Specific Requirements for Carriers Used in SCR Catalysts for Diesel Vehicles
Briefly introduce the specific requirements for carriers used in SCR catalysts for diesel vehicles.
Specific Requirements for Carriers Used in SCR Catalysts for Diesel Vehicles
The Selective Catalytic Reduction (SCR) system for diesel vehicles is an after-treatment device that functions by injecting an aqueous urea solution—which decomposes to generate ammonia gas—to reduce nitrogen oxides into nitrogen under the action of a catalyst. Compared to the catalytic converter substrates used in gasoline vehicles, SCR substrates face significantly different operating environments, failure modes, and performance requirements.
Material Property Requirements
Base Material
SCR substrates for diesel vehicles predominantly utilize cordierite—the same material used for gasoline vehicle substrates—yet they are subject to more stringent requirements regarding performance specifications:
Performance Specifications | Typical Requirements for SCR Substrates | Function |
Coefficient of Thermal Expansion (CTE) | ≤1.0×10⁻⁶/℃（20-800℃） | Requires superior thermal shock resistance to withstand the high-temperature transients associated with DPF regeneration. |
Softening Temperature | ≥1400℃ | Withstands the extreme temperatures encountered during active DPF regeneration. |
Compressive Strength (Axial) | ≥5.0 MPa | Withstands canning stresses and vibration loads. |
Compressive Strength (Radial) | ≥1.4 MPa | Ensures canning reliability. |
Channel Structure Requirements
Mesh Count and Wall Thickness
The requirements for channel specifications in SCR substrates differ from those for gasoline-powered vehicles:
Parameters | Typical Specifications for SCR Carriers | Typical Specifications for Gasoline Vehicle Carriers | Reasons for Differences |
Cell Density | 400-600 cpsi | 400-1200 cpsi | SCR reaction rates are relatively fast, so an excessively high cell density is not required. |
Wall Thickness | 4-6 mil（0.10-0.15mm） | 2-4 mil（0.05-0.10mm） | Must balance performance with resistance to particulate clogging. |
For China VI diesel vehicles, the mainstream SCR catalyst substrates feature specifications of 400/4 (400 cells per square inch / 4-mil wall thickness) and 600/4, while certain applications with more stringent requirements utilize the 600/3 specification. Unlike gasoline vehicles—which prioritize ultra-thin walls—SCR substrates must retain a certain wall thickness to ensure adequate mechanical strength and thermal shock resistance.
Geometric Dimensions
Volume Matching: Approximately twice the engine displacement.
Large-Scale Specifications: For medium-to-heavy-duty diesel engines, diameters of ≥285.8 mm (11.25 inches) are typically required.
Aspect Ratio Optimization: A lower aspect ratio (length-to-diameter ratio) helps reduce pressure drop and improves airflow distribution.
Durability Requirements
Thermal Stability: Must withstand thermal cycling within the 200–500°C range under normal operating conditions, as well as thermal shock exceeding 650°C during regeneration cycles.
Mechanical Strength: Must meet durability requirements for a service life of 1 million kilometers.
Thermal Shock Resistance: A coefficient of thermal expansion (CTE) of ≤1.0 × 10⁻⁶/°C is required to ensure structural integrity.
Key Considerations for Specification Selection
Based on the requirements outlined above, the selection of SCR substrates for diesel vehicles should adhere to the following principles:
Volume Determination (Based on Displacement): The substrate volume should be approximately twice the engine displacement.
Size Selection (Based on Available Space): Priority should be given to specifications featuring larger diameters and lower aspect ratios.
Cell Density Selection (Based on Target Requirements): For China VI applications, the mainstream choices are 400/4 or 600/4.
Strength Verification: Axial compressive strength must be ≥5.0 MPa, and radial compressive strength must be ≥1.4 MPa.
Thermal Shock Verification: The coefficient of thermal expansion (CTE) must be ≤1.0 × 10⁻⁶/°C.
Summary
Unlike substrates used in gasoline vehicles, SCR substrates for diesel vehicles place greater emphasis on high-temperature tolerance, mechanical strength, and thermal shock resistance. The 400/4 and 600/4 specifications represent the mainstream choices for China VI standards, while larger-sized substrates are typically employed in medium-to-heavy-duty diesel engines. The selection process requires a comprehensive assessment of engine displacement, available space, mechanical strength, and durability requirements. We are a manufacturer of honeycomb ceramics based in China; for further information, please contact us via email at annayu@169chem.net or via WhatsApp at +8618909016373.