What are the advantages and disadvantages of a rotor engine versus a piston engine?

Reciprocating piston engines are commonly used in commercial automobiles today. There is another type of engine that is well known but rarely used, which is the delta-piston rotary engine. The rotary engine is also known as the Miller cycle engine. It uses a triangular rotor rotating motion to control compression and emissions, very different from the linear motion of the traditional piston reciprocating engine. This kind of engine was invented by the German Figgas Wangkel, on the basis of summarizing the results of previous research, solved some key technical problems and developed the first successful rotor engine. General engine is a reciprocating engine, the work of the piston in the cylinder to do reciprocating linear motion, in order to convert the linear motion of the piston into rotary motion, you must use the crank connecting rod mechanism. Rotary engine is different, it will directly convert the combustion of gas expansion force into driving torque. Compared with the reciprocating engine, the rotor engine eliminates the useless linear motion, so the same power rotor engine size is smaller, lighter weight, and lower vibration and noise, with greater advantages. Rotor engine motion is characterized by the center of the triangular rotor around the output shaft center rotation at the same time, the triangular rotor itself around its center rotation. In the triangle rotor rotation, the triangle rotor center as the center of the inner gear ring and the output shaft center as the center of the gear mesh, gear fixed in the cylinder block does not rotate, the inner gear ring and gear teeth ratio of 3 to 2. The above movement relationship makes the apex of the triangular rotor trajectory (i.e., the shape of the cylinder wall) like the "8" shape. Triangle rotor cylinder into three independent space, three space each successively complete the intake, compression, work and exhaust, triangle rotor rotation week, the engine ignition work three times. As a result of the above movement relationship, the output shaft speed is three times the rotor rotation speed, which is completely different from the reciprocating engine piston and crankshaft 1:1 movement relationship. [edit this paragraph] The history of the development of the rotor engine Rotor engine (Wankel Engine, Rotary Engine) is also known as the Miller cycle engine (Miller Cycle Engine). It uses a triangular rotor rotary motion to control compression and emissions, and the traditional piston reciprocating engine linear motion is very different. This engine was invented by German Felix Wankel (1902-1988), who, on the basis of summarizing the research results of his predecessors, solved some key technical problems and successfully developed the first rotor engine.

Wankel was born in Germany in 1902, and from 1921 to 1926 was employed in the sales department of a scientific and technical publishing house in Heidelberg. 1924, Wankel established his own company in Heidelberg, where he spent a great deal of time working on the development of the rotor engine, and in 1927, a series of technical problems such as airtightness and lubrication were finally solved. During World War II, Wankel served the Luftwaffe Ministry.

In 1951, Figgas Winkel signed a contract with the German company NSU for cooperation in the development of rotor engines. 1954 April 13, NSU developed the first rotor engine, and in 1958 a series of tests were carried out on the engine. 1960, Winkel's rotor engine was discussed for the first time in public at a symposium of the Association of German Engineers. In 1960, the Winkel rotor engine made its first public presentation at a symposium of the German Society of Engineers. Three years later, NSU company in Frankfurt motor show on display equipped with Winkel rotor engine of the new model. 1964, NSU company and Citroen in Geneva to form a joint venture COMOBIL company, the first time the rotor engine in the sedan to become an official product. 1967, Japan's Toyo Kogyo will also be installed in the rotor engine in the Mazda sedan to start batch production. At that time, the industry believes that this engine structure is compact and lightweight, running quietly and smoothly, may replace the traditional piston engine.

Mazda, which has always had a penchant for new technology, invested heavily in the technology and bought it from Winkel. Because this is a high-tech, know the technology of very few people, no one will repair the engine is broken, and fuel consumption, some people in the automotive industry on the market prospects of this engine doubt. 70 years the outbreak of the oil crisis, the countries are busy coping with all aspects of the difficulties and do not have time to pay attention to the development of rotary engine, only Mazda is still convinced of the potential of rotary engine, alone research and production of rotary engine Mazda was the only company that was still convinced of the potential of rotor engines and researched and produced them on its own, paying a considerable price for it. They gradually overcame the shortcomings of the rotor engine, successfully transitioned from experimental to commercial production, and impressively entered the U.S. market with the RX-7 sports car fitted with a rotor engine.

