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 converter consists of a monolith, a metal mesh support for damping impacts and vibrations and an outer stainless steel housing resistent to high temperatures and atmospheric agents. The monolith consists of a honeycomb structure comprising a ceramic material coated with a very thin layer of catalytically active substances, platinum or rodium. These accelerate the chemical decomposition of the harmful substances contained in the exhaust gases which, passing through the core cells at temperatures of over 300-350 degrees C, activate the catalyzers, thus starting the oxidoreduction reactions.
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