Catalytic Converters
Modern car exhaust systems are fitted with a catalytic converter to reduce harmful emissions of fuel hydrocarbons, carbon monoxide and nitrogen oxides into the atmosphere.
The catalytic converter converts the hot fuel combustion gases into water vapour and the less harmful gases: Nitrogen, Oxygen and Carbon Dioxide.
At the heart of a catalytic convertor is a ceramic core with a minute honeycomb structure containing thousands of small pores. It is designed this way to create a reactive surface with a huge surface area. The pores have a thin film of powdered catalysts that contain precious metals such as platinum, palladium and rhodium.
The precious metals form two very different types of catalyst: A reduction catalyst to convert harmful Nitrous Oxides into Harmless Nitrogen and Oxygen.
An oxidation catalyst that converts harmful Carbon Monoxide into harmless Carbon Dioxide. The catalyst makes it easier for the chemical reactions to take place but are not normally transformed by the reaction.
Catalytic Converter Failure - MOT Emission Fails
Often, a catalytic converter failure can be due to a fault in the engine management system. Fitting a new catalytic converter does not solve the problem and the new catalytic convertor fails shortly after fitting and must again be replaced.
Oxygen Sensor Works with the Catalytic Convertor
The oxygen sensor or Lambda Sensor also helps to reduce carbon emissions by monitoring the level of oxygen present in the exhaust gases and transmitting information to the electronic control unit (ECU), the brain at the centre of the engine management system.
ECU - Oxygen Monitoring and Fuel Air Mix Control
The ECU (Electronic Control Unit) constantly monitors and adjusts the air/fuel mixture so that the cleanest combustion is achieved under virtually all operating conditions.
Oxygen Sensors
The oxygen sensor monitors the oxygen level in the exhaust after combustion so the ECU can determine how rich or lean the fuel mixture is and make dynamic adjustments to maintain optimal conditions.
Engine and Emission Management
The engine electronic control unit (ECU) has to monitor and interpret information from a variety of other input sensors to provide the optimal amount of fuel and air for every possible set of operating conditions.
Mass Airflow Sensor
The mass airflow sensor tells the ECU the mass of air entering the engine. As air typically contains about 21% of oxygen the ECU can calculate how much oxygen is available for combustion and derives the optimal amount of fuel it can burn.
Throttle Position Sensor
The position of the throttle valve interprets the rate of fuel combustion. Pressing down on the throttle-accelerator pedal tells the ecu to burn more fuel increasing or decreasing the pedal gives the ecu feedback for fuel demand and alters the fuel injection rate as necessary.
Coolant Temperature Sensor
Monitors Engine-Coolant Temperature and the ECU can determine when the engine has reached its normal operating temperature.
Voltage Sensor
The voltage sensor monitors system voltage. The ECU can adjust the engine idle speed if voltage is dropping suggesting a high electrical load.
Manifold Absolute Pressure Sensor
Engine air intake helps interpret the amount of power produced by the engine. More air going in means lower manifold pressure.
Engine Speed Sensor
Monitors engine rotation speed (rpm), and ensure the correct pulse width and injection timing. This works with multi-port systems to control fuel injection for either simultaneous or sequential fuel injection.