ABOUT DPF

How DPF works, how it is regenerated, and what to pay attention to？

1.How it works

DPF is the most effective technology for reducing particulate matter (PM) in diesel exhaust emissions. The Diesel Particulate Filter (DPF) is installed in the exhaust system of diesel vehicles to reduce particulate matter (PM) in the exhaust gas. Compared with aftertreatment technologies such as DOC, POC, SCR, etc., DPF can effectively purify 70%-90% of the particles in the exhaust, and is one of the most effective and direct ways to purify particulate matter in diesel engines.

2.Regeneration method

DPF can filter most of the particles, but in the process of the trap work, particles will accumulate in the filter, resulting in an increase in the exhaust back pressure of the diesel engine, when the exhaust back pressure exceeds a certain value, the diesel engine work begins to deteriorate significantly, resulting in the reduction of engine power and economy and other performance, the deposited particles must be removed in time, so that the filter can return to the original working state, that is, what we call "regeneration."

The regeneration system can be divided into two categories: active and passive regeneration systems according to the different regeneration principles

Active regeneration: The use of external energy to raise the temperature in the trap, so that the particles ignite and burn, when the temperature in the trap reaches 550 °C, the deposited particulate matter will be oxidized and burned, if the temperature does not reach 550 °C, too much sediment will clog the trap, then it is necessary to use external energy (such as electric heater, burner or engine operating conditions change) to increase the temperature in the DPF, so that the particulate matter oxidizes and burns.

Passive regeneration: the use of fuel additives or catalysts to reduce the ignition temperature of particles, so that the particles can ignite and burn at the normal diesel engine exhaust temperature, additives (with cerium, iron and strontium) to add to the fuel in a certain proportion, too many additives will affect the life of DOC, but if too little, it will lead to a delay in regeneration or an increase in regeneration temperature.

There are many methods of active and passive regeneration, and the following regeneration methods are easier to achieve:

One is fuel injection heating, the second is electric heating regeneration, the third is DOC-assisted DPF regeneration, and the fourth is CRT/CCRT However, the damage of electric heating batteries is large, and it is not easy to achieve in small and medium-sized cars, and the cost of regeneration is high; Fuel injection heating: burner heating regeneration is to set up a burner at the inlet of the filter, inject diesel fuel and secondary air, and ignite particles for regeneration after combustion

Taking Isuzu as an example, when the DPF needs to be regenerated, it needs to be completed by operating the button, and the control system judges the regeneration time of the DPF according to the preset exhaust back pressure, for example, when the preset value is reached, the fuel injection pump works and generates pressure, and the fuel injector injects diesel in the exhaust pipe in the DOC, in which the injected diesel and the exhaust are mixed and atomized in the straight pipe, and the diesel is oxidized and emitted heat through the DOC to increase the exhaust temperature of the engine. The control system adjusts the amount of fuel injected through the injection pulse width to reach the ignition point of PM (particulate matter) and ignite the PM in the DPF; When the temperature reaches the ignition temperature of the PM and maintains a preset time, the fuel injection system automatically stops the fuel injection and the regeneration is completed

Passive regeneration refers to a regeneration method that does not require external intervention, and uses a regeneration method that uses NO and soot to react with low-temperature combustion on the surface of the filter carrier Compared with active regeneration, passive regeneration requires a lower temperature, which can achieve continuous regeneration of DPF The difference between CRT and CCRT: CRT DPF without catalytic coating, while CCRT's DPF particulate trap carrier is coated with a catalyst In the regeneration work, the NO produced by the oxidizer can continue to produce NO2 in the particle trap to oxidize particulate matter. In general, this regeneration system is simple to install, and the maintenance work is relatively small, and these common methods have advantages and disadvantages, and the cost of fuel injection heating may be higher for the driver, because when a certain pressure is reached, it needs to be regenerated by fuel injection; In fact, most of the current car companies use the SCR technology route, but the DPF technology route is also available, because it involves the problem of regeneration, so there are fewer people who use this route in reality

3.Pay attention to the problem

Why can't DPF be cleaned with water?

The first point: the structure of the DPF determines that the internal structure of the DPF is actually a ceramic structure, and a layer of precious metal structure is added to the surface, so that the method of adsorbing particles can be satisfied, which is very similar to the structure of the SCR, but there is still a big difference, because the ceramic structure of the DPF is wall-through, that is to say, the gas through the DPF is very similar to our air filter, and the gas must pass through the filter paper, so if it is cleaned with water, the precious metal characteristics of the surface will be destroyed. And it will only make the soot more and more blocked, and it will have no effect

The second point: the function of DPF is determined, the function of DPF is to adsorb PM particles, when the surface of DPF is blocked by carbon ash, the system will give DPF a "regeneration" command, that is, to force the surface of the carbon ash to burn again to generate gas that can pass through the DPF structure, but if we do not follow the original function, directly use water to clean, carbon and water are mixed and solidified, then it is completely blocked

The third point: the performance of DPF determines that the working temperature of DPF itself is between 400~650 °C, so when the content is not dried after washing with water, it will cause the explosion of the entire structure, and it is a ceramic structure, if there is water at high temperature, then it is very easy to crack, resulting in the loss of the function of the whole system