Talk:Wankel engine

Misinformation about oil changes

Article suggests that because some Wankel Engines don’t expose their oil to the combustion chamber there is no need for an oil change. This is misleading because oil breaks down with heat and oxidation so that even in ideal conditions it is still going to require oil changes as that oil breaks down with time. 174.246.130.111 (talk) 17:25, 29 March 2022 (UTC)

An example an Audi NSU RO80 need no oil change. The oil is only topped up and the oil filter is changed from time to time.--HDP (talk) 12:00, 16 May 2022 (UTC)

Depending on which oil. Fully synthetics last and last if not contaminated. Wisdom-inc (talk) 16:31, 25 November 2022 (UTC)

Balance in lead

For some reason, this article reads like Popular Mechanics back in the 1970s, which I still vividly recall. This was the engine of eternal promise, set to toss the piston engine onto the junk heap. All of those glowing articles spoke at length about the reduced complexity and the other conceptual assets, before doing a deep dive on the perplexing and nonintuitive mechanical geometry. Just now, on YouTube, I revisited this topic, and in the space of 30 minutes learned more about the real trade-offs than every darn thing I read from the mid-1970s to the mid-1980s combined (it was covered regularly). Without even getting into the perpetual thermal gradient while requiring such tight tolerances, we could at least be honest that this engine poses some deep challenges which factored into its failure to unseat the traditional piston engine in the promised timeframe, pretty much over its entire existence.

Perhaps we could have rolled up our sleeves long ago and invested a billion dollars to make this the perfect replacement engine for all applications. But that's not how technology works. What happens is that something good enough becomes established, and is then polished relentlessly over many decades, which is why novel technologies often need to outperform incumbent technologies by an decimal order of magnitude (10×) on some key figure of merit to gain enough capital investment to make the grade.

Here's a quick pass to bring balance back into the lead:

Compared to the reciprocating piston engine, the Wankel engine has more uniform torque; less vibration; and, for a given power, is more compact and weighs less—though combining high power with long service life often entails poor fuel efficiency and a problematic emissions profile, especially when running on gasoline. Ongoing research seeks to mitigate these disadvantages. The most direct solution appears to be switching from gasoline to a faster burning, cleaner fuel such as hydrogen. For hydrogen, designs would need to target applications where low volumetric density of the fuel tanks is not a problem. For specialized applications, such as loitering munitions, the reduced complexity, compact size, and high power of gasoline-powered Wankel engines easily outweighs concerns over fuel conversion efficiency (more than repaid by improved aerodynamics), service life, or emissions profile.

Then it continues on with the Popular Mechanics version of the world, as before. The sad thing here is that the lead obsesses over the internals because the design has never achieved huge success, and so there isn't a long list of rave accomplishments to forestall the deep technical dive.

I'm sure my quick cut could be improved immensely, but that's my two cents, and now I'm off to other pastures. — MaxEnt 08:13, 14 October 2022 (UTC)

Just about all the negative aspects of the engine have been solved. The article points out the improvements. Patents and the likes acts as a barrier to the merging of the improvements into one engine package. What has emerged is that the engine is best suited to constant speed generator applications and running on hydrogen. The article does cover these two points, although it does not throw it into your face.

Japan is moving to a hydrogen society (few 100% battery EVs come from Japan), aiming to produce hydrogen in gas cooled nuclear reactors (helium as it reaches 1,000C which ideal and efficient for cracking water into hydrogen). Info on Youtube on this advance - two bit de vinci. Mazda are 100% certain to introduce in March 2023 the Mazda MX-30 rotary hybrid with the rotary turning only a generator, running at a constant speed. The rumour is that it is easily converted to hydrogen then being 100% clean in emissions. So, the rotary may have met its niche after all this time. Once more info on Mazda's hybrid rotary is available on hydrogen running, the article should present this, highlighting a new role of the rotary on road vehicles. Wisdom-inc (talk) 15:21, 19 November 2022 (UTC)

Restructured article

Information was scattered about. for example, motorcycles was in two separate sections. I restructured the article added sections and merged text from differing sections. Now it is more readable. Wisdom-inc (talk) 15:07, 19 November 2022 (UTC)

Wankel or rotary

@Wisdom-inc: I've reverted (most of) your recent changes of "Wankel" to the more vague "rotary", as "Wankel" is used purposefully in this article to avoid confusion with other types of rotary engines. While you're welcome to disagree with me, this has long been this way in the article, and really needs to be discussed before being changed again. Thanks. BilCat (talk) 01:52, 21 November 2022 (UTC)

I have no problems with that. But the manufacturers do call the engine a rotary. Wisdom-inc (talk) 02:02, 21 November 2022 (UTC)

And so do the myriad fan-people who occasionally show up at Rotary engine or its talk page to tell us that the article is incorrect! BilCat (talk) 02:05, 21 November 2022 (UTC)

Article re-structured

After years of additions and deletions the article was all over the place. I greatly re-restructured and tidied it up, making it easier to read an navigate thru. The contents page shows it is now easier to navigate. The disadvantages appear to have been largely eradicated on the engine, with some disadvantages now largely myth, so this may need some work. Wisdom-inc (talk) 13:48, 4 December 2022 (UTC)

Splitting article

I has been suggested that the Cars section be split off into a separate article. Parts of the car section does provide tech info and history. Also most of the applications of the engine has been in cars. I think it should stay. Wisdom-inc (talk) 14:29, 4 December 2022 (UTC)

Special:Diff/1128297522

This article was (and still is) in need for a decent overhaul, which I began with a couple of days ago. My recent efforts have been reverted so I feel the urge to explain my actions in some more detail. While this is (or should be) obvious to the experienced Wikipedian, I still think that it's reasonable to say that Wikipedia is not a hearsay compilation, instead, it is an encyclopedia which depicts what is (considered to be) established knowledge. In my personal experience, internal combustion engines are machines that are very difficult to comprehend which has lead to a lot of conspiracy theories, so one needs to be careful not to include any "information" that is false. Therefore, I mainly base my edits on Bensinger's 1972 book "Rotationskolben-Verbrennungsmotoren", which is the "bible" of the Wankel engine. Springer has not released a new edition of that work and I have recently (a couple of years ago) used it in a scientific context, so we can presume that this book is accurate and among the best sources one could possibly base this article on. Also keep in mind that any unreferenced claims in Wikipedia articles may be removed with a good reason, and that a lot of the material that I have removed was indeed unfererenced hearsay. I shall try to summarise key points of my recent edits in chronological order:

