Home Citroënët home

Site search powered by FreeFind
Do NOT include 'Citroen' in your search terms

Engines

2.2 HDi engine (DW12ATED) and particle filter (PF)

  • The highly reputed HDi engines offer the following major advantages :

  • lower fuel consumption ;

  • increased driving comfort (greatly reduced noise and vibration, plus high torque at low engine speeds) ;

  • low exhaust emission levels.

The 2,179 cm3 2.2 HDi unit develops a maximum power output of 98 kW (136 bhp) at 4,000 rpm, with torque of 317 Nm (31.2 m.kg) at 2,000 rpm.

The engine uses common-rail direct injection technology (high pressure, 1,350 bars), with combustion chamber geometry designed for maximum fuel / air mixing. Engine design has been optimised to reduce friction and component weight, especially for moving parts.

State-of-the-art technologies used on the engine include the variable-geometry turbocharger, an air inlet system with a butterfly choke valve providing variable swirl, two balancer shafts to reduce vibration, and a twin-damped engine flywheel.

Camshafts and valves

The aluminium cylinder head is fitted with two cast camshafts linked by a drive chain. The camshafts act on 16 valves by means of roller cam followers and hydraulic tappets that take up any play in the system.

Variable geometry turbocharger

The variable geometry turbocharger provides increased turbocharge pressure at low engine speeds and improved maximum power output at high engine speeds.
At low engine speeds, the cross-sectional area of the exhaust gas nozzles driving the turbine is reduced to increase the pressure of the gas hitting the turbine blades with a consequent increase in turbocharge pressure. In contrast, at high engine speeds, the gas nozzles open progressively under the control of the engine control unit to reduce the turbocharge pressure.
The engine control unit controls a piston that varies the gas nozzle diameter by means of a pneumatic capsule in response to driver demand (engine speed and load) and data from the pressure sensor located downstream of the air-to-air intercooler.
 

Variable swirl air inlet

The variable swirl system increases the rotational movement of the air in the combustion chamber to ensure that the fuel is completely burned. This ensures high performance and low emissions.
The air intake system includes a helical air duct, causing the air flow to rotate into a vortex (swirl), and a tangential duct providing an axial flow. The tangential duct is fitted with a butterfly valve that opens when the engine reaches a preset speed (2,100 rpm at 80 °C) and the injection rate reaches a preset flowrate (40 mg per cycle).The formation of particles at low engine speeds is reduced as a result of the improved fuel / air mixing in the swirl. At higher engine speeds, more air flows through the tangential duct and the swirl is reduced, thereby optimising airflow into the combustion chamber.The piston tops are machined to provide valve clearances, a central dome and the cavity needed to create the swirl. 
The injectors, located centrally in the combustion chamber, ensure uniform fuel spray.

Twin-damped engine flywheel

This flywheel damps out cyclical variations at low engine speeds. These variations in crankshaft acceleration give rise to vibration in the vehicle drive train, especially gearbox rattle. 
They are a major source of noise at low engine speeds, from 1,200 to 2,400 rpm. The twin-damped flywheel filters out these cyclical variations by increasing gearbox inertia and reducing the stiffness of the damping hub. 

The end result is improvement in driving comfort and reduction in noise and vibration.

Balancer shafts

Two balancer shafts reduce rotating assembly vibration. 
The masses on the shafts are at their lowest position when a pair of pistons are at top dead centre. The two shafts are driven by the crankshaft and mounted on a unit within the sump.

Emission control

Exhaust gases are recycled to minimise release of NOx (nitrogen oxides). The emission control subsystem consists of three main components :

  • an exhaust gas recirculation (EGR) valve (proportional solenoid valve controlled by the engine control system) recirculates some of the exhaust gases back to the engine 

  • air inlet ;

  • an air / water intercooler located immediately after the EGR valve cools the recycled gas to increase its density and thereby maximises mass per unit volume for engine infeed ;

  • a butterfly valve located in the air inlet is controlled by the engine control unit to adjust airflow according to engine speed, load and temperature.

Because of the high injection pressure, no pre-heating is required if the engine is started at ambient temperatures above 0 °C.
The oil-change service interval is 20,000 km if a semi-synthetic oil such as Total 10W40 is used.

Particle filter (PF)

Particles have a diameter of around 0.09 microns and consist mainly of carbon and hydrocarbons. The PF traps these particles and periodically burns them off.
Particles burn naturally at approximately 550 °C, but the normal temperature of exhaust gases leaving the manifold is only 150 °C.
The particle filter system overcomes this problem in a number of ways :

  • post-injection during the expansion phase, resulting in post-combustion in the cylinder and a 200 to 250 °C increase in exhaust gas temperature (i.e. to between 350 and 400 °C) ;

  • additional post-combustion by means of an oxidising catalyst located upstream of the filter. The catalyst acts on any unburned hydrocarbons resulting from the post-injection and raises the temperature by a further 100 °C (to between 450 and 500 °C) ;

  • use of Eolys, a cerine-based additive that reduces the particle combustion temperature to 450 °C.

The particle filter system consists of the following :

  • a housing containing the pre-catalyst and filter. The filter is a porous block of silicon carbide that traps all particles in the exhaust gases. Sensors monitor clogging pressure across the filter and the gas temperatures at the inlet and outlet of 

  • the system ;

  • a software programme in the engine control unit that controls regeneration of the filter by post-injection every 400 to 500 km depending on the clogging pressure across the filter. The software also provides diagnostic information on the system. During regeneration, the inlet air is no longer cooled by passing through the air-air intercooler but is instead heated to raise the temperature of the mixture in the combustion chamber with a consequent increase in the temperature of the exhaust gases ;

  • a fuel additive system consisting of a probe tube, a system to inject Eolys into the main fuel tank and a dedicated electronic controller. The Eolys is stored in a tank adjacent to the main fuel tank and injected in proportion to the volume of fuel added during refuelling. For example, when filling up with 60 litres of fuel, the system will inject 37.5 ml of solution containing 1.9 g of cerine. The Eolys tank has a capacity of 5 litres, sufficient for 80,000 km.

The filter is cleaned and the Eolys tank refilled during dealer servicing every 80,000 km.

© 2000 Julian Marsh/Citroënët/SA Automobiles Citroën