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32-40 Exhaust gas emissions
Composition of exhaust gas of medium
speed four-stroke Diesel engines
The exhaust gas of a medium speed four-stroke Diesel engine is composed of numerous of constituents. These are derived from either the combustion air and fuel oil and lube oil used, or they are reaction products, formed during the combustion process. Only some of these are to be considered as harmful substances.
The table below show the typical composition of the exhaust gas of an MAN B&W Diesel four stroke Diesel engine at full load and without any exhaust gas treatment devices
Main exhaust gas constituents |
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Inert gases Ar, Ne, He... |
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Additional gaseous exhaust gas constituents considered as pollutants |
approx. [% by volume] |
approx. [g/kWh] |
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Sulphur oxides SOx 1) |
0.08 |
12.0 |
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Nitrogen oxides NOx 2) |
0.08 - 0.15 |
9.6 - 16.0 |
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Carbon monoxide CO 3) |
0.006 - 0.011 |
0.4 - 0.8 |
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Hydrocarbons HC 4) |
0.1 - 0.04 |
0.4 - 1.2 |
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Total |
<0.25 |
26 |
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Additionally suspended exhaust gas constituents, PM 5) |
approx. [mg/Nm3] |
approx. [g/kWh] |
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operating on |
operating on |
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MGO 7) |
HFO 8) |
MGO 7) |
HFO 8) |
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Soot (elemental carbon) 6) |
50 |
50 |
0.3 |
0.3 |
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Fuel ash |
4 |
40 |
0.03 |
0.25 |
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Lube oil ash |
3 |
8 |
0.02 |
0.04 |
Table 2-2 Exhaust gas constituents (only for guidance)
Note : At rated power and without exhaust gas treatment
1) SOx according to ISO-8178 or US EPA method 6C, with a content in the fuel oil of 3% by weight
2) NOx according to ISO-8178 or US EPA method 7E, total NOx emission calculated as NO2
3) CO according to ISO-8178 or US EPA method 10
4) HC according to ISO-8178 or US EPA method 25A
5) PM according to VDI-2066, EN-13284, ISO-9096 or US EPA method 17; in-stack filtration
6) Pure soot, without ash or any other particle-borne constituents
7) Marine gas oil DM-A grade with ash content of the fuel oil of 0.01 % and an ash content of the lube oil of 1.5 %
8) Heavy fuel oil RM-B grade with an ash content of the fuel oil of 0.1 % and an ash content of the lube oil of 4.0 %
Carbon dioxide CO2
Carbon dioxide (CO2) is a product of combustion of all fossil fuels.
Among all internal combustion engines the Diesel engine has the lowest specific CO2 emission based on the same fuel quality, due to its superior efficiency.
Sulphur oxides SOx
Sulphur oxides (SOx) are formed by the combustion of the sulphur contained in the fuel.
Among all propulsion systems the Diesel process results in the lowest specific SOx emission based on the same fuel quality, due to its superior efficiency.
Nitrogen oxides NOx (NO + NO2, )
The high temperatures prevailing in the combustion chamber of an internal combustion engine cause the nitrogen contained in the combustion air and also that contained in some fuel grades to react with the oxygen of the combustion air to form nitrogen oxides (NOx).
Carbon monoxide CO:
Carbon monoxide (CO) is formed during incomplete combustion.
In MAN B&W four-stroke Diesel engines, optimization of mixture formation and turbocharging process successfully reduces the CO content of the exhaust gas to a very low level.
Hydrocarbons HC
The hydrocarbons (HC) contained in the exhaust gas are composed of a multitude of various organic compounds as a result of incomplete combustion.
Due to the efficient combustion process, the HC content of exhaust gas of MAN B&W four-stroke
Diesel engines is at a very low level.
Particulate Matter PM:
Particulate matter (PM) consists of soot (elemental carbon) and ash.
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