About carbon dioxide and sulphur oxide emissions

General

• Alongside water, carbon dioxide (CO₂) is an end-product of the complete combustion of hydrocarbons
  
• CO₂ is a colourless, odourless and non-toxid gas
  
• CO₂ is exhaled by humans
  
• CO₂ is a naturally occurring component of the atmosphere
  
• Sulphur dioxide (SO₂) and sulphur trioxide (SO₃ ) are grouped together under the general term sulphur oxides (SO_x)
  
• Sulphur oxides are corrosive toxic gases with a pungent smell.
  

Environmental impacts

• CO₂ is the most important “greenhouse gas”; its increasing presence in the atmosphere is believed to cause climate warming
  
• SO_x emissions increase acid rains and acidification
  
• SO_x have an unfavourable effect on vegetation and human health, and a corrosive effect on buildings
  
• SO_x contributes to formation of "secondary" particulates in the atmosphere
  
• Estimates disagree on the negative impact of SO_x emissions into the oceans because seawater is alkaline and the importance of the long-range transboundary atmospheric transport of SO_x is not fully understood.
  

Formation in engines

• The carbon and sulphur in the fuel oxidizes in the engine’s combustion chamber into CO₂ and SO_x. Hence, in practical terms the emissions levels of CO₂ and SO_x can be considered directly proportional to the carbon and sulphur content of the fuel
  
• Comparisons of different combustion processes show that the diesel engine has the lowest specific CO₂ and SO_x emission because the diesel process has the highest efficiency
  
• The typical ratio of  SO₂ to SO_x is 0.95
  
• The typical ratio of SO₃ to SO_x is 0.05.
  

Emissions reduction methods in engines

• Raising the engine’s efficiency, i.e. reducing its specific fuel consumption
  
• Using low-sulphur fuels, e.g. changing from heavy fuel oil with a high-sulphur content to low-sulphur heavy or light fuel oil, or moving over entirely to the use of natural gas
  
• Changing to fuels with a lower carbon-to-hydrogen ratio. Changing from fuel oil to natural gas, for example, reduces CO₂ emissions. Correspondingly, adopting the use of biofuels essentially eliminates net CO₂ emissions altogether.
  

Feasible emissions reduction technologies

• No commercial technology exists for reducing CO₂ emissions
  
• Several alternatives are available for reducing SO_x emissions e.g. wet scrubber tehchnologies.