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Combustion in auto engines

  1. Sep 6, 2011 #1
    I want to find papers of studies done on combustion in automobile engines. I know there was a lot of work doine on this, unfortunatelly I cannot find ANYTHING. If I type "combustion in engines" in the search field of any journal/search engine, I get completely unrelated junk.

    I'm looking for experiments for things such as piston shape, head shape, combustion timing etc. People have tried to maximize the work done on the piston from the combustion reaction the entire time, and I want to know more about it (what was tried, what works, what doesn't, etc).

    I was thinking of studying this type of thing myself for graduate studies, but I need to know what has been done first, so I don't try to repeat experiments that were already done.

    Thanks in advance.
     
  2. jcsd
  3. Sep 7, 2011 #2

    SteamKing

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    I would recommend you try the various professional societies dealing with auto design, like the SAE in the US or the IMechE in the UK. Also, try to limit the scope of your searches, so you are trying to find info on spark ignition engines or compression ignition engines. If you use a specific term in the search box, like "valve timing in SI engines", you probably will get more relevant hits than the more general "combustion in engines".

    Given the number of engineers, mechanics, and back-yard tinkerers working on IC engines over the past century, I would be surprised that you DIDN'T duplicate something someone else has already tried.
     
  4. Sep 7, 2011 #3
    Buy John B. Heywood - Internal Combustion Engine Fundamentals.

    It goes quite deep, you'll never find a paper on combustion in engines because it's too broad a topic.

    Also you'll find that pretty much everything has been tried already. There really isn't anything new to discover about the IC engine. When you read about some new revolutionary peice of engine design, and then realise the idea was thought up 20 years (nominal figure) after the engine was first invented. Almost all development now comes from materials science or control systems, which allows engineers to implement the old ideas.

    EDIT: Basically, what Steamking said.
     
    Last edited: Sep 7, 2011
  5. Sep 7, 2011 #4
    Sounds like you already have a few questions, maybe we can answer them and save you some search time.
     
  6. Sep 8, 2011 #5
    Yeah so I just thought up some ideas I could research but I just want to see things that were already done, that way I can avoid repeating (wouldn't be "research" if it was done already).
    This way I can move on and think of something else. But I need to apply for grants/fellowships etc. so I got to figure this out pretty soon, that's why I was asking if there is some resource that documents such things.

    SAE has a bunch of papers on ceramics and BS like that; I'm more interested in the dynamics of the combustion with application of maximizing force on the piston (could be a rotary piston, not necessarily the cliche cylinder).

    xxChrisxx I took a look at the table of contents of that book and the last few chapters look really good. Thanks a lot. Any resources are welcome and appreciated.
     
  7. Sep 8, 2011 #6
    The force acting on the piston (or rotor) is psi times the effective surface area. For a given bore size, that leaves only the pressure in the chamber; maximizing the force means maximizing the pressure.

    Sounds simple but isn't (obviously); what things are you wanting to research? Maybe we can point to more specific reference material.
     
  8. Sep 9, 2011 #7
    rofl, the simple "pressure X area = force" formula is true for EQUILLIBRIUM situations only. During the 1ms combustion reaction, the gas is obviously not in equilibrium.

    That's what I want to study.
     
  9. Sep 9, 2011 #8

    cmb

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    It sounds like what you really need to read up on is fluid flow in pistons - swirl, stratified flow, variable stoichiometry, piston crown shape, valve timing. It's not surprising that you cannot find a really 'general' paper on IC engines. As mentioned, refine your question, be more specific, and there might be a better lead to offer you.
     
  10. Sep 9, 2011 #9
  11. Sep 9, 2011 #10
    Actually the "pressure X area" describes the force that is acting on the piston at any given instant; no equilibrium required. It is the cumulative net force that determines the output of the engine. Getting the highest average net force (BMEP) acting on the piston during a complete combustion cycle is the name of the game.

    Maybe this will be along the line of what you're looking for:
    http://www.circletrack.com/enginetech/ctrp_1004_engine_development_cylinder_pressure/index.html

    Or:
    http://www.epi-eng.com/piston_engine_technology/bmep_performance_yardstick.htm
    If not, there are addition articles in the sidebars of each article.

    Hard to know what you're really asking for and where you're presently at with your understanding of IC engines, so a little feedback would help.
     
    Last edited: Sep 9, 2011
  12. Sep 10, 2011 #11
    Say, what now? And what happens at a single point in the combustion process matters... how?
    See above, Mender is right, you are wrong.
     
  13. Sep 10, 2011 #12

    Ranger Mike

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    Mender, great article by Jim Mcfarland,,I have read him for over 48 years..he is up there with Smokey Yunick , Duntov, imo
     
  14. Sep 10, 2011 #13
    Yes, I've also watched for his writing, always informative and clearly presented. Also like David Vizard for his clarity and thought processes.
     
  15. Sep 12, 2011 #14
    The only pressure that matters is the one on the boundary of the piston. What goes on elsewhere in the combustion chamber is irrelevant. So I guess that is my question, does the pressure vary with spacial coordinates in the combustion chamber, and if so, how (is it significant, at any point in time?).

    Piston crown shape, yes. That is what I was looking for too. I didn't know the name, that's why I have trouble searching for papers. I was never looking for a "general paper", on the contrary, I want HIGHLY specific papers.

    I'll see what I can find now that I got better keywords to type in the search. Thanks everyone.

    Update: Nope, haven't found anything. My googling skills must be really bad, all I found was this:
    http://www.metacafe.com/watch/1755655/engine_piston/
    but it has no information on the theory. What is the reason for making bowl shaped piston crowns?
     
