What are the disadvantages of traditional power?

Are many people confused when they see the professor's technical articles? It doesn't matter. Starting from today, the professor will start from the beginning, starting with the difference between the original gasoline engine and the diesel engine (several articles may be serialized, and I feel that I have dug a hole for myself), and explain the knowledge of gasoline engine from the technical point of view and the use point of view. If it's not too boring, you can "read" it to the professor. Oh, the professor will see how many people like it, and then consider whether to write more articles.

Engine is a general term, which can be called internal combustion engine in professional field. According to different fuels, it can be roughly divided into gasoline engine and diesel engine.

We can start with a picture. The main working part of the engine is the fuel nozzle. The fuel nozzle is generally arranged at the intake manifold of the vehicle using manifold injection, and the fuel is mixed with air through injection. Camshaft, the camshaft is responsible for controlling the opening and closing of the valve, so that air enters and exits the cylinder; The rocker arm is a connecting part between the camshaft and the valve; The valve controls the opening and closing of the intake and exhaust manifolds so that air can enter or be exhausted from the cylinders.

The whole is called cylinders, and the number or structure of cylinders depends on the design of the main engine factory, such as L4, V6, L6, V8, etc. The number represents the number of cylinders, and L or V represents the linear or V-shaped cylinder arrangement.

The piston, the piston moves up and down to do work, and the connecting rod and crankshaft convert the force of the piston's linear movement into the rotating force. The piston is connected with the crankshaft through a connecting rod, and the crankshaft is the main component of the engine power output; The crankshaft is connected with all the pistons in the engine, so that the work generated by all the pistons will be transferred to the crankshaft.

Spark plug, spark plug is the part that ignites the mixture. The article mainly discusses the four-stroke engine, but the following two-stroke engine will continue to talk about it. Most of the remarks below are based on the four-stroke engine.

Intake, if it is an engine with manifold injection, the intake stroke is to suck the mixture in the intake manifold into the cylinder. The camshaft will open the intake valve (the cam acts on the rocker arm, and the rocker arm acts on the valve, compressing the upper spring. After the camshaft leaves the rocker arm, the valve closes due to the spring). When the intake valve is opened, the piston moves downward and the mixture enters the cylinder.

Compression: After the intake stroke, the piston reaches the bottom dead center, and neither the intake valve nor the exhaust valve will open during the compression process. At this time, the piston rises and the mixture in the cylinder is compressed.

Work (work), after the compression stroke, the piston reaches the top dead center, the spark plug generates cremation, ignites the mixed gas, the flame will gradually disperse, and the piston will be pushed down again by the ignited and expanded mixed gas.

Exhaust: When the piston reaches the bottom dead center after the power stroke, it is necessary to exhaust the burnt exhaust gas from the cylinder. This is the exhaust stroke. At this time, the camshaft will push the rocker arm, open the exhaust valve, and the piston will move upward to push the burnt exhaust gas out of the cylinder through the exhaust valve.

Of course, all the strokes above are based on the alto cycle, excluding Atkinson cycle and Miller cycle.

The main difference between gasoline engine and diesel engine is that diesel engine only injects fuel into the cylinder after the compression stroke, and gasoline has certain explosion-proof performance. For example, 92# and 95# are labels to measure the explosion-proof standard of gasoline, but diesel engines are different.

The difference between diesel engine and gasoline engine is that only air enters the cylinder in the intake stroke of diesel engine, and no gasoline is mixed with it; Then the piston rushes on the compression stroke like a gasoline engine, and the spark plug of the gasoline engine is replaced by a nozzle. Because there is no fuel in the cylinder during compression, the compression ratio can be higher than that of the gasoline engine, for example, 15: 1 (ordinary gasoline engines are generally around 10: 1). Of course, the current gasoline engine can claim to achieve a higher compression ratio through Miller cycle and other means.

Higher compression ratio means higher pressure and temperature. With the increase of pressure and temperature, the air at the end of the compression stroke becomes very hot. Diesel fuel will be ignited when injected, and the subsequent power stroke and exhaust stroke are the same as those of gasoline engines.

Compression ratio is directly related to fuel economy. Theoretically, the higher the compression ratio, the higher the fuel efficiency. Therefore, a diesel engine with high compression ratio will theoretically have better fuel economy than a gasoline engine.

In addition, the diesel engine with high compression ratio has another advantage. When you want to modify a diesel engine, such as replacing a larger turbine and supercharger, the only thing you need to worry about is mechanical strength. However, for gasoline engines, if the compression ratio is 15: 1, the mixture may start to burn before the spark plug is ignited, causing problems such as knocking and jitter, while diesel engines only compress air, so this situation does not exist.

Rotor engine is a kind of engine form different from piston engine, which was invented by German Wankel, so rotor engine is also called Wankel engine.

As can be seen from the figure, there is a cavity in the middle of the rotary engine, inside which is a triangular rotor. The structure of a rotary engine is quite simple, consisting of a front side wall, a rotor chamber, a middle side wall, a rotor chamber and a rear side wall (because a general rotary engine consists of two rotor chambers, it can be understood as two cylinders).

The most famous one is Mazda's 65438+3B rotary engine, which is used in the famous RX7 and RX8 models. Let's take the 65438+3B engine as an example to introduce the rotary engine.

The rotor is equivalent to the piston of a piston engine; The eccentric shaft is equivalent to the crankshaft of a piston engine, and connects two rotors to rotate around the eccentric shaft, thus outputting power.

The working process of the rotary engine can be clearly seen from the rotor room. Similarly, a rotary engine is a four-stroke engine. There is an air inlet on the side of the rotor chamber. When the rotor rotates and sweeps them, it creates a vacuum to suck in air. It should be noted that there are air inlets on both sides of the rotor, namely the front and rear side walls and the middle side wall, so air will enter from both sides at the same time.

