In short, tip erosion.

What makes you think that major motor manufacturers are *not* studying other engines?

They were always difficult: the original by NSU back in the 70s was not stable and consumed a lot of fuel. And even Mazda didn't manage to get the latter problem fixed. The development went away from combustion engines because of (1) prognosis of lack of oil etc in the early years of the century, (2) the deleterious effects on climate.

Funny, that this question shows up under question they think I can answer for me, as I'm a neurologist ...

Thank you very much sir for the reply. Nice to meet you

As far as I know, the Wankel engine was obtained by Felix Wankel considering rotary piston systems. Briefly, working with the NSU factory, he proposed two different mechanisms based on a peritrochoid, in which the operating chamber was created when the rotating piston was moving respect to the statoric case. The research started in 1954 and several working engines were built during 1957-1960. As consequence, several industries (e.g. Nissan, Toyota, Rolls Royce, Curtiss Wright) bought the patents of the Wankel engines to start a commercial production of their products. The theorical advantages of rotating engines, such as Wankel engine, are due to:

-compactness;

-low vibration magnitude level;

-absence of valves for the intake and exhaust;

-light weight;

-low noise.

On the other hand, the main problems of the Wankel engine are:

-friction of the apex seal;

-combustion, that is bound by the geometry of the rotor and the statoric case ;

-non-homogeneous temperatures of the statoric case, that requires an accurate study of the cooling system.

Clearly, the current requirements due to the reduction of polluting substances in the combustion, especially of the internal combustion engines, requires a series of expedients to improve the quality of the combustion in terms of fuels, geometry of the combustion chamber, air flow and injection time. As consequence, the Wankel engine suffers these problems, because the combustion chamber is long and narrow with the consequence that the ratio total volume to external surface is less favourable than that of reciprocating engines.  As result, a great loss of unburned gas and a slow combustion process, that may influence the formation of polluting substances, occur. However, other reasons are possible and, even if the answer to your question would require further explanations,   I hope that my answer has been useful.

Best regard

Good evening Joe,

 I know that Alfa Romeo had the patent, as well as Porsche, Graupner and others industries. Certainly the research about Wankel, has solved  several problems about mechanical stresses, oil consumptions and reliability. However, in literature I found several studies about apex sealing system (and also about combustion)  that aimed to improve the efficiency of the Wankel engine. In my opinion, I think that the problems of the sealing and friction are a characteristic of the Wankel engine as demonstrated by several paper proposed in literature during the last 20 years. 

About micro cars in Europe:

In Italy,  I usually see several micro cars driven by young people;  I do not know the costs, even if I think that it would be higher than a normal motorcyle for people that have not obtained yet the driving license for cars. However, in Italy (and maybe in the other countries of the Europe) it is necessary to pass a little exam to obtain a driving license for micro cars and motorbike. 

Best regards and  best wishes for a happy new year.

Marco

Dear Joe,

thanks for your answers and for your documents. My previous statements were only general considerations due to my research on Wankel engines in which I found several papers about the modelling of the dynamic of the apex sealings, as well as the the modelling of the combustion. Clearly, many problems of the engine were solved (such as wear, lubrication and leakages) otherwise it would have been impossible to create Mazda RX8. Moreover, it is important to highlight that several applications were characterized by different operating conditions entailing different considerations about lubrications or bearing loads.

Best regards

Marco

Dear T.Karthikeya Sharma,

I think due to poor fuel efficiency (consumes more fuel) and generate high emission it is outdated now.

The Wankel engine is a type of internal combustion engine using an eccentric rotary design to convert pressure into rotating motion. For transportation earlier it used, wankel engine a vehicle engine operating with a three-part rotor that turns in a close-fitting chamber, so that the power stroke is applied sequentially to each of the faces of the rotor. Unlike a piston 4 cycles engine the Wankel rotary only needs one crank shaft revolution to complete its cycle, just like a two stroke piston engine Compared to a reciprocating engine, a wankel engine is simpler, lighter, contains fewer moving parts, and can burn lower octane fuel. However, it produces incomplete combustion and therefore high emissions and typically consumes more fuel than a piston engine. It has poor fuel efficiency and emissions. It has continued to work on the technology, however, as it is one of the company's signature features.

Exact problem

(1) The Wankel engine has problems in fuel efficiency and emissions when burning gasoline. The slowness of a gasoline mixture to ignite, its slowness in flame propagation speed and the quenching distance of 2mm to hydrogen's 0.6mm on the compression cycle, results in the fuel mixture in the long moving combustion chamber not being fully burnt, wasting fuel that would have created power reducing efficiency. The gap between the rotor and the engine housing is too narrow for gasoline on the compression cycle; however this narrow gap is fine for hydrogen. The narrow gap is needed to create compression. This unburnt fuel when burning gasoline is ejected into the atmosphere via the exhaust pipe, giving emission problems. This is not a problem when using hydrogen fuel as all the fuel mixture in the combustion chamber is burnt, using all the fuel to create power, giving near zero emissions and raising fuel efficiency by 23%.

