In recent years, the emission upgrade has become a big problem for the development of Chinese vehicle technology. With the increasing quantity of motor vehicles, the environmental pressure in big cities is enhancing day by day. To connect the tracks with the world fast, China is positively implementing the more strict emission rule, especially the emission standard for the middle-sized and heavy-duty diesel vehicles.
After the leading implementation of state IV emission standard of motor vehicle in Beijing,  Shanghai, Shenzhen, Xi’an and other cities are also planning to implement the standard in the next two years. Although it mainly aims at light petrol vehicle, the new standard which will be implemented soon or later, just like a sword holding on the air, reminding the enterprises to do the preparing work well as soon as possible.
■SCR system: the direction for the development of State IV technology route
For the diesel engines, because of the reciprocal on the generating conditions between the main pollutant particles in the exhaust gas and nitrogen oxide, there comes up different technology routes for the upgrade of diesel engine emission, especially the upgrade above the state III stage.
One is through selective catalytic reduction(SCR) technology, using urea solution to deal with the nitrogen oxide of the exhaust gas. The other is though particulate trap or the converter for particle catalysis, which is called the EGR(exhaust gas recirculation) technology, used to deal with the particles generated by combustion.
On the technical routes, the main diesel engine manufacturers in China have basically reached the consensus, that SCR will be the main technology direction for the upgrade of diesel engine emission in China.
At present, the heavy commercial vehicles, including DAF, Mercedes Benz, IVECO, Renault, Volvo, Daimler Chrysler, Cummins, large Jinlong, Iveco, Weifang and Yuchai, all have adopted the SCR technology.
■SCR system is more suitable for Chinese market.
The Chinese condition is more suitable for using SCR technology. The emerging of KLS makes the urea solution supply more easy. Ultra-low fuel is truly a great difficulty for China. At present, the fuel standard in China will reach to Eur. III standard(with 350ppm sulfur content) in 2010. It’s impossible to reach the standard of 30ppm in 2010. If using the SCR technology, the desulfurization work of the diesel oil which reaches to the ultra-low fuel standard could be delayed to carry out when introducing the Eur. VI standard, which supplies more time of adjustment for the oil industry.   
Besides, there is the research report pointing out that, on the maximum torsion and maximum power, the Eur. IV engines using the SCR technology upgrades nearly 10% to the Eur. III engines with the same output volume. While the Eur. IV engines using the EGR technology is basically equal to the Eur. III engines. At the time time, the Eur. IV engines using the SCR technology lags 5%-7% on the oil consumption comparing with the Eur. III engines with the same output volume. While the engines using the EGR technology are about 3% higher. That is to say, for the Eur. IV engines with the same output volume, using SCR technology can save nearly 10% oil than using EGR technology, and using SCR technology is also more powerful.
For both the advantages of fuel economy and strong power, we can nearly ignore the defect of adding urea solution during the fuel filling of the SCR engine. And the Chinese consumers are very sensitive to the fuel consumption. The fuel-saving product means there will be a more broad market.
The following are some other reasons for why the SCR system is more suitable for the Chinese market.
（1）It can make the fuel consumption lower. As has been stated, the fuel consumption of SCR system is lower than the EGR＋DPF system. Its consumption on the urea solution can also be compensated on the fuel consumption.
（2）Adopting such technology, we can meet the requirements of emission regulations in a long period of time, until the introduction of Eur. VI standard.
（3）This system is different from EGR＋DPF system. It just needs a additional storage tank if want to increase the the volume of the cooler, which causes little effect on the design of the vehicle driving cab.
（4）The engine has low complexity.
The system can meet the Eur. IV and Eur. V standard at the same time, and can be introduced in advance in some regions.
■KLS: the indispensable part for the SCR system
The SCR technology is the best choice for meeting the State IV emission standard. But the SCR system can just transform the nitrogen oxide into N2 and H2O by reductant. The reductant here is the urea solution with given concentration—KLS. The KLS is the special urea catalyst for diesel engines. It conforms to the requirement of SCR technology. And it’s an indispensable part for buses and heavy-duty trucks to meet the state IV emission standard. 
The KLS is safe, non-toxic, tasteless, non-hazardous, and its operation is very convenient. The KLS is gasified and analyzed into CO2 and ammonia under the exhaust gas temperature and airflow through injecting into the vent-pipe of catalyst upstream direction. Then the ammonia revert NOx into pollution-free nitrogen and water as the reductant, so as to reduce the emission of nitrogen oxides and particles.
The active substrate of KLS—urea, is made from natural gas. The urea is the white crystalline powder and it commonly exists in the environment. It’s non-toxic and stable, having no limit in storage and transportation, causing little pollution to water, and it is used very easily and safely. At the same time, it has very low consumption, the consumption of the KLS meeting Eur. IV standard is just about 3.5% of fuel consumption.
The concentration requirement of KLS is 32.5%. It must be stored in the storage tank of the vehicle, and it must meet the strict quality standard so as to make sure the smooth working of the SCR system. The high-pure urea solution with such concentration has another specific name abroad—Adblue. In Europe and North America, there are many gas stations which can supply Adblue, offering the necessary infrastructure for the SCR application. Besides, the urea requested in the Adblue is very cheap, if also considering the saved oil cost, the whole cost is very little. At present, many vehicle manufacturers in Europe and Asia are introducing the SCR system so as to reduce the pollution caused by the vehicle exhaust gas emission.
With the soaring of the oil price, there are more and more enterprises prefer SCR technology both at home and abroad. Couple of years ago, United States Environmental Protection Agency has taken SCR as the official technology. Adblue, the indispensable part for the SCR technology, will surely have a good market.
On the application of SCR technology, Adblue has solved the technical problem of the storage, injecting and ejecting strategy of urea. It has good durability and ripe experience of applying in the diesel engine. With the further development and research of the SCR technology and the more and more strict emission regulation, the Adblue will surely get a more wide application and popularization in various State IV engines.