Rotary engine breakthrough (?)

Discussion in 'Mazda Rotary' started by Pale Bear, Sep 27, 2013.

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  1. Sep 27, 2013 #1

    Pale Bear

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    Hello all,

    As far as I can tell, there has been no mention of this Mazda rotary engine modification on this forum, yet.

    I'm curious to hear what anyone of you has to say about this.

    Especially, the 2nd mod of his, the "combustion chamber offset". If this is as good as it looks ...

    Here's the link, ... Rotary Engine Breakthrough? - YouTube

    Thanks, everyone.
     
  2. Sep 27, 2013 #2

    Aviator168

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    No.
     
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  3. Sep 27, 2013 #3

    Hot Wings

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    Probably not real significant developments, though they do seem logical. His explanation of the offset doesn't seem valid to me because the combustion chamber pressure distribution is unchanged. As long as there is area over the trailing half of the rotor that is connected to the leading half the pressure will equalize at the speed of sound.

    That doesn't mean there is no benefit from his modification. There very well could be benefits similar to those gained by increasing the squish area in a piston engine.

    The only way to verify his claims would be with comprehensive and systematic dyno testing.
     
  4. Sep 27, 2013 #4

    Aviator168

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    Mazda did tried those two. Making the hole for the spark plug small does not help where as the offset compression induces vibration on the rotor. The problem with the wankel is the moving flame front, cooling and lubricating of the seals.
     
  5. Sep 27, 2013 #5

    Hot Wings

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    If Mazda did try it then there is a reason they didn't adopt it. They seem to be wiling to look at just about any option to improve their engine.
     
  6. Mar 9, 2014 #6

    SHIPCHIEF

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    I was talked into opening up the upper spark plug hole (trailing plug) to improve redundant combustion in the event of a leading ignition failure. It may have been responsible for a compression stroke detonation that blew out the side of the case. The pressurized flame from combustion can jump the large hole back into the compression chamber and light it off. That's why the trailing plug hole is so small that the tip seal can fully cover it.
    As for the face of the rotor, the dish needs to hold the main fuel charge in front of the spark plugs. The greatest benefit would be direct fuel injection, so the fuel could all be in the chamber and not squeezed into those heat absorbing ends near the tip seals, which remain unburned hydrocarbons, the cause of poor efficiency and bad emissions.
     
  7. Mar 10, 2014 #7

    wizzardworks

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    Oh well, wrong on both points. At the point where the apex crosses the leading plug hole compression has barely started so ther is nothing to force mixture through the depression
    to the exhaust chamber. On the other hand there is still some pressure in the expansion stroke which would be at a higher relative pressure than the compression side that could
    migrate back to the compression chamber. The exhaust pressure at this point is mostly spent and not much higher than the exhause back pressure so very little back flow.
    The second point about offsetting the combustion recess to increase torque is at best stupid. What it would accomplish if it worked would be to try and spin the rotor on the
    rotor bearing. The eccentricity of the shaft is the stroke of a wankel and that is where torque is generated. The stationary gear meshes with a gear inside the face of the triangular
    shaped piston. This internal gear is a sliding fit and relies on 6 tiny roll pins to keep it in time with the stationary gear. If something tried to spin the rotor those tiny roll pins
    would have a bad day.
    Mazda used 3 spark plugs on the car that won Lemans and the two previous attempts at Lemans. While fitting a third plug could be an improvement the better route woul
    be a multistrike capacitive discharge ignition on the leading plug fireing 10 or 12 sparks before reaching the trailing plug rotation. Paul Lamar is developing such a system with
    30 sparks for aircraft installations. Mazda has a laser ignition running on their current dyno rotary which was developed while they were operating with close ties to Ford who
    also is testing this technology. The result is continuous ignition during the combustion cycle through the entire charge.
    wizzardworks
     
  8. Mar 11, 2014 #8

    Geek1945

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    I often wondered if with today's technology like multi-injection direct injection to tightly control the combustion flame front coupled with laser/plasma ignition and Orbit air injection might do much to reduce the Wankel engine problems. The Wankel engine reminds me the flying wing concept which had to wait till technology made it practical. There is always a heavy penalty when introducing new ideas with the "I'll wait and see" being typical. Meantime always present financial pressures to being new ideas to market often force product to market before fully developed (i.e. software).