In a world where environmental awareness is growing and petroleum resources are being depleted, the study of hydrogen as a power source has become a major issue. When Mazda insisted on the rotor engine is structurally the most suitable for combustion of hydrogen, and the most "clean", because hydrogen combustion is discharged after the water vapor, the environment does not have any pollution. Mazda adapted the rotor engine of the RX-7 sports car so that it could be fueled by hydrogen. This engine was assembled in the Mazda HR-X car, and the 1-cubic-meter fuel tank absorbed and stored 43 cubic meters of compressed hydrogen, and it was able to travel 230 kilometers at a speed of 60 kilometers per hour, which aroused the attention of people from all walks of life. Since rotor engines are very different from conventional engines, from production and assembly to maintenance and repair, development costs are large. Coupled with the reciprocating piston engine in the power, weight, emissions, energy consumption, etc. than in the past have improved significantly, the rotor engine did not show significant advantages, so the major automotive companies are not motivated to develop and utilize, the only Mazda a bitter support.

The general engine is a reciprocating engine, the work of the piston in the cylinder to do reciprocating linear motion, in order to convert the linear motion of the piston into rotary motion, you must use the crank connecting rod mechanism. Rotor engine is different, it will directly convert the combustion expansion force of combustible gas into driving torque. Compared with the reciprocating engine, the rotor engine eliminates the useless linear motion, so the same power rotor engine size is smaller, lighter weight, and lower vibration and noise, with greater advantages.

The motion of the rotor engine is characterized by: the center of the triangular rotor rotates around the center of the output shaft at the same time, the triangular rotor itself rotates around its center. In the triangular rotor rotation, the triangular rotor center as the center of the inner gear ring and the output shaft center as the center of the gear mesh, gear fixed in the cylinder does not rotate, the inner gear ring and gear teeth ratio of 3:2. The above movement relationship makes the triangular rotor apex of the trajectory (i.e., the shape of the cylinder wall) like a "8" shape. Triangular rotor cylinder into three independent spaces, three spaces each successively complete the intake, compression, work and exhaust, triangular rotor rotation week, the engine ignition work three times. Due to the above movement relationship, the output shaft speed is three times the rotor rotation speed, which is completely different from the reciprocating engine piston and crankshaft 1:1 movement relationship. [edit] The working principle of the rotor engine General engine is a reciprocating engine, the work of the piston in the cylinder to do reciprocating linear motion, in order to convert the linear motion of the piston into rotary motion, you must use the crank connecting rod mechanism. The rotary engine is different, it will directly convert the combustion and expansion of gas into driving torque. Compared with the reciprocating engine, the rotor engine eliminates the useless linear motion, so the same power rotor engine size is smaller, lighter weight, and lower vibration and noise, with greater advantages.

The motion of the rotor engine is characterized by: the center of the triangular rotor rotates around the center of the output shaft at the same time, the triangular rotor itself rotates around its center. In the triangular rotor rotation, the triangular rotor center as the center of the inner gear ring and the output shaft center as the center of the gear mesh, gear fixed in the cylinder does not rotate, the inner gear ring and gear teeth ratio of 3:2. The above movement relationship makes the triangular rotor apex of the trajectory (i.e., the shape of the cylinder wall) like a "8" shape. Triangular rotor cylinder into three independent spaces, three spaces each successively complete the intake, compression, work and exhaust, triangular rotor rotation week, the engine ignition work three times. Because of the above movement relationship, the output shaft speed is the rotor rotation speed of three times, which is completely different from the reciprocating engine piston and crankshaft 1:1 movement relationship

Comparison of rotary engine and traditional reciprocating engine reciprocating engine and rotary engine rely on the air-fueled mixture combustion of the expansion pressure generated to obtain the rotary force. The difference in the mechanism of the two engines is in the way the expansion pressure is used. In a reciprocating engine, the expansion pressure generated on the top surface of the piston pushes the piston downward, and the mechanical force is transmitted to the connecting rods, which turn the crankshaft.

In rotary engines, the expansion pressure acts on the sides of the rotor.　This pushes one of the three sides of the triangular rotor toward the center of the eccentric shaft (see force PG in the diagram). This movement takes place under the force of two component forces. One is a centripetal force pointing toward the center of the output shaft (see Pb in the diagram), and the other is a tangential force (Ft) that rotates the output shaft.　

The internal space of the housing (or rotor wire chamber) is always divided into three studios.　During the movement of the rotor, the volume of these three chambers keeps changing, and the four processes of intake, compression, combustion, and exhaust are accomplished one after another in the oscillating-wire cylinder. Each of these processes is carried out at a different location in the oscillating cylinder, which is clearly different from the reciprocating engine. In a reciprocating engine, all four processes take place in a single cylinder.

