About rotary internal combustion engines

Mazda has a sports car that uses this technology.

Introduction to rotary engines

Reciprocating piston engines are now commonly used in commercial automobiles. There is another type of engine that is well known, but rarely used, and this 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, thus 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 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. Because 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]History of the rotor engine

The 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 kind of engine was invented by a German, Figgas Wankel (Felix Wankel, 1902-1988), who, on the basis of summarizing the research results of his predecessors, solved some key technical problems and developed the first successful rotor engine.

Wankel was born in Germany in 1902, and from 1921 to 1926, he 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 lot of time working on the development of the rotor engine. 1927, a series of technical problems such as airtightness and lubrication, etc. were finally overcome. During World War II, Wankel served the Luftwaffe Ministry.

In 1951, Figgas Winkel signed a contract with the German company NSU on the development of rotor engines. 1954 April 13, NSU developed the first successful rotor engine, and in 1958, a series of tests on this engine. 1960, Winkel rotor engine in a seminar in the German Association of Engineers for the first public discussion. 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 quiet and smooth, may replace the traditional piston engine.

Mazda, which has always had a penchant for new technology, invested heavily in this 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, the automotive industry, some people have doubts about the market prospects of this engine. 70's oil crisis broke out, 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, research and production of rotary engine alone, and pay a considerable amount of money to this rotary engine. Mazda was the only company that was still convinced of the potential of rotor engines, and researched and produced rotor engines on its own, at considerable cost. They gradually overcame the shortcomings of the rotor engine, and successfully transitioned from experimental to commercial production, and the RX-7 sports car installed with a rotor engine entered the U.S. market, impressively.

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 from the structure is the most suitable for burning hydrogen, and the most "clean", because hydrogen combustion is discharged after the water vapor, there is no pollution of the environment. 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 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 is directly the combustion of gas expansion force into driving torque. Compared with the reciprocating engine, the rotor engine canceled the useless linear motion, so the same power rotor engine size is smaller, lighter weight, and lower vibration and noise, has a greater advantage.

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 body does not rotate, the inner gear ring and gear teeth ratio of 3:2. The above movement relationship makes the apex of the triangular rotor 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 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

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 piston's linear motion into rotary motion, you must use the crank connecting rod mechanism. Rotor engine is different, it is directly the combustion of gas expansion force into driving torque. Compared with the reciprocating engine, the rotor engine canceled the useless linear motion, so the same power rotor engine size is smaller, lighter weight, and lower vibration and noise, has a greater advantage.

The motion of the rotor engine is characterized by: the center of the triangular rotor rotates around the center of the output shaft while 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 body does not rotate, the inner gear ring and gear teeth ratio of 3:2. The above movement relationship makes the apex of the triangular rotor trajectory (i.e., the shape of the cylinder wall) like the "8" shape. 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.

With a rotary engine, the expansion pressure acts on the sides of the rotor. This pushes one of the three faces of the triangular rotor towards 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 towards the center of the output shaft (see Pb in the figure), 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 is constantly changing, and the four processes of intake, compression, combustion, and exhaust are accomplished one after another in the cycloidal cylinder. Each of these processes is carried out at a different location in the oscillating cylinder, which is clearly different from the reciprocating engine. Reciprocating engines have all four processes in one 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 the model 13B twin rotor engine, 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 variation in working volume for a rotary engine is shown below, along with a comparison to a four-cycle reciprocating engine. Although in both engines the studio volume varies steadily in a wavy 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 quite slowly, resulting in more relaxed intake and exhaust times, facilitating the operation of systems that are capable of higher power performance.

[edit]Rotor engine applications

Now that Mazda's rotor engine has been passed down to the RX-8, what advances have been made with this RENESIS? First of all, the intake hole area has been increased by 30%, making the engine's 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 and intake port are located on the front and rear sidewalls, which solves the HC pollution problem on the spot, and also makes the intake and exhaust completely non-overlapping, so that there is no intake air leakage into the exhaust pipe, and also opens a vent hole on each of the front and rear sidewalls, so that the engine exhaust holes become two to enhance the efficiency of the exhaust, in order to achieve the purpose of the high-revolutionary speeds. (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 didn't happen overnight, it was continually modified bit by bit to create the current RX-8!

[edit]Advantages and Disadvantages

The rotor engine's rotor makes one revolution every time it rotates, which has the advantage of a high horsepower-to-volume ratio (more power from a smaller engine volume) compared to the two revolutions of a typical four-stroke engine. 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 greatly reduces the possibility of failure 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 a smaller size, light weight, low center of gravity, and so on.

In contrast, because the three combustion chambers of a rotary engine are not completely isolated, it is easy for the oil seals to wear out and cause air leakage after a period of time, significantly increasing fuel consumption and pollution. The unique mechanical structure also makes this type of engine more difficult to maintain.

Although rotary engines have the characteristic of producing high output at high speeds with small exhaust volumes, due to the difference in operating characteristics between rotary engines and reciprocating engines, countries around the world use the actual exhaust volume of rotary engines multiplied by two as a benchmark for comparison with reciprocating engines when formulating tax rules related to engine exhaust volume. 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.