Engine Emission Control - Description & Operation
Crankcase Ventilation
The crankcase ventilation system on the 2.7L Diesel ensures that all gases emitted from the crankcase during engine running are separated from any oil particles.
Scheme 69
| Item Number | Description |
|---|---|
| 1 | Left-hand breather tube |
| 2 | Crankcase vent oil separator |
| 3 | Right-hand breather tube |
| 4 | Crankcase oil return tube |
| 5 | Crankcase oil return valve |
| 6 | Oil return tube |
Crankcase ventilation is by a cyclone separator. The oil separator is constructed from a plastic composite material. The oil separator is located between the 'V' at the back of the engine block by means of three seals. The oil separator contains a diaphragm and spring which opens under intake vacuum.
The ventilation systems first chamber is a horizontal void cavity fed by eight points. Once primary separation is complete, the partially cleaned vapor is sucked through a cyclone where the process further reduces the oil content. Prior to the vapor entering the air supply at the compressor, a diaphragm pressure balance valve operates to minimize the crankcase pressure variations caused by engine air demand and service condition.
Due to the shape and design of the cyclone unit, the oil and vapor are separated more effectively. Vapor is directed into the inlet system and the heavier oil drains back into the engine.
Exhaust Emission Control
The exhaust of a diesel engine contains the following pollutants
- Carbon Monoxide (CO)
- Hydrocarbons (HC)
- Particulates
- Oxides of Nitrogen (NOx)
These pollutants are primarily produced as a result of incomplete combustion of the fuel.
The particulates in the exhaust gases consist of pure carbon and various compounds such as metal oxide and sulphur.
Scheme 70
| Item Number | Description |
|---|---|
| 1 | Exhaust gas recirculation (EGR) valve |
| 2 | EGR cooler |
| 3 | Gasket |
The exhaust gas re-circulation (EGR) system is fitted to the engine in order to reduce the amount of nitrogen oxide (NOx). This is done by reducing the temperature of the combustion process by introducing some waste exhaust gases into the inlet manifold. The effect of this is that there is a depletion of oxygen which reduces the temperature of the combustion process and in turn reduces the amount of NOx produced.
The engine control module (ECM) will determine the amount of EGR operation depending on the engine RPM, intake air temperature, coolant temperature and fuel flow rate. The amount of exhaust gas being recirculated is measured by a combination of position sensing of the valves and a mass air flow (MAF) sensor.
The EGR valves are operated through their full range at each engine start-up. This is to clear any carbon deposits that may have built up whilst the engine was running.
The EGR system is continually monitored for faults. Depending on how the system fails, the ECM will dictate whether the malfunction indication light (MIL) is on or off. In the event of a failure of the EGR system, the ECM will use substitute values and the EGR function will become inoperative.
The EGR cooler is connected to the vehicle cooling system via hoses and is there to cool the exhaust gases being recirculated.
The EGR valve and cooler are supplied as separate components. The EGR valve itself should not be disassembled.
Principle of operation
Exhaust gas recirculation (EGR)
The EGR system recycles exhaust gases back through the combustion process to reduce NOx emissions.
By introducing this gas into the air intake, oxygen content and combustion temperatures are reduced, which reduces the NOx emissions.
High EGR flow is necessary during cruising and mid-range acceleration, when combustion temperatures are typically very high, while lower EGR flow is needed during low speed and light load conditions.
No EGR flow should occur during conditions when it could adversely affect engine operating efficiency or vehicle driveability, such as engine warm-up, idle, etc.
The EGR function of the 2.7 L engine is managed by the engine control module (ECM), which controls the operation of stepper motors, allowing precise control of the EGR valve actuators.
The ECM determines the optimum EGR flow using inputs from sensors in the engine management system, including the mass air flow meters, coolant temperature sensor, and intake air temperature sensor.
Positive crankcase ventilation
The crankcase ventilation system uses the depression created in the air intake to draw vapors from the crankcase through the engine where they are burnt with the fuel/air charge.
By doing this, any build-up of pressure inside the crankcase is avoided, reducing blow-by and potential oil leakage problems, while still reducing emissions into the atmosphere.
The 2.7 L engine crankcase ventilation is through a cyclone separator mounted in the engine 'V'.
The separator consists of a diaphragm and spring inside the casing which respond to crankcase pressure variations and separate the oil from the vapor, allowing the oil back into the engine while the vapor is directed to the intake system.