• The complexity and inefficiency of the 4-stroke piston engine contrasts with the rotational simplicity of the Wankel engine – this is just wrong and contradicts all reliable sources. The Wankel engine is the inefficient engine, the reciprocating piston engine is much more efficient because of its superior design.
• Wankel has invented the Wankel engine, and Paschke has designed it. This is actually a summarization of what the article had previously described in the "Early Developments" section. Now, Bensinger does not describe this in his book, but the currently cited sources are sufficient for this claim.
• The Wankel engine suffers from poor thermodynamics – this should be obvious to any knowledgable ICE engineer, but in case there's still someone who disputes this, Bensinger writes about this on page 85: "Zweifellos ist der Wankelmotor in der Thermodynamik den Hubkolbenmotoren unterlegen, wie die Form des Verbrennungsraumes und die großen wärmeabführenden Flächen sofort erkennen lassen". (Undoubtably, the Wankel engine is, seen from a thermodynamics perspective, inferior to reciprocating piston engines, which is immediately obvious because of the combustion chamber shape and the huge surface area, which causes heat losses).
• Usage: The Wankel engines does not give advantages in "automobiles, motorcycles and racing cars", quite the opposite is true. The ridiculous fuel consumption and bad exhaust gas behaviour make the Wankel engine unsuited for these applications. There is not a single advantage that the Wankel engine has that is useful for any of these applications. Back in the 1960s, engineers thought that the low mass and small size would give Wankel-powered cars a lower mass and better aerodynamics, which would ultimately reduce fuel consumption, but in practice, the Wankel engine's awful thermal efficiency outweighed these advantages.
• The Wankel engine's problems are being eradicated – frankly, this is impossible, because it would require reshaping the combustion chamber and reducing the surface by converting the Wankel engine into a reciprocating piston engine. There is not a single source that describes how the Wankel engine can be designed to have a decent fuel consumption of, let's say 190 g/(kW·h). Practical Wankel engines can compete with the first Diesel engine, but that is not an achievement. Any 1950s naturally IDI Diesel outperforms a bog-standard Wankel engine with ease.
• The Wankel engine is returing to cars – well, it has been announced. In practice, there has not been a Wankel car since the Mazda RX-8, which was effectively discontinued with the Euro 5 emissions standard taking into effect in 2011. Also note that all internal combustion engines have a BSFC, this does not only apply to Wankel engines, so "the efficiency of the engine rises when run at a constant speed" is true for all internal combustion engines (when assuming an ideal load).
• Hydrogen fuel increases thermal efficiency by 23 per cent – that is very misleading. Any internal combustion engine has a high efficiency if run at (decently) high epsilon and high lambda values; now, hydrogen has a very wide ignition range and thus favourable ignition limits. Of course one may choose lambda = 4 when using hydrogen, which obviously increases efficiency. But that is not a feature of the Wankel engine – it is a feature of the fuel. An Otto engine will also have the exact same benefits from running on hydrogen. While the Wankel engine is better suited for hydrogen due to its design, the overall problems of hydrogen operation have still not been solved (hydrogen is the first element in the first group and the first period of the periodic table of the chemical elements – it reacts with virtually anything). More interestingly though is that an increase in efficiency by 23 per cent would require an efficiency of >37 per cent to be a significant achievement. That is, because practical (lorry) Diesel engines would still outperform a Wankel engine with a "23 per cent increase in efficiency" if it had a base efficiency of less than 37 per cent. The problem is, however, that practical Wankel engines are not that efficient. So even if the efficiency is significantly increased in a prototype engine running on hydrogen, that particular engine would still be inferior to a bog-standard, mass production Diesel engine.
• The description of the design should be moved up; the "more uniform torque" is due to the short ignition interval – this is an advantage that is especially useful for hand-held devices such as chainsaws; this advantage doesn't need to be explained twice in the lead section.
• The taxing of automotive engines is not particularly interesting for Wankel engines, because they are not particularly well-suited for automobiles.
• The section on chamber volume and displacement is self-explanatory I reckon – the article previously didn't explain this and I think it is very helpful to include it. Everything is based on Bensinger, and even the example of the KKM 612 is taken from Bensinger's book; the specs for the Mazda R26B are taken from Shimizu et al. (1992).
• The torque delivery section was previously placed in the disadvantages section, and the torque delivery of a Wankel engine is much more uniform, which is an advantage over a conventional reciprocating piston engine (Bensinger, p. 72).
• The first part of the "Fuel economy and emissions" section was again very misleading. Yes, Wankel engines have a poor fuel consumption and emissions behaviour, but, as previously mentioned, hydrogen does not magically solve the Wankel engine's problem. The source was also poorly cited, and the alleged "near zero emissions" are, according to the source, high NOx emissions that are so high that the engine would fail emissions testing. Calling that "near zero emissions" is technically the same as calling a Volkswagen 2.0 TDI a "Clean Diesel".
• Attempts to produce a compression ignition Wankel have failed, and in practice, no such engines exist. The problem is that the design doesn't really allow high epsilon values without having a ridiculously unfavourable surface to volume ratio (cf. Bensinger, p. 60, 67, 86), which means that all attempts that have been made either rely on precompression, or spark igintion. Bensinger also argues that a Wankel Diesel is "not promising" (Bensinger, p. 86). This is a pretty strong argument and I doubt that present engineers can magically eradicate this "feature" of the Wankel engine. Anyone may cite a source that is equivalent in quality to Bensinger (i.e., a source that is a scientific journal or monograph) that describes a functioning Wankel Diesel. Ignore the usual suspects (e.g., Wankel Supertec engines hardly outperform the Mazda R26B, and are outperformed by any IDI Diesel).
• Speaking of Wankel Supertec: a BSFC of 270 g/(kW·h) for a stationary engine is very poor (a Diesel can do <190 g/(kW·h), and also nothing particulary interesting given the fact that the exact same engine has a BSFC of 290 g/(kW·h) when used as a vehicular engine, which the aforementioned Mazda R26B outperforms (286 g/(kW·h)).
• The claim that the Curtiss-Wright RC2-47 has a BSFC of 226 g/(kW·h) is very likely a false claim (such a figure is outright unrealistic), and it is also unreferenced. Given the fact that whoever wrote this compares it with the MTU MB 873-Ka 501, and makes the MTU MB engine a common-rail engine while it is an old-fashioned IDI Diesel, completely destroys that comparision. It's like comparing the first Diesel engine with a 21st century Wankel engine design that was made using computer technology and then arguing that the Wankel slightly outperforms the very first Diesel, by 14 grams per kilowatt hour. That is obviously unreasonable, and that comparision is made up.
• Again another section on hydrogen use; the claim that Otto engines are not well suited for hydrogen operation is "false" if one argues that a Wankel engine is well suited for hydrogen operation. The Wankel engine does have the advantage of lacking exhaust valves, but the major problem of hydrogen operation still applies to Wankel engines. Thus, I have rewritten that section to explain better why hydrogen is a good fuel for a Wankel engine; I have already explained the part on that "23 per cent increase in efficiency".
• A homogeneous mixture of hydrogen and air is avoided in a Wankel engine, according to the cited source. There is no reason to explain things in a contradicting fashion.
• The surface-to-volume ratio of Diesel engines is not poorer than that of Otto engines. In IDI Diesels that is true, but IDI Diesels have always been a stopgap solution, and since the 1960s, IDI Diesels have largely fallen out of favour in good engine design.
• A reciprocating piston engine with equal power to a Wankel will be approximately twice the displacement is wrong, because there is no significant difference. Let's compare the KKM 612 (cf. Bensinger, p. 133) with the BMW M10: Both engines perform virtually identically: p_me= 1.02 MPa (KKM 612) / 1.04 MPa (BMW M10); P=85 kW, V_h= 1.99 dm³. The major difference is that the KKM 612 Wankel engine has a significantly worse fuel efficiency than the BMW M10. The BMW E12 has a rated fuel consumption (DIN 70030) of 7.6 l/100 km at 90 km/h, while the NSU Ro80 has a rated fuel consumption (DIN 70030) of 11.2 l/100 km at 90 km/h. Some of that is definitely due to the hydrodynamic torque converter and the three-speed gearbox, but still, that difference is significant, and shows how bad the Wankel engine really is (the NSU Ro80 is much better designed than the BMW E12, it even outperforms the BMW E28).
• Bensinger does not describe pumping losses in his book, and the surface-to-volume ratio of the reciprocating piston engine is smaller than the Wankel engine's, according to Bensinger.
• GM tested and enhanced safety: There is no reference for that section, and it is quite obviously original research. The claims, as well this entire section are very misleading. Turboshaft engines also don't have valves – are they not as safe as Wankel engines? And what about aircraft noses: What about aircraft with the engines installed in the wings? Wankel engines operating within their original design parameters are almost immune to catastrophic failure – isn't that true for any engine designed with reasonable design paramters, and isn't it false for any engine designed with unreasonable design parameters? The KKM 612 for instance, was very prone to catastrophic failure because it shared its oil system with the gearbox.
• The entire disadvantages section was bloated and didn't focus on the key points (i.e., poor thermodynamics).
• The Mazda R26B engine did not outperform its competitors in terms of fuel economy (b_e=286 g/(kW·h), I mean, that is not exactly fuel efficient, it is quite the opposite); the cited source doesn't make that claim.
• The picture of the Žiguli is quite obvious I hope (the depicted car is a bog-standard 2106, and doesn't have a Wankel engine); also, the claims (even stating that little specific information has surfaced) are unsourced and dubious.

