Page 36 - CARILEC CE Journal CEMAY2021

When operating on liquid propane with the

required amount of pilot diesel oil or on diesel fuel,
the THC production is estimated to be less then
<130 ppm-vol. as CH @ 15% O dry.
3 2

In the W32 and W32LG engines, application of Miller SO emissions are expected to be well below 3 ppm–
2
(advanced intake valve closure) cycle is effectively vol. dry at 15% O
2
reducing NOx emissions of diesel engines at medium
and high loads. Up to 30% NOx reduction is achieved THC EMISSIONS
with single-stage turbocharging system. In the Total Hydrocarbon (THC): In the context of this paper,
earlier applications of the Miller cycle there was the 32LG engine will be burning liquid propane with
some performance deterioration - to some degree ultra-low sulphur diesel oil (<5%) as pilot fuel and at
at low load (increased smoke, high component other times will burn ultra-low sulphur diesel oil only
temperatures, worse load pick-up capability) due (anticipated as a back-up fuel in situations where
to air deficiency. However, this has been mitigated propane is not available). When operating on liquid
by the introduction of Wärtsilä’s variable inlet valve propane with the required amount of pilot diesel oil
closing timing (VIC) in relation to engine load resulting or on diesel fuel, the THC production is estimated
in optimum performance of the Miller cycle over the to be less then <130 ppm-vol. as CH @ 15% O dry.
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whole load range of the engine. THC emissions are coming from unburned or partly
Considering all of these factors, Wärtsilä has combusted fuel (including pilot fuel) and lubrication
designed the W32 and the W32LG engine with two oil. The THC composition will thus vary dependent
ratings: (i) an emission rated model where NOx on the fuel used, when burning LPG there will be
emitted is limited to 710 ppm –vol. dry at 15% O ., lighter hydro carbons present in the THC fraction
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and (ii) an efficiency rated model where the efficiency compared to diesel operation. VOC is per definition;
of the engine is optimized and NOx production is Non Methane Non Ethane hydrocarbons and for
>710 ppm. The W32LG engine being offered to engines burning diesel fuel or LPG most of the THC
WAPA is emission rated. can thus be considered to be present as VOC in the
exhaust.
PM EMISSIONS
Particulate matter emission is influenced mostly COMPARISONS ACROSS THE W32/34
by the ash and Sulphur content in the fuel. PM ENGINE PLATFORM
emissions are also reduced by optimal fuel injection Although focused on the 32LG engine, this paper
control. has examined the thermodynamics associated
with the entire Wärtsilä 32/34 engine platform,
SO2 EMISSIONS which we believe is fundamental to understanding
SO emissions is mainly based on the sulphur the emissions associated with the 32LG engine.
2
content in the fuel. However, the engine lubricating Consequently, we have appended (Appendix 1) a
oil contains some sulphur contributing to some table that compares all of the engine types in this
SO emissions. In the WAPA case, where ultra-low platform. The table shows raw (primary) emission
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sulphur diesel (max 15 ppm S) is the fuel of choice data from the engines in various units and also EPA
and the LPG is assumed to be free of odorants, the AP-42 values.

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