Product technical route
DPF (Diesel Particulate Filter) diesel particulate trap (also known as DPF tail gas post-processing system), after a long time of particulate trapping, will block the porous media channel of the filter, resulting in the back pressure rise in the exhaust system, and then affect the normal operation of the engine. Therefore, measures need to be taken to remove soot particles filtered by DPF and restore the filtering capacity of DPF. This method is called regeneration. Regeneration methods are generally divided into active regeneration and passive regeneration.
The products developed by Zhongzi Company are to reduce the emission of CO, HC and other pollutants in exhaust gas through DOC catalytic oxidation reaction. At the same time, DOC oxidizes NO in exhaust gas to NO2. Under appropriate temperature conditions, CDPF (a catalyst coated on DPF carrier, namely CDPF) can capture PM passively and regenerate PM. When the condition of active regeneration is reached, the control unit controls the injection device to inject fuel before DOC, and uses DOC to raise the exhaust temperature substantially, so that PM in CDPF can be burned and regenerated. The catalytic performance of DOC and the filtration performance of CDPF make the tail gas purified.
The company's products are tested according to the Ministry of Ecology and Environmental Protection test standards and industry test standards (HJ451-2008). The conversion efficiency of DOC to HC and CO is more than 80%, the capture efficiency of DPF to particulate matter is more than 90%, and the regeneration efficiency of particulate matter is more than 90%.
The control unit monitors the temperature of the catalyst and the pressure difference before and after CDPF, and judges whether regeneration is needed according to the carbon load and working conditions. If regeneration is needed, the controller will control the active regeneration system and have a remote online monitoring device.
In view of the actual situation of diesel vehicle emissions in use, considering the longitude and latitude of different regions and the environmental temperature in winter, Zhongzi Environmental Protection provides two different transformation schemes, the main difference is that the regeneration technology routes are different to meet the transformation requirements of different vehicles.
The self-made products can be adapted to the five-stage automotive diesel oil in China (sulfur content S < 10ppm)
Product Safety Requirements
Remove the muffler of the original vehicle, install the product on the exhaust manifold of the engine, and fix it on the frame of the vehicle. On the premise of ensuring the installation space of catalytic muffler, the distance from the engine should be as short as possible. If necessary, the exhaust pipeline should be heat preserved, and the maximum distance after heat preservation should not exceed 2000 mm.
After the installation of the product, it ensures that the original safety performance of the vehicle is not changed and meets the relevant safety regulations. In view of the safety of the system control strategy, in some special circumstances and occasions, the control system will forcibly terminate the active regeneration of the product. Including: stop active regeneration process after parking, in special occasions (such as gas stations, inflammable and explosive places, etc.).
(2) Structural security
All products and accessories such as mounting brackets are made of materials that meet the strength requirements of the whole vehicle to prevent products from breaking and falling off due to severe vibration during driving. The structure and size are similar to the original muffler, which will not affect the original safety performance of the vehicle. Good thermal insulation measures to prevent fire or burns caused by high temperature.
(3) Security of control strategy
Accurate regeneration condition judgment ensures timely and effective regeneration of products. Set strict regeneration conditions threshold, including vehicle speed, exhaust temperature, CDPF back pressure, cumulative running time to reach the set value before regeneration, after parking or in special occasions (such as gas stations, flammable and explosive places) to force the termination of active regeneration.
The power is collected from the spare terminal of the original vehicle, and the system automatically loses power after parking, without affecting the electric system of the vehicle. With its own air source, the system does not need to take air from the original vehicle, and does not affect the braking performance of the vehicle.
Passive Type of DPF Tail Gas Post-treatment System
Passive regeneration scheme is adopted in DPF tail gas post-treatment system. Passive regeneration relies on DOC to oxidize NO in tail gas to NO 2. NO 2 reacts with soot in DPF to remove carbon particles and realize passive regeneration. At the same time, a catalyst (CDPF) is coated on DPF carrier to reduce the reaction temperature of carbon particles and NO 2 and increase passive regeneration. Temperature range, improve the efficiency of passive regeneration.
The products of the two modification schemes adopt the structure of DOC+CDPF catalytic muffler with direct air intake or side air intake. According to the different engine displacement, the products with different diameters and lengths are designed. The overall structure and size are similar to the original muffler. The muffler of the original car can be removed and installed. The installation height is equal to that of the original muffler, so as to ensure that the passing ability of the vehicle is not affected.
CDPF is designed as a detachable structure. When there is a large amount of non-combustible ash in the device, the CDPF segment can be easily disassembled. The ash can be blown out by compressed air with a special device, and the air blown out can be filtered by water without affecting the environmental air. There is no additional outlet for the product to prevent the occurrence of emission fraud at the source.
DOC oxidizes NO in engine exhaust to NO 2. When the temperature in exhaust reaches 250 - 500 C, NO 2 reacts with particles in DPF catalyst. The principle of passive regeneration is as follows:
Passive products require good performance of catalysts, and have certain requirements for the original emission of vehicles, the running status of vehicles and the quality of fuel, so their application is limited.
Thermal management scheme
The first one is the two renovation schemes developed by Zhongzi Company. The thermal management schemes are to add a layer of thermal insulation cover (commonly known as "thermal insulation coat") outside the main body of the product. The function of the thermal insulation cover is as follows:
The product has a sound absorption rate of more than 90%, and can prevent noise and anti-interference, which is higher than the average requirement of NRC.
It has the characteristics of heat resistance up to 700 C, good toughness, corrosion resistance and so on.
With high tensile strength and length stability, no dust will be produced.
The shrinkage rate is very low at high temperature and the service life is long.
High sound absorption rate can achieve noise reduction effect. High heat insulation and heat resistance make fuel react adequately in high temperature environment of exhaust pipeline, thus achieving low emission.
Technical requirements for heat shield:
The heat shield is a composite product of inorganic fibers. Its physical and chemical properties are as follows: the thermal conductivity at room temperature is less than 0.04W/mK.
Tensile strength (> 0.72 MPa), non-flammability is non-flammable grade A, safe use temperature is not less than 600 C.
The heat shield should be reliable, geometrical shape unchanged, continuously cracked, not peeled, not agglomerated, not falling, not producing dust, etc.
The heat shield shall not burn, be harmless and produce toxic substances and gases.
When the heat shield is installed, it should be fitted on the outer surface of the fittings, which requires close fitting.
The connecting pin matched with the heat shield passes through the opening pin round holes on the lap joints on both sides in turn, and is tightened and fixed.
The second scheme is to stop injection when the temperature of DOC outlet is higher than the set value or when the temperature of CDPF outlet is higher than the set value. Both approaches can achieve a thermal management effect.
Solutions to Low Temperature Environment and Failure to Reach Regeneration Conditions
Passive products of DPF tail gas post-treatment system can increase the probability of passive regeneration by adding catalyst coating and a heat shield; in low temperature environment and unable to achieve regeneration conditions, drivers can be advised to increase load or run at high speed for 15-30 minutes, or to consider disassembly or periodic manual maintenance of CDPF and manual removal of soot, such as high pressure. Emergency measures such as air backblowing.
Physical drawings of products