The exhaust capacity of a rotary engine is usually expressed in terms of unit studio volume and the number of rotors. For example, for a two-rotor engine model 13B, the displacement is "654cc × 2".

The unit studio volume is the difference between the maximum and minimum studio volumes; and the compression ratio is the ratio of the maximum and minimum volumes. The same definition is used on reciprocating engines.

The following figure shows the variation in working volume of a rotary engine and a comparison with a four-cycle reciprocating engine. Although in both engines the studio volume changes steadily in a wave pattern, there are significant differences between the two. The first is the angle of rotation of each process: the reciprocating engine rotates 180 degrees, while the rotor engine rotates 270 degrees, which is one and a half times more than the reciprocating engine. In other words, in a reciprocating engine, the crankshaft (output shaft) makes two revolutions (720 degrees) during the four processes, while in a rotor engine, the eccentric shaft makes three revolutions (1,080 degrees) and the rotor makes one. In this way, the rotor engine gets a longer process time and creates smaller torque fluctuations, resulting in smooth and fluid operation.

In addition, even at high speeds, the rotor rotates fairly slowly, resulting in more relaxed intake and exhaust times, facilitating the operation of systems that are capable of higher power performance. [edit] Application of the rotor engine Now that Mazda's rotor engine has been passed down to the RX-8, what advances have been made with this RENESIS? The first is that the intake hole area has been increased by 30%, making the engine intake enough to cope with the demand up to 10,000rpm. But we all know that this low speed will become very bad, so Mazda will be the original three intake holes two-stage design, and then evolved into three intake holes three-stage design, try to avoid the phenomenon of powerlessness of low speed, and in order to high-revolution, the unprecedented rotor will be made into a skeletonized shape, significantly reducing the weight of the rotor, so that the natural intake of the RX-8 can be pulled by the way of revs, to reach the 250hp The RX-8 can achieve 250 horsepower by pulling the revs. But the most innovative part of the RENESIS engine is the exhaust port. In the past, the exhaust port of the rotor engine was made on the wall of the air chamber, where some unburned oil and gas and a little bit of lubricating oil would be scraped into the exhaust pipe, causing pollution problems.

But on the RENESIS, the exhaust port is located on the front and rear sidewalls as well as the intake port, which solves the HC pollution problem on the spot, and also makes the intake and exhaust completely non-overlapping without any intake leakage into the exhaust pipe, and also opens up a vent hole on each of the front and rear sidewalls, so that the engine venting can be changed into two to enhance exhaust efficiency, in order to achieve the purpose of the high-revving engine. (I've heard that this is already the case with the 280ps RX-7.) That's why the RX-8 is able to produce 250 horsepower with a 1.3L exhaust volume and a natural air intake. Mazda's rotor engine achievement was not achieved overnight, it was through constant modification that the current RX-8 was created! [edit paragraph] Advantages and disadvantages The rotor engine's rotor operates once per revolution, which has the advantage of a high horsepower-volume ratio (more power can be produced from a smaller engine volume) compared to a typical four-stroke engine that operates once every two revolutions. In addition, due to the rotor engine's axial running characteristics, it does not require precise crankshaft balancing to achieve high running speeds. There are only two rotating parts in the whole engine, which greatly simplifies the structure and reduces the possibility of malfunction compared to the general four-stroke engine with more than twenty moving parts such as intake and exhaust valves. In addition to the above advantages, the advantages of the rotor engine also include smaller size, light weight, low center of gravity and so on.

Relatively, because the three combustion chambers of a rotary engine are not completely isolated, the engine is susceptible to air leakage due to wear and tear of the oil sealing material after a period of time, which can significantly increase fuel consumption and pollution. The unique mechanical structure also makes these engines more difficult to maintain.

While rotor engines have the characteristic of producing high output at high speeds with small exhaust volumes, due to the difference in operating characteristics between rotor engines and reciprocating engines, countries around the world use the actual exhaust volume of rotor engines multiplied by two as a benchmark for comparison with reciprocating engines when formulating tax rules related to engine exhaust volumes. For example, Mazda's RX-8 sports car with a rotor engine has an actual exhaust volume of only 1308 cubic centimeters, but in Japan it is 2616 cubic centimeters as the basis for calculating the tax level.