions, so-called 'after-treatment systems' are deployed, although cold starting still remains a problem. These after-treatment systems are fitted as standard on off-highway and construction vehicles, and they are also used in the energy sector for making diesel generator sets more sustainable.
Actual working situations have all too often demonstrated performance levels that differ from the anticipated performance. After-treatment systems are used to prevent high levels of NOx emissions. Various technological solutions are being tested (read more about this in this blogpost). NH3/urea SCR for example is a very effective and widely applied technology for reducing NOx levels in diesel engine exhaust fumes. The problem with NH3/urea mixtures is that it normally freezes around -11°C, therefore tests have to be carried out to find out whether such systems can continue operating in the winter without causing damage to the environment.
In order to obtain the best results it is essential to test the complete vehicle or machine. Testing the complete set-up is the best way of collecting data about the general environmental suitability and operational sustainability of the machine so that potential problems of interference between the various subsystems can be detected. This makes it possible to evaluate the subsystems from the various manufacturers together and therefore identify installation faults or other difficulties before production begins.
Engine builder MTU carried out tests on its engines at the extremely low temperature of -25°C for example. A climatic test chamber allows designers to carry out tests in controlled conditions into how easy, or difficult it is to start the engine at various temperatures. The test engineers altered the pressure, the volume and the timing of the fuel injection system in order to improve the starting characteristics. The test data is used for programming the engine management system and provide the engine with suitable start settings based on external ambient and coolant temperatures, while taking account of improvements to the lifespan and sustainability.
Such tests are valuable for vehicles and machinery used in mining activities in places like Siberia and Canada where the temperatures can drop to Arctic levels of -60°C. Polar diesel is used there which has a kerosene content of 60 percent that makes it substantially less viscous than the standard winter diesel fuel. This is why the injector settings have to be altered in order to prevent the very thin fuel causing them damage. An air grill is fitted in front of the radiator to ensure that the engine is not over-cooled. The grill closes whenever the temperature drops too low. This means that the engine can always be started even with extremely low external temperatures. The engine management system automatically adjusts the volume of fuel and the injection timing in order to match the air temperature. Depending on the ambient temperature, a pilot injector located on top of the main injector can be activated during the starting routine.
Sirris is also involved in this area and our facilities at the Port of Antwerp is one of the only technology centres in Europe to have a large climatic test chamber for testing such vehicles and machinery at Siberian temperatures. The climatic test chamber is unique in that it is possible to test machinery weighing up to 150 tons at -60°C. This is quite different from many other climatic test chambers for cars where the weight and temperature levels are not suitable for this niche market.
Materials and cold work conditions
It's not just fuels and hydraulic fluids that react differently at extremes of temperatures, because materials used for making engines and components are also affected. For example, bearings can suffer problems on starting up caused by differences between internal and external temperatures. The combination of cold, brittle materials and vibration can lead to even more problems. As well as metals, synthetic and rubber materials also behave differently.
For example synthetic hoses for hydraulic circuits lose their flexibility at low temperatures by initially becoming leathery, then hard, stiff and brittle once the 'glass point' has been reached. The use of an elastomer for low temperatures depends on this point. At or below this temperature pressure, tension or impact on the synthetic material will damage or break it. Moreover, elastomers can degrade when exposed to thermal cycles. However, when the elastomers are treated with additives for resisting low temperatures, problems can arise when the temperature increases (the additives start to leach), so that the performance is reduced when the temperature is lowered once again.
Large climatic test chamber for eliminating risks
The availability of a large climatic test chamber with substantial dimensions, weight capacity and an extensive temperature range is essential for testing materials being used such as engines, drive systems and after-treatment systems on large vehicles or other machinery that is exposed to extreme conditions. In addition to the subsystems, the best results can only be obtained by testing the complete vehicle or machine. Therefore Sirris offers a specially adapted set-up and a unique testing infrastructure for companies involved in sectors including off-highway, construction and agricultural vehicles, wind energy applications, energy transmission systems, aerospace, defence, etc.
The climatic test chamber is mainly used for testing very large and heavy wind turbine components including gearboxes, converters and transformers at extreme temperatures. The chamber was designed with a number of unique features, such as the large dimensions (10.6 m x 7 m x 8 m), extreme temperature range (-60°C to +60°C), 150 ton weight capacity and a facility for compensating 250 kW of heat at -20°C.
Since last year the laboratory has been able to carry out air humidity tests with a range of ± 2% RH to ± 95%. Regarding the off-highway and construction vehicles market, the laboratory has also invested in the ability to test IR sunlight up to a density of 950 W/m², so that it can carry out tests on the cabs of large vehicles in accordance with ISO 14269-3 and ISO 10263-6 HVAC.