Marine exhausts???

Discussion in 'Diesel Engines' started by burt2, May 8, 2006.

  1. alex fletcher
    Joined: Jun 2006
    Posts: 54
    Likes: 2, Points: 0, Legacy Rep: 18
    Location: Ettalong Beach NSW Aust.

    alex fletcher Junior Member

    as a professional engineer here is what i would do measure the exhaust gas temperature and pressure both are vitally important to a diesel motor. to little pressure your ex valves will burn out to much will reduce power considerably to high a temp will burn valves and to little u may get pre detonation any question email me Alex also twin screw to single? have you thought of the safety ramification of one drive 2 is alway safer than one
  2. bilgeboy
    Joined: Dec 2005
    Posts: 157
    Likes: 7, Points: 0, Legacy Rep: 45
    Location: Boston

    bilgeboy Senior Member

    Diesel Theory

    Hi Alex,

    I like to discuss diesel engine theory, especially hashing out some of the finer points. I am not sure I fully understood your post. I would appreciate it you could explain a couple of points.

    When you mention exhaust gas pressure, I was thinking that this is also called "back pressure" by alot of folks. I didn't understand why too little back pressure would be harmful to exhaust valves. I thought you always wanted to minimize back pressure as much as possible, as it is poorly tolerated by diesels, causing the effect you mentioned (loss of power).

    Also, why would a low exhaust gas temp cause predetonation? As I understand it, most elevated EGT's are caused by excess fuel to air ratio, causing the unburned diesel to continue burning as it exits the manifold, thereby increasing the EGT. Well combusted diesel cools rapidly as the volume of gas expands on the piston downstroke. Predetonation should only be caused by an abnormally high cylinder temperature (engine to hot), injection timed too early so that diesel is injected way before TDC, or too much diesel is injected (from dribbling injectors or an extremely overloaded engine.

    I would appreciate your thoughts,



  3. alex fletcher
    Joined: Jun 2006
    Posts: 54
    Likes: 2, Points: 0, Legacy Rep: 18
    Location: Ettalong Beach NSW Aust.

    alex fletcher Junior Member

    to much EGP will slow the hot gas passing over the Ex valve this allows the heat to transfer to the valves thus heating them
    A diesel engine is designed to operate with a amount of EGP but never no pressure the pressure differential between CYL. compression and EGP is greater and the valve is under more stress and is more likely no to hold a seal we all Know what happens when EX Valves leaks.
    low EGT cools any unspent fuel vapour in the Ex gases allowing them to condense in the exhaust structure i actually should have typed Post det sorry
    contact the engine manufacturer and get the specs the the engine as thay are all different and adhere to the specs and measure the parameters to make shire thay r correct and you will have years of trouble free boating
    hopes this helps
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