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Closed loop fuel injection system.

Closed loop fuel injection system.

The system is regulated electronically with an oxygen sensor located in the exhaust manifold in front of the catalytic converter. The catalytic converter comprises a carrier of ceramic material coated in a porous layer containing the catalyser rhodium plus either platinum or palladium.

The catalytic converter has a high conversion rate within a very narrow range. If the fuel-air mixture is not kept within this range, one or more gases will inevitably exceed the permitted values. A closed loop fuel injection system guarantees that the fuel-air mixture remains correct.

Assuming that the closed loop fuel injection system gives optimum fuel-air mixture conditions, the catalytic converter reduces nitrous oxides (NOx ) and oxidises carbon monoxide (CO) and hydrocarbons (HC). The end products are carbon dioxide (CO2 ), water (H2 O) and nitrogen (N2).

The condition for a catalytic converter to reduce emissions is that a car is only filled with lead-free petrol. This is because lead will destroy the active elements of the catalytic converter.

Oxygen sensor


The oxygen sensor comprises a primary cell with fixed electrolyte. The electrolyte is ceramic (titanium oxide TiO2) and temperature stabilising through the addition of a small amount of yttrium oxide. The electrolyte is tube shaped and hollowed out at one end. In order to work well, the catalytic converter must be supplied with an air/fuel ratio of exactly 14.7:1.

When the engine runs lean, the oxygen content in the exhaust gases increases and the oxygen sensor output voltage is then around 0.1 V (lambda over 1). The engine control module responds by extending the injection time.

When the engine runs rich, the oxygen sensor output voltage is around 0.9 V (lambda under 1) and the injection pulses are shortened.

The working range of the oxygen sensor is between 200°C and 850°C (392°F - 1562°F) and it is therefore fitted with electric preheating. The preheating is controlled by the system control module. At high load and high engine speed, the exhaust gas temperature is high and preheating is disconnected.