Passive Diesel Particulate Filter (DPF)

Release time:2019-04-26 17:19

Product Technical Approach

DPF (Diesel Particulate Filter) is alsoknown as DPF Exhaust Post-treatment System, after a long time of particulatecapturing, the porous media channels of the filter will be blocked, which willresult an increase of back pressure within the exhaust system, thus affectingthe normal operation of the engine. Therefore, it is necessary to adoptmeasures to remove the carbon soot particles filtered by DPF and restore thefiltration capacity of the DPF, which is termed as regeneration. Regenerationapproaches are generally categorized as active and passive regenerations.

The products developed by Sinocat are designed to reduce theemission of pollutants such as CO and HC in exhaust gas through DOC catalyticoxidation reaction, while DOC oxidizes NO to NO2 in exhaust gas. At the propertemperature, the passive regeneration of PM captured by CDPF (a catalyticconverter coated with a layer of catalyst on a DPF carrier, known as a CDPF) willbe realized. Upon fulfilling the conditions for active regeneration, thecontrol unit manages the injection device to inject fuel in front of the DOC,and the exhaust temperature is greatly increased by DOC, so that the PM in CDPFcan be regenerated. The catalytic performance of DOC and the filteringperformance of the CDPF contribute to the purification of exhaust gases. 

The company’s products are tested according to the test standard of Ministry of Ecology and Environment, and industry test standard (HJ451-2008). The conversion efficiency of DOC of catalyst for HC and CO exceeds 80%, the capturing efficiency of DPF for particulate matter reaches more than 90%, while the regeneration efficiency of particulate matter attains over 90%.

The control unit monitors the temperature of the catalyst and thepressure difference before and after CDPF, and judges whether the regenerationis needed according to the carbon load and working conditions. If regenerationis needed, the controller will regulate the regeneration system and it isequipped with remote online monitoring device. 


In view of the actual situation of diesel vehicle emissions inuse, the longitude and latitude of different regions and the temperature inwinter, Sinocat provides two different schemes of modifications, whoseprincipal difference lies in the varying regeneration technology approaches, soas to meet the transformation requirements of diverse automobiles.

Product Categories

Adaptability of fuel

The products of Sinocat can adapt toNational V stage for diesel automotive (sulfur content S10ppm)

Product SafetyRequirements

Product Installation

Remove the muffler of the original vehicle, install the product behindthe engine exhaust manifold, and fix it on the vehicle frame. While ensuringthe installation space of catalytic muffler, the distance from the engineshould be minimized. When necessary, the exhaust pipe should be insulated, andthe maximum distance after insulation should not exceed 2000mm. 

After the installation of the product, it ensures that the original safety performance o the vehicle is unchanged and meets the relevant safety regulations. In view of safety of system control strategy, the control system will mandatorily terminate the active regeneration of the product under some special circumstances and occasions, including terminating the active regeneration process after parking and in special occasions (such as gas stations, flammable and explosive places, etc.).

(2) Structural Safety 
All products, mounting brackets and other accessories shall be made of materialsmeeting the strength requirements of the whole automobile, to prevent theproducts from fracturing and falling off by severe vibration during driving.The structure and size of the muffler are similar to those of the originalvehicle, which will not affect the original safety performance of the vehicle. Excellentinsulation measures are in place to prevent fire or personnel scald caused byhigh temperature.

(3) Security of Control Strategy 
Precise regeneration condition evaluation ensures the product regeneration in atimely and effective manner. As a result, it is necessary to specify stringentregeneration condition threshold, including vehicle speed, exhaust temperature,CDPF back pressure, setting value of cumulative operation time for regeneration,and mandatory termination of active regeneration after parking or under specialoccasions (such as gas stations, flammable and explosive places, etc.). 

The power is taken from the standby terminal of the originalvehicle, and the system will automatically power off after parking, withoutaffecting the electrical system of the vehicle. The system is equipped with itsown gas source, therefore, there is no need to take gas from the originalvehicle, which will by no means affect the braking performance of the vehicle. 

