194002365 - INTRODUCTION - EMISSION CONTROL SYSTEM

INTRODUCTION

The emission control system includes the devices designed to reduce atmospheric levels of harmful emissions.The main emissions caused by the car are:- exhaust emissions;- vapour/gas emissions from the crankcase;- fuel vapour emissions.

EXHAUST EMISSIONS

Lambda sensors

The Lambda sensor upstream of the catalytic converters is the linear type whilst the downstream one is the planar type and they notify the engine management control unit of the combustion progress (stoichiometric ratio).The upstream sensor (? = 0.65) determines the mixture strength check (except during idling) known as the 1st closed loop (for the upstream sensor).The sensor downstream of the catalyzer is used for the fault diagnosis of the catalyzer and for modulating the 1st loop control parameters.The second loop is therefore adaptive to make up for production discrepancies and slight drift that upstream sensor responses could experience due to ageing and contamination.This control is known as 2nd loop control (downstream sensor closed loop).The electronic control unit identifies mixture composition (lean or rich) from the lambda sensor output voltage.This adjusts injected fuel quantity to ensure optimum mixture composition (? = 1 to create ideal conditions for treatment of exhaust gas in the catalytic converter.If the mixture is too rich (? < 1) the quantity of fuel should be reduced and if the mixture is too lean (? > 1) the quantity of fuel should be increased.Planar Lambda sensora - Rich mixture (lack of air)b - Lean mixture (excess air)The Lambda sensors are in contact with exhaust gases and generate an electrical signal with voltage dependent on oxygen level in the gas.This voltage changes abruptly when mixture concentration deviates from a value of ? = 1.The injection control unit manages lambda sensor heating in proportion with exhaust gas temperature.This avoids thermal shocks to the ceramic case due to contact with condensed water present in exhaust gas when the engine is cold.The measurement chamber and heater are built into a planar (laminated) ceramic element that offers the benefit of fast chamber heating. This allows closed loop (? = 1) control within 10 seconds of engine start-up.1. Connection lead2. Protective sleeve3. Planar sensor element4. Ceramic support pipe5. Sensor seat6. Ceramic seal7. Protective pipe

Catalytic converter

The three-way catalytic converter makes it possible to keep down the levels of the three pollutant gases in the exhaust gases at the same time:- unburnt hydrocarbons (HC);- carbon monoxide (CO);- nitrogen oxides (NOx).Two types of chemical reaction take place inside the converter:- oxidation of CO and HC to carbon dioxide (CO2) and water (H2O)- reduction of NOx to nitrogen (N2).The converter consists of a structure, a metal gauze support to dampen impacts and vibrations and a stainless steel outer casing that is resistant to high temperatures and atmospheric agents.The honeycomb structure is made from a ceramic material covered in an extermely thin layer of catalytically active substances, platinum or rhodium, which accelerated the chemical decomposition of the harmful substances contained in the exhaust gases which, when passing through the core cells at temperatures above 300° - 350°C, activate the catalyzers setting off the oxidation/reduction reactions.A perforated steel cone improves the diffusion of the exhausts gases in the ceramic core cells to ensure the optimum efficiency and lifespan of the catalyzer.1. Ceramic structure2. Metal support3. Outer casing4. Perforated steel cone

CRANKCASE VAPOUR/GAS EMISSIONS

The system controls the vapour emissions, coming from the crankcase, made up of an air/petrol mixture, unburnt gases that escape from the piston seals and lubricant oil vapours recirculating them to the intake.There is a labyrinth inside the tappet cover through which some of the gases are condensed to the oil sump.As a result of the vacuum created following the opening of the throttle, the remaining gases are drawn into the combustion chamber together with the fresh charge and they are eliminated following subsequent combustion.

FUEL VAPOUR EMISSIONS

Evaporation control system

The vapours coming from the tank (1) are sent, via the two float valves (2) to the separator (3) where they are partly condensed.The residual fuel vapours are sent, by means of special pipes, to the canister (4) where they are absorbed by and stored in the active charcoal.The vapours flow to the intake manifold through a special pipe (6) in the solenoid by means of the solenoid (5) controlled by the injection control unit.

Canister

This is fitted to the left side of the fuel tank and consists of an activated carbon filter element that absorbs fuel vapours from the separator.An opening in the canister allows the intake of air and is like a labyrinth to prevent the intake of water.The fuel vapour inlet and outlet pipes are thermowelded onto the canister and cannot therefore be dismantled.

Fuel vapour solenoid valve

This is fitted on the upper part of the modular intake chamber and is controlled by the injection control unit.The solenoid allows fuel vapours stored in the canister to flow through to the engine intake.If the power is off, the solenoid is closed and prevents fuel vapours from enriching the mixture excessively.The solenoid valve is controlled by the injection control unit depending on given parameters such as the engine load.When electromagnet inside the valve is energized, it attracts valve core which overcomes the load of spring bringing the canister in contact with the modular intake manifold.1. Direction of fuel vapour flow

When fitting the fuel vapour solenoid valve, avoid positioning the electrical connector towards the bottom.