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Thread: 2013 FSUK

  1. #31
    Originally posted by Simon Dingle:
    Plus, an FS car can use a turbo to further expand the exhaust gas and therefore has another possible efficiency advantage. The turbo also gets you an added efficiency bonus in that you can choke the restrictor at lower engine speed and make your 90kW where the fritional losses are smaller.
    Turbocompounding is also allowed by the rules...
    Jan Dressler
    07 - 09 High Speed Karlsruhe / UAS Karlsruhe: Engine & Drivetrain Team
    09 - 10 High Speed Karlsruhe / UAS Karlsruhe: Engine & Drivetrain Team Leader
    10 - 13 High Speed Karlsruhe / UAS Karlsruhe: hanging around & annoying the team with random FSAE wisdom
    13 - ?? Gätmo Motorsport

  2. #32
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    From where do you have the ~35% efficiency of an F1 engine?? I doubt that number. For a gasoline engine this is a very high efficiency and I've never heard of such efficiency numbers at such high engine speeds. Unfortunately no F1 team will tell, what efficiency they really reach.

    And you should be aware that assuming stuff like isentropic mass flow in the restrictor is also quite an idealised assumption. I didn't recalculate your numbers, but they show quite nice how idealised all your numbers have to be to reach a power level which Z considers to be comfortably achievable.
    In 25 years of FSAE no team ever got near such a number. So if you REALLY want to tell this is "comfortably achievable" you should demonstrate it...
    Rennteam Uni Stuttgart
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    GreenTeam Uni Stuttgart
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    Formula Student Austria
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  3. #33
    Hi Bemo,

    I was slightly surprised myself, so I'm happy to be corrected if I'm wrong.

    I calculated the efficiency in the same way that I did for checking Z's 90kW.

    F1 are regulated to 2.4L displacement, 18,000rpm and normally aspirated. So that (roughly) defines the upper limit for mass flow rate of air (+5% for ram air effect at 300kph). I made that to be 378L/s or 463g/s of air.

    Assuming a lambda value of 0.9, the mass flow rate of fuel comes out at 35.2g/s. Gasoline's energy density is 46MJ/kg. So that works out to be 1621kW of chemical power.

    Mercedes AMG list their power as ">750PS" so that's about 547.5kW. One over the other is ~34%.

    I think my working is good, albeit with a few assumptions. Let me know if you think I've got anything wildly wrong.

    Cheers,
    Simon
    ----------------------------------------
    Powertrain Research Student 2010-2013

    Team Principal 2009-2010
    Engine Development 2008-2009
    Brunel Racing

  4. #34
    The math certainly looks solid, but I just don't see these two engine types as similar enough. There's got to be a reason an F1 engine costs >10x what your typical FSAE donor vehicle costs. Not to mention the design goals are entirely different. F1 engines are designed for peak power, and are strung out much, much closer to their absolute capacity than a usual FS engine, which is designed to be controllable by biker-Joe and last tens of thousands of kilometers without a rebuild.

    I could see a maximum efficiency closer to 30% as being reasonable, which with your math gives ~101bhp (76kW). The highest I've heard is around 95hp; of course it was an in-house dyno and all things considered is probably a lie, but never the less it is close. I really think the key here is that it's a maximum efficiency that we're looking at. Again, these engines aren't designed to stretch the maximums, and sacrifice peak volumetric efficiency for gains elsewhere in the RPM range.

    Back to the argument at hand, I agree that e-vehicles have a power advantage. The key thing though is the torque control. 100% of peak torque at 0 RPM is certainly useful, and I'm guessing the good electric vehicles control wheelspin with a smart PWM program on launch to make it even better. Tuning an engine for peak power and running a finely calibrated CVT (or IVT) seems to be the closest an IC car can get to this sort of thing.

    I would also argue about electric vehicles as a "dead end". Historically, they have not done well, but modern technology is quite an amazing thing. Plus, the general public see e-cars as "green", and I can guarantee you that if there's a market for something, it will be produced and sold, then improved and sold again. However, I definitely agree that choosing your vehicle concept to accomodate 10% of the points because it is trending is not rational. Right now, though, it seems that a well-made e-car outperforms a well-made IC car. I suspect rule changes will be coming if SAE intends to keep a single class.
    Owen Thomas
    University of Calgary FSAE, Schulich Racing

  5. #35
    Z,
    assuming you actually could get 90kW from an engine, who cares? Acceleration is won or lost at the starting line, long before you're power limited.
    Case in point: There have been plenty of high powered ICE cars at Hockenheim. In eight years not a single one got under 3.8 seconds, only 5 got below 3.9.
    Meanwhile, DUT12 only used 55kW, yet managed 3.45.