I hope that this is a better explanation and helps with understanding. Again, keep in mind that most claims that I have removed were unsourced and outright false, or the cited sources didn't support the claims. In Wikipedia, the editor who makes a claim needs to cite sources that support that claim. Best regards, --Johannes (Talk) (Contribs) (Articles) 15:22, 19 December 2022 (UTC)

I would say that the new version sounds at least as biased as what was there before, just in the opposite direction. Why can we not mention advantages AND disadvantages? While the original was a bit of a fluff piece, the new version only focuses on the negatives.  Mr.choppers | ✎  18:30, 19 December 2022 (UTC)

As an example: "The taxing of automotive engines is not particularly interesting for Wankel engines, because they are not particularly well-suited for automobiles." They have still been installed in automobiles (which are still being taxed), and their lower tax rating did help wankel sales in many markets such as Japan and Greece.  Mr.choppers | ✎  18:32, 19 December 2022 (UTC)

• This is just an explanation for why I removed an unreferenced claim. I could simply argue that everything I remove is unreferenced, and that'd be it. But well, I reckon that one should think about whether something could be true, and then try citing a source that supports the unreferenced claim (per WP:AGF). One should have a good reason for removing something unreferenced (that is, that it doesn't make sense in its context, that it's misleading, or outright false).

  So, the "Wankel engines are not well-suited for passenger cars" claim is basically just something that I say on the talk page. Unless a decent source is cited, nobody should write this in the article, because that would be OR. On the other hand, nobody should write that Wankel engines "give advantages in a variety of vehicles (…), such as: automobiles, motorcycles, [and] racing cars", because that is an unsourced claim, and false. And if I have a decent explanation for why that is wrong, I can remove that claim.

  My explanation is that the last mass production Wankel car was the Mazda RX-8, which was discontinued because of its bad exhaust gas behaviour and high fuel consumption. In the EU, the RX-8 failed emissions testing for the Euro 5 standard. And "Wankel engine power density" is certainly among the Wankel engine's advantages, but passenger cars do not necessarily need to have an engine as compact and lightweight as a Wankel engine – in passenger cars, this is not an advantage. So, why exactly would a Wankel engine be well-suited for a passenger car? Which source says this?

  I hope that this is clear?

• Now, while it may be true that some cars were taxed in a certain way, I suppose that it is a much better idea to use a generic approach that applies to any Wankel engine, not just passenger car engines installed in cars sold in certain markets. This is why I cited Bensinger (among the best sources) to describe how the displacement of the Wankel engine is calculated. Anyone can create artifical advantages (for instance, in Germany, fuel for Diesel cars used to have a lower tax than petrol), but taxation advantages are not design advantages, and they do not always apply to any engine. Therefore, Wikipedia should not describe these as advantages (Wikipedia may still describe that these exist, but should not say "the advantage of the Wankel engine is its taxation").
• There is a reason why Bensinger writes "There is no doubt that the Wankel engine is inferior to reciprocating engines in terms of thermodynamics, as the shape of the combustion chamber and the large heat-dissipating surfaces immediately reveal." This is the Wankel engine's biggest problem that nobody can solve. The article should not contradict this reliable source's claim by implying that this fact doesn't exist. Yes, this is a huge disadvantage that outweighs a lot of the advantages. But that is how it is. Wikipedia depicts what sources say, and if the sources are that clear, Wikipedia should be, too. Best regards, --Johannes (Talk) (Contribs) (Articles) 21:26, 19 December 2022 (UTC)

There is a crackpot on Youtube who is exactly like you. He went by the name of docktorbimmer, then when banned came back with another name of, Sander Van der Kammen. The likeness is to well for this man not to be the YouTube nut. Wisdom-inc (talk) 22:25, 19 December 2022 (UTC)

I am pretty certain this is this Sander Van der Kammen nut job seen on Youtube. He also says the Germans invented the jet engine as well, when even Ohain said Frank Whittle invented it. Wisdom-inc (talk) 16:34, 22 December 2022 (UTC)

Youre 100% correct about this, and yes this guy is a nut job. The guys literally been trolling "rotary" videos for at least over a decade. Guys got no life. 68.224.75.51 (talk) 08:50, 4 May 2023 (UTC)

I have been restructuring the article for a number of weeks off and on. It was a mess, now it more in order with structure. I have slickened up explanations. Some refs were added. Then much was stripped away by disruptive POV. It is this sort of POV that is disruptive. The taxing of automotive engines is not particularly interesting for Wankel engines, because they are not particularly well-suited for automobiles. The Wankel is being introduced in a Mazda in Jan 2023. Mentioned in the article. Wisdom-inc (talk) 18:47, 19 December 2022 (UTC)

Bensinger's method is not the universal or even a common way of describing rotary engine displacement. Hence the names 13B and R26B, and various countries taxing the twin-rotor Mazda engine as a 1.3 - because the typical way to describe the displacement of this engine is 1308cc. Your selective choice of sources is at least as troublesome as Wisdom-inc's opposite view. SCCA slaps rotary engines with a 2X equivalency factor, making the 1.3 a 2.6, but this is in no way the same as saying that the engine's displacement is 2.6 liters. FIA currently calculates it as "In the case of a rotary engine, the engine cubic capacity is the volume determined by the difference between the maximum and minimum capacities of the combustion chambers."  Mr.choppers | ✎  22:17, 19 December 2022 (UTC)

FIA used a 1.8 multiplication factor for many years, while the Japanese government used a 1.5 factor. Meanwhile, FIA used a 1.9 multiplication factor for two-strokes, but that doesn't mean that the Lloyd LP400 has a 733 cc engine.

Equivalence formula between 2‐stroke and 4‐stroke engines
The nominal cylinder capacity of a two strokes engine must be multiplied by 1.9.
3.3 Equivalence formula between reciprocating piston and rotary engines (of the type covered by the NSU Wankel patents)
3.4 The equivalent cubic capacity is 1.8 times the volume determined between the maximum and minimum capacities of the combustion chambers.

