Table of contents: Controlled crankcase ventilation… ↓ Exhaust gas recirculation (EGR)… ↓ Catalytic converter and lambda probes ↓ Diesel Particulate Filter (DPF) ↓ System for reducing the… ↓
The exhaust system (EG) consists of: an exhaust manifold, a diesel particulate filter (DPF), a catalytic converter, sensors and an exhaust pipe with mufflers.
The engine management system is designed to maximize engine performance while minimizing fuel consumption and emissions. The following exhaust gas toxicity reduction systems are installed: crankcase ventilation (PCV), exhaust gas recirculation (EGR), catalytic converter with lambda probes, and SCR system (only on 3.0L models with SCR).
Controlled crankcase ventilation (PCV) system
In internal combustion engines, due to the difference in pressure between the combustion chamber and the crankcase, air flows arise between the piston rings and the working surface of the cylinder, the so-called crankcase gases. To prevent leakage of unburned hydrocarbons into the atmosphere, the engine is completely sealed. Gases and oil vapors generated in the crankcase are fed into the intake manifold and burn in the cylinders along with the fuel (except for oil vapors retained in the oil separator).
Gases are removed from the crankcase due to the pressure difference in the crankcase and the intake manifold (crankcase pressure is higher).
The pressure regulating valve regulates the pressure in the PCV system. It consists of a diaphragm and a spring. The valve limits the vacuum in the crankcase when crankcase gases are pumped out of it. If the vacuum is too strong, the engine seals may be damaged. When there is a slight vacuum in the intake manifold, the valve opens under the action of the spring. When there is a strong vacuum in the intake manifold, the valve closes. To reduce the harmful effects of gas flow turbulence, an outlet stilling chamber is installed at the inlet of the intake pipeline after the centrifugal oil separator. In this chamber, the movement of gases leaving the centrifugal oil separators slows down and calms down. In addition, some amount of oil remaining in the gas flow also settles on the walls of this chamber.
Exhaust gas recirculation (EGR) system
The EGR system allows to reduce the amount of nitrogen oxides (NO) in the exhaust gases. To achieve this, a small portion of the exhaust gases is diverted back into the combustion zone of the fuel-air mixture. At the same time, the proportion of oxygen in the fuel-air mixture decreases, which leads to a slowdown in the combustion process. The peak combustion temperature of the mixture is reduced and the level of nitrogen oxide emissions is reduced.
The amount of exhaust gas returned is regulated by the EGR valve using signals from the ECM, and depends mainly on the crankshaft speed, the amount of fuel injected, as well as the volume, temperature and pressure of the intake air.
On Euro 5-compliant diesel engine models, a wide-band oxygen sensor is located in the exhaust line before the diesel particulate filter, monitoring the oxygen content of the exhaust gas over a wide range. The oxygen sensor's signal is used in the EGR system as a correction variable to regulate the amount of exhaust gas recirculated. If the oxygen content of the exhaust gas deviates from the specified EGR characteristic, the ECM sends a control signal to the EGR valve, adjusting the amount of exhaust gas recirculated accordingly.
A liquid EGR cooler further reduces combustion temperatures by cooling the returning exhaust gases and allows for greater exhaust gas recirculation. With a switchable EGR cooler, the engine and diesel particulate filter reach the required operating temperature faster (exhaust gas cooling is carried out only after reaching the operating temperature). The supply of uncooled exhaust gases ensures that the engine and diesel particulate filter reach operating temperature in a shorter period of time during a cold engine start. The supply of cooled exhaust gases, especially at high combustion temperatures, helps to reduce the level of nitrogen oxides in the combustion chamber. The EGR cooler switching valve is an electro-pneumatic valve and is responsible for supplying the pneumatic actuator of the EGR cooler with the vacuum required to activate the cooling. The EGR cooler is activated when the coolant temperature exceeds 37°C. The EGR cooler is a compact module that includes a heat exchanger, a control valve, an EGR valve, and a valve position sensor.
The EGR valve is an assembly of a disc valve with an electric actuator and a position sensor. The electric drive provides precise, stepless adjustment. The rotary motion of the electric motor is converted by the eccentric and the rocker arm into reciprocating motion. The valve plate stroke regulates the amount of exhaust gas returned.
Catalytic converter and lambda probes
To reduce the amount of harmful emissions into the atmosphere, an oxidation catalytic converter is built into the exhaust system of diesel models, which serves to carry out the following chemical reactions: 2CO + O₂ → 2CO₂ and 2C₂ H ₆ + 7O₂ → 4CO₂ + 6H₂ O.
A wideband lambda probe on diesel models continuously informs the engine control unit about the exhaust gas composition. Based on the received data, the control unit adjusts the mixture quality supplied to the combustion chambers, thereby optimizing combustion conditions. The lambda probe's working surface is sensitive to changes in the oxygen content of the exhaust gas. The lambda probe is used to adjust the amount of fuel injected and optimize the operation of the EGR system.
Diesel Particulate Filter (DPF)
Note: Soot particles may accumulate in the exhaust pipe after the DPF. The accumulation of soot particles should not be considered a problem, as the DPF is not 100% efficient in filtering soot. During the DPF regeneration process, white smoke may come out of the exhaust pipe - this is a side effect of the regeneration process, which is also not considered a sign of any malfunction.
To comply with Euro 5 emissions standards, a diesel particulate filter (DPF) is installed as standard near the engine. The presence of a diesel particulate filter can be identified by the PR code "7GG." The DPF reduces the pollution produced by diesel-powered vehicles by filtering soot particles from the exhaust gases. The DPF system also includes a lambda probe, as well as exhaust gas pressure and temperature sensors. The signals from these sensors are used by the engine control unit to control DPF regeneration (the need for regeneration and the optimal time for its implementation). Under normal operating conditions, the regeneration process occurs when the ECM calculates that the diesel particulate filter requires regeneration and a number of pre-set conditions are met (for example, coolant temperature, vehicle speed and engine load).
Because the operating temperature of the diesel particulate filter is reached quickly, continuous passive regeneration is possible. Active regeneration via the engine control unit is carried out if the diesel particulate filter is filled with soot particles (for example, after short trips with a partial load). In this case, the soot particles are burned by specially increasing the exhaust gas temperature.
System for reducing the concentration of nitrogen oxides in the exhaust gas (SCR)
Caution: AdBlue (purified 32.5% urea solution) may cause irritation to skin, eyes and respiratory system, and may damage paintwork and trim. If you come into contact with this liquid, wash it off with plenty of water. Crystallized AdBlue liquid should be removed from the car body using a sponge and warm water. Do not add AdBlue to fuel - it is intended for injection into the exhaust system.
To reduce nitrogen oxide concentrations in the exhaust gases of diesel models equipped with a nitrogen oxide catalytic converter (SCR), AdBlue is used. This fluid is injected into the exhaust gas stream before the SCR catalytic converter. The SCR catalytic converter breaks down the nitrogen oxides in the exhaust gases into nitrogen and water.