    Good luck coming up with a lightweight CVT and traction control that can match the smooth torque delivery of an electric motor right from the start.

    For FSAE, I don't really care how much air could theoretically flow through a restrictor. The extra 5kW compared to the max power of an electric car will not bring you anything in any realistic scenario. Of course in a world where combustion cars can apparently accelerate at >1.8G from start to finish line, reaching about 186km/h in the process (your claim of 75m being possible in 2.9 seconds), we can argue about that forever.
    Which I’m sure you will.

    Thijs
    Delft

    PS. On topic, Congrats to Zürich!

  6. #36
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    Kopito, Bemo, Stef de jong,

    You guys really are idiots! Which, very sadly, means you are well on your way to becoming perfectly typical Engineers; "Oh, no, no, no... That will never work! I know all about these things, you see, ... because I calculated it, and I are an Engineer!"

    Along with being a disgrace to your chosen profession, you apparently can't even read. I covered maximum power and the Acceleration event barely a month ago on the Michigan 2013 thread, starting on page 10.

    The really disgraceful part is that I am told that you students are nowadays taught some sort of subject called "Systems Engineering". This appears to be nothing more than a collection of bulldust buzz-phrases, intended to obfuscate what used to be a common sense approach to doing things. Anyway, one of the buzz-words is "Benchmarking", meaning nothing more than checking what others are doing, or have done (ie. "doing your homework").

    If any of you had done that, then you would know how much power literally thousands of other racecars, for many, many decades, have been getting through their restictors (or just read page 11 of above thread). (For anyone else interested, the power figures of the recent Le Mans cars will be coming out soon. Typically these are around 35 hp/sq.cm.restictor, for the 24+ hr, 5,000+ km engines.)

    And regarding the Acceleration event, if any of you can drag yourselves out of your ivory towers (or take time off from calculating Claude's 59+ Damper "magic numbers") and get down to your local dragstrip, then the toothless hillbillies there might be kind enough to educate you as to what is important in drag-racing. Ie, Learn the difference between TRACTION-LIMITED and POWER-LIMITED!!! (Bemo, a ~50kW car will "comfortably" do ~3.5s FSAE Acceleration runs. This is the simplest to understand straight-line Mechanics that is taught in secondary schools!!! )
    ~~~~~o0o~~~~~

    Simon,

    Here is a cut-and-paste from a post I sent someone a few years ago (the post also included the typical empirical figures).

    "My old textbooks give maximum (choked) mass flow through a nozzle as,

    M-dot = 0.0404 x AreaThroat x Pressure / (sqrt(TempKelvin)) kg/s.

    There are other equations, but this one is in terms of easily measurable atmospheric pressure and temperature. This gives,

    Mass-flow/sq.cm-restrictor = 0.024 kg/s (same as your weblink).

    Good quality (ie. racing) gasoline fuel has energy-content = ~47 Mj/kg, and stoichiometric air/fuel ratio = 14.7, giving,

    Power/sq.cm-restrictor = ~77 kw x overall-engine-efficiency.

    So with ~35hp/sq.cm, ie. 26kW/sq.cm, efficiency = 26/77 = 34%.

    Or with ~40hp/sq.cm, ie. 30kW/sq.cm, efficiency = 30/77 = 39%.

    The 34% figure is quite believable, given that these engines have very high compression ratios (13-15+:1), and are built with minimal internal friction.

    The 39% figure also makes sense as a practical limit for four-stroke SI engines."


    So, pretty much the same as your calcs. The biggest variables are fuel-energy-content + stoichiometric-ratio for the given hydrocarbon fuel, and overall efficiency (although cold days also help a bit).

    If FSAE really wants to encourage good engineering, then they should allow all types of combustion cars, especially two-stroke diesels (as you mentioned). Then the E-cars really would "not stand a chance"!

    Z

    (Edit: Just saw last post. Thijs, you are right about "at the start line" vs "power limited" (about time someone gets it!). Now if you go and talk to some of those toothless hillbillies at the drag-strip, then you might learn how to get below 3 seconds (although I have already explained that...).)

  7. #37
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    Originally posted by Owen Thomas:
    Right now, though, it seems that a well-made e-car outperforms a well-made IC car. I suspect rule changes will be coming if SAE intends to keep a single class.
    I've talked with SAE CDS staff, they have no intention of running the e-cars with the c-cars in North America. The two competitions that I know run the two classes together are FSUK and FS Austria (the later otherwise known as FSNK: No Kangaroos)

    FS Austria started as a combustion competition in 2009, then let e-cars enter and run with the c-cars in 2011. I think the single class at FSA is mostly convenience.

