Page 35 - CARILEC CE Journal CEMAY2021

In summary, the Wärtsilä 32 LG engine combines Precise injection timing, efficient turbocharging
two long established technical features associated and good cylinder scavenging all contribute to
with the W32 engine series: pressurized common rail lower combustion temperature and lower NOx
fuel delivery and twin needle injection giving it the formation. Wärtsilä’s early attempt to lower NOx
versatility to burn a wide variety of liquid fuels. emissions from its diesel engines were concentrated
on retarding injection timing of the fuel (together
EMISSIONS IN WARTSILA DIESEL AND with a shorter fuel injection time) in order to reduce
MULTI-FUEL ENGINES combustion temperatures. In the year 2000, Wärtsilä
For Wärtsilä engines including the W32 operating on introduced the Miller timing concept – commonly
the diesel cycle and burning diesel fuel, the primary referred to as the Miller Cycle on its diesel engines.
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emissions are: Nitrous Oxides (NOx), Carbon The goal was to improve efficiency and to reduce
Monoxide (CO), Particulate Matter (PM), Sulphur NOx emissions.
Dioxides (SO ) and Total Hydro Carbons (THC). We The basic concept of the Miller Cycle is to close
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will touch on the key emissions: NOx, PM, SO and the inlet valve before the piston reaches BDC. When
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THC. this is done, the cylinder is closed while the piston
is still travelling down. When a fixed amount of gas
NOx EMISSIONS is expanded within an enclosed space, a cooling
NOx formation in the diesel engine (Diesel Cycle) is affect occurs. Because of this cooling affect, the
as a result of the nitrogen content in the intake air compression stroke starts at a lower temperature
and depends to a large extent on the combustion and also finishes at a lower temperature. This then
temperature (typically Nitrogen content in the results in a cooler combustion temperature and a
fuel is low and thus a minor NOx contributor). reduction in the NOx emission level.

Lift (mm)

CA (deg)

Preassure (barg)

Crank angle [deg]

3 Miller Cycle is essentially early closure of inlet valves, typically before piston is at bottom dead centre (BDC).

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