Passive Type of DPF Exhaust Gas Post-treatment System
 Principle of Regeneration 

The passive type of DPF exhaust gas post-treatment system employsa passive regeneration scheme. Passive regeneration relies on DOC, whichoxidizes NO in the exhaust gas to NO2. NO2 reacts with carbonsoot in DPF to remove carbon particles and realize passive regeneration. At thesame time, a layer of catalyst (CDPF) is coated on the DPF carrier to reducethe reaction temperature between carbon particles and NO2, to increasethe temperature interval for passive regeneration and to improve the efficiencyof passive regeneration. 

Product Structure 
 Products of both modified solutions adopt the structure of DOC+CDPF catalytic muffler with direct air intake or side air intake. According to different engine displacements, the products with different diameters and lengths are designed. The overall structure and size are similar to the original muffler, it can be installed after the original muffler is removed. The installation height is equivalent to that of the original muffler, so as to ensure that the trafficability of the vehicle will not be affected.

The products of Sinocat has high maintainability. CDPF is designed as a detachable structure. When there is a lot of unburned ash in the device, the CDPF can be easily disassembled. Dedicated device is used to blow out the ash through compressed air, and the blown air is filtered by water, which poses no impact on the air quality. There is no additional vent for the product, which can eliminate emission falsification at the source.

Regeneration Conditions
The DOC oxidizes NO from the NOx in the engine exhaust to NO2. When thetemperature is between 250°C and 500°C in exhaust process, NO2reacts with the particles in the DPF catalytic converter. The passiveregeneration theory is given as follows:
Passive-type product requires good performance of catalyst, and has certain requirementson original emissions of the vehicle, operating condition of the vehicle, andquality of the fuel. And the application of this kind of catalyst is relativelylimited.

Thermal Management Solutions

The First Solution:
For both of the modified solutions developed by Sinocat, their thermalmanagement solutions are designed to incorporate a heat shield (commonly knownas an "thermal insulation jacket") on the exterior of the productbody. The functions of the heat shield are as follows:

---   It features a sound absorption rate of more than 90%, which isresistant to noise, exceeding the average requirements of NRC;

---   It is characterized by good toughness and corrosion resistance,and its heat resistance is up to 700℃;

---   It offers high tensile strength, so it will not produce any dust

---    It possesses extremely low shrinkage and long service life at hightemperature;

---   The high sound absorption rate can achieve the effect of noisereduction, while high thermal insulation and heat resistance enable fuel toreact fully at high temperature in the exhaust pipe, thus attaining goal of lowemission

TechnicalRequirements for the Heat Shield:
- The heat shield is an inorganic fiber composite product, whose physical andchemical properties are as follows:
 thermal conductivity at roomtemperature is ≤0.04W/mK. Tensile Strength is ≥ 0.72MPa, non-flammability isgrade A, and the safe use temperature is ≤ 600 ℃. The heat shield shall not be changed,broken, peeled off, agglomerated, dropped or dusted.;

---   The heat shield shall not burn and produce toxic substances andgases;

---    During installation of the heat shield, it should be fitted on theexterior surface of the pipe, and it is required to fit tightly;

---   It is required to connect the joint pinsof the heat shield through the round holes of the cotter pins on both lapjoints in sequence and tighten them.

The Second Solution:

Fuel injection will be discontinued when the temperature at theDOC outlet is higher than the set value, or when the temperature at the CDPFoutlet is higher than the set value. Both methods can achieve thermalmanagement effect.

Solutions for low temperatureenvironment and unachievable regeneration conditions

The passive-type product of DPF post-treatment system increasesthe probability of passive regeneration by adding catalyst coating and a layerof heat shield. In the cases of low temperature and the failure to achieveregeneration conditions, it is recommended that the driver shall increase theload, or drive at high speed for 15-30 minutes, or consider dismantling or conductingregular manual maintenance of the CDPF to remove the soot, such as taking emergencymeasures for back blowing of high-pressure air flow. 

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