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Exhaust fume composition

  1. May 22, 2008 #1
    In regards to two types of engines..

    What gases (by percentage) are to be found in conventional petrol driven internal combustion engines, such as found in cars ?

    What gases (by percentage) are to be found in conventioanl diesel driven internal combustion engines, such as found in trucks ?

    I have tried to search for an accurate breakdown of the two, but ploughing through the internet has left me more confused than clarified.

    So, if any of you guys knows for sure...then please help me out..

    Thanks in advance..



    Mods, if you feel that this thread should be in chemistry, feel free to move it...
  2. jcsd
  3. May 22, 2008 #2


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    Depends quite a lot on the engine type, purpose, and how it's being run. This is a complex field, and (as you're probably aware), a huge amount of engineering work is done in this field.

    In brief, there are thousands of different chemicals found in engine-out exhaust gases for both Diesel and petrol engines. The bulk of the gaseous emissions are made up of N2, O2, CO2, and water vapour (and maybe some CO). Typically, the N2 level will not change much before/after the combustion event. CO2, CO and O2 levels are all relative, and depend on the air fuel ratio. Lean operation will give high O2, moderate CO2, and low CO; where rich operation will give very low O2, moderate CO2, and very high CO.

    Now, SO2, NOx and hydrocarbons are all pretty much universally present, but in very variable quantities (and these quantities are measured in ppm, rather than %). Sulphur compounds are a feature of sulphur in the fuel (which is why you now see low sulphur fuel), NOx is from atmospheric air, and is a feature of high peak cylinder temperatures; and HC are a result of incomplete combustion for whatever reason. Other components (notably alcohols and aldehydes) are present in smaller quantities still.

    Diesel engines typically have high levels of particulate matter within the exhaust (as compared petrol engines). This particulate matter comprises of soot and sulphur compounds (from lube oil and fuel), all kinds of organic matter, and varying amounts of metals. Again, these are in tiny amounts compared with the main gaseous components.

    Does this help?
    Last edited: May 22, 2008
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