    As an owner of a RX-4 I recall just how vibration-less the rotary was not suffering from torsion vibrations and reciprocating engine inherit problems. Oh my, the RPM's without complaint along with torque Zoom Zoom. Consider many motorcycles had more displacement than the rotary yet, it competed well against much larger piston engines. >>BUT<<

    Being 'different' also plagued the rotary, remember GM's air cooled Corvair vs. Nader, chrome plated aluminum bores (recall GM's Vega), special tooling required (i.e. introduction of disk brakes), Opel's cam-in-head engine, VW CIS fuel injection, and oil injection did much to demise of Mazada's efforts.

    Looking at my son's W12 bi-turbo engine with 3 cams per cylinder bank, I wonder how a W6 or W8 engine might look. One ride in a W16 quad-turbo engine closely approaches a 2 bank rotary in smoothness of course displacement is vastly greater. Note: For me 100 mph+ in a ground vehicle, or 55knts in water, is plenty fast for this old fart! Yet, when we compare today's W16 to Andy Ganitelli's axial turbine designed in the late 1950's it's easy to see why only small aircraft have piston engines which remain essentially unchanged.

    Considering the power to weight, even the remaining 2 strokes would have a difficult time competing not to mention their emissions, seizing, and detonation problems. Only time will tell if the Wankel engine problems will be resolved or a new concept will replace the status quo with improvements will continue dominate.
     
  9. Oct 28, 2016 #9

    Billrsv4

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    Couldn't let this be the last comment on a rotary thread. This post has so much hearsay and misinformation. Nader was wrong, the Vega didn't have chromed bores, they were 390 aluminum. The rotary is very reliable in both it's current and previous incarnation. Direct injection will help the rotary in cars. It will improve fuel economy. In aircraft the rotary is in a better environment. The harder you run the rotary the better it works. It is very competitive at 50-100% power levels. I believe the rotary makes a better aircraft engine than a car engine!
    Bill
     
  10. Nov 28, 2017 #10

    PMD

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    Couldn't agree more, and if you will allow, I would like to expand on your comment. Corvair was far more than just another design. The element that made it such an easy target for the ambulance chaser Nader was its "swing axle" single jointed rear suspension and rear weight bias - a design feature shared with all VWs and some other contemporary Euro cars including Porsche. Year-for-year, Corvairs had greater cornering ability than Corvettes. What they DID do, was lead in "unibody" construction, that allowed cars around the world to be far, far better in passive safety than body-on-frame could accomodate.

    Side note: the Reynolds 390 aluminum system used in Vegas was intended to be used in the cylinders of Corvairs, but the technology was not yet ready for prime time. An alternative goal was to sell the engine into the genav market against O-200 Continentals. Vega engine failures were not due to the bore material, but difficulty in sealing the flexible open deck against the hastily re-designed cast iron cylinder head. The etched bores went on to dominate the CanAm series (until the 917K came along) and the whole programme was sold on to Thunder engines, again to Orenda to become the certified OE600 that is today produced by Trace (not sure if the 390 bores are still used, though).

    The whole Corvair thing reminds me of what my mentor in the thermal spray business used to say: "You can always tell the pioneers by the arrows in their backs". Ed Cole must have looked like a porcupine.

    BTW: I believe gasoline is a foolish fuel for aircraft use, and the future lies in kerosene. Rotaries have a place there because they are truly multi-fuel capable, and when developed for that purpose, should do very well as some kind of catalytic and/or compression ignition engine.
     
  11. Nov 28, 2017 #11

    tspear

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    Can you explain the moving flame front problem? That is the first I have heard of it.
    Lubrication I think I follow, and has been an issue for a long time.
    Cooling issues from my very primitive understanding are caused by three factors. One, lack of expansion so less thermal energy converted to mechanical which leaves mroe heat in the engine and the exhaust. Two, more combustion events by displacement in a specific interval. Means more heat... Third is the lack of "piston" cooling by oil in the galley to pull heat away from the cylinder.

