1. DOC structure and working principle: Under the action of precious metals, HC, CO, etc. in the exhaust gas of the engine undergo oxidation reaction to generate CO2 and H2O. At the same time, the exothermic reaction in this reverse process can appropriately increase the exhaust temperature of the engine. The role of the DOC system is to provide a chemical reaction site and a catalyst required in the chemical reaction process.
2. DPF structure and working principle: The DPF filter body is a ceramic carrier with the small holes at both ends blocked. The diesel exhaust gas enters the intake port. Because the end of the intake port is blocked, the exhaust must pass through the filter wall of the intake port and enter the adjacent exhaust port. The exhaust channel discharges the exhaust gas into the atmosphere, and the particulate matter in the exhaust gas is filtered and trapped by the filter wall during this process.
3. SCR structure and working principle:SCR is the English abbreviation of Selective Catalytic Reduction. Its working principle is to inject the reducing agent into the exhaust pipe, so that the nitrogen oxides in the exhaust gas react with the reducing agent to be reduced to nitrogen and water (as shown in the figure) under the action of the catalyst. The agent is a 32.5% (or 40%) urea aqueous solution.Aqueous urea is decomposed into NH3 and CO2 at high temperature:
NH2CONH2+ H2O → 2 NH3 +CO2
NH3 reacts with NO and NO2 in the exhaustto produce nitrogen and water:
NO+NO2+2NH3 → 2N2+3H2O
4NO+O2+4NH3 → 4N2+6H2O
2NO2+O2+4NH3 → 3N2+6H2O
In order to prevent the leakage of ammonia gas during the entire use of the SCR system,The SCR catalyst can be provided with an ammonia oxide layer. In the ammonia oxide layer, NH3 reacts with O2 to generate nitrogen and water.
4NH3+3O2 → 2N2+6H2O