Technical countermeasures for loaders to adapt to high-altitude environments

China boasts the world's largest plateau region, covering an area of approximately 2.7 million square kilometers, with an average altitude ranging from 2,000 to 4,500 meters. The Qinghai-Xizang Plateau is the most representative among them, with an average altitude of 4,500 meters. Its unique climatic characteristics include thin air, low air pressure, low oxygen content, large temperature differences between day and night, low-temperature earthwork, strong ultraviolet radiation, heavy wind, sand and dust, little rainfall, and dry climate. The construction of the Qinghai-Xizang Railway not only needs to solve the problems of railway survey, design and engineering construction in the permafrost area of the plateau, but also needs to address the "plateau disease" of construction equipment in this region. These problems have no precedent in the world. We need to base ourselves on the current level of science and technology, free our minds, keep innovating, and overcome one technical difficulty after another in the construction process.

In response to the unique environment of the Qinghai-Xizang Plateau, Changlin Co., Ltd. listed plateau-type construction machinery as a technological research and development project in 2000 (it was listed as a national-level technological innovation project of 2000 by the State Economic and Trade Commission). After extensive investigation and research, technical analysis and design development, as well as high-altitude experiments and improvement verification, a series of studies have been conducted on the high-altitude adaptability technology of loaders.

1. Power system

1.1 The Influence of Plateau environment

1) As altitude increases, atmospheric pressure decreases, and air density reduces, the oxygen content in the air also decreases. This has a particularly significant impact on construction machinery powered by internal combustion engines. Experiments show that for naturally aspirated internal combustion engines, for every 1,000 meters increase in altitude, their power and torque decrease by 8% to 13%, fuel consumption increases by 6% to 9%, and thermal intensity increases by 2% to 5%. When the altitude reaches 4,000 meters, its power decreases by about 45%. This is due to reasons such as reduced cylinder inflation volume, decreased heat dissipation performance, increased heat load, and incomplete combustion. Therefore, the high-altitude environment has a very serious impact on the engine's power performance.

2) In plateau areas, the low air pressure, low oxygen content, large temperature difference between day and night, and long cold seasons cause the compression pressure and temperature of internal combustion engines to decrease with the increase in altitude. The experimental results show that for every 1,000 meters increase in altitude, the compression pressure of the internal combustion engine decreases by 17%, the temperature drops by 23%, and the minimum limit starting temperature of the original machine increases by about 22℃. Meanwhile, when the auxiliary devices are used on the plateau, all aspects related to ignition, combustion and oxygen consumption performance show varying degrees of inadaptability. Especially under low-pressure and hypoxic conditions, the difficulty of starting is much greater than that at low altitudes.

3) In plateau areas, there is a lot of sand and dust. The dust content in the air is 5 to 15 times that of low-altitude areas. It increases the intake resistance, reduces the filtration effect, and due to the low oxygen content in the air, the combustion performance of the engine drops rapidly. This not only reduces the power but also accelerates the wear of diesel engine components and shortens the service life of parts such as air filters.

1.2 Countermeasures

To fully ensure the reliability and adaptability of the loader in high-altitude environments, we have selected the C6121 high-altitude compensation turbocharged engine produced by Shangchai with the introduction of Cat3306B technology. It is equipped with an imported turbocharger. In high-altitude areas, the power drop of the diesel engine is less than 3% and the smoke density is lower than 3.0. Thus, the problem of insufficient power caused by the decline in power in the plateau environment has been overcome.

2) It adopts a large-capacity, maintenance-free imported Wotema solid-state level, which can operate normally within the temperature range of -40 to 65℃. Add an ether combustion aid device or a water jacket preheating device as an optional accessory to the engine system to enable the loader to start normally at -25℃ in high-altitude areas.

3) A low-intake resistance three-stage cyclone large-capacity air filter is adopted, and an exhaust ejector pipe is installed on the exhaust muffler to achieve automatic dust removal, solving the problem of heavy wind, sand and dust in high-altitude areas, which can easily clog the air filter and affect the engine's power performance.

2 Heat dissipation System

2.1 The Impact of Plateau Environment

For the engine, due to the reduction of air in the cylinder, the excess air coefficient drops, the combustion condition is poor, and the afterburning phenomenon is severe, which increases the thermal load of the engine. Due to the reduction in air density, the mass flow rate of the cooling fan decreases. Due to the increase in altitude, the boiling point of cooling water decreases (the boiling point of water along the Qinghai-Xizang Line is 78 to 85 degrees Celsius), all of which lead to a decline in heat dissipation capacity and a further increase in heat load.

2) For the transmission system, due to the deterioration of matching performance, in addition to failing to fully utilize and exert the maximum power of the engine, there are also insufficient power transmission and inefficient transmission, which cause part of the power to be converted into heat energy due to internal loss, resulting in the overall operating temperature of the machine exceeding the specified value and affecting normal operation.

2.2 Countermeasures

1) Use enlarged fans and keep the linear speed of the fans within a reasonable range; An increased water tank with a larger heat dissipation area is adopted to ensure sufficient heat dissipation space under low air pressure.

2) Optimize the matching of the transmission system and the layout of the hydraulic pipeline system, and adopt a special heat dissipation system to ensure that the loader has an appropriate operating temperature.

3. Rubber parts and seals

3.1 The Impact of Plateau Environment

In plateau areas, the duration of sunlight is long, ultraviolet rays are intense, and the temperature difference between day and night is large. The annual average temperature in the Qinghai-Xizang Line region is -27 to -45℃, and the daily average temperature remains below 0℃ for 235 to 330 days. These environments accelerate the cracking of hydraulic rubber hoses and the aging of rubber parts and sealing parts.

3.2 Countermeasures

The rubber hoses for the steering system, working hydraulic system, braking system, etc. are produced by Lufthansa Flex of Germany. They can withstand low temperatures of -40℃ and have an ultraviolet resistance that is more than 8 times that of ordinary rubber hoses. The sealing parts of key components such as oil cylinders are imported to ensure reliability and durability in low-temperature environments.