Diesel engines are used as the main power source of marine transport and the continuous improvement of their performance offers better specific fuel oil consumption (SFOC). From the standpoint of Carbon Dioxide (CO
2) emission, marine engines are environment friendly compared to those used in land transportation and other industries. Attention should be focused only on CO
2 emissions but also on other greenhouse gases (GHG), such as Nitrous Oxide (N
2O), which is the result of a reaction between nitrogen and sulfur components of low-grade fuels.
N
2O is known as the third major GHG following CO
2 and methane (CH
4). The global warming potential (GWP) of N
2O is 310 times as large as that of CO
2 because N
2O in the atmosphere is very stable, and it becomes a source of secondary contamination after photo-degradation in the stratosphere. N
2O concentration 1800 years before was less than 280 ppb, but in the last 200 years it has increased rapidly. Since N
2O emission from natural sources is very difficult to control, discussions on N
2O emission reductions should be centered on artificial N
2O which represents 35% of the total N
2O emissions. To argue this point, it should be noted that there are some reports on the N
2O exhaust characteristics from stationary power plants and land transportations, but those of marine transportations are very limited.
In this experimental study, the authors investigated N
2O emission characteristics of an actual ship at the sea, and examined relationships between N
2O and other gaseous emissions. The experimental results showed that N
2O emission exhibited different characteristics compared with NO which makes up over 80 percent in NO
X, and had exhaust characteristic very similar to SO
2 emission. But when based on the excess air ratio, the difference between these two species increased with decreasing excess air ratio.
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