    Did I miss anything?

    Tim
     
  12. Nov 28, 2017 #12

    tspear

    tspear

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    I like the idea of burning kerosene. But why is a rotary any more practical for a multi-fuel than any other engine?
    Also, how do you solve the efficiency problems of the rotary?

    Tim
     
  13. Nov 28, 2017 #13

    PMD

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    I will have to defer to the actual combustion experts, but my understanding is that as a piston port engine with a lot of quench area, detonation is either less likely and/or far better tolerated. Not that all alternative fuels are prone to detonation but jet fuel certainly can be.

    To make jet or diesel work, though, you need to do one of two things: use catalytic ignition on an aspirated charge, or start the engine on aspirated charge or spark assisted direct injection, but get some boost on right away to switch to compression ignition. Modern diesels can have pretty decent efficiency, part of which is due to the ability of HPCR (high pressure common rail) piezzo injectors to fire a nice little "pre shot" into which all subsequent injection events occur. This allows "rate shaping", i.e. tailoring the delivery of fuel to shape the BMEP curve to look like whatever you want - something spark ignition engines can not do. What is missing is the understanding of how the airflow within the combustion chamber should look and be optimized for compression ignition. Piston engines have a shape in the crown that makes a nice torroid, whereas rotaries have a "moving target" that needs to be optimized for best propogation. That geometry plus firing into the preshot fireball means atomised fuel burns before it can contact surface of the piston (or in this case rotor).

    (on edit) I should embellish a bit: the limit of spark ignition engines is their aspirated charges detonating at cylinder pressures far too low to be efficient. The beauty of compression ignition is that the very high cylinder pressures needed for efficiency, and the high temperatures within the cylinder that would detonate an aspirated charge are simply not there in compression ignition, as the fuel has not been introduced - and it wants to burn (NOT detonate, as diesels actually can do that) that is easily accomplished with modern HPCR with digital control of piezzo direct injectors. The things that limit SI engines are the things that CI needs to be more powerful and efficient. That should be able to plug the efficiency hole in rotaries quite well.
     
  14. Nov 28, 2017 #14

    rv6ejguy

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    What do you consider "low"? In 2016 production SI engines from Toyota exceeded 40% thermal efficiency. Production CRs are now up to 14 to 1 on these engines.

    The new 2.3 Ford Focus turbo engine makes 350hp from 2.3L on pump gas with a 10 to 1 CR.

    The OEMs are still making gains every year in reduced BSFC and specific hp output on SI engines.
     
  15. Nov 28, 2017 #15

    tspear

    tspear

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    Look at Nissan "Skyactive" technology. CI engine with gas (although they call it something else and has a super narrow range).
    From every discussion I have seen/read, higher compression ratios are the single largest factor in improving efficiency in engines. Gas, diesel or otherwise. This is why the bleeding engine designs are now moving even gas to a continuous or multi-squirt injection; the same as diesel.
    Historically diesel ran with a higher compression, and in many cases still does today. But that may not hold much longer; e.g. Skyactive.
    Further, most multi-fuel solutions have failed on the efficiency benchmarks because they are after good enough and are not tuned for a specific fuel.

    Even with all those random points, I still do not follow why/how the flame front in a Wankel causes problems compared to a traditional cylinder.

    Tim
     
  16. Nov 28, 2017 #16

    rv6ejguy

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    Slight correction, Mazda developed the Skyactive engines. All the Japanese OEMs now offer similar or higher CRs and technology now on production engines.
     
  17. Nov 28, 2017 #17

    tspear

    tspear

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    Oops. You are correct!

    Tim
     
  18. Nov 28, 2017 #18

    PMD

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    As does the CI world. However, heavy distillate fuels have more energy density vs. volume, CI is not limited by ultimate cylinder pressures at all and one is not riding a napalm bomb to the scene of the crash. We are very unlikely to get FADEC direct injection SI technology in genav before most of us die off, but we WILL get (and can right now) CI engines that make SI stuff currently installed look exactly like what it is - half century out of date boat anchors.
     
