The Z17 DTR has a new exhaust gas recirculation cooler with a bypass duct.
When the engine is cold, a pneumatically-actuated bypass valve opens the bypass duct and thereby bypasses the exhaust gas recirculation cooler. In this mode, 70% of the exhaust gases are led through the bypass duct and 30% through the exhaust gas recirculation cooler. Feeding in uncooled exhaust gases helps to increase the exhaust gas temperature more quickly. This has the advantage of more effectively reducing hydrocarbon (HC) emissions in the catalyst in cold start conditions. In addition, controlled combustion in the cold start phase helps to reduce noise, the so-called diesel knock.
Once the engine has reached its operating temperature, the bypass valve is closed fully so that the exhaust gases are cooled via the exhaust gas recirculation cooler and fed in regulated quantities to the engine via the EGR valve. This method substantially reduces nitrogen oxide (NO x ) formation, since a higher level of exhaust gas cooling makes it possible to increase the exhaust gas recirculation rate without increasing particulate formation.
The bypass valve is only ever completely shut or completely open. An intermediate position between these two is not required. The solenoid valve required for actuation is installed on the intake manifold.
Illustration of Exhaust Gas Recirculation Cooler
| 1 | Exhaust gas outlet |
|---|---|
| 2 | Exhaust gas recirculation cooler |
| 3 | Vacuum unit for bypass valve |
| 4 | Housing for bypass valve |
| 5 | Exhaust gas inlet |
| 6 | Coolant outlet |
| 7 | Bypass duct |
| 8 | Coolant inlet |