SCR Exhaust Gas Post-treatment System of Dual Reduction Type

Release time:2019-04-26 17:27

Product TechnicalApproach

According to the requirements of transformation and treatment ofin-service diesel vehicle market, the product should meet not only the requirementsof reducing particulate matter (PM) in exhaust gas, but also meet therequirements of reducing nitrogen oxides (NOx). Therefore, Sinocat has speciallydeveloped a dual reduction post-treatment product (DOC+DPF+SCR) for dieselautomobile to better satisfy market demand.

Working principle of Post-treatment Products of dual reduction

Sinocat has successfully developed a DOC+CDPF+SCR dual reduction post-treatment product by integrating Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), and NOx Selective Catalytic Reduction (SCR) (a catalytic converter with a precious metal catalyst coated on a DPF carrier, namely CDPF). On the one hand, the DOC in this product oxidizes NO to NO2 in an appropriate temperature range, providing sufficient NO2 for the downstream CDPF to achieve passive regeneration smoothly, while also supplying NO2 for the rapid reduction reaction for SCR. On the other hand, by using excellent fuel ignitability of DOC, CDPF’s active regeneration can be realized smoothly, improving CDPF’s active regeneration efficiency, reducing fuel consumption, therefore booting economic efficiency of fuel.

The DOC+CDPF+SCR system integrates numerous modern high technologies such as precious metal catalysts for diesel automobiles, selective catalytic reduction technology, polymer ceramic materials, high-precision sensor technology, SCR injection control technology and online supervision and alarm technology. It is the industry-leading product of China’s road diesel exhaust emission control technology.

The product monitors the internal working conditions of the system in real time through temperature and pressure sensors, and uploads the informations to the monitoring platform of the modified vehicle. At the same time, it precisely controls the treatment of NOx through multiple temperature and nitrogen-oxygen sensors, gas flow or speed sensors

By optimizing the integrated system of DOC+CDPF+SCR, the CO, HC, NOx and PM in exhaust gas of reformed diesel engine are significantly reduced and meet emission requirements. After the product is installed, fuel consumption increases by no more than 5% and urea consumption will not exceed 5% of fuel consumption.

Product Categories 

The product of DOC+DPF+SCR developed by Sinocat for diesel automobiles includes air-assisted and non-air-assisted exhaust gas post-treatment system. According to different layout of the original car, products with different structures are designed.

Three Structures ofthe Product

"" ShapeStructure

Such a structure is simple, practical and detachable. It issuitable to replace the truck with cylindrical muffler at the bottom of thevehicle, or the vehicle with the original muffler in "one" shape atthe bottom of the vehicle.

“S” Shaped Structure

Such structure is relatively compact, with the front and rear barrels being connected side by side or at different angles, and the detachable design is suitable to replace the original muffler on the side of the car.

Box-type Structure

It is the most compact structure and is very suitable to replace the square muffler on most of the diesel trucks. Thanks to the direct replacement of the original muffler, the product can be installed through original method at the fixed position of original muffler, which is convenient and secure. In this way, the structure of the whole vehicle will not change and its safety is guaranteed.

Product performance parameters

Product Performance Parameters

Control Strategy
The control strategy of Sinocat is an open-loop control strategy based on the model, which adopts the dual nitrogen oxygen sensor and adds the feedforward control link.

Adaptability of Fuel

Sinocat products can adapt to National V stage ofdiesel vehicle (sulfur content S10ppm). The Company’s pre-sales and after-sales techniciansand instructions will also emphasize and stipulate that the use of diesel fuelabove National IV standard is mandatory, which means that the sulfur content mustbe lower than 50PPM. If our company’s after-sales personnel have doubts aboutthe use of substandard diesel oil, they can negotiate with customers to samplethe diesel oil in the tank under the condition of third-party authenticationand send it to a third-party professional testing agency for oilidentification.

The catalyst utilized in this system exhibits excellent sulfur resistance and is capable of operating for at least 200 hours with 350 ppm fuel. If the truck driver accidentally adds substandard oil, it will not have an irreversible impact on the whole system in a short time.

Experiments have also been performed on thefuel even with a sulfur content of 3500 ppm. Although continuous operation ofthe catalyst for approximately 20 hours, its performance has been significantlydiminished.


After switching to diesel of National V standard, the sulfates covered on catalyst will be removed from the catalyst surface (SO3&SO4) after approximately 30 minutes at 350°C or above. It is also observed that the catalyst can be regenerated smoothly for desulfurization, with a significant recovery in performance, which basically attains the initial performance state. Hence, it is proved that the modified catalyst can withstand diesel fuel with high sulfur content for a short time to the utmost extent.

After extracting the online monitoring data of 100 diesel vehicles, it is found that the exhaust temperature above 350℃ will also occur. In addition, if the DOC effect decreases, the regeneration performance of CDPF will also decrease, and the increase of back pressure will lead to the increase of engine exhaust temperature. We can also heat and regenerate the post-treatment system during maintenance to ensure that the service life of the system is not limited by occasional accidents.

Image of Product (Image of S-type Product of Dual Reduction)

Thermal Management Solution
Diesel Particulate Trap (DPF)

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