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Diesel Engines Running Underloaded / Lube Problems?

Discussion in 'Engines' started by C4ENG, Jun 13, 2012.

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  1. C4ENG, Jun 17, 2012
    #41
    C4ENG

    C4ENG Senior Member

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    To verify your statements, I talked to a mechanic who has rebuilt more marine diesel engines than I have seen and asked him how often he sees sulfuric acid pitting issues in today's real life situations. He told me he only see's the issue when the engine has very low usage and they have not changed the oil on proper schedules. Running low load causes other issues but not sulfur pitting related issues and the sulfur in today's fuel is getting lower and lower as the years go by.

    As the debate of the cylinder temperatures from other postings, the mechanic explained to me that the exhaust temperature is slightly higher than combustion temperature. This is because when the exhaust meets the air, the oxygen fuels the heat to rise. Most engines that have exhaust monitoring alarm will be set for mid 1200 ferinheight range to sound (which means your combustion temperatures would be slightly less than that). Any temperatures over 1200F (not Celsius) can have damaging effects within your cylinders. 1200F = 648C
  2. Capt J, Jun 17, 2012
    #42
    Capt J

    Capt J Senior Member

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    That is true. However, EGT temperatures vary for engine and engine management software or lack thereof. For example on a DD 2 cycle, you don't really want to run EGT temperatures higher than 850 degrees F and it is considered detrimental. MAN common rails run higher than 1200 degrees....and that is considered normal. They usually run closer to 1300-1400 ndegrees F under normal conditions.
  3. Marmot, Jun 17, 2012
    #43
    Marmot

    Marmot Senior Member

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    C4 you really ought to quit before you get even further behind.

    Start by finding another source for bogus information. Your guy might be good at turning wrenches but he is way out of the park with regard to what happens in a cylinder.

    An exhaust temperature probe reads a mean temperature derived from burst of exhaust followed by a period of cool scavenging air. When a cylinder probe is mounted on a turbocharged engine, valve overlap blasts it with relatively cold air.

    Until the engine is at or approaching smoke point there is already a great deal of excess oxygen so his theory about after burning needs to be returned to gas engines where it came from. Combustion temperatures easily reach over 2000*F during injection. Get your class notes out again and look for a mention of "expansion" during the power stroke. The gases cool dramatically as the piston moves downward.

    If you spent a it more time studying how an engine works and less listening to diesel mythology you might avoid much of the nonsense you keep posting.
  4. C4ENG, Jun 18, 2012
    #44
    C4ENG

    C4ENG Senior Member

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    I am still feeling very uncertain about the diesel combustion cylinder temperature.

    Should I believe this diesel mechanic that I know in person who is a well known and respected man in this S FL industry with an impressive clientele of 150ft+yachts that he services regularly with a whole shop of other mechanics to ask questions with that say temps should be under 1200F in the cylinder?
    Or should I believe this other guy on the internet that claims to be a knowledgeable experienced engineer and has proven to be a repeatedly rude insulting poster that seems to enjoy provoking others while trying to prove them wrong within his demeaning unnecessary statements like this one here and says temps reach over 2000F in the cylinder?

    So which is it?

    Cylinder temps under 1200F?

    Cylinder temps over 2000F?
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