What are EGR and High Efficiency SCR?

Firstly, let's talk about what high efficiency SCR means. It is actually the treatment of nitrogen oxides and other harmful substances that are not treated cleanly by the engine by injecting more urea into the aftertreatment.

The main reason why high efficiency SCR has to spray more urea into the aftertreatment is that the engine eliminates the EGR component, the engine exhaust gas will not be burned twice, only the exhaust gas from one combustion is discharged directly into the aftertreatment, so more nitrogen oxides will not be disposed of in the engine combustion process, and can only rely on the SCR system to spray more urea to break down more ammonia to neutralise the nitrogen oxides to meet the emission standards.

The advantage of high efficiency SCR is the elimination of the EGR system, which requires a higher single exhaust emission standard for the engine and a higher requirement for the engine components to work together, which simply means that the engine will be more high-tech.

But it also has the disadvantage that it requires more urea spraying to solve the exhaust treatment problem. On average, you have to spray 20% more urea per 100 km than an EGR truck, and the cost of using the vehicle will increase. But the good thing is that the price of urea is not as outrageous as the price of fuel, and these costs are acceptable.

The EGR is a component that is mounted on the valve cover of the engine and looks like a box. The box is a sandwiched hollow structure in which the antifreeze is circulated and the hollow structure allows the engine exhaust gases to pass through.

After passing through the turbocharger, the exhaust gases are split into two paths, one that is discharged directly to the after-treatment, and one that will be cooled by the EGR to reach a temperature that is in relative balance with the atmospheric temperature and mixed with fresh air to re-enter the engine for secondary combustion, resulting in a further reduction in the nitrogen oxide content of the exhaust gases, which is discharged to the after-treatment.

This is where the engine computer controls the opening of the throttle flap, depending on the ratio of the amount of exhaust gas entering the EGR for re-burning to the exhaust gas discharged directly into the aftertreatment. It should be noted that the use of EGR technology does not eliminate the need for SCR technology, urea must still be injected, but at a much lower rate than with high efficiency SCR.

With EGR engines the exhaust gases are cleaner after combustion, there is less pressure on the after-treatment and less urea is used.

The disadvantage is that EGR has more parts to install on the engine body than high efficiency SCR and can have a relatively high failure rate, especially in extremely cold weather conditions.

However, as technology continues to upgrade, the reliability of EGR technology is not a concern at all. Under normal use it is basically possible to achieve the same life cycle as the engine.