6. Fuel Oil System
6.1 Acceptable fuel characteristics
6.1.1 Gas fuel specification
As a dual fuel engine, the Wärtsilä 31DF engine is designed for continuous operation in gas
operating mode or diesel operating mode. For continuous operation in the rated output, the
gas used as main fuel in gas operating mode has to fulfill the below mentioned quality
requirements.
Table 6-1 Fuel Gas Specifications
ValueUnitProperty
70Methane number (MN), min
3)
70% volumeMethane (CH
4
), min
0.05% volumeHydrogen sulphide (H
2
S), max
3% volumeHydrogen (H
2
), max
4)
0,01mg/m
3
NOil content, max.
25mg/m
3
NAmmonia, max
50mg/m
3
NChlorine + Fluorines, max
50mg/m
3
NParticles or solids at engine inlet, max
5umParticles or solids at engine inlet, max size
0…60°CGas inlet temperature
Water and hydrocarbon condensates at engine inlet not allowed
5)
The methane number (MN) of the gas is to be defined by using AVL’s “Methane 3.20” software. The MN is a calculated value
that gives a scale for evaluation of the resistance to knock of gaseous fuels. Above table is valid for a low MN optimized engine.
Minimum value is depending on engine configuration, which will affect the performance data.
However, if the total content of hydrocarbons C5 and heavier is more than 1% volume Wärtsilä has to be contacted for further
evaluation.
3)
Hydrogen content higher than 3% volume has to be considered project specifically.4)
Dew point of natural gas is below the minimum operating temperature and pressure.5)
6.1.2 Liquid fuel specification
The fuel specifications are based on the ISO 8217:2017(E) standard. Observe that a few
additional properties not included in the standard are listed in the tables. For maximum fuel
temperature before the engine, see chapter "Technical Data".
The fuel shall not contain any added substances or chemical waste, which jeopardizes the
safety of installations or adversely affects the performance of the engines or is harmful to
personnel or contributes overall to air pollution.
6.1.2.1 Light fuel oil operation (distillate)
The fuel specification is based on the ISO 8217:2017(E) standard and covers the fuel grades
ISO-F-DMX, DMA, DFA, DMZ, DFZ, DMB and DFB.
The distillate grades mentioned above can be described as follows:
● DMX: A fuel which is suitable for use at ambient temperatures down to –15 °C without
heating the fuel. Especially in merchant marine applications its use is restricted to lifeboat
engines and certain emergency equipment due to reduced flash point.
DBAE248994 6-1
6. Fuel Oil SystemWärtsilä 31DF Product Guide
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