 Mr.choppers | ✎  22:27, 19 December 2022 (UTC)

You missed it. The words "because they are not particularly well-suited for automobiles" This POV nonsense. Wisdom-inc (talk) 22:27, 19 December 2022 (UTC)

The selective choice of sources is a key to ensure that Wikipedia articles are reliable. WP:SOURCETYPES states that "academic and peer-reviewed publications, scholarly monographs, and textbooks are usually the most reliable sources". Bensinger's book is a scholary monograph and describes the basic functionality and aspects of the subject. This is different from a regulation; see, FIA's goal is, I suppose, to ensure fair motor racing. They don't necessarily need to describe the Wankel engine in a scientific context. The same is true for "taxation agencies"; the best example for this is RAC horsepower, which is not a unit of power, but technically an area (L²) that describes taxation. So if the Japanese government multiplies the total chamber volume by 1.5, then the resulting figure is a volume (L³) used for taxation purposes, but not a displacement figure.

Don't get me wrong, I'm not saying that this particular article should only rely on that particular book. Any source that is, in quality, equivalent to Bensinger's scholary monograph may (and should!) be cited in this article. Sources that are not as good in quality should be avoided. The Wankel engine is an internal combustion engine, difficult to comprehend and subject to myths and even conspiracy theories. Low quality sources may be prone to promote myths, which Wikipedia is not a place for.

The claim that Wankel engines have advantages that make them well-suited for cars is an opinion piece, exactly as the claim that they are not well-suited for cars. These two claims are opinions or personal points of view that are both totally fine on talk pages, but one should not make either of these claims in a Wikipedia article. Imagine if the article read "The Wankel engine is unsuited for cars": I'd certainly argue that the claim is "false" because the NSU Ro80 is an example of a car with a Wankel engine (albeit, not a very economical car seen from a fuel consumption perspective). Best regards, --Johannes (Talk) (Contribs) (Articles) 23:52, 19 December 2022 (UTC)

"So if the Japanese government multiplies the total chamber volume by 1.5, then the resulting figure is a volume (L³) used for taxation purposes, but not a displacement figure" Yes, that is exactly what I am saying. FIA used a factor of 1.8 and later 2.0, Japan used 1.5, but all are factors applied to the actual displacement. The actual displacements remain 1146 or 1308 or 995cc etc as per all sources. You need to read WP:OR and not apply Bensinger's formula to the chamber dimensions of the R26B, for instance.  Mr.choppers | ✎  18:00, 21 December 2022 (UTC)

What does Yamamoto have to say about displacement? Do you have pdfs of his book or anything else you could share?  Mr.choppers | ✎  18:11, 21 December 2022 (UTC)

Applying an "arbitrary" equivalence factor is different from the fact that a Wankel engine can, by design, "process" twice its chamber volume per output shaft rotation. This is what Bensinger writes in his book, and what – at least what I have found – tends to be the universally accepted way of determining Wankel engine displacement (I have a huge selection of scientific literature at had; i.e., high quality reliable sources tend to use "Bensinger's definition" if they include a displacement figure).

Many sources only give chamber volume, but omit displacement. This is also what Yamamoto does: he defines working chamber volume (i.e., $V_{k}$), but doesn't define displacement (i.e., $V_{h}$). Yamamoto introduces, on page 37, "formulas for calculating rotary engine output", but those only work with correction factors, and by using units of the technical (MKS) unit system (V=dm³, P=PS, M=kp·m, p=kp·cm⁻², n=min⁻¹).

The universally accepted formula for deriving torque from BMEP and displacement in a four-stroke engine is $M={\frac {V_{h}\cdot p_{me}}{4\pi }}$ (literally the first result on Google). This works fine with the KKM 612: ${\frac {1992\,cm^{3}\cdot \,1.02MPa}{4\pi }}\approx 162\,N\cdot m$

Now, Yamamoto uses this formula: $M={\frac {10\cdot V\cdot p_{me}}{2\pi }}$; he defines $V=i\cdot V_{k}$ (i.e. $V_{h}=10V$) which results in ${\frac {10\,dm^{3}\cdot \,10.4\,kp\cdot cm^{-2}}{2\pi }}\approx 16.55\,kp\cdot m\approx 162\,N\cdot m$

I mean, it works, but I think that it's safe to say that the KKM 612 doesn't displace 10 dm³ = 10,000 cm³.

I access most scientific sources through the TU Wien library.

By the way, are there any sources for the (what I call arbitrary) equivalence factors? You wrote (not literally) that, in Greece, displacement is defined as V_k·i; while I believe that you don't purposely introduce "false" information, this contradicts with ECE Regulation No. 83. I think that Greece might have used that definition in the past (but nowadays they don't). I tried googling this, but couldn't yield any satisfactory results. Best regards, --Johannes (Talk) (Contribs) (Articles) 08:29, 22 December 2022 (UTC)

References

Special:Diff/1089152178: Removing of the comparison between the C-W RC2-47 and the MTU MB 873-Ka 501

I think it's best to briefly comment on that particular edit to make my own editing transparent, and more comprehensible. User:HDP introduced a comparison of the C-W RC2-47 and the MTU MB 873-Ka 501. No source make the described comparison, which is problematic because the edit effectively introduces an unreferenced opinion (i. e., original research). This alone is a reason to revert, but there are additional things very wrong (which is the reason why I'm making this edit on the talk page). If we ignore the aforementioned OR, then the biggest problem is that the RC2-47 engine does not exist, i. e., it is a proposed design of an engine and thus all technical specifications were obtained using some sort of mathematical model. The cited source ([1]) clearly indicates this by stating that figures are estimates. Therefore, comparing this hypothetical model with a production engine in the presented context is unreasonable and misleading. The false depiction of the MTU MB engine as a common-rail engine also adds to the misleading of the reader – in fact, it is antechamber-injected, which is significantly less efficient than the claimed common-rail injection and presents the illusion that common-rail engines are not as efficient as they actually are. The MTU MB 873-Ka 501 was designed in the early 1970s (maybe even late 1960s), which is a disadvantage when compared against something that is effectively 20 years newer (the Advanced stratified charge rotary aircraft engine design study foresees that the C-W RC2-47 might be introduced in the 1990s). Therefore, I technically reverted Special:Diff/1089152178 on 17 December 2022 with Special:Diff/1127989616. Best regards, -- Johannes (Talk) (Contribs) (Articles) 20:46, 27 December 2022 (UTC)

We should also not underestimate your Bogus claims regarding the first Diesel, the fuel consumption was lousy. The values that are so published come from the 22/40 and not from the first diesel engine 15/40. Even the 22/40had a specific consumption of 519g/kWh at the beginning. 15/40 and 22/40 were not pure diesels and still had spark ignition.It was not until early ~August 1895 that the 22/40 no longer relied on spark ignition. Furthermore, specific consumption in Nov 1895 was 350g/PSh= 476g/kWh at 167 rpm and maximum power ~12hp. HDP (talk) 08:27, 24 February 2023 (UTC)

