Exhaust Emissions - Wartsila 31 Product Manual

Wärtsilä 31 Product Guide
12.

Exhaust Emissions

Exhaust emissions from the diesel engine mainly consist of nitrogen, oxygen and combustion
products like carbon dioxide (CO
(CO), sulphur oxides (SO
hydrocarbons (HC) and particulate matter (PM).
There are different emission control methods depending on the aimed pollutant. These are
mainly divided in two categories; primary methods that are applied on the engine itself and
secondary methods that are applied on the exhaust gas stream.
12.1 Diesel engine exhaust components
The nitrogen and oxygen in the exhaust gas are the main components of the intake air which
don't take part in the combustion process.
CO
2
monoxide, hydrocarbons, nitrogen oxides, sulphur oxides, soot and particulate matters.
In a diesel engine the emission of carbon monoxide and hydrocarbons are low compared to
other internal combustion engines, thanks to the high air/fuel ratio in the combustion process.
The air excess allows an almost complete combustion of the HC and oxidation of the CO to
CO
2
12.1.1 Nitrogen oxides (NO
The combustion process gives secondary products as Nitrogen oxides. At high temperature
the nitrogen, usually inert, react with oxygen to form Nitric oxide (NO) and Nitrogen dioxide
(NO
2
to the combustion temperature.
NO can also be formed through oxidation of the nitrogen in fuel and through chemical reactions
with fuel radicals. NO in the exhaust gas flow is in a high temperature and high oxygen
concentration environment, hence oxidizes rapidly to NO
approximately 5 % of total NOx emissions.
12.1.2 Sulphur Oxides (SO
Sulphur oxides (SO
combustion process the fuel bound sulphur is rapidly oxidized to sulphur dioxide (SO
small fraction of SO
12.1.3 Particulate Matter (PM)
The particulate fraction of the exhaust emissions represents a complex mixture of inorganic
and organic substances mainly comprising soot (elemental carbon), fuel oil ash (together with
sulphates and associated water), nitrates, carbonates and a variety of non or partially
combusted hydrocarbon components of the fuel and lubricating oil.
12.1.4 Smoke
Although smoke is usually the visible indication of particulates in the exhaust, the correlations
between particulate emissions and smoke is not fixed. The lighter and more volatile
hydrocarbons will not be visible nor will the particulates emitted from a well maintained and
operated diesel engine.
Wärtsilä 31 Product Guide - a1 - 18 October 2016
), nitrogen oxides (NO
x
and water are the main combustion products. Secondary combustion products are carbon
, hence their quantity in the exhaust gas stream are very low.
), which are usually grouped together as NO
) are direct result of the sulphur content of the fuel oil. During the
x
may be further oxidized to sulphur trioxide (SO
2
), water vapour and minor quantities of carbon monoxide
2
), partially reacted and non-combusted
x
)
x
emissions. Their amount is strictly related
x
)
x
12. Exhaust Emissions
. The amount of NO emissions is
2 2
).
3
). A
2
12-1