SCR technology is known as one of the most popular and widespread off-road diesel engine exhaust emission control technologies. Abbreviated as Selective Catalytic Reduction, this technology features a highly selective converter, primarily designed for NOx emission control. The reductant in its reduction system can be various ammonia compounds or hydrocarbons (HCs). Urea is most commonly used (Urea-SCR), being a 32.5% urea aqueous solution (Adblue). It can convert up to 95% of NOx. The catalyst typically uses a zeolite system, with operating temperatures ranging from 250 to 500 degrees Celsius.

However, SCR technology's catalyst is susceptible to the influence of sulfur oxides. One sulfur compound can deposit on the catalyst surface, rendering it ineffective. Additionally, when using urea, attention must be given to the temperature range and urea supply to prevent secondary contamination. Of course, this can be accomplished through an electronic control system.

A system using HC in fuel as a reducing agent should be combined with the application of common rail fuel injection systems to enhance its effectiveness.

Leaving the SCR system unused for an extended period or removing it directly can cause the chemicals inside to oxidize rapidly, leading to clogging of the urea nozzle and rendering the entire system unusable. The cost of replacing an SCR system is significantly higher than the cost of using urea.

What is the role of OBD?

To meet China IV emission standards, the trucks have been equipped with an additional urea solution injection system using Selective Catalytic Reduction (SCR) technology to reduce NOx emissions from the optimized combustion. OBD can monitor NOx emissions, and when the NOx output exceeds the OBD limit, the malfunction indicator lamp is activated. Meanwhile, the torque limiter restricts engine power by limiting torque, thereby achieving the purpose of monitoring excessive emissions.

The Dangers of Not Using Automotive Urea

1. If the SCR system is not used for an extended period or directly dismantled, the chemicals within the system will quickly oxidize, and the urea injectors will also become clogged, leading to the entire system being rendered unusable. The cost of replacing an SCR system is significantly higher than the cost of using urea.

2. Diesel nitrogen oxide emissions without urea solution are four times higher than those with urea solution. Additionally, due to the OBD's torque limiting feature, diesel vehicles with urea solution tend to have more power, while those without it experience a decrease in performance.

Tampering with OBD can convert Euro IV to Euro II.

The significance of OBD lies in the monitoring it enables. Tampering with OBD, by turning off the OBD switch or disconnecting the relevant line interface, disables real-time monitoring functions, leading to potential fault risks. Moreover, it will significantly increase pollutant emissions, even failing to meet the second national emissions standard.

Drivers in Hong Kong, Macau, and other regions that implemented motor vehicle environmental emission restrictions earlier than the mainland have also previously resorted to shutting down SCR systems to save costs. However, with the strict enforcement of policies and increased understanding of SCR vehicle technology, such issues have now been completely eradicated.

Generally, the normal consumption rate of diesel exhaust fluid is within 5% of the fuel consumption. Advanced technologies such as in-cylinder braking and precise injection in diesel engines above Euro IV standards, combined with good operating practices, can offset the cost of the exhaust fluid. The trend of engine high-horsepower and advanced technology applications will only highlight the fuel economy even more.

Additionally, with the enhanced environmental protection law enforcement, vehicles will face severe penalties during annual inspections or road checks. Disabling the SCR system can only result in a loss without gain.