Special:Diff/1130061529: Removing of the HCCI section

I decided to remove the HCCI section because there simply aren't any sources that discuss the matter in sufficient detail. I spent several hours browsing through sources, and frankly, the best source is Resor's 2012 Master thesis; Resor uses a mathematical model (CFD simulation), i. e., HCCI engines do not (yet) exist in practice, they have been proposed. Throughout the past 10 years, no HCCI Wankels have been made (at least I couldn't find any sources that describe one). The speculation about Mazda's new rotary engine requires no explanation I hope; any speculation about unconfirmed rumors or future developments/concepts is just not a sufficient source for the HCCI section. Best regards, --Johannes (Talk) (Contribs) (Articles) 12:03, 28 December 2022 (UTC)

Post Scriptum: The HCCI section also claimed that "Rotaries generally have high compression ratios, making them particularly suitable for the use of HCCI" which is outright false: Obtaining high compression in a Wankel engine requires high K-factors (R/e), but using a K-factor for high compression results in an even worse combustion chamber and increased surface area, therefore, making rotaries with high compression is not feasible, cf. Bensinger (1973), p. 86. --Johannes (Talk) (Contribs) (Articles) 12:09, 28 December 2022 (UTC)

Sadly, the same applies to the SPCCI section: No sources discuss the existance of an SPCCI WANKEL engine. --Johannes (Talk) (Contribs) (Articles) 13:29, 28 December 2022 (UTC)

At least Mazda's engine development head has spoken out once in this regard.

At the Tokyo Motor Show in 2015, Mazda Motor Corporation announced the next development steps for its rotary engines, which on the one hand include increasing electrification of the powertrain and on the other pursue highly efficient combustion processes such as homogeneous compression ignition (HCCI). HDP (talk) 20:18, 4 February 2023 (UTC)

HCCI is an abbreviation for homogeneous charge compression ignition; this technology doesn't necessarily give an engine a highly efficient combustion process; ideal conditions for ideally efficient ICEs look quite different (cf. Pischinger, Kell, Sams (2009). Are there any papers that describe how Mazda's latest Wankel engine works? And is there any evidence for the HCCI announcement at the Tokyo Motor Show in 2015? Best regards, --Johannes (Talk) (Contribs) (Articles) 21:13, 4 February 2023 (UTC)

Heuristische Potentialabschätzung eines Kreiskolbenmotors mit homogener Kompressionszündung

mittels quasidimensionaler Methoden. Dissertation Timo Simshäuser Bochum 2016. HDP (talk) 08:21, 5 February 2023 (UTC)

Well; the work compares a hypothetical HCCI Wankel engine with the Mazda Renesis 13B; on page 41, Simshäuser states that the Renesis 13B has a fuel consumption of b_e=280 g/(kW·h) at 4000 min⁻¹. (It outperforms an OM 636 by 6 grams per kilowatt-hour, what an achievement.) According to Simshäuser, HCCI enables, in theory, a fuel consumption of 257 g/(kW·h) (cf. p. 107). This would be good for a Wankel engine. The problem is, however, that the work also implies that an HCCI Wankel engine wasn't built. (And this is no surprise considering that a bog-standard Otto engine outperforms a hypothetical HCCI Wankel engine, even Simshäuser acknowledges that.) So? Best regards, --Johannes (Talk) (Contribs) (Articles) 20:11, 5 February 2023 (UTC)

References

Special:Diff/1131314528

The previous edit introduced a lot of assumptions/claims, including the conspiracy theory that the Wankel engine's poor efficiency and emissions behaviour have been solved with a revolutionary new technology. A good look reveals that the edit was blatant advertising for a Wankel engine manufacturer. The "referencing" is WP:REFSPAM (as I have demonstrated and explained back in December), and don't get fooled by the patents. Best regards, --Johannes (Talk) (Contribs) (Articles) 16:10, 3 January 2023 (UTC)

Illustration missing on volumes calculations

The formulae are difficult to interpret without illustrations showing what each parameter means. Laranjatomate (talk) 00:23, 8 November 2023 (UTC)

Displacement

@Johannes Maximilian: https://en.wikipedia.org/wiki/Wankel_engine#Displacement I think there are two flaws here. I try to explain myself here before edit the page.

1. Taken a multi-cylinder engine, unitary displacement is the volume swept by a piston stroke, that is the working fluid of a single thermodynamic cycle. Each cylinder operates his own cycle, so displacements sums up. Why you shouldn't apply the same logic to a Wankel engine also? Each face swept a volume and operate his own cycle. Worth noting that "how many revolutions the cranksahft does" is not relevant.

2. Since a Wankel rotary engine has three combustion chambers, all four cycles of a four-cycle engine are completed within one full rotation of the eccentric shaft (360°) This doesn't make sense. To identify the thermodynamic cycle you have to focus on the single rotor face. Why don't apply the same logic to a three-cylinder engine? Two weights, two measures.

Some time ago I argumented this topic more clearly here https://www.rx8club.com/new-member-forum-197/displacement-mazda-rotary-engine-274456/

Edoriel (talk) 19:32, 21 December 2023 (UTC)

The thing is that Wikipedia doesn't depict what its editors believe. An article explains what the sources cited say about the topic, and that's what's done here. Best, --Johannes (Talk) (Contribs) (Articles) 13:47, 22 December 2023 (UTC)

Post Scriptum: Also note that we're talking cycles as in intake, compression, combustion and exhaust; what you say "doesn't make sense" is literally what is depicted in Fig. 1. --Johannes (Talk) (Contribs) (Articles) 13:54, 22 December 2023 (UTC)

Thermodynamic process and Thermodynamic cycle are different things. Several "cycle" in the text need to be replaced with "phase/stroke/period".

You can make sense out of point 2. only if you gather phases from the three different cycles that are occourring in the three different chambers. This is a (faulty) mental stretch that you (also Ansdale and Bensinger) don't do for a three-cylinder engine. You can not judge things with different criteria, this is not how scientific work is done.

Note https://www.hemmings.com/stories/article/how-big-are-wankel-engines and SAE J1220. I think in the article should be pointed out that there is a debate on this topic.

Edoriel (talk) 09:33, 23 December 2023 (UTC)

The idea of three chambers is absolute nonsense. Because, for example, with 500cm3 that is not 3 times 500ccm. If you determine the volume of each side of the rotor, you don't get 3 times the chamber volume. Because the duration of the cycle is 270°, each side surface requires 3 revolutions for the complete 4-stroke process. The Wankel engine therefore has one power stroke for each revolution of the eccentric shaft. However, since the four-stroke process in the 4T reciprocating piston engine has an idle stroke, the chamber volume must be doubled in order to calculate with the four-stroke formula. As the factor two is reduced, the two-stroke formula is used to calculate the power. With a two-stroke engine, the displacement is not taken twice. If you really want to compare apples with oranges, then take the chamber volume twice.--HDP (talk) 10:30, 23 December 2023 (UTC)

Don't use "cycle" instead of "phase/stroke/period", they have different meaning.

If you determine the volume of each cylinder of the three-cylinder engine, you don't get 3 times the chamber volume. Because the duration of the phase/stroke is 180°, each cylinder requires 2 revolutions for the complete 4-stroke process. The three-cylinder engine therefore has one power stroke for each 2/3 revolution of the crankshaft. So you think we need to apply a corrective factor to calculate the displacment of a three-cylinder engine also? Can't you see you are using different criteria to evaluate analogue situations?

