Discussion

Soot particles formed in combustors are important for many well-known reasons: their contribution to radiant heat transfer, their industrial value as pigments and tire additives, their capacity to clog flow passages, etc. We discuss two recent developments that provide additional motivation for understanding and reducing soot formation.

The climate-change community refers to soot particles suspended in the atmosphere as black carbon. These particles warm the atmosphere directly by absorbing sunlight and indirectly by affecting cloud formation. Most other atmospheric particles, such as sulphates, primarily scatter sunlight and cause cooling. The magnitude of warming from black carbon is difficult to estimate: the short atmospheric lifetime of particles causes their concentrations to vary greatly with time and geographical location. Several recent calculation conclude that the radiative forcing due to the black carbon is 0.5 – 0.8 W/m², while other studies put it much lower. If the larger values are correct, then black carbon plays a critical role in warming: its forcing would be one-third to one-half of the forcing due to CO₂(1,46 W/m²) and would be larger than the forcing from the second most important greenhouse gas (CH₄; 0.48 W/m²). This comparison has led several atmospheric scientists to argue that reducing soot emissions is a better strategy for countering warming than reducing CO₂ emissions. Some of the reasons for focusing on soot include: (1) it has other adverse consequences, whereas warming is the only issue associated with CO₂, (2) its short atmospheric lifetime means that soot reductions will rapidly affects the global temperature, and (3) it results from combustion inefficiency, which can be prevented with proper engineering, whereas CO₂ is an inevitable product of hydrocarbon combustion.

Lesson 10

Part 1

<== попередня сторінка	\|	наступна сторінка ==>
Fine particle toxicity and soot formation	\|	Practice

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