    Last edited: Sep 12, 2011
  16. Sep 13, 2011 #15

    Ranger Mike

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    Curl
    Your initial post stated that you were interested in the the piston shape, head shape, combustion timing etc. Then you totally disregard what goes on in the combustion chamber. What the hey hey??? This goes contrary to basic problem solving and brain storming.

    You also stated you were trying to seek government grants/ fellowships etc.. to explore this area. OK..

    Is this an inquiry for the purpose of securing a grant or is it an endeavor to understand the combustion process?


    I think a bit of reflection and thought toward the goal would help. Specific, time bound, obtainable and measurable statement of your objective would help us help you.
     
    Last edited: Sep 13, 2011
  17. Sep 13, 2011 #16
    Looking at a an indirect injection spark ignition engine is flogging a dead horse anyway, there's just nothing else to be learned. It's all a boring optimisation excersise.

    The advancements now are high pressure direct injection, stratified charge and lean burn. Making petrol engines run more like a diesel.
     
  18. Sep 13, 2011 #17
    Some factors in deciding the shape of the piston crown are the valve angle and placement, which determine the shape of the combustion chamber in the head, and the desired compression ratio.

    The majority of gas engines use a flat-top piston and shallow included angles on the valves (wedge heads and modern 4 valve heads), and the compression ratio is adjusted by varying the depth (and thereby the volume) of the combustion chamber. This basic configuration, along with a mostly central spark plug location, gives a relatively efficient burn by allowing the flame front to smoothly progress through the fuel/air mixture. A fast consistent burn that reaches all the outer edges of the chamber at the same time is the goal.

    By having flat surfaces on the piston that match flat surfaces on the head and having the piston almost touch the head at TDC, turbulence can be generated to stir up the burning mixture and give faster more complete combustion. This is called squish or quench, and helps ensure that no pockets of the mixture lag behind the main burn. These pockets can either end up unburned or can cause the engine to be sensitive to detonation, both conditions lowering efficiency and raising emissions and the later possibly causing engine damage.

    If a domed piston is used in a large chamber to get the compression ratio desired, the dome can temporarily block off some of the flame front and cause erratic and incomplete combustion, as described in the first article I linked. For example, a head with steep angles between the valves (old Chrysler Hemi) has a large combustion chamber and requires a large dome to get the compression ratio up. The burn on these engines is not very consistent or efficient so is not well suited for low emissions. The popularity of the Hemi at the time was mainly because the ports flowed well and the engines were able to make a fair bit of power for their size.

    A current rule of thumb for present engines is that a dome of more than about 0.150" is going to start causing problems and costing horsepower. This is more of a concern with engines that are used for the higher levels of racing where every bit counts but should still be considered when deciding on a particular engine package.

    On the other side of things, the Ford 1600 cc Cortina GT engine is an example of a successful racing engine that used a flat "combustion chamber" and a piston with a large dish. It was the mainstay of Formula Ford for several decades, mainly because of its rugged design and reasonable cost. The central dish allowed for a decent consistent burn and had a squish ring around the perimeter of the piston to also help the burn.

    The power was good for the day ('60s) but the straight-up valve design required for the flat head limited the port flow and cam timing and thus power. These limitations are why gas engines are not designed to use pistons with large dishes; most modern 1600cc engines produce considerably more than the 110-115 hp that the GT engine made in race trim, and are much cleaner as well.

    Large domes or dishes expose more surface area of the piston to the high combustion temperatures generated, requiring more cooling to keep temperatures reasonable and wasting heat that otherwise could power the vehicle. As a result, both extremes are avoided unless a particular shape has a benefit that offsets the heat loss.

    Did that help?
     
    Last edited: Sep 13, 2011
  19. Sep 13, 2011 #18
    Here are some names you should look for besides the SAE papers. Look into patents and read them if you come across a related piece.
    Charles Fayette Taylor
    Sir Harry Ricardo
    Larry Widmer - check out his Soft heads article that debuted in the mid 80's
    Smokey's Hot Vapor Engine is a good example of fuel conditioning (its a very simple machine)
    Jim Mcfarland has some great articles on reading burn patterns and other combustion topics
    I haven't looked for what Darin Morgan of Reher Morrison Racing engines has as far as combustion. Air flow, as some call it the working fluid, has a direct hand in how our combustion process occurs and how efficient it ends up.
    Michael May from Switzerland I believe. I haven't gotten to read any of his work yet.
    The list goes on, but I can't name much off the top of my head right now.

    Studying lean and rich burning rates is a long topic in itself. Combustion is pretty wicked!

    The list of designs/theories tried is probably so great, your brain might just be in overload trying to think what has not been tried.
     
  20. Sep 13, 2011 #19
    Just look at engines throughout the years as far as chambers and pistons used. There is an immense amount.

    The stuff that doesn't or didnt work probably isn't able to be found unless there is some shelf untouched collecting dust or in the recycling I am sure. The past designs are out there for everyone to see you just have to find them.

    Pressure is the result of combustion. WHAT HAPPENS IN THE CHAMBER IN ALL AREAS MATTERS.

    Mender wrote
    Squish is the action done by the piston
    Quench is the area its done at which is the cylinder head

    If these are too weak or too strong combustion will not be optimum! Another aspect many overlook are the crevice volumes of the combustion space.

    EDIT: Research lean and rich A/F mixtures burning rates to begin your pursuit for your goal. Have fun with it.
     
    Last edited: Sep 13, 2011
  21. Sep 13, 2011 #20
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