Edoriel (talk) 18:00, 23 December 2023 (UTC)

I suppose this is a language problem: "cycle" in this context doesn't mean thermodynamic cycle, it means what in a reciprocating piston engine is called a "stroke". The German language has a very nice word for this that applies to any kind of internal combustion engine: Arbeitsspiel. Best regards, --Johannes (Talk) (Contribs) (Articles) 18:38, 23 December 2023 (UTC)

Professor Othmar Baier has done enough theoretical work on the subject of four-stroke wankel engines and geometry. This is the man who first worked out the mathematical principles of the Wankel engine. Almost all the formulas in Benzinger's book are from Baier. For a full four cycles (stroke), each side of the rotor requires three eccentric shaft revolutions 1080° vs 720° for a four-stroke reciprocating piston engine. It's hard to say stroke if there is no stroke! Incidentally, Benzinger's work was written before 1971, because Mercedes Benz withdrew from Wankel development in 1971. Benzinger had already retired by then. So refrain from original research--HDP (talk) 10:41, 24 December 2023 (UTC)

Answering to your last edits:

- A three-cylinder displaces 50% more than a single-rotor Wankel if the shaft rotates the same amount. Jorbye's point is that if you compare the two based on the number of revolution needed to complete the Otto cycle (three-cylinder's shaft rotates 2/3 of Wankel's), than the two displace the same amount. The key is to compare the two on a thermodynamic level, not on "for the same shaft revolutions". Read the source to the end.

- 3*V_k is inappropriate in your opinion. It is supported by several sources I mentioned. Read Wankel's and Küttner's.

Edoriel (talk) 14:36, 1 January 2024 (UTC)

2/3 turns results in what? A two-cylinder engine! 2/3x3 = 2. What you are claiming is not your source. The third cylinder does not magically disappear. The Norbey source says that a four-stroke, three-cylinder engine displaced 50% more volume whether you like it or not. Küttner would be how old and at what level of technology? The mathematician Ottmar Baier has deduced what the Wankel engine is comparable to, which Wankel and Küttner were not capable of. J.B. Hege 2015 The Wankel Rotary Engine: A History publisher McFarland series EBL-Schweitzer isbn=978-0-7864-8658-8 page 44. HDP (talk) 07:35, 2 January 2024 (UTC)

Let's discuss it here by points.

1) Norbye'analysis p.5: Air consumption can be measeured as gas pumped through the engine during a given number of shaft revolutions... The three-cylinder 1500 cc engine has an air consumption of 750 cc per shaft revolution or 50 percent more than the Wankel with a 500 cc Vmax.

p.11: the single-rotor Wankel engine operates like a three-cylinder piston engine running at 2/3 the speed of the Wankel.

p.13: If you were to install a simple gear set with a 3:2 ratio at the end of the Wankel engine's gear shaft, the output shaft from the gear set would rotate at a lower speed wich would have the effect of matching air consumprion perfectly with that of the three-cylinder piston enigne. Conversely, you could apply a 2:3 "overdrive" to the three-cylinder piston engine while leaving the Wankel engine in its original form, and obtain the same results: identical air consumption and torque impulse patterns.

This is what Norbye said. You can compare for the same number of shaft revolution and get 2*V_k, or for the thermodynamic cycles involved and get 3*V_k. Please explain how I'm not claiming what the source says.

2) Please read Wankel and Küttner sources I mentioned. They recognize that all the chambers need to be counted.

3) Hege reports that Baier prooved the stator epitrochoidal shape. Please mention Baier's source where he compares the Wankel with a multi-cylinder.

Edoriel (talk) 15:42, 2 January 2024 (UTC)

I don't know what you're citing there, but various sources use the exact same approach of V_h= 2 · V_k · i:

• Norbye: "With a single rotor and a chamber volume of 500 cc., the intake volume of a Wankel engine is only 500 cc. per mainshaft revolution. That means it is equivalent to a one-liter (1,000 cc.) four-stroke piston engine. A two-cylinder, one-liter engine will complete an intake stroke during one crankshaft revolution or, an equivalent of 500 cc. A four-cylinder engine, with 250 cc. per cylinder, has only two intake strokes during one crankshaft revolution, and again there is 500 cc. intake air volume."
• Bensinger: "The eccentric angle α is counted from ignition dead centre: it must be noted that in the mathematical calculations, on the long axis, γ=0, i.e. it occurs 90° earlier. From dead centre to dead centre, the eccentric shaft rotates by 270°, the piston by 90°. A piston face only reaches its end position again after 4 × 270° = 1080°, i.e. 1.5 times as many eccentric shaft revolutions are required for the four-stroke working process for this piston face when compared with the crankshaft of the four-stroke reciprocating piston engine. However, as the working processes take place simultaneously on the other sides of the piston, 360° out of phase, each eccentric shaft revolution is followed by one cycle of the process, i.e. a complete chamber volume worth of charge is drawn in once and ignited once per eccentric shaft revolution. The mode of operation is similar to that of a 2-cylinder four-stroke engine, with its strokes offset by 360° to each other. The same theoretical quantities of fresh gas are drawn in per shaft revolution if the cylinder volume is equal to the chamber volume, but the Wankel engine's thermodynamic process is very different from that of a two-cylinder four-stroke reciprocating piston engine, although this has no significance for the design of the engine. In order to be able to determine a working volume V_h comparable to that of the reciprocating piston engine and to base calculations on, the following must be set: V_h = 2 V_k · i"
• Hege (2005): "Taking into consideration that a single-rotor engine produces one power stroke per revolution of the output shaft, as opposed to one power stroke per two revolutions for a single cylinder four-stroke piston engine, the sanctioning bodies adopted the formula that most of the rest of the rotarians have: that of multiplying the chamber displacement by two, then by the number of rotors."

Karl Ludvigsen's notes count as a primary source and must not be cited in any Wikipedia article(s). Interestingly, Ludvigsen writes: "The validity of this conclusion has yet to be proved", i.e., he acknowledges that the claim that V_h ≠ 2 · V_k · i (or V_h ≠ V_k · i) has yet to be proved. Also note that, Ludvigsen argues that a single-rotor Wankel is equivalent to a three-cylinder four-stroke engine running at 2/3 the speed of a Wankel, effectively resulting in V_h = 3 · V_k · i · 2/3 = 2 · V_k · i, but who am I to judge this. Anyways, I am not aware of any sources supporting that idea though, and I cannot immediately cite any sources that argue in favour of V_h = 3 · V_k · i. I reckon that it's safe to base the article on what the most reliable sources say, and that's that "the formula that most of the rest of the rotarians have (adopted is) that of multiplying the chamber displacement by two, then by the number of rotors", i.e., V_h = 2 · V_k · i. Best regards, -- Johannes (Talk) (Contribs) (Articles) 19:40, 2 January 2024 (UTC)

I was citing Norbye's analysis contained in Ludvigsen's note and I understand that by Wikipedia policy it is considered less reliable than others.

I mentioned two others sources. You can search them.

This theoretical experiment leads inevitably to the conclusion that Wankel engines must run at 50 percent higer shaft speeds than piston engines in order to be compared on even terms. The validity of this conclusion has yet to be proved, but I am personally convinced it will be borne out. It is in fact proven by figure 10 and 11.

