NERNST CONCEPT
The outside of the oxygen sensor's electrode extends into the exhaust stream, while the inside remains in contact with the surroundings air. The essential component of the oxygen sensor is a special ceramic body featuring gas-permeable platinum electrodes on its surface. Sensor operation relies on the porus nature of the ceramic material, which allows oxygen in the air to diffuse. This ceramic becomes conductive when heated. Voltage is generated at the electrodes in response to differences in the oxygen levels on the inside and outside of the sensor. A stoichiometric air-fuel ratio of lambda=1 produces a characteristic jump in the response curve.

NERNST SENSOR
A precisely stoichiometric air-fuel mixture is vital for optimal oeration of the catalytic converter. The lambda closed-loop control system uses the signals form the oxygen sensors to maintain this mixture.

NEUTRAL SAFETY SWITCH
This is a part found on all cars with automatic transmissions. It prevents the starter from engaging if the transmission is in any gear other than 'Park' or 'Neutral'. It also turns on the back-up lights when the transmission is shifted into "reverse". It can get out of adjustment or fail.

NEWTON
The newton (N) is the unit of measure of forces according to the International System.

NEWTON-METER
Unit of measure of torque according to the International System.

Normally Aspirated
An engine that intakes air or "breathes" without the assistance of a supercharger or turbocharger.

NOx STORAGE CATALYTIC CONVERTER
The most promising potential for reducing the NOx content in the exhaust gas is shown ny the NOx accumulator type catalytic converter. Making use of the oxygen in the lean exhaust gas, it is able to store the nitrogen oxides on its surface in the form of nitrates. As soon as the storage capacity is exhausted though, the catalytic converter must be regenerated. This is done by briefly switching over to rich homogeneous operation whereby, in combination particularly with the CO, the nitrates are reduced to nitrogen . A catalytic converter model which defines the converter's absorption and regeneration phases. The exhaust-gas figures are monitored by lambda oxygen sensors upstream and downstream of the catalytic converter.