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Exhaust air flow parameters for car engines (otto & diesel cycles)?

  1. Aug 7, 2011 #1
    Does anyone know any sources (i.e. car manufacturers) that provide the exhaust air flow parameters for the some specific car engines? I need stats on various otto & diesel cycle engines (small compact car engines, large semi truck engines, etc.). When I say exhaust air flow parameters, I need to know: the temperature, pressure, and flow rate (or density) of the exhaust air immediately after it leaves the engine's cylinders.

    Any input would be greatly appreciated! And if you have sources please provide them. Thanks in advance!

    Additional comment: Would there be a way to calculate flow rate from the engine's displacement & rpm?
    Last edited: Aug 7, 2011
  2. jcsd
  3. Aug 8, 2011 #2
    It will require a supersonic flow bench.

    I had a friend working on one but I'll bet only the bigwigs like Pratt&whitney and large manufacturers have anything like this.....maybe nasa.
  4. Aug 8, 2011 #3


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    It won't require a supersonic flow bench, and it won't require NASA; these are ludicrous claims. This kind of data is routinely captured during development simulation and test by every engine manufacturer out there. Your first step is asking them. I have no problems sharing this kind of data with customers who ask.

    Alternatively, if you want some approximate answers, have a stab at the following:

    - For exhaust temperature, make a thermodynamic approximation from cycle and rating (pretty easy to get a good approximation for a given fuel type and IMEP).

    - For exhaust volume flow rate, use exhaust mass flow rate and temperature

    - For exhaust mass flow rate, use air-fuel ratio and fuel consumption

    You can indeed calculate flow rate from the number of cylinders and the number of cycles per second, but you're much better off doing this on the inlet side (rather than exhaust), and then adding fuel and doing a mass balance across the cylinder, and converting back to a volumetric flow rate at your exhaust temperature.
  5. Aug 9, 2011 #4

    Thanks a ton. Very VERY helpful response. Just 3 more questions... How might I go about estimating the exhaust pressure? Do you think I could apply Bernouli's Equation and/or the Ideal Gas Law? If so, how would I get my density value?
  6. Aug 9, 2011 #5
    I know I said only 3 more questions :blushing: but I have to ask... you said you "have no problems sharing this kind of data with customers who ask," if you don't mind me asking, what is it that you do for work? Being a mechanical engineering student, I'm always curious about what different mechanical engineering type professions entail.
  7. Aug 9, 2011 #6
    So what happens to the reynolds number when flow through an exhaust port reaches supersonic speeds?
  8. Aug 9, 2011 #7

    What are you the world's biggest douche?
    Last edited: Aug 10, 2011
  9. Aug 10, 2011 #8
    Do you really want help?

    I think you should consider supersonic air flow through the exhaust port because the flow is......supersonic.

    If you name the car/engine type/model, maybe we can get you to your goal.

    Yes, we will be looking to break our own world record at NASA next week.

    BTW........your exhaust pressure in the port should peak at 2.5 bar unless there is a restriction downstream or a turbocharger which will raise pressure and temperature which will affect viscosity.
    Last edited: Aug 10, 2011
  10. Aug 10, 2011 #9
    By that time you have reached choked flow, with subsonic flow, and supersonic. So it's all one big mess anyway.

    Engineering is about being reasonable with what you have to work with. Quite a lot of this could be done on a low speed water flow bench. May not be perfect, but it'll give reasonable results.

    If he walks into University/School and tells them, this task is impossible. I require X00 thousand to pop down hire a supersonic flowbench for an afternoon, he'd get told boil his head.
    Last edited: Aug 10, 2011
  11. Aug 10, 2011 #10
    Perhaps suggesting the supersonic flow bench is a bit of an extreme and is able to reduce data to a far higher resolution than the original poster requires.

    Supersonic flow benches were a hot topic at the superflow dyno conference I attended back in 1991 so more than a few people have addressed the fact that airflow through an exhaust port does reach supersonic speed.

    The term "customers" tells me this query is aimed at an advancement in engine construction or management for profit.

    That said, I would like more information as to the reason for this question and his intended practical application because it could better help us to help him.

    Name the vehicles and engine families and a lot more help can be given.
    Last edited: Aug 10, 2011
  12. Aug 10, 2011 #11
    Sorry, not trying to be a hypocrite by hating on you. It just kinda seemed like a littttle bit of a douche comment... Just sayin :/ But ya thank you for the help!

    I wanted to get exhaust flow parameters so that I could develop a model of BMW's "turbosteamer" concept for a senior design project. I'm thinking friction will be the only restriction, since the exhaust will be closed to the working fluids throughout the cycle (the working fluids run turbines).

    I'm in the very early stages of research, so I don't have any exact engine models yet... but I wanted to develop a wide span of mathematical models for comparison: all the way from a small 4-cylinder engine to an enormous semi-truck engine.

    I was mainly thinking about developing mathematical models on standard Otto cycle engines, but if I can find the info & time I will model diesel cycles as well, just to see if a turbo-steamer is possible with diesels. Might compare 2-strokes & 4-strokes as well.

    For my physical model/build I am going to use any car/truck engine I can get my hands on for a decent price (and still run hot enough to run a turbo steamer of course!).

    Given my small amount of funds and doubting that my school (UCF) has any air flow benches, I'm probably going to have to make rough theoretical calculations to obtain my airflow parameters (based upon manufacturer-rated values, such as air:fuel ratio, piston displacement, and rpms) :/ You think it would be okay to treat it as an ideal & inviscid gas throughout the cycle?
  13. Aug 10, 2011 #12

    Now that I'm thinking about it, I'm betting that at least one of my professors can get me access to a flow bench.

    And you make a very good point. I don't want to waste my time making unreasonable calculations. I only have four and a half months (one semester) to design my project, develop a mathematical model & CAD model, collect funds from local businesses, and order all my parts. :bugeye:

    I'm also a little unsure about what kind of turbines I should use. BMW is a little secretive about this part of their concept... And I can't find their patent listing anywhere. :grumpy:
  14. Aug 11, 2011 #13
    I used to work on wright 3350 turbo compound engines in Airframe and Powerplant school and have always been intrigued with "power recovery" in all of it's forms.

    I spent some time working on using a high speed motor/generator acting on the turboharger's shaft and using power generation as the boost controller in which the ability to produce excess boost was drained off as electrical power which could then be used to accelerate the turbo in conditions where one would normally encounter lag.

    Of course, now there are working models being tested by large manufacturers.


    The problem with a lot of these is that they require a pretty steady state concerning rpm and torque production to be efficient so it's mostly long haul trucks or aero engines that benefit.
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