  19. Nov 28, 2017 #19

    rv6ejguy

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    Ah but those boat anchors with 10-12 to 1 CRs, when equipped with EFI/EI are capable of showing BSFC figures almost the same as the current crop of aero CI engines. One of our testers is showing better than .36 running LOP in cruise.

    daveanders.jpg

    EFI Lycoming 360 in an RV4. 6.2 gph (37.2 PPH) truing 197mph.

    The flash point of diesel or jet fuel is well below the exhaust temperatures in CI engines. Jet aircraft burn really good when they crash too. That's a weak supposed advantage IMO.

    In North America, the CI aero engines currently available show no reduction in overall costs per flight hour mainly due to their high initial and maintenance costs: http://www.aviationconsumer.com/iss...t/Diesel-Reset-Improved-Economics_6962-1.html

    CI engines are not detonation limited but they certainly are limited by the physical strength of the engine. I don't see any CI engines approaching the 1000hp/L specific outputs that SI race engines achieved 30 years ago.
     
    Last edited: Nov 28, 2017
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  20. Nov 29, 2017 #20

    rv7charlie

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    Ross, While I agree that Anders' -4 is very efficient, and a/c engines are a lot more efficient when using properly tuned electronic engine control/injection (and you should get a lot of the credit for that), I think it's a bit of a stretch to claim any particular BSFC number for an engine that's actually flying on an a/c. Way too many variables; especially the efficiency of the airframe itself.

    On various rotary issues:

    1st, everything's a compromise. Real world experience with rotaries in a/c indicate that they are at most, ~10% less efficient than a more or less stock Lyc, if the Lyc is properly leaned (which the vast majority of Lyc drivers are afraid to do, because they worry about burning valves). In actual operation, they are often within 5% -- equal to a Lyc. I'm personally acquainted with a Renesis powered RV-7A that flies regularly with a 180 HP Lyc powered RV (-8, if memory serves), and flying the same profile on the same day, they pump the same amount of fuel at the end of the flight. Now, the 180 Lyc requires, at the very least, premium ethanol-free auto fuel, and Lyc would tell you to burn only 100LL. The rotary, on the other hand, is happy on whatever off-brand 87 octane mogas you can find; ethanol is fine, and even lower octanes are ok, too. So do the math. Lets assume the rotary is 10% less efficient in terms of BSFC. Do the math on the price spread between 87 octane mogas in your area, and 100LL. Which is more efficient on your wallet? Can you adjust your flight leg length by 10% to take that spread on fuel cost?

    On heavy fuel rotaries: There are already a few out there, but they are typically for military/intelligence operations. Some (most?) are actually spark ignition, even though they're using heavy fuel. One real limitation of rotaries is that it's difficult to get static compression as high as a piston engine. That's due simply to the geometry of the combustion chamber. It's just difficult to manage very high static compression given the shape of the combustion chamber seals, so a 'traditional' compression ignition rotary is difficult. In more general terms, the attractiveness of heavy fuels has more to do with availability and safety, than efficiency. The military *hates* having gasoline around, not because of flight safety, but because of *ground* safety. And they hate having to manage two fuel supplies. They're kinda not wrong; our lives would probably be a lot safer if we didn't have to play with gasoline.

    On flame front & moving combustion chamber: Maintaining flame front is a bit tougher in a rotary, but not a significant factor. In cars, running low power levels & low rpms, multiple spark plugs with 'spread' timing help complete combustion. Flying rotaries have discovered that there's little advantage in 'spread' timing, but using two plugs in each chamber do help with combustion, just like they do in large bore Lycs/Conts. (Mazda actually used three plugs per chamber in their Lemans-winning 4-rotor engine.) A bigger factor related to the 'moving combustion chamber' relates to point one, above. Spreading the combustion heat around so much combustion chamber area does impact fuel efficiency (but again, not as much as you might think).

    Charlie
     

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