    FSUK, on the other hand, had two classes until 2012: class 1 "c-car" and class 1A "all other" (ignoring class 2 for the sake of this discussion). IMECHE made a conscious decision to combine two existing classes, with the caveat that both classes would remain competitive. I disagreed with that decision in 2011, and I disagree now. I agree with Bemo and Luniz, combining classes is nonsense and changing the rules every year to advantage or disadvantage one set of cars or another is inconsistent.

    On the other hand, GFR builds both an e-car and a c-car. So if we ever return to FSUK in the future I guess we can go with the car that the rules advantage that year.
    Bob Paasch
    Faculty Advisor
    Global Formula Racing team/Oregon State SAE

  8. #38
    Originally posted by Z:
    Kopito, Bemo, Stef de jong,

    You guys really are idiots! Which, very sadly, means you are well on your way to becoming perfectly typical Engineers; "Oh, no, no, no... That will never work! I know all about these things, you see, ... because I calculated it, and I are an Engineer!"
    That's classy...anyways I won't argue with you about your tone, because as I am an Idiot, I am wondering, why, if you are so smart and know so much, you have so much time bashing "us students" (which most of us aren't anymore btw).
    Two suggestions:
    1. Get a job, and put your "tremendous" knowledge into use. I am stunned that somebody who is so smart, that he calls three people, that have all been responsible for some of the fastest FS-Cars from the past 5 years "idiots" (with regard to FS), still has the time to "live" in this forum... go on get that nobel prize!
    2. PLEASE build a FS-Car!!!! (or have some of your underlings do it, as I am sure you have some, the way you talk down to "us students") If you do that, and it achieves all those goals that you describe as "comfortably" achievable, I'll come to Australia and watch it. I am sure Bemo and Stef will join.
    AMZ Racing ETH Zürich
    ------------------------------
    2012 - now cranky old guy who knows everything better
    2011 - 2012 Team Leader
    2010 - 2011 Suspension

  9. #39
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    Definitely I would love to see that car!

    BTW I'm not a student anymore (I took part in the competition three years ago. Right now I'm working for Porsche Motorsports and am involved in this year's Le Mans car you are so looking forward to see the power numbers

    Just comparing the ratio of power and restrictor area is quite a tremendous simplification as you loose quite a lot of mass flow near the restrictor walls. This effect is much bigger for smaller restrictors like in FS.

    BTW: I'm not sure what Kopito's position in his team was. But you're definitely the first one calling two former team captains of winning teams idiots within one sentence.
    We showed up with our efforts and competed (and won). What have you done?

    "I know all about these things, you see, ... because I calculated it, and I are an Engineer!"

    Funny you are critising others with these words. We have built something. You're the one who just tells others what is possible and what you have calculated.

    Build that 90kW C-car which is doing acceleration runs in 3.0s. I promise, I will come to Australia and all your drinks are on me for a month if you manage to keep your promises.
    As all this is "comfortably achievable" I don't see any reason, you shouldn't do this.

    And to get back to topic: Congratulations to Zürich, really nice job, although according to Z it was quite simple as all the others (without any exception) are just morons.
    Rennteam Uni Stuttgart
    2008: Seat and Bodywork
    2009: Team captain

    GreenTeam Uni Stuttgart
    2010: Seat and Bodywork / Lamination whore

    Formula Student Austria
    2012: Operative Team

  10. #40
    Z,

    Of course when I said ‘Combustion car‘, I meant ‘FSAE (combustion) car’.
    I’m aware of what top fuel dragsters can do with their >5MW engines, but I didn’t think you would really draw that parallel. Fun fact: apparently these things create 3.5kN of downforce from standstill from their upward directed exhausts alone.
    Since you’ve repeated the 2.9 seconds claim on multiple threads now, I’d like to press you on it though.

    Consider the following car:
    -65% rear weight (that’s your number)
    -Wheelbase 1525 mm (I wouldn’t want to take a slalom in a top fuel dragster)
    -CoG height at 260mm (that’s fairly generous)
    Now comes the good part:
    -Its tires somehow have unlimited traction
    -90kW available at the wheels whenever you want it
    -It does not suffer from mundane things like drag. All this power goes purely into accelerating the car
    -200 kg including driver

    Unless you propose wheelie bars, this thing will simply fall over at accelerations over 0.35*1525/260=2G, so let’s take that as our continuous acceleration up until the point where we’re power limited.

    You can write your own code, but take it from me that this car will cover exactly 75 meters in 2.9 seconds, crossing the finish line at ~164km/h.
    Are you suggesting this is a car that can actually be built?

    Anyway, I’m off writing mr. Royce an email asking him to consider introducing nitromethane.

    Thijs
    Delft

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