Rotary engine (discussing the advantages of rotary engine)
Speaking of rotary engine, I believe many riders can chat for a while, such as the famous Mazda RX7, or the Le Mans champion 787B; It shined brilliantly in the development of internal combustion engines, but quickly declined after a short period of glory. How strong is the rotary engine? Why can’t internal combustion engines become mainstream?
White Comet
This article only gives a reasonable description of the advantages and disadvantages of the rotary engine. Although the rotary engine was promoted by Mazda, the rotor does not belong to Mazda alone. Although the rotary engine is classic, it also has many shortcomings. The problems brought by the shortcomings have outweighed the benefits brought by the advantages, so the rotary engine will gradually wither and decline. Hats off to Mazda nonetheless. Without Mazda and the rotary engine, it will be difficult to be praised and remembered by the world, and a miracle may appear in the industrial field!
The origin of the engine
The prototype of the rotary engine was developed by the German Figas Wankel ) built (one of the modern prototypes). The similarity between a rotary engine and a reciprocating piston engine is that both rely on the expansion pressure generated by fuel combustion to push parts to do work (chemical energy is converted into mechanical energy); the difference lies in the way the expansion pressure generated by fuel combustion is pushed. The expansion pressure obtained by burning fuel in a reciprocating piston engine pushes down on the piston (connecting rod), which rotates with the crankshaft!
Mercedes-Benz C111 equipped with a rotary engine
The expansion pressure obtained by the engine burning fuel is to push the side of the triangular rotor, so that the rotor starts The rotating rotor drives the eccentric shaft to rotate; Mazda was not the only company that developed and mass-produced the rotary engine in the first place, but four car companies at the same time, GM, Honda, Ford, and Mercedes-Benz also purchased the patent of the rotary engine from NSU. For example, the Mercedes-Benz C111 is equipped with a rotary engine as shown in the picture above; however, compared with these rich and powerful car companies, Mazda (Toyo Kogyo), which had insufficient financial resources at that time, had already bet all its wealth on the rotor!
Super power density of the rotor
The rotary engine is different from the reciprocating piston engine, the crankshaft of the reciprocating piston engine rotates twice Once, four strokes are completed, and only one work is done (two strokes are another matter); as shown in the figure above, the triangular rotor rotates once (360°), and three ignitions can be completed (three times of work, and each ignition is a process of doing work. ), and the triangular rotor rotates once, which can drive the eccentric shaft (equivalent to the crankshaft of the piston engine) to rotate three times, which is equivalent to doing work by rotating the eccentric shaft (crankshaft) once!
The crankshaft of the piston engine makes two revolutions to do work once, so the power density of the rotary engine is stronger. Under the same displacement, the power of the rotary engine can reach twice that of the piston engine. Of course this is relative (assuming that the speed phaseThe difference is not big, there is no supercharger system); so when calculating the displacement of the rotary engine, the actual displacement*2. For example, the displacement of the rotary engine of the Le Mans champion 787B is 2.6L, but after multiplying by a factor, it is 5.2L, and the machine equipped by the opponent is a 5.0L V8 (1991). This is the conversion method of the displacement of the rotary engine. The actual displacement *2 is calculated according to the purchase procedures of participating groups and ordinary consumers!
Simple structure
The stable structure can easily obtain super high speed.
In the era of prototype development, turbocharging technology was not yet common. In that period, increasing the power of an internal combustion engine was nothing more than increasing displacement and revs. Power = torque * speed means that the higher the speed, the higher the output power. However, the rotary engine has no crank connecting rod part, gas distribution part, and is not even integrally formed with the eccentric shaft (crankshaft)! We must know that if the reciprocating piston engine wants to achieve high speed, it needs the high precision of the crankshaft. In that era, it was very difficult for a reciprocating piston engine to achieve a stable high speed!
The rotary engine has a simple structure, consisting of a cocoon shell (engine cylinder), a triangular rotor and an eccentric shaft, and has very low requirements for the accuracy of the eccentric shaft . In other words, in the era when the processing technology and precision were not ideal, the rotary engine was a better solution to achieve lower cost (processing and materials) and stronger performance. At that time, the speed can reach 13,000 rpm, which is why the rotary engine has attracted the attention of many car companies. Rotary engines are a better solution for lower cost (processing and materials) and higher performance.
Small in size and light in weight
The rotary engine has no crank connecting rod and valve mechanism, and the small displacement is used as a large displacement It is used in large quantities (such as 1.3L RX8 and 2.6L racing car 787B), so the volume of the rotary engine is small, which has the advantages of being easy to arrange and not occupying space. Even if the car is equipped with a double-wishbone suspension, it is not difficult to equip it with a large suspension, and it is also beneficial to the balance and center of gravity of the vehicle. No one can say anything about this part.
