Camshaft And Valve Mechanism - Wartsila 31 Product Manual

Wärtsilä 31 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
4.2.8

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.
4.2.9 Camshaft drive
The camshafts are driven by the crankshaft through a gear train.
4.2.10 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 flywheel
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 connected
to an external washing unit. The turbochargers are supplied with inboard plain bearings, which
offers easy maintenance of the cartridge from the compressor side. 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 also in case of engines
equipped with exhaust gas after treatment based on Selective Catalytic Reaction (SCR).
By using Air Waste Gate (AWG) for bleeding air out from the charge air system, the charge air
pressure and the margin from LP compressor surging is controlled. The charge air pressure
control is used to avoid excessive charge air pressure preventing excessive firing pressure.
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. When the ABP
valve is open part of charge air is released to the exhaust side.
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. Fresh water is used for both
circuits.
Wärtsilä 31 Product Guide - a1 - 18 October 2016
4. Description of the Engine
4-3