Power Plant Engineering

Typical Exhaust Gas Emission Values For Modern 4-stroke
Diesel Power Plants Using Heavy Fuel
Fuel
FO-kV(2.1% sulphur)
FO (4.5% sulphur)
Load(%)
100.0
100.0
Mech, output (kW/cyl.)
990.0
990.0
Speed (rpm)
500.0
500.0
O
2 
(volume %,dry)
12.7
12.9
NO
x 
(ppm,dry, 15% O
2
)
1045.0
1600.0
CO (ppm,dry, 15% O
2
)
60.0
95.0
HC (ppm,dry, 15% O
2
)
155.0
155.0
SO
2 
(ppm,dry, 15% O
2
)
405.0
1200.0
TSP(mg/m
3
,15% O2)
65.0
90.0
Carbon dioxide (CO
2
): CO
2
actually is not noxious as a product of combustion of all fossil
fuels. It is now considered to be one of the main causes of the greenhouse effect. A reduction of CO
2
emission can only be achieved by improving the engine efficiency or by using fuels containing lower
concentration of carbon such as natural gas.
Sulphur oxides (SO
x
): Sulphur oxides are formed due to the combustion of sulphur contained in
the fuel. They are one of the primary causes of acid rain. The sulphur oxide emission is primarily
influenced by the amount of sulphur contained in the fuel used. Much less influence can be taken by the
fuel consumption of engine. The major part (> 95%) of sulphur oxides contained in the exhaust gas of
the diesel engines is SO
2
.
Nitrogen oxides NO
x
 (NO, NO
2
, N
2
O): Nitrogen oxides which are generally referred to as NO
x
in
the case of internal combustion engines comprise nitrogen monoxide-NO (colourless, water insoluble
gas), nitrogen dioxide-NO
2
(reddish brown gas, highly toxic) and dinitrogen monoxide-N
2
O (laughing
gas, colourless gas previously used as a narcotic). Nitrogen oxides, together with the sulphur oxides are the
main causes of acid rain. They also contribute essentially to ozone formation in the air and ground level.
The high temperatures and pressures produced in the combustion space of an IC engine stimulate
the nitrogen content in the air and also in the grades used (such as heavy fuel oil) to react with oxygen in
the combustion air. In this reaction mechanism, the formation of nitrogen oxides proportionally in-
creases with the temperature rise. This behavior unfortunately combats the efforts of improving on
engine efficiency because conversion of energy at the highest possible temperature level is to be aimed
for to reach the optimal efficiencies of combustion processes.
The NO
x
formation during combustion in the diesel engine is predominantly NO and which is
converted to a minor extent to NO
2
by oxidation either in the combustion space or in the exhaust gas
systems downstream (exhaust gas piping, exhaust gas turbo charger etc.). In general, exhaust gas leav-
ing the engine is 95% NO and approximately 5% NO
2
. To simulate the process of NO oxidation, to form
NO
2
in the atmosphere, practically, all the legislation stipulate that in the calculation of NOx mass flow
emitted, the entire NO
x
must be taken as NO
2
. The N
2
O concentration in the exhaust gas of medium
speed diesel engines, burning heavy fuel is limited to a few ppm. Therefore, it can be neglected from the
viewpoint of environmental protection.

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POLLUTION AND ITS CONTROL
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