The relationship between atmospheric pollutant emissions and fuel qualities

What is it about?

Air pollution caused by ship exhaust emission is receiving more and more attention. The actual ship testing method was used for exploring the relationship between fuel quality and major air pollutants emissions from inland vessels in this study. It was found that the specific SO2 emissions per unit of sulfur content for different tested fuels increased in proportion to the S content, when the ship rotating speed was 360 r/min, the specific SO2 emissions per unit of S of fuel A, fuel C and fuel D was 40%, 94% and 17% of fuel B. Particulate matter (PM) emission shows an overall decreasing trend with the increase of ship rotating speed, take fuel D as an example, the specific PM emissions were 7.35 g/kw·h, 7.05 g/kw·h and 3.93 g/kw·h when ship rotating speed were 360 r/min, 500 r/min and 600 r/min, respectively. The formation of NOx is mainly related to the temperature of the engine working process. The impact of reducing the content of S and Polycyclic aromatic hydrocarbons (PAHs) in fossil fuels on the engine temperature is very limited.

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Why is it important?

In recent years, shipping traffic has been rapidly developed. As people's awareness of environmental protection is enhanced, air pollution caused by ship exhaust emission is receiving more and more attention(Petzold et al. 2008; Folkert Boersma et al. 2015). Relevant studies show that SO2, NOx and particulate matters (PM) emitted from ship exhaust account for 4-9% (Corbett et al. 1999), 15% (Eyring et al. 2005) and 1% (Jacoby and Kann 2007) of anthropogenic emission sources, respectively. Moreover, ship exhaust has also been proven as an important source of atmospheric pollutants in multiple port cities (Yang et al. 2015; Tan et al. 2014; Kesgin and Vardar 2001; Air and Programs 1976). Numerous studies have confirmed that SO2 emissions from ships mainly come from the combustion of sulfur-containing substances, so the use of fuels with lower sulfur content can greatly reduce SO2 emissions (Murphy et al. 2009; Saputra 2013) and thus reduce SO2 pollution from ships. As for PM, there is a high correlation between the PM generation in the ship exhaust and the fuel combustion efficiency. Meanwhile, biodiesel can significantly reduce the PM emissions from ships compared with that of ordinary diesel (Lapuerta et al. 2010). This difference is due to the high adiabatic combustion temperature of polycyclic aromatic hydrocarbons (PAHs) in common diesel fuel, making it difficult to be fully burned and causing the formation of a large amount of PM (Tang et al. 2005). However, the PAHs content and sulfur content in biodiesel are almost negligible, reducing the probability of generating PM (Song et al. 2012). The production of NOx is related to the combustion temperature. Higher temperature is favorable for the reaction between N2 and O2 to generate NOx. Glaude et al. (Glaude et al. 2010) found that NOx emissions will be significantly reduced using synthetic diesel fuel. This is because the main component of synthetic diesel is straight-chain alkane, almost without aromatic hydrocarbons, making the partial combustion with lower temperature. At the same time, synthetic diesel has the characteristics of low density and high quality calorific value, so that less fuel would be required for the engine at the same output power, and the excess air coefficient would be slightly higher than using common diesel fuel, which is beneficial to lower the combustion temperature in the cylinder, thus reducing NOx generation. The above studies were carried out in the laboratory diesel engine test bench, lacking of research on the pollutants emission in the actual operation of the ship. And reducing the S content in fossil fuels whether has an impact on NOx and atmospheric PM emissions remains to be studied. Based on the actual ship testing method, this subject is aimed at exploring the relationship between fuel quality and major air pollutants emissions from inland vessels, providing the basis and reference for the strategy to achieve the emission reduction targets of air pollutants by controlling the fuel quality.

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