Each stroke of the rotor
Uneven heating of the cylinder block
As shown in the figure above, each process when the rotor engine is running It can be seen that the air intake and fuel injection (not shown in the figure) of the rotary engine always appear in the upper part of the cocoon shell, while the ignition and work are completed in the lower part of the cocoon shell (for easy understanding, the upper and lower two part), which would result in a lower temperature in the upper left part of the cocoon shell and a higher temperature in the lower right part of the cocoon shell. Long-term operation of the cocoon shell will inevitably deform due to uneven heating for a long time, and some sealing parts will fail. The piston engine completes four strokes in the same position!
The dynamic combustion chamber leads to poor combustion.
After the engine piston reaches the top dead center, there is still a part of the air in the cylinder (the right of the picture above). this emptiness is burningroom. For a reciprocating piston engine, the combustion chamber is stationary (relatively speaking), and a relatively stationary combustion chamber is very helpful for combustion. However, rotary engines are not. The combustion chamber of this product is dynamic, that is, the position is moving (the double spark plug on the left side of the figure below). The chaotic vortex makes the flame spread disorderly, resulting in poor combustion. Even if Mazda gives two spark plugs, it can only be improved, not solved!
This results in a rotary engine with very low fuel consumption and emissions. For example, the 1.3L dual-rotor self-priming engine on the Mazda RX8, nicknamed 3.0L power, is 5.0L friendly; the 1.3L dual-rotor self-priming engine on the RX8 can provide about 231 horsepower, 211nm torque, and 8200 rpm. This data is indeed similar to 3.0L for grocery shopping, but it is not eye-catching for some performance versions of reciprocating piston machines, such as Honda’s 2.0L self-priming F20C/K20A, Nissan’s 2.5L self-priming VQ25. After all, the 1.3L=2.6L reciprocating piston machine
2.5L VQ25 can provide 240 horsepower, and the 2.0L self-priming K20A/F20C developed by Honda It can also reach 240 horsepower or even higher. Therefore, the advantages of high-speed and high-power rotary engines are not obvious. Because the processing technology and technology have been greatly improved in this era, reciprocating piston engines can also obtain ultra-high speed and high rising power. So, what is the significance of the existence of the rotary engine? Nissan VQ25 is super easy to maintain, uses mineral oil, has a long service life, does not need high oil to start, and high-speed flameout, except that it does not have the characteristics of small size and light weight of the rotor machine, but these are useless for civilian vehicles. Significance (low fuel consumption, low emission and weight loss are meaningless)!
So the rotary engine back then was really strong, but today’s rotary engine has little performance advantage over the piston engine, and it can be said that there is no such advantage. The performance that the rotary engine can obtain is the same as that of the piston engine, but the piston engine could not achieve it in the 1960s and 1970s, when the performance of the rotary engine crushed the piston engine. In fact, as early as the 1980s, the advantages of the rotary engine were no longer obvious, otherwise Mazda would not have accompanied Le Mans for more than 10 years!
However, 787B won the championship in the end. Although there are too many elements of luck, it is undeniable that luck is also part of strength. But there’s no conspiracy behind the rotorcraft ban. Mazda 787B won Le Mans in 1991, but as early as 1989, the FIA launched a plan to match the 3.5L piston engine used by Le Mans to match F1. In 1990, it was finally determined that the rotary wing engine was banned at Le Mans. In 1991, the C1 group began to ban rotary engines, while the C2 group gave a one-year grace period. The Mazda 787B belongs to the C2 group, which means Mazda knew about Le Mans before winning the title in 1992.
So, there is no conspiracy behind the ban on rotary engines, just a compromise under environmental rules; The advantage of the engine over the piston engine is no longer there. In 1991, the 787B did win by two laps, but Le Mans had to run 3 or 400 laps for endurance. In previous years, it took dozens of laps to win the championship. Examples abound; over 10 years, the Mazda 757 was 35 laps behind the winner in 1987, 56 laps behind in 1988, 23 laps behind in 1989 and 50 laps behind in 1990.
This is actually the most authentic rotary engine, not as powerful as many riders imagined; in 1991, 787B received special care to lose 170kg , with the help of Mercedes-Benz Jaguar (both failed), the 787B won the championship. It is undeniable that 787B is very strong. Which player is not strong in the top field? However, the rotary engine was banned and Mazda won the championship, but many drivers would rather believe that Mazda was sad. The rotor has its powerful performance, but today it seems that the advantages are not great, and the disadvantages still exist. Enough if not durable and eco-friendly to make it obsolete!