The cross cancellation is a merely matemathical result. Be careful counting displacement on shaft revolutions, you may end up saying that running at different speeds changes displacement.Edoriel (talk) 06:09, 3 January 2024 (UTC) Edoriel (talk) 06:09, 3 January 2024 (UTC)

Yamamoto's diagram on page 109 Fig 10.40 is about 1080° and not as fiddled together with omissions as your diagrams. It also explicitly states equal intervals and three revolutions of the eccentric shaft and crankshaft. "The ignition intervals of the two-disc engine are identical to those of a four-cylinder four-stroke engine." Quote from Yamamoto page 110 above. This is also easy to see from the diagram. Also, if you quote, then quote correctly. Because the other diagram regarding the torque does not correspond to Yamamoto's diagram either. HDP (talk) 11:32, 3 January 2024 (UTC)

Furthermore, where does Felix Wankel write anything about Vk*3? If so, please state exactly where this is in the explanation of the patent. If you quote, please quote the page number!HDP (talk) 12:04, 3 January 2024 (UTC)

It is a lot of work to reproduce those diagrams. The reciprocating engines repeat themself after 720°, there's no meaning on extending them to 1080°. The axis scale is the way it is because the wankel one is the six-cylinder stretched horizontally, but if you insist I can add the other marks.

Although the ignition intervals of the 2-rotor engine is the same as thet of a 4-cylinder reciprocating engine, it has the advantage that the total sum of explosion/expansion periods is comparable to that of a 6-cylinder reciprocating engine. This is the complete quote.

The pressure and torque ones are obtained with ideal Otto cylcle, as stated. To simulate real pressure requires an elaborate matlab model. I think they serve their purpose as they are, but if you insist I can do it in some time.

I quoted p.16, although it is more a "column": The output N is proportional to the product V_H · p_me · n. In this product V_H is the displacement of the engine and is equal to the sum of the individual displacements of all working chambers, p_me is the brake mean effective pressure, and n is the rotational speed.

I'm waiting for your replies to my third-last message.Edoriel (talk) 19:18, 3 January 2024 (UTC) Edoriel (talk) 19:18, 3 January 2024 (UTC)

"Although the ignition intervals of the 2-rotor engine is the same as thet of a 4-cylinder reciprocating engine, it has the advantage that the total sum of explosion/expansion periods is comparable to that of a 6-cylinder reciprocating engine. This is the complete quote."

However, this refers to the longer duration of the stroke and not to the displacement. This can be clearly seen in the torque diagram on page 86. It is called expansion overlap and is clearly visible in the diagram on page 109. It has nothing to do with the displacement or chamber volume. Incorrect source Yamamoto 1981 is only 72 pages long. The correct source is Yamamoto 1971. HDP (talk) 08:48, 4 January 2024 (UTC)

However, this refers to the DKM and not the KKM. Whereby Pme was calculated because it cannot be measured.HDP (talk) 09:26, 4 January 2024 (UTC)

I reply here to avoid mixing the discussions.

1) I didn't mention Yamamoto for the displacement, but only to complete you partial citation that you brought to the table.

You are right, I cited the 81 one instead of the 71 one.

2) DKM and KKM have analogue thermodynamics.

p_em is always calculated from measured power or torque. Mean indicated pressure is the one that can be "measured" from cylinder pressure sensor, impractical for DKM. But how this matters for the displacement evaluation?

3) In your 08:15, 4 January 2024 (UTC) message you cited from Norbye's book (1971). We were talking about Norbye's analysis (1975) and how I was not mentioning it correctly.

4) Please report where Baier compares the Wankel engine with something else, from your 07:35, 2 January 2024 (UTC) message. Edoriel (talk) 22:21, 4 January 2024 (UTC)

• Yamamoto doesn't discuss equivalent displacement (cf. Yamamoto (1981) p. 14), he only calculates the chamber volume V_k and multiplies this with the number of rotors i (cf. Yamamoto (1981) p. 37). --Johannes (Talk) (Contribs) (Articles) 20:46, 5 January 2024 (UTC)

You can search them? Please cite your sources. Where does the displacement formula $V_{h}=i\cdot y\cdot V_{k}$ come from? Please cite a proper source for that. --Johannes (Talk) (Contribs) (Articles) 14:06, 3 January 2024 (UTC)

I cited them on the article, but here they are againg.

I placed $y$ in the formula so it can accomodate one, two or three chambers counted. It is needed to be able to mention all the three school of thought. I think we can agree on this. Edoriel (talk) 19:23, 3 January 2024 (UTC)

I have the 2009 (7th) edition of that book and it doesn't explain how the equivalent displacement is calculated, it only gives the formula for the chamber volume, and it explains that a Wankel engine performs all four cyclines of a four-cycle engine in one eccentric shaft rotation. --Johannes (Talk) (Contribs) (Articles) 20:29, 3 January 2024 (UTC) Johannes (Talk) (Contribs) (Articles) 20:29, 3 January 2024 (UTC)

The 1993 (6th) edition is the last one written by Küttner (then it has been revised by new authors retaining Küttner's name in the title). It explain the concept of "number of cycle over time" and apply it to the Wankel.

I'm sure you can find a previous edition. I'll find the 2009 edition. Edoriel (talk) 22:51, 3 January 2024 (UTC)

Source Norbey Page 28 "The Wankel engine "Others argued that the Wankel engine represents a three-cylinder, four-shoke engine, maintaining that positive torque is produced over 240 degrees of mainshaft rotation, just as a three-cylinder engine produces torque over two-thirds of each crankshaft revolution (it goes through three cycles in two revolutions). This argument was effectively Put to rest when the leading independent expert on Wankel engines, Richard F. Ansdale, delivered a paper entitled "Rotary Engine Development and its Effect on Transport" to the Society of Automotive Engineers of Australasia (October 15, 1968), in which he proved conclusively that the torque characteristics of the single-rotor Wankel engine correspond to those of a two-cylinder, four-stroke piston engine and not to those of a three-cylinder engine." Source Norbey Page 29 " Gas turbine cars have completecl in the 24-hour race at Le Mans and the Indy 500 race, equivalent formulae, based on air consumption, have been worked out to produce a rclative cylindcr displplacement rating for them. The Commission Sportive Intemationale of the Federation Internationale de I'Automobile (the international governing body for motor racing) then looked into ways of applying the same rule to Wankel-powered cars. With a single rotor and a chamber volume of 500 cc., the intake air volume of a Wankel engine is only 500 cc per mainshaft revolution. That means it is equivalent to a one-liter (1,000 ccm.) four-stroke piston engine. A two-cylinder, one-liter engine will complete an intake stroke during one crankshaft revolution or, an equivalent of 500 cc. A four-cylinder engine, with 250 cc. per cylinder, has only two intake strokes during one crankshaft revolution, and again there is 500 cc. intake air volume. These facts influenced the CSI to adopt a formula which rated the Wankel engine's displacement at twice the combustion chamber yolume multiplied by the number of rotors, this formula is still in effect."HDP (talk) 08:15, 4 January 2024 (UTC)

Could you find a work that includes a displacement formula for the Wankel engine that's $V_{h}=i\cdot y\cdot V_{k}$? --Johannes (Talk) (Contribs) (Articles) 20:33, 5 January 2024 (UTC)

Küttner states gesamthubvolumen $V_{H}=3\cdot V_{h}$. He counts three chambers per rotor, but takes only one rotor.

Yamamoto states total displacement $V=Z\cdot V_{H}$. He counts one chamber per rotor, taking $Z$ rotors.

