Thread Content
The last edit to this post was made by beyondbeiyang on 2017-6-12 at 06:49. The basic framework for oil quality standards consists of four aspects: physical and chemical properties of the oil, simulation tests, bench tests, and road tests. Within this basic framework of engine oil quality standards, the importance of road tests is second only to bench tests. The climate, road conditions, and vehicle conditions vary from region to region; therefore, compound manufacturers provide driving test reports to prove that their products are suitable for use with engines in those areas. In a dozens-of-pages vehicle test report, numerous test data are presented; this article will analyze the significance of the parameters measured during these vehicle tests. Rate of change of dynamic viscosity (100°C): The viscosity of oil is a fundamental requirement for proper lubrication of engines. During engine operation, changes in the viscosity of the oil are influenced by various factors. For example, the degradation of thickeners in the oil due to shear forces, as well as fuel dilution, can lead to a decrease in viscosity, while oil oxidation, the formation of sludge, and an increase in insoluble substances can cause an increase in viscosity. The rate of change in kinematic viscosity to some extent reflects the degradation of oil quality. A rapid increase in the dynamic viscosity of oil indicates increased oxidation and more sludge formation, which reduces the oil’s fluidity and lubricity, and may lead to engine failures ； A decrease in kinematic viscosity leads to a thinner oil film in the oil, resulting in reduced lubrication properties; the engine may suffer from cylinder scoring due to insufficient strength of the oil film. Flash point (closed cup): When fuel dilution occurs during the use of oil, its flash point value drops significantly. Fuel dilution reduces the load-bearing capacity of the oil film, increases wear, and affects the performance of the oil. Using the closed-cup method allows for an effective assessment of the dilution level of engine oil and fuel, enabling timely replacement with fresh oil. Moisture can enter the oil due to reasons such as leakage caused by aged cylinder liners and water vapor generated in the combustion chamber. The presence of water weakens the oil film and leads to the hydrolysis of additives; organic acids can also corrode engine components. When the water content in the oil is low, the high operating temperature of the engine means that only a small amount of water can evaporate, posing little harm to the engine. As the water content in the oil increases, emulsification of the oil worsens, leading to corrosion of metal components. Increase in acid value and changes in alkalinity 1. The acid value of oils is primarily used to determine the consumption of certain functional agents in the oil as well as the degree of aging of the oil. During use, oil products deteriorate gradually due to factors such as temperature, moisture, and others. As the oil ages, more acidic substances are produced, resulting in an increase in the acid value of the oil ； A large amount of acidic substances causes certain degree of corrosion to the equipment, and under the catalytic effect of metals, it further accelerates the aging of the oil, affecting the normal operation of the engine. 2. The alkali number of oils is used to neutralize the strongly acidic substances produced by combustion as well as the organic acids formed by the oxidation of the oil itself; therefore, a decrease in the alkali number directly reflects the consumption of the active components in the additives present in the oil and a decline in its performance. N-Pentane insolubles: N-Pentane insolubles are an indicator of a fuel’s ability to accommodate contaminants. When the content of insoluble matter in n-pentane reaches a certain level, the viscosity of the oil increases and its fluidity declines. The insoluble substances in the oil aggregate into clumps, blocking the oil passages and leading to serious consequences such as poor lubrication. ◆The content of wear metals such as iron, copper, and aluminum: The main components that wear out in an engine are cylinder liners, crankshafts, piston rings, etc.; therefore, the anti-wear properties of the oil, as well as the degree of wear on these components during operation, can be evaluated by regularly analyzing changes in the levels of metals like Fe, Cu, and Al in the oil samples. Silicon content: The source of silicon in used oil is primarily related to the driving conditions of the vehicle. When a vehicle operates in dusty and harsh environments, or when the air filter is not functioning properly, this can lead to a significant increase in the silicon content in the oil, thereby causing abrasive wear on engine components. Understanding the significance of the tests conducted in road tests allows us to read a road test report from a more professional perspective, which helps us assess the performance of engine oil more effectively. Of course, a road test report also contains some data that is unrelated to the actual testing process, such as simulation test data, which will not be discussed in detail here.