Speaking of air filters, everyone must be familiar with them. In the general impression of people, air filters are the filter elements inside that block dust and allow clean air to enter the engine to participate in combustion. In fact, simple air filters have great mysteries. Let's take a look at what mysteries there are.

The most common air filter we see on trucks is called inertial air filter.

The filter element inside is like this: one large and one small. The large one outside is called the "main filter element" and the small one inside is called the "safety filter element".

▎Mystery: The paper filter element is only responsible for filtering 15%-20% of the dust
Where does the rest of the dust go?

Truckers who are familiar with the engine structure know that many engines have a coarse filter called the rotor filter in the oil filter. It allows the pressurized oil to be sprayed through two small holes in opposite directions to drive the oil rotor to rotate at high speed, and the impurities in the oil are separated from the oil through centrifugal force. Because of the effect of inertia, the impurity particles will be thrown farther.

In this way, when the particles rotate and collide with the filter housing, they will reduce their speed and slowly settle at the bottom of the oil filter. This is the working principle of the oil rotor filter.

Similarly, the inertial air filter also has this structure and function: when the dust-containing air passes through the blade ring or swirl tube, a vortex will be generated (the air of the inertial filter rotates into the next filter).

When buying a car, the salesperson will tell us that this car has two-stage filtration. The inertial rotary filtration mentioned above is the first stage of the two-stage filtration, also called the pre-filter. The inertial pre-filter can filter out more than 80% of the dust particles.

After the pre-filtered air is filtered by the second-stage paper filter element, it can ensure that the dust content in the air reaches an extremely low level. The filtration efficiency of a qualified paper filter element can reach more than 99%.

Although there are two paper filters inside and outside, it is the main filter element outside that plays the role of filtering. The function of the safety filter inside is to block dust in case the main filter outside fails or other unexpected situations occur, so as to protect the engine from being damaged by dust.