Besinger states arbeitsvolumen $V_{H}=2\cdot V_{K}\cdot i$. He counts two chambers per rotor, taking $i$ rotors.

Don't you agree that to take account of all the three school of thought we need a formula like $V_{h}=i\cdot y\cdot V_{k}$? If you prefer something else than $y$ we can change it. Edoriel (talk) 21:32, 5 January 2024 (UTC)

• From "Küttner Kolbenmaschinen" 2009 (7ed.): Das arbeitsverfahren beim Wankel-motor entspricht dem 4-takt-verfahren beim hubkolbenmotor und läuft, um jeweils um 360° exzenterwinkel versetzt, in den drei kammern des motors ab. Auf jede volle umdrehung des kolbens, d. h. auf drei umdrehungen der exzenterwelle, kommen somit drei vollständige arbeitsspiele

Translation I got: The working process for the Wankel engine corresponds to the 4-stroke process for the reciprocating piston engine and runs, offset by 360° eccentric angles, in the three chambers of the engine. For every full revolution of the piston, i. e. for three revolutions of the eccentric shaft, there are thus three complete work games.

So it doesn't seem that they draw the conclusion you added (Ansdale argument of one complete cycle every shaft revolution through fraction simplification). They also take (in 4.9.1) the contributes of all the three chambers to calculate the total torque, although as you said they don't state a total displacement.

• Küttner deals with Wankel engine in "Kolbenmaschinen" 1971 (2 ed.) the same as he does in 1993 (6 ed.).
• I found other sources that convey that a single-rotor Wankel is analogue to a three-cylinder with a 2/3 gear set applied, and that to compare the two is necessary to use the thermodinamic cycle frequency (thermodynamische spielzahl). Huber also uses the same displacement and power formulas as Küttner.

Edoriel (talk) 17:39, 16 January 2024 (UTC) Edoriel (talk) 17:39, 16 January 2024 (UTC)

By chance, I came across the VDI 1961 report by Froede. I wonder what is so difficult to understand about the VDI report by Walter Froede from 1961? On page 2, Froede compares the Wankel engine with a single-cylinder two-stroke engine in terms of displacement.HDP (talk) 17:08, 28 March 2024 (UTC)

Page 2 point a.: It is therefore functionally equivalent to the two-stroke engine, which is also prepared to deliver power every crankshaft revolution. Here, two other flanks of the triangular rotor take on auxiliary functions, similar to those carried out by the underside of the crankcase two-stroke engine. This ensures that the gas pump, i.e. the expulsion of the burnt gases and the suction of fresh mixture, is carried out by mechanical displacement, just as in the four-stroke engine. It is not possible to consider it as a multi-cylinder engine because, according to the definition, every multi-cylinder engine is to be viewed as a series of several single-cylinder engines and can be traced back to a single-cylinder engine. Such a split into several single-cylinder units is not possible with the NSU Wankel engine. The simplest view of the displacement of the rotary piston engine is when viewed as a single-cylinder, two-stroke engine with a four-stroke gas exchange. As is well known, the two-stroke formula is also valid for determining the mean effective pressure. The displacement is the difference between the maximum and minimum value of the volume of a working chamber. For a technician, the question of engine capacity evaluation is of no interest, since only the average working pressure, the power-to-weight ratio and the fuel consumption are criteria for evaluating an internal combustion engine.

Page 2 point c.: Since ignition occurs after every 360° rotation of the eccentric shaft and each work cycle extends over 270°, the gas force curve for a motor with a rotor is as shown in Figure 3. The size of the forces is based on the most developed and developed KKM 250. The course of the gas forces was taken from theoretical diagrams that assume a maximum pressure of 60 at. The course of the indicated torque, which is shown in Figure 4, is determined from the gas pressures in the same way as with reciprocating piston engines. This torque curve corresponds to a three-cylinder four-stroke engine with a ratio of 2:3. Such engines are generally not built and it therefore makes more sense to describe a 2-rotor rotary piston engine as equivalent to a six-cylinder four-stroke engine, although this equivalence only applies to the torque curve.

Edoriel (talk) 17:54, 29 March 2024 (UTC)

Of course I meant the MTZ and not VDI. Orginal Froede. "Eine Betrachtung als Mehrzylindermaschine erscheint nicht möglich, da definitionsgemäß jeder Mehrzylindermotor als eine Aneinanderreihung mehrerer Einzylinder aufzufassen ist und auf einen Einzylindermotor zurückgeführt werden kann. Eine derartige Aufspaltung in mehrere Einzylinder-Einheiten ist beim NSU-Wankelmotor nicht möglich. Die einfachste Auffassung über den Hubraum der Kreiskolbenmaschine ergibt sich bei Betrachtung als Einzylinder- Zweitaktmotor mit einem Viertakt-Gaswechsel. Zur Ermittlung des mittleren effektiven Druckes hat bekanntlich auch die Zweitakt-Formel Gültigkeit. Als Hubraum ist hierbei der Unterschied zwischen Größt- und Kleinstwert des Rauminhalts einer Arbeitskammer aufzufassen. Für einen Techniker ist die Frage der Hubraumbewertung ohne jedes Interesse, da ausschließlich der mittlere Arbeitsdruck, das Leistungsgewicht und der Kraftstoffverbrauch Kriterien für die Bewertung eines Verbrennungsmotors sind." Where does Froede say anything about a three-cylinder engine?! He clearly uses a single-cylinder engine as a comparison. HDP (talk) 18:53, 29 March 2024 (UTC)

This torque curve corresponds to a three-cylinder four-stroke engine with a 2:3 gear ratio [....], but such engines are generally not built, so it makes more sense to describe a two-rotor rotary engine as equivalent to a six-cylinder four-stroke engine, although this equivalence only applies to the torque curve. Obviously translated using an online translation site. Some of the important meaning of the original has been lost. "Dieser Drehmomentverlauf entspricht einem im Verhältnis 2:3 ins Schnelle übersetzten Dreizylinder-Viertaktmotor. Solche Motoren werden im allgemeinen nicht gebaut und es ist daher sinnvoller, eine 2-Läufer-Kreiskolbenmaschine als gleichwertig mit einem Sechszylinder-Viertaktmotor zu bezeichnen, wobei diese Gleichwertigkeit nur für den Verlauf des Drehmomentes zutreffend ist." HDP (talk) 19:25, 29 March 2024 (UTC)

+1. Nothing to add here. --Johannes (Talk) (Contribs) (Articles) Johannes (Talk) (Contribs) (Articles) 20:26, 29 March 2024 (UTC)

About Figure 11: you are right, I wrote MPa instead of bar, and also didn't realize that the source reported a six-cylinder with same torque, so necessarily with different V_k. I edited the image.

Also I see you edited the formulas of the "two chambers" section. Why is that? Isn't now less readable because the three section are formatted differently? Edoriel (talk) 21:59, 23 May 2024 (UTC)

Please tell me what is lost via the google translation.

To me it is all very clear from the text I posted: he recognize both the analogy, the single cylinder two-stroke and the three cylinder with gear-set. Edoriel (talk) 22:08, 23 May 2024 (UTC)

The thing is that the source states that your theory only applies when one compares the gradients of two engines' torque curves. That is lost in Google Translate I reckon. Best regards, --Johannes (Talk) (Contribs) (Articles) 05:50, 24 May 2024 (UTC)

References