Wartsila ?31DF Series Product Manual page 69

Wärtsilä 31DF Product Guide
A small side air receiver is located in the hot box, including charge air bends with integrated
hydraulics and charge air riser pipes.
Following components are connected to the cylinder head:
● Charge air components for side receiver
● Exhaust gas pipe to exhaust system
● Cooling water collar
● Quill pipe with High Pressure (HP) fuel pipe connections
● Main gas admission valve
4.2.9 Camshaft and valve mechanism
The cams are integrated in the drop forged shaft material. The bearing journals are made in
separate pieces, which are fitted, to the camshaft pieces by flange connections. The camshaft
bearing housings are integrated in the engine block casting and are thus completely closed.
The bearings are installed and removed by means of a hydraulic tool. The camshaft covers,
one for each cylinder, seal against the engine block with a closed O-ring profile. The valve
tappets are of piston type with self-adjustment of roller against cam to give an even distribution
of the contact pressure. Inlet and exhaust valves have a special steam coating and hard facing
on the seat surface, for long lifetime. The valve springs make the valve mechanism dynamically
stable.
The step-less valve mechanism makes it possible to control the timing of both inlet & exhaust
valves. It allows to always use a proper scavenging period. This is needed to optimize and
balance emissions, fuel consumption, operational flexibility & load taking, whilst maintaining
thermal and mechanical reliability. The design enables clearly longer maintenance interval,
due to the reduced thermal and mechanical stress on most of the components in the valve
mechanism.
4.2.10 Camshaft drive
The camshafts are driven by the crankshaft through a gear train.
4.2.11 Turbocharging and charge air cooling
The selected 2-stage turbocharging offers ideal combination of high-pressure ratios and good
efficiency both at full and part load. The turbochargers can be placed at the free end or fly
wheel end of the engine. For cleaning of the turbochargers during operation there is, as
standard, a water washing device for the air (compressor) and exhaust gas (turbine) side of
the LP stage and for the exhaust gas (turbine) side of the HP stage. The water washing device
is to be connected to an external unit. The turbochargers are lubricated by engine lubricating
oil with integrated connections.
An Exhaust gas Waste Gate (EWG) system controls the exhaust gas flow by-passing for both
high pressure (HP) and low pressure (LP) turbine stages. EWG is needed in case of engines
equipped with exhaust gas after treatment based on Selective Catalytic Reaction (SCR).
By using Air Waste Gate (AWG) the charge air pressure and the margin from LP compressor
is controlled.
A step-less Air By-pass valve (ABP) system is used in all engine applications for preventing
surging of turbocharger compressors in case of rapid engine load reduction.
The Charge Air Coolers (CAC) consist of a 2-stage type cooler (LP CAC) between the LP and
HP compressor stages and a 1-stage cooler (HP CAC) between the HP compressor stage
and the charge air receiver. The LP CAC is cooled with LT-water or in some cases by both
HT- and LT-water. The HP CAC is always cooled by LT-water and fresh water is used for both
circuits. When there is a risk for over-speeding of the engine due to presence of combustible
gas or vapour in the inlet air, a UNIC automation controlled Charge Air Blocking device, can
be installed.
DBAE248994
4. Description of the Engine
4-3