Interim Tier 4/Stage IIIB emission regulations require a reduction in oxides of nitrogen (NOx) coming from the exhaust. NOx is formed by high-combustion temperatures in the cylinders as the air/fuel mixture is burned.How exhaust gas recirculation (EGR) works
EGR reduces the high temperatures where these compounds are formed in the engine cylinders by replacing excess oxygen with a prescribed amount of cooled exhaust gas.
Exhaust gases contain more carbon dioxide than oxygen. The EGR valve in conjunction with the venturi and engine control unit (ECU) allows a controlled amount of exhaust gas to enter the intake manifold to mix with the incoming fresh air. Replacing excess oxygen with cooled exhaust gas leads to lower combustion temperatures, creating less NOx. In addition, EGR allows for advanced timing, leading to optimal performance of the engine, maximizing fuel economy.
The following diagrams illustrate how air flows through the engine (PSX and PVX).
For added performance and efficiency, the engine passes the exhaust gases through an EGR cooler before it enters the engine.
PSX engine exhaust gas recirculation (EGR)
PSX engine diagram key:
1. Fresh air
2. Fixed turbocharger
3. Variable geometry turbocharger
4. EGR cooler
5. EGR valve
6. Intake throttle valve
7. Compressed air from turbochargers
8. Air-to-air cooler
10. Diesel oxidation catalyst (DOC)
11. Diesel particulate filter (DFP)
12. Exhaust out
PVX engine exhaust gas recirculation (EGR)
PVX engine diagram key:
1. Fresh air
2. Hydrocarbon (HC) metering unit
3. HC injector
4. Variable geometry turbocharger
5. EGR cooler
6. EGR valve
7. Intake throttle valve
8. Compressed air from turbochargers
9. Air-to-air cooler
13. Exhaust out
Flow of exhaust during engine operation
Exhaust airflow enters into the EGR cooler from the exhaust manifold near the turbocharger.Based on engine load, air temperatures, and rpm, the engine control unit (ECU) opens or closes the EGR valve, allowing a measured percentage of exhaust gas to enter the intake manifold.
The gases mix with the rest of the incoming air from the turbocharger and aftercooler before entering the cylinders.