(2) The shape of the Wankel combustion chamber is more resistant to preignition operating on lower-octane rating gasoline than a comparable piston engine.

(3) If we see the HC emissions level, seal leakage into the exhausting chamber is a source of unburned HC in addition to the quench layer and crevice(the pressure ratio between the combusting chamber and the preceding exhausting chamber is usually above the critical ratio) too. The distribution of HC emissions with time throughout the exhaust process is also different from a piston engine. Also, while NO concentrations decrease somewhat as HC concentrations increase, mixing between quench layer and leakage gas where the hydrocarbon concentration is high, and burnt gases which contain the CO2, CO and NO, is apparently extensive.

Mazda had improved the fuel efficiency of the thermal reactor system by 40% with the RX-7 introduction in 1978. However, Mazda eventually shifted to the catalytic converter system. Mazda is still continuing development of next-generation of Wankel engines.

Ashish

Dear Joy,

Thank you very much for your letter.

Yes I am agreeing with you in a totality. Very interesting written by you. I think you are excellent with auto knowledge. Couple of improved approach what you said it is absolute correct can fit wankle, such as LDR (rotor recess in the leading edge of combustion chamber) engine, which has better exhaust emissions profiles, and reed-valve controlled intake ports, which improve part-load and low rpm performance.

Two references you can use for quenching distance are given below.

1. https://www.cder.dz/A2H2/Medias/Download/Proc%20PDF/PARALLEL%20SESSIONS/%5BS22%5D%20Internal%20Combustion%20Engines/13-06-06/169.pdf

2. ^ Jump up to:a b https://core.ac.uk/download/pdf/47252483.pdf

It’s very interesting you have quoted with example of Florida University proposal. I am adding one more; the simplicity of the Wankel engine makes it well-suited for mini, micro, and micro-mini engine designs. The Microelectromechanical systems (MEMS) Rotary Engine Lab at the University of California, Berkeley, has previously undertaken research towards the development of Wankel engines of down to 1 mm in diameter, with displacements less than 0.1 cc.

There are many uses of wankel design. There are plenty of developments still continuing from the major auto manufacturer’s whole over the world. Couple of manufacturers effort I am going to highlight.

The sailplane manufacturer Schleicher uses Wankel engines in its self-launching models ASK-21 Mi, ASH-26E, ASH-25 M/Mi, ASH-30 Mi, ASH-31 Mi, ASW-22 BLE, and ASG-32 Mi.

Pratt & Whitney Rocketdyne has been commissioned by DARPA to develop a diesel Wankel engine for use in a prototype VTOL flying car called the "Transformer".

The French company Citroën had developed Wankel powered RE-2 [fr] helicopter in the 1970s.

The Wankel design is used in the seat belt pre-tensioner system in some Mercedes-Benz and Volkswagen cars.

Ingersoll-Rand built the largest-ever Wankel engine, with two rotors, which was available between 1975 and 1985, producing 1,100 hp (820 kW). A one rotor version was available producing 550 hp (410 kW). The displacement per rotor was 41 liters, with each rotor being approximately one meter in diameter. The engine was derived from a previous, unsuccessful Curtiss-Wright design, which failed because of a well-known problem with all internal combustion engines: the fixed speed at which the flame front travels limits the distance combustion can travel from the point of ignition in a given time, thereby limiting the maximum size of the cylinder or rotor chamber which can be used.

In addition for use as an internal combustion engine, the basic Wankel design has also been used for gas compressors, and superchargers for internal combustion engines, but in these cases, although the design still offers advantages in reliability, the basic advantages of the Wankel in size and weight over the four-stroke internal combustion engine are irrelevant.

Aixro of Germany produces and sells a go-kart engine, with a 294 cc-per-chamber charge-cooled rotor and liquid-cooled housings. Other makers are: Wankel AG, Cubewano, Rotron and Precision Technology USA.

Yanmar of Japan produced some small, charge-cooled rotory engines for chainsaws and outboard engines.One of its products is the LDR (rotor recess in the leading edge of combustion chamber) engine, which has better exhaust emissions profiles, and reed-valve controlled intake ports, which improve part-load and low rpm performance.

Ashish

Dear Joe,

Thanks for sharing information.I have replied your reference query.

Ashish