3022422 - 1080B exhaust emission control system
OPERATION
Lambda sensors
They are the 'planar' type and are fitted upstream and downstream of the catalyzer.The upstream sensor carries out the check on the mixture strength known as the first loop.The control unit controls and manages the injection so that the air/fuel ratio is always sufficiently close to the stoichiometric value to maximize the conversion efficiency of the catalyzer; in full power and high usage conditions, the mixture is enriched to guarantee maximum performance.The downstream sensor is designed to diagnose the conversion efficiency of the catalyzer(s).Thus:
- Lambda = 1 ideal mixture
- Lambda > 1 lean mixture
- Lambda < 1 rich mixture
a - Rich mixture (lack of air)
b - Weak mixture (too much air)The Lambda sensor, placed in contact with
the exhaust gases, generates an electrical signal whose voltage
depends on the concentration of oxygen present in the gases. This
voltage is characterized by a sudden change when the composition
of the mixture moves away from Lambda = 1.The heating of the Lambda sensor is managed
by the fuel injection control unit in relation to the exhaust gas
temperature.This avoids thermal shocks on the ceramic
casing due to the contact with condensed water, present in the exhaust
gases when the engine is cold.The measuring cell and heater are built
into the 'planar' (stratified) ceramic element, with the advantage
of obtaining quick heating of the cell, thus permitting a closed
loop' check (Lambda = 1) within 10 seconds of engine start-up.
1 - Connecting cable
2 - Protective sleeve
3 - Planar sensor element
4 - Ceramic tube casing
5 - Sensor housing
6 - Ceramic seal
7 - Protective tubeThe operation of the Lambda sensor is based
on the principle of an oxygen concentration cell with solid electrolyte.The surfaces of the measuring cell are coated
with microporous layers of noble material.
1 - Exhaust gas
2 - Passage of reference air
3 - Heater
4 - Lambda sensor voltage
SPECIFICATIONS
- Supply: 12V
- Internal resistance: 0.5 - 1 kOhm
Catalytic converter
The three-way catalytic converter simultaneously reduces the three polluting gases present in the exhaust gases:
- unburnt hydrocarbons (HC);
- carbon monoxide (CO);
- nitrogen oxides (NOx).
Two types of chemical reactions take place in the converter:
- oxidation of the CO and HC, converted into carbon dioxide (CO2) and water (H2O)
- reduction of the NOx converted into nitrogen (N2).
The noble metals contained in the catalytic converter, because of the high temperature, are chemically attacked if lead is present. For this reason the use of petrols containing lead should be avoided, otherwise the converter will be quickly and irreversibly damaged. Never use petrol containing lead, not even in an emergency or for a very short time. |
1 - Ceramic monolith
2 - Metal support
3 - Outer casing
4 - Perforated plate metal cone