Inlet air Temperature

Discussion in 'Inboards' started by anthony goodson, Jul 11, 2020.

  1. anthony goodson
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    anthony goodson Senior Member

    I am running a BMW M47R common rail turbodiesel engine ,post intercooler inlet air temperature can rise to 100 degrees centigrade I am quite happy with the power produced but will this do damage long term,
     
  2. baeckmo
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    baeckmo Hydrodynamics

    Hi Anthony,
    I think 100 cg sounds a bit on the high side, even with an aircooled intercooler. I dug out some old test bench protocols from "back then" to compare. For marine diesels with about the same charge pressure and specific power output, but with seawater cooled ic's, the goal was to keep inlet air temperature below ~65 cg's at full power.

    The control unit for the injection in most common rail systems has a temperature input (as well as pressure and/or air mass flow) from inlet air after ic. This will adjust fuel injection mass and injection timing as required by the inlet conditions. But unfortunately, I have no specific info on the M47 engine and its settings. Anyway, all diesel engines thrive better with inlet air temperatures in the 30 to 60 degree range; not too low to delay ignition and not too high to reduce air mass flow etc.

    I think it would be wise to check the ic for blockage and dirt, both outside and inside.
     
  3. anthony goodson
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    anthony goodson Senior Member

    Hi baeckmo
    Nice to hear from you thanks for the reply. This is a hobby project to amuse me in my dotage,and for me to explore the vagaries of a fully electronic CR diesel engine. The engine performs well maintains temperature and power etc and shows no signs of distress. By taking a feed from the ECU K line to a bluetooth OBD2 reader I have a digital wireless dashboard displayed on a Google Nexus tablet running torque pro.This gives me most of the engine parameters, however despite changing the sender unit, the IAT presents as no data.I havent worried too much about this ,but out of curiosity I introduced a thermocouple into the airflow post intercooler and was a little surprised and quite concerned at the readings.
    I know that most vehicles aim for 10 to 20 degrees above ambient,but then a vehicle is not being driven up hill all the time,as a boat is even so the readings I am getting are too high I think and you have confirmed this . Even though the intercooler is first in line for cooling water it would appear to be inadequate so I will try to source one with a bigger tube bundle. Many thanks stay safe. ps Just for clarification this is in a 21ft Tremlett with a waterjet.
     
  4. BlueBell
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    BlueBell Ahhhhh...

    Have you considered adding water injection to lower the intake temperature?
     
  5. Eric ruttan
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    Eric ruttan Senior Member

    It will not do damage long term.
    All a high intake temp will do is reduce power, because warm air has less air per cylinder than cooler air. Reduced power will make you engine last longer and save you fuel.

    You could increase cooling to your intercooler to reduce intake temp, add power and increase fuel consumption, and, perhaps, add wear.

    You can also do water injection, where you squirt water into your intake stream. This is what the car racers do. This can actually save fuel and increase power.

    Intake temp is important in gas motors. It not matter with diesels.
     
  6. anthony goodson
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    anthony goodson Senior Member

    Many thanks to you and Blue Bell for your replies ,I think water injection is a little too radical in this situation ,truth is I fitted an intercooler which is too small because I had it to hand and hoped I'd get away with it, I will source a larger one and all should be well.
     
  7. Eric ruttan
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    Eric ruttan Senior Member

    As you wish friend. Just know you don't need to. Do you see a need for the full 130+ hp?
     
  8. anthony goodson
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    anthony goodson Senior Member

    I am normally quite happy at 21kts and 2300rpm ,and at this the engine is not working hard, the sea conditions around here will normally dictate a comfortable and dry speed ,the Tremlett is a good sea boat, but it has a fine bow and can be very wet in a chop. However as the revs increase beyond that so does the turbo boost ,the engine temperature is steady ,but the iat goes up very quickly ,the max revs are 3300 and the boost at this is 18psi.I am concerned about EGT. The boat weighs about a tonne .I think a larger intercooler will sort it.
     
  9. Eric ruttan
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    Eric ruttan Senior Member

    Do you have the ability to monitor EGT?
    If you want to reduce EGT, which is a real concern, you may wish to take the dollars you would consider spending on a new IC, and look at a water ingector. It is just a small dribble of water that feeds into the intake. It will drop egt, add power and save fuel. And the design for your motor is well sorted.

    At full throttle it is something like the feed from a window wiper. Infact this is often how water injection is done. So it is relatively inexpensive.
     
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  10. anthony goodson
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    anthony goodson Senior Member

    I know nothing of this, I will look into it thank you.
     
  11. kapnD
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    kapnD Senior Member

    Have you looked at ducting your air intake to utilize outside air rather than preheated engine room air?
     
  12. BlueBell
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    BlueBell Ahhhhh...

    That's exactly how I did mine. I had two pressure sensors on the intake manifold and two windshield washer reservoirs with built in pumps. One came on at 3 psig and the other at 9 psig. Cleanest engine I have ever rebuilt. Steam cleaned.
    I'd simply check water levels every fill-up.

    EGT is critical. Get a sensor and read-out.
     
    Last edited: Jul 14, 2020
  13. anthony goodson
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    anthony goodson Senior Member

    Thanks for the reply, that is already in place
     
  14. baeckmo
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    baeckmo Hydrodynamics

    There is more to the inlet air temperature issue than indicated in the replies above. The engine's original fuel injection mapping is matched to injectors and specific inlet and ambient conditions in order to produce the power required at any instance, AND to do so within very close limits regarding flame propagation, burning rate aso. For instance, if the inlet temperature is increased beyond specification, the ignition delay is reduced and the time for fuel evaporation is reduced. This will change the flame pattern due to reduced charge homogenity (larger local variations in fuel/oxygen distribution). Local temp spikes will increase NOx formation and fuel rich mixture spots may increase soot formation. An additional effect may be longer flames, that eventually will touch piston- or cylinder surfaces, causing glazing and lubrication issues.

    In fact, the charge air temperature has a marked influence on diesel engine long term operation and its environmental impact; the intercooler function is an integrated part of the picture.
     

  15. anthony goodson
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    anthony goodson Senior Member

    Thanks baeckmo I intend to go the larger intercooler route.
     
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