General information (Peugeot 106)

All petrol models have the ability to use unleaded petrol and also have various other features built into the fuel system to help minimise harmful emissions. In addition, all engines are equipped with the crankcase emission control system described below. All later petrol models have a catalytic converter and some are also fitted with exhaust and evaporative emission control systems. Certain later engines to emission standard L4, also utilise a secondary air injection system to quickly bring the catalytic converter up to normal working temperature.

Diesel engine models are also designed to meet strict emission requirements and have a crankcase emission control system. Certain models may also be fitted with a catalytic converter and an exhaust gas recirculation system, to reduce exhaust emissions.

The emission control systems function as follows.

Crankcase emission control

To reduce the emissions of unburned hydrocarbons from the crankcase into the atmosphere, the engine is sealed and the blow-by gases and oil vapour are drawn from inside the crankcase, through a wire-mesh oil separator, into the inlet tract, to be burned by the engine during normal combustion.

Under conditions of high manifold depression (idling, deceleration) the gases will be sucked positively out of the crankcase. Under conditions of low manifold depression (acceleration, full-throttle running) the gases are forced out of the crankcase by the (relatively) higher crankcase pressure; if the engine is worn, the raised crankcase pressure (due to increased blow-by) will cause some of the flow to return under all manifold conditions.

Exhaust emission control - petrol models

To minimise the amount of pollutants which escape into the atmosphere, some models are fitted with a catalytic converter in the exhaust system. On all models where a catalytic converter is fitted, the system is of the closed-loop type, in which one or two lambda sensors in the exhaust system provide the fuel-injection/ignition system ECU with constant feedback on the oxygen content of the exhaust gases. This enables the ECU to adjust the air/fuel mixture ratio to provide the best possible conditions for the converter to operate.

The lambda sensor has a built-in heating element, controlled by the ECU through the lambda sensor relay, to quickly bring the sensor's tip to an efficient operating temperature. The sensor's tip is sensitive to oxygen and sends the ECU a varying voltage depending on the amount of oxygen in the exhaust gases; if the intake air/fuel mixture is too rich, the exhaust gases are low in oxygen, so the sensor sends a low-voltage signal, the voltage rising as the mixture weakens and the amount of oxygen in the exhaust gases rises. Peak conversion efficiency of all major pollutants occurs if the intake air/fuel mixture is maintained at the chemically-correct ratio for the complete combustion of petrol - 14.7 parts (by weight) of air to 1 part of fuel (the "stoichiometric" ratio). The sensor output voltage alters in a large step at this point, the ECU using the signal change as a reference point and correcting the intake air/fuel mixture accordingly, by altering the fuel injector pulse width (injector opening time).

Exhaust emission control - diesel models

To minimise the level of exhaust pollutants released into the atmosphere, a catalytic converter is fitted in the exhaust system on some models.

The catalytic converter is a canister containing a fine mesh impregnated with a catalyst material, over which the hot exhaust gases pass. The catalyst speeds up the oxidation of harmful carbon monoxide, unburned hydrocarbons and soot, effectively reducing the quantity of harmful products released into the atmosphere via the exhaust gases.

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Exhaust gas recirculation system - diesel models

An exhaust gas recirculation (EGR) system is fitted to certain diesel models. This reduces the level of nitrogen oxides produced during combustion by flowing a proportion of the exhaust gases back into the inlet manifold, via a plunger valve, under certain engine operating conditions.

Evaporative emission control - petrol models

To minimise the escape into the atmosphere of unburned hydrocarbons, an evaporative emission control system is fitted to models equipped with a catalytic converter. The fuel tank filler cap is sealed and a charcoal canister is mounted underneath the right-hand wing, to collect the petrol vapours generated in the tank when the car is parked. It stores them until they can be cleared from the canister (under the control of the fuel injection/ignition system ECU) via the purge valve into the inlet tract, to be burned by the engine during normal combustion.



To ensure that the engine runs correctly when it is cold and/or idling and to protect the catalytic converter from the effects of an overrich mixture, the purge control valve is/are not opened by the ECU until the engine has

warmed-up and the engine is under load; the valve solenoid is then modulated on and off to allow the stored vapour to pass into the inlet tract.

Secondary air injection - petrol models

Certain later engines to emission standard L4 are also equipped with a secondary air injection system. This system is designed to reduce exhaust emissions in the period between first starting the engine, and until the catalytic converter reaches operating (functioning) temperature. Introduction of air into the exhaust system during the initial startup period, creates an "afterburner" effect which quickly increases the temperature in the exhaust system front pipe, thus bringing the catalytic converter up to normal operating temperatures very quickly.

The system consists of an air pump, an air injection valve, and interconnecting air hoses.

The system operates for between 10 and 45 seconds after engine start-up, dependant on coolant temperature.