During operation, a diesel generator needs to draw in a large amount of air. If the air is not filtered, the suspended dust in the air will be sucked into the cylinder, which will increase the wear of the piston and the cylinder. Larger particles entering between the piston and the cylinder can cause severe cylinder pulling, which is particularly serious in dry and sandy working environments. The air filter must supply clean and sufficient air to the diesel generator with as little reduction in power as possible, reduce intake noise, and at the same time, its service life and durability should also be good. These requirements are contradictory and cannot all be optimized. Usually, the final conclusion is made through dedicated test benches, diesel generator bench tests, etc. The principle of the air filter is shown in Figure 5. Its basic performance includes three items: intake resistance at the rated air flow rate, filtration efficiency and ash storage capacity.
The intake resistance of the air filter directly affects the power and economic efficiency of the diesel generator, and is also related to the service life of the air filter. The resistance of the intake system of diesel generators is mostly composed of air filters, intake pipes and intake valves on the cylinder head. Currently, the characteristics and development of diesel generators are mainly reflected in high speed and lightweight. The main obstacle to achieving high-speed diesel generators is intake resistance. Nowadays, diesel generators are available in 3-valve, 4-valve and 5-valve types. The adoption of a multi-valve structure to reduce intake resistance has been regarded by scholars as a new direction for the development of modern light-duty diesel generators. Therefore, the flow pressure loss of the air filter and the air inlet that are matched with it should be reduced as much as possible. For air filters of the same model, under the same rated air flow rate, the structural resistance is equal, but the total resistance is not the same. This is mainly due to the different resistance of the filter materials, which leads to different total resistances. The resistance of the filter material is caused by the head-on resistance of the fibers when the airflow passes through the fiber layer. The following introduces several main technical indicators closely related to the resistance of filter paper:
Air permeability
Air permeability is the first performance index to be considered for filter paper. The greater the air permeability of the filter paper, the better its air permeability and the smaller the original resistance; conversely, the opposite is true. There exists an opposite qualitative relationship between air permeability and the original resistance.
(2) Filter paper thickness
The thickness of the filter paper can limit the maximum filtering area of the air filter. That is to say, increasing the effective filtering area of the filter paper also has a significant impact on the resistance of the air filter. This is because when the effective filtering area is increased, the air flow velocity passing through the unit area decreases, so the resistance of the air filter will become smaller. To increase the filtration area, filter elements are made in various shapes, among which cylindrical and rectangular ones are the most commonly used.
(3) Raw materials
If the filter material is nonwoven fabric, it is mainly made of chemical fibers. Its characteristics are low resistance, high filtration efficiency and large ash storage capacity. However, the stiffness and strength are somewhat inferior. To make up for this defect, filter paper is used as the backing to form a composite material of filter paper and nonwoven fabric. Comparing the diameter of the fibers can also distinguish the magnitude of the resistance. If the fibers are fine, there will be more fibers per unit volume, and the resistance generated by the airflow moving around the fibers will be greater. Conversely, if the fibers are coarse, the resistance generated will be smaller.
At present, the filtration efficiency of air filters in various countries refers to the percentage of the amount of dust filtered out by the air filter within a unit of time to the amount of dust entering the air filter with the air. In essence, the size and quantity of particles entering a diesel generator directly affect its service life. Small dust particles entering a diesel generator will not cause damage to it. Only when the dust particles reach a certain size will they cause damage to the diesel generator. Therefore, the original traditional concept of filtration efficiency must be changed and a new concept, namely the appropriate filtration efficiency, should be adopted. The so-called appropriate filtration efficiency refers to the minimum filtration efficiency that ensures the reliable operation of diesel generators. The appropriate filtration efficiency is determined by the ratio of the diameter and quantity of dust particles filtered by the air filter to the diameter and quantity of dust particles entering the air filter along with the air. The appropriate filtration efficiency unifies the filtration capacity of the air filter with the degree of protection for the diesel generator.
According to the new concept of appropriate filtration efficiency, that is, the minimum filtration efficiency that provides reliable protection for diesel generators, the air filter should filter out dust particles that cause damage to diesel generators. Its efficiency curve is shown in Figure 6. The key now is to determine exactly what filtration accuracy a certain type of air filter needs. It is generally believed that if the air filter can remove dust particles larger than 6μm, it will not cause wear and damage to the diesel generator. Since a single air filter can only meet the requirements of a certain type of diesel generator, it is necessary for diesel generator manufacturers and filter manufacturers to work closely together. Diesel generator manufacturers should design dust-resistant materials to reduce wear and choose the appropriate air intake position to minimize the amount of dust entering the diesel generator.
Qinghe County Dongsen Auto Parts Co., Ltd. is located in Qinghe County, Xingtai City, Hebei Province. It was established in 2024. Although the company was established a short time ago, it has more than 10 years of production experience. We are a manufacturer specializing in the production of air filters, air conditioning filters and oil filters. The filters produced by our factory serve the domestic and foreign markets and have won unanimous praise from customers in Southeast Asia, Africa, South America and other regions.
