“We have considered the technical trend of Euro 6 heavy-duty diesel engines. The conventional route is to use EGR to reduce the nitrogen oxides in the cylinder to about 3 grams, and then use DPF to reduce the particulate matter to the standard required by Euro VI, and then reduce it through SCR. Residual nitrogen oxides. According to this technical route, we have successfully developed the Euro 6 diesel engine and obtained EU certification.†From December 2nd to 3rd, Weichai Power Co., Ltd. held a meeting to promote the energy-saving, emission reduction and sustainable development of internal combustion engines. Company Dr. Li Qin said: "But there is a problem, the characteristics and difficulties of the traditional European 6 technical route is that the high EGR rate of the whole spectrum leads to the shortage of full-loaded oxygen. To maintain the previous power, it needs high boost to compensate. This raises the highest burst pressure in the cylinder and requires a redesign of the engine."
It is understood that the bottleneck of the traditional European 6 technical route is that it needs to withstand the outbreak pressure of more than 200 bar. It will take 5 to 10 years for this platform to be upgraded to the market acceptance level. Another approach is to significantly reduce engine power (by more than 15%), but it is difficult to gain market acceptance.
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“In this context, we invented our own low-explosive pressure program without altering the engine. Later, we found a better solution, which was to remove the EGR cooler, that is, the SCR + non-cooled EGR solution. Now, from Europe, another One piece of information is the pure SCR solution.†Li Qin further explained: “The advantages of the non-EGR diesel engine include not requiring too high boost pressure, not generating excessive explosion pressure, and relatively indispensable requirements for supercharger and fuel injection system. Low, no need to increase the demand for vehicle cooling system, and reduce various failures caused by EGR system.In addition, under the same conditions, pure SCR has the advantage of operating cost, and this advantage is more important for the Chinese market that value the cost. Based on the above analysis, I think there is no prospect for EGR on heavy-duty engines."
Another major problem facing Europe VI is the regeneration of DPF, which includes passive regeneration and active regeneration.
"The active regeneration is achieved through engine measures to achieve a DOC front-row temperature of 300°C or more. The fuel injected in the cylinder or after the exhaust pipe undergoes an oxidation reaction in the DOC, raising the temperature of the exhaust gas entering the DPF to over 600°C, driving the PM. DPF is oxidized, but its biggest problem is to accurately estimate the carbon load.If the carbon load is too large, it will cause the DPF to burn; if the carbon load is too small, it will cause the DPF regeneration is not complete, and the effective length is shortened. It can be seen that the DPF regeneration control has a high requirement for product consistency and a large workload of calibration. From my experience, DPF is the most difficult to do with so many post-processing tasks.â€
Fortunately, passive regeneration occurs when the emission control level is upgraded to Euro 6, and the principle is to oxidize nitric oxide in the DOC to nitrogen dioxide. Nitrogen dioxide is more active than oxygen and can oxidize PM at 300°C. In addition, passive regeneration does not require much calibration work.
Therefore, Li Qin concluded that efficient SCR and passive regeneration will be key technologies for heavy-duty diesel engines in the future.
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