Fuel Evaporative Mist Recovery System (Skoda Felicia)

Emission control systems

All petrol models must be fuelled with unleaded fuel only. The engine management system performs overall control over the operation of the power unit, ensuring optimal balance between the power developed by the engine, vehicle controllability and the composition of exhaust gases. Additionally, the vehicle is equipped with a number of systems that reduce the toxicity of exhaust gases. All petrol engines are equipped with a crankcase ventilation system and a catalytic converter as standard. Due to the operation of these systems, the overall level of emissions of toxic fuel combustion products and crankcase gases into the atmosphere is reduced. In addition to the above systems, petrol models are also equipped with a fuel evaporation capture system.

The crankcase ventilation system is also standard on all diesel-powered models. In addition, diesel models are equipped with a dual-function catalytic converter and exhaust gas recirculation (EGR) system, which help reduce overall emissions.

Crankcase ventilation system

In order to reduce emissions of crankcase gases containing unburned hydrocarbon compounds into the atmosphere, the engine block is hermetically sealed, and the gases and oil vapors that accumulate inside it and break through from the combustion chambers are removed from the crankcase and enter the combustion chambers through the air cleaner, where they are burned out during normal engine operation.



Under the influence of deep vacuum in the intake manifold (movement at idle or engine braking) crankcase gases are drawn out of the engine by gravity. When the vacuum depth decreases, (acceleration, driving with the throttle fully open) the removal of gases and vapors occurs due to a relative increase in the crankcase pressure. As a result of wear of the piston group components and engine cylinders, the crankcase pressure increases due to a more intense breakthrough of gases from the combustion chambers, which leads to a forced return of part of the discharged flow at any vacuum in the intake manifold.

Exhaust gas composition control system (petrol models)

In order to minimize the toxicity level of exhaust gases emitted into the atmosphere, a catalytic converter is included in the exhaust system of all gasoline models. An oxygen sensor (λ-probe) installed in the exhaust system closes the feedback loop of the power supply system, informing the ECU of the engine management system about the level of O2 content in the exhaust gases. Based on the analysis of incoming data, the ECU makes the appropriate adjustment of the air-fuel mixture, thereby optimizing the combustion process.

A heating element is built into the oxygen sensor, the operation of which is controlled by the ECU via a special relay. The task of the element is to accelerate the heating of the λ-probe to the optimum operating temperature. The working tip of the sensor is sensitive to the oxygen content in the surrounding space. As a result, depending on the level of oxidation of the exhaust gases, the sensor sends a signal of the corresponding amplitude to the ECU. The minimum toxicity of the combustion products of the air-fuel mixture is achieved with a very specific weight ratio of its components, namely: there should be 14.7 parts of air per 1 part of fuel. This ratio is called the stoichiometric number. The change in the amplitude of the sensor output signal near this point occurs in large steps, which allows the ECU to use the incoming signals as reference when calculating the required composition of the combustible mixture. The mixture composition is adjusted by changing the opening duration of the fuel injectors. A description of the procedures for removing and installing the λ-probe is given in Section Removal and installation the λ-probe.

Exhaust gas composition control system (diesel models)

(Material is available on the website: SkodaBook.ru)

A dual-function catalytic converter is installed in the exhaust system of all diesel models. The converter prevents the emission of most gaseous hydrocarbon compounds, carbon monoxide (CO) and solid microparticles into the atmosphere.

Additionally, diesel models are equipped with an exhaust gas recirculation (EGR) system. The system reduces the level of emissions of toxic nitrogen oxides formed during combustion of the air-fuel mixture by periodically returning part of the exhaust gases to the intake manifold. The return of exhaust gases is carried out through the EGR plunger valve under certain engine operating conditions. The EGR system is controlled by the diesel electronic control unit.

Fuel Evaporative Mist Recovery System (petrol models)

In order to minimize the emission of unburned hydrocarbon compounds into the atmosphere, all gasoline models are equipped with a fuel vapor capture system. The fuel tank filler neck is closed with a sealed cap. A carbon adsorber is installed on the mudguard of the left wheel arch, into which all fuel vapors that accumulate in the tank while the car is parked are discharged. Evaporating fuel accumulates in the adsorber and after the engine is started is removed from it through the plunger purge valve into the intake tract, where it is burned during normal operation of the car. In order to protect the catalytic converter from the effects of over-enrichment of the mixture during engine warm-up or during its idling, the ECU does not allow the purge control valve of the adsorber to open until the unit is completely warmed up. When the engine load increases, the electromagnetic valve begins to function in a pulse mode, sequentially removing the contents of the adsorber into the engine intake tract.

Exhaust system

The exhaust system consists of an exhaust manifold, a downpipe, a catalytic converter, two box mufflers, a set of support brackets and tubular connecting sections. On diesel models and 1.6L petrol models, the catalytic converter is included in the downpipe section of the exhaust system, while on 1.3L models, the downpipe and converter are installed separately from each other.