Marine Diesel Engines - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 159

Table 11.4 Influences of changing environment conditions on operation

Environment
conditions

Operation measures

Ambient air
temperature

Higher ambient air temperatures decrease the mass of the charging air
and the Lambda number of the combustion. Disadvantageous results
are the higher thermal load of combustion relevant parts, the higher
temperatures of the exhaust gas and the after treatment system and the
deterioration of the SFC. In principle, two-stroke and the four-stroke
engines behave similarly [ 19 ]

Charging air
temperature

Increasing the charging air temperature reduces the requirements of the
exhaust gas after treatment system, because the quality of the
combustion improves and the concentration of unburned substances
decreases [ 20 ]

Exhaust gas counter
pressure

Highly turbocharged marine diesel engines are very sensitive to changes
in the exhaust gas counter pressure downstream to the turbines.
Particularly two-stroke engines consume more fuel with high counter
pressure. Manufacturers usually do not permit exhaust gas counter
pressures more than 20 to 30 mbar, i.e. from 2,000 to 3,000 Pa (from
41.8 to 62.7 lbf ft -2 or from 0.29 to 0.44 psi) [ 21 ]

the fuel consumption and exhaust gas emissions of the engine. Improving the
turbocharger's efficiency from 60-70% decreases fuel consumption up to 2% [ 17 ].
Two-stroke engines must operate with a constant pressure in all cylinders and
the charging air has to be equally distributed to all cylinders. Differences in the
operation significantly influence the flow resistance. The result could be a
lengthways flush with small air throughput in the cylinders. Precisely, regulating
charging air supports the changing exhaust gases in the cylinders. The charging
process can be further optimized by using additional compressors, e.g., electric
boosters [ 18 ].

11.3.2 Operation in Changing Environment Conditions

A ship can gain or lose efficiency as the weather changes. The most important
factors influencing fuel consumption and emissions are:

• Ambient air temperature;
• Charging air temperature; and
• Exhaust gas back pressure (see Table 11.4 ).

Figure 11.3 shows the reaction of the engine to increased exhaust gas counter
pressure.