Contents: Controlled Crankcase Ventilation…⬇ Exhaust Gas Recirculation (EGR)…⬇ Catalytic converter and lambda probes ⬇ Diesel Particulate Filter (DPF) ⬇ Fuel Evaporative Emissions (EVAP)…⬇
The exhaust system consists of: exhaust manifold, particulate filter (only on diesel models, except CLJB engine), catalytic converter and exhaust pipe with mufflers. The exhaust manifold is integrated with the turbocharger.
The principle of operation of the engine management system is designed to obtain maximum output from the engine with minimum fuel consumption and content of toxic components in the exhaust gases. The following exhaust gas toxicity reduction systems are installed: crankcase ventilation system (PCV), exhaust gas circulation system (EGR, only on diesel models and petrol models 1.4L) and a catalytic converter with lambda probes. On gasoline models, an additional fuel vapor trapping system (EVAP) is installed. On diesel engines, in addition to the "CLCB", a diesel particulate filter (DPF) is installed, as evidenced by the PR number "7MG" on the vehicle's delivery sticker (see Introduction). The presence of a particulate filter may also be indicated by the PR number "7GG" or "7MB".
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 leaks of unburned hydrocarbons into the atmosphere, the engine is completely sealed. Gases and oil vapors formed in the crankcase are fed into the intake manifold and burn in the cylinders together 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 is used to regulate the pressure in the PCV system. It consists of a membrane and a spring. The valve limits the vacuum in the crankcase when pumping out crankcase gases. 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 reduces the amount of nitrogen oxides (NOx) 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 models with diesel engines that comply with the Euro 5 standard, a wide-band lambda probe is located in the exhaust gas line before the particulate filter, which monitors the oxygen content of the exhaust gas over a wide range. The lambda probe signal is used in the EGR system as a correction value for adjusting the amount of exhaust gas returned. If the oxygen content of the exhaust gas differs from the specified EGR characteristic parameter, the ECM sends a control signal to the EGR valve and, accordingly, changes the amount of exhaust gas returned.
The liquid EGR cooler allows for an additional reduction in combustion temperature by cooling the returning exhaust gases and enables the recirculation of a larger amount of exhaust gases. With a switchable EGR cooler, the engine and particulate filter reach the required operating temperature faster (exhaust gas cooling is carried out only after reaching operating temperature). The supply of uncooled exhaust gases ensures that the engine and 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 changeover 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 radiator is connected when the coolant temperature is above 37°C. The EGR radiator 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 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, a catalytic converter is built into the exhaust system. Diesel models use an oxidation catalytic converter, which is used to carry out the following chemical reactions: 2CO + O₂ → 2CO₂ and 2C₂ H ₆ + 7O₂ → 4CO₂ + 6H₂ O. Gasoline models use a three-function catalytic converter, in which the following chemical reactions occur: 2CO + O₂ → 2CO₂; 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂ O; 2NO + 2CO → N₂ + 2CO₂.
The wideband lambda probe on diesel models constantly informs the engine control unit about the composition of the exhaust gas. On the 2.0 l "CLCB" diesel engine, the lambda probe is not used. Depending on the data received, the control unit adjusts the quality of the mixture supplied to the combustion chambers and thus optimizes the fuel combustion conditions. The working surface of the lambda probe is sensitive to changes in the oxygen content in the exhaust gas. The lambda probe is used to correct the amount of fuel injected and optimize the operation of the EGR system.
On petrol models, the fuel injection control system has a feedback loop, which includes two lambda probes that constantly inform the control unit about the composition of the exhaust gas. Depending on the data received, the control unit adjusts the quality of the mixture supplied to the combustion chambers and. thus optimises the conditions of fuel combustion. The working surface of the lambda probes is sensitive to changes in the oxygen content in the exhaust gas. Depending on its concentration, the output voltage of the sensor changes. If the mixture is over-enriched (the oxygen content in the exhaust gas is very low), the lambda probe sends low voltage signals. The voltage increases as the mixture becomes leaner and the oxygen content in the gases increases. The converter operates most efficiently with an optimal composition of the combustible mixture (14.7 parts air to 1 part gasoline).
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 emission standards, a diesel particulate filter ("DPF") is fitted as standard near the engine. The DPF reduces the pollution produced by diesel vehicles by filtering soot particles from the exhaust gases. The DPF filter 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 the regeneration of the particulate filter (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 DPF 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 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 means of a special increase in the exhaust gas temperature.
Fuel Evaporative Emissions (EVAP) System
The EVAP system is designed to reduce the emission of unburned hydrocarbons into the atmosphere from gasoline engines. The main element of the EVAP system is an adsorber with activated carbon granules that adsorb fuel vapors that form in the tank while the vehicle is parked. The fuel tank filler neck is hermetically sealed by a spring-loaded valve. Fuel vapors are retained in the charcoal canister until the ECM signals the canister to purge. During the purge, fuel vapors are fed through the purge valve into the intake manifold, where they combine with the working mixture and then burn in the usual way in the combustion chambers.
To ensure normal engine operation at idle and during warm-up, the engine control unit keeps the EVAP solenoid valve closed. This prevents unburned fuel from entering the catalytic converter (at high idle speed the mixture is too rich). After the engine warms up, the valve begins to open and close, regulating the supply of fuel vapors into the intake tract.