Citroën Xantia

since 1993 release

Repair and operation of the car

Systems of decrease in toxicity and production of the fulfilled gases

All petrol models are adapted for filling with unleaded fuel. In addition, systems of their food are developed taking into account the last strict requirements to environmental protection and allow to lower rather effectively toxicity of the fulfilled gases produced in the atmosphere. The system of ventilation of a case is included in a basic equipment of all models. The majority of petrol models are equipped with the catalytic converter and system of catching of fuel evaporations (EVAP) (see above in the present Chapter).

On all diesel models strict control of composition of the fulfilled gases is also provided and the system of ventilation of a case is provided. On some models the catalytic converter is installed. Even more elimination of toxic components is promoted by introduction on separate models of system of recirculation of the fulfilled gases (EGR). On the EGR cars equipped with system of a turbo-supercharging it can be used in couple by system of compensation of changes of atmospheric pressure.

Below the principles of functioning of separate systems and devices which use promotes decrease in toxicity of the fulfilled gases are in more detail described.

Petrol models

System of ventilation of a case

The system allows to reduce issue level in the atmosphere of the hydrocarbons which are contained in crankcase gases. The block of the engine is executed hermetically, the gases breaking in it bypassing piston rings from combustion chambers together with oil evaporations forcibly are removed from a case in the inlet pipeline, and destroyed in the course of normal functioning of the engine. Before getting to the inlet pipeline crankcase gases are banished through a mesh oil separator.

At increase in depth of depression in the inlet pipeline (single turns, braking by the engine) crankcase gases are exhausted from the engine. If depth of depression is low (acceleration, the movement with completely open butterfly valve), gases are pushed out due to relative increase in pressure in a case. If the engine is strongly worn-out, pressure in its case will be constantly raised (due to more intensive blowing off of gases from combustion chambers bypassing piston rings) that provides constant return of a part of a gas stream with any pressure in the inlet pipeline.

Catalytic converter and l-probe

For the purpose of decrease in level of issue in the atmosphere of toxic products of combustion in system of release of some models the catalytic converter is installed. At the same time the oxygen sensor (l-probe) which is switched on in system of release provides feedback with ECU of a control system of the engine. On the basis of the analysis of information on the level of content in the fulfilled gases of ECU oxygen obtained from the sensor carries out instant correction of composition of air-fuel mix, constantly supporting optimum conditions for functioning of the catalytic converter.
the l-probe is equipped with the built-in electric heating element which functioning via the relay of the oxygen sensor carries out ECU of a control system of the engine. The working tip of the sensor registers the level of content in the fulfilled O2 gases and functions effectively only at rather high working temperatures which maintenance provides a heating element. The sensor develops tension which amplitude is directly proportional to the level of content of oxygen in the fulfilled gases. At injection in the engine of the reenriched air-fuel mix the content of oxygen in products of combustion is rather small, and the sensor develops a low-voltage signal. In process of mix impoverishment amplitude of the signal developed by the sensor increases. To the fullest combustion of mix with the minimum maintenance of toxic components in products of combustion there corresponds the ratio of content of gasoline to air 1 : 14.7, i.e. one weight part of fuel has to fall on one weight part of air. This ratio is called stoichiometric number. Near this point change of amplitude of the signal developed by the sensor happens wide jumps, ECU at the same time immediately develops the command for the corresponding correction of composition of air-fuel mix due to change of time of opening of injectors/nozzles.

System of catching of fuel evaporations (EVAP)

This system allows to reduce significantly issue level in the atmosphere of not burned down hydrocarbonic connections. The system is installed on the models equipped with the catalytic converter. The cover of a jellied mouth of the fuel tank is closed hermetically. Behind a radiator, on the left wall of a motive compartment the coal adsorber accumulating in itself the fuel evaporations which are allocated in a tank during the parking of the car is established. The adsorber purge after start of the engine is carried out at the command of ECU of a control system. The special valve, opening, provides a conclusion of the fuel which accumulated in an adsorber to the inlet highway from where it comes to combustion chambers and is burned out in the course of normal functioning of the engine.

In order to avoid violation of stabilization of turns of idling and for protection of the catalytic converter against effect of influence of the reenriched mix the valve of a purge of a coal adsorber opens only after the engine does not get warm up to the normal working temperature and it will not appear under loading. Further ECU develops commands for periodic turning on switching off of the electromagnetic valve. In the course of such modulations there is also a conclusion of the fuel which accumulated in an adsorber to the inlet highway of the engine.

System of release

Information on functioning of system of release is provided in the section System of Production of the Fulfilled Gases - the general information, removal and installation.

Diesel models

System of ventilation of a case

See above the subsection "Petrol Models — Systems of Ventilation of a Case".

Catalytic converter

The catalytic converter is included in the package of separate models and represents the close-meshed grid placed in a metal container with inclusions of catalytic metals. Through a grid the fulfilled engine gases warmed to high temperature are banished. The catalyst promotes the accelerated oxidation of such connections as monoxide of carbon (SO), not up to the end burned down hydrocarbonic connections, soot, etc., allowing it is essential to reduce toxicity of an exhaust.

System of recirculation of the fulfilled gases (EGR)

The system provides recirculation of a part of the fulfilled gases to the inlet highway of the engine and their inclusion in process of burning of air-fuel mix. At the same time contents level in products of combustion of toxic nitrogen oxides (NOx) decreases.

The volume of recirculation is controlled by a system electronic control unit.

The function chart of system of recirculation of the fulfilled gases (EGR)

The system functions at a temperature of cooling liquid of 60 °C and loading not above adjusting value of the switch (2) on TNVD. The control unit opens the electromagnetic valve (7) controlling functioning of all system. The depression created by the vacuum pump located on the end of the camshaft forces to work the EGR (5) valve installed in a final collector, and this operation happens only at the open valve of management (7).

In addition, the inlet pipeline is equipped with the lamellar gate allowing to correct a ratio of composition of mix of the fulfilled gases given to an inlet path with the air which is soaked up in the engine. Besides, the gate prevents giving in the pipeline of the fulfilled gases at the engine working at single turns or under low loading when the valve in a final collector is completely open.
The control unit of system develops teams on the basis of the analysis of information on temperature of cooling liquid arriving on it and the frequency of rotation of the engine (VMT sensor).

System of compensation of changes of atmospheric pressure

The system allows to suspend correction of an advancing of the moment of injection for the purpose of decrease in level of smoke at certain ratios of temperature of the engine and atmospheric pressure. The system functions together with system of preheat (see System of preheat - diesel models), using information arriving from the sensor of temperature of cooling liquid and the sensor switch of atmospheric pressure.

System of release

Information on functioning of system of release is provided in the section System of Production of the Fulfilled Gases - the general information, removal and installation.