As can be seen from the side, there are two round holes on the side of the rotor chamber, which are the locations where spark plugs are installed. Because the combustion chamber is very long when the rotor rotates, it is necessary to add the combustion speed of the mixture, so two spark plugs are used. With the rotation of the rotor, the burned exhaust gas will be discharged from the exhaust hole, and four strokes have been completed.

It should be known that the cycles in different stages in the rotor chamber occur at the same time (the rotor has three faces and the three faces are in different strokes at the same time). In addition, there is a rotor with a phase difference of 180 degrees from the first rotor, and the rotors in the two rotor cavities are in opposite states (as can be seen from the eccentric shaft). In this way, the balance on the shaft is also balanced when rotating. If the two rotors are in opposite states, there will be pitching moment before and after the eccentric shaft due to the phase difference of 180 degrees between the two rotors. Because the eccentric shaft rotates at any time and the force perpendicular to the axial direction is balanced, the vibration of the engine will be small and stable.

As can be seen from the figure, in addition to the above-mentioned hole, there is also an oil hole in the rotor cavity. The reason for this is to inject oil from here to lubricate various sealing strips. Piston engine can inject oil below the piston to lubricate the piston ring, while rotary engine needs oil nozzle to inject oil due to structural reasons. An oil pump is connected to each nozzle. Essentially, the oil pump is controlled by the throttle. As soon as the driver steps on the accelerator, the oil pump will start to inject oil into it, so the rotary engine needs to burn oil in design.

Another challenge of rotary engine is the sealing problem. It is necessary to ensure the sealing between each chamber in order to have good efficiency. In order to achieve the purpose of sealing, rotary engines will have edge seals and diamond seals. The diamond seal is installed at the top of the triangular rotor, which is pressed by the spring, so that it can be attached to the inner wall of the rotor cavity at any time, and at the same time, it is fixed by the corner seal, so that the rotor can maintain the seal when rotating. The same is true of the edge seal, which is tightly attached to the inside of the rotor cavity through the spring. Finally, the oil ring also needs a spring to keep the seal.

At the same time, there will be different holes in the rotor. When the rotor is manufactured, the engineer will put the rotor on the dynamic balancing machine, and then we can see the imbalance of the rotor, and then make it more balanced according to the instructions, so each rotor may have different holes. A machining groove for increasing the displacement of the rotor by cutting a part of the material on the rotor side.

First, there are few parts in the rotary engine, and it is precisely because of its simple design that it is more reliable.

Second, the rotary engine does not reciprocate, but all the movements are rotary. One of the disadvantages of reciprocating engines is the existence of reciprocating parts. When the reciprocating parts rotate at high speed, there will be a situation similar to the valve suspension effect (because the speed is too high, the valve can't keep up with the movement of the cam when it is closed, which leads to the decrease of engine efficiency, poor emission and even damage to the engine), while the rotary engine can reach a very high speed because it has no reciprocating parts.

Third, the power output is stable, because every time the eccentric shaft rotates, each rotor will have a power stroke (the piston engine only has one power stroke after two revolutions).

Fourth, the structure is compact. Because many unnecessary parts are omitted and there is no reciprocating motion, the volume of the rotary engine is quite compact. In this way, the output of high power is very small and light, which creates more space for the engine layout.

First of all, due to design problems, the thermal efficiency of rotary engine is low. At the same time, low compression ratio is also a problem of rotary engine, which is determined by the shape of combustion chamber of rotary engine. After the spark plug ignites the mixture, the rotor rotates and the flame begins to burn at the same time, but the shape of the combustion chamber gradually begins to become larger and the propagation distance is very long. At the same time, all oil and gas must be completely burned. With the expansion of the combustion chamber, it will become more difficult to ignite all the mixtures. Then, after the exhaust port is opened, some unburned mixture will be directly discharged to the outside of the engine, which is why the exhaust gas of the rotary engine is often seen spraying flames. This is because all the fuel can't be completely burned in the power stroke, so its thermal efficiency is low, fuel economy is not good, and emissions are poor.

Second, the problem of sealing. Because each chamber has a different stroke, it is not expected that gas can shuttle freely in the chamber, and each stroke will become meaningless, so there will be diamond seals, oil rings and edge seals to seal the rotor and prevent gas from flowing. However, the difficulty lies in that one side of the rotor cavity sucks air and the other side does work, and the temperature of the work stroke will be higher than that of the suction, resulting in a large temperature difference between the two, and it is very difficult to maintain the sealing performance, so there will be some air leakage.

Third, the emissions are poor. As mentioned above, when the rotary engine is burning, a certain amount of engine oil will be injected into the rotor cavity to help each side seal and lubricate and prevent wear, so the owner needs to check the engine oil regularly and add engine oil to ensure that the engine oil is at a normal level. When the engine oil is involved in combustion, the emission will become worse.

Fourth, the fuel economy is poor. Comparing the rotary engine with the traditional piston engine, we will find that the fuel economy of the rotary engine is really poor and the power has not been greatly improved. Take the engine on Mazda RX-8 as an example. The average fuel consumption per 100 kilometers 12.8L, but the engine output is only 235. Mercedes-Benz A45 AMG2.0T engine is 38 1 horsepower, and the fuel consumption per 100 kilometers is about 12. 1 1L, which shows how poor the fuel consumption performance of rotary engines is.

HEMI is an abbreviation. In the early 1900 s, the top of the engine cylinder was flat, which was called flat head design. This has the advantages of small volume and large area of lever head. HEMI is the name of the hemispherical cylinder head, which is also the origin of the name Hemi. It minimizes the surface area and maximizes the internal volume. During combustion, the internal surface of the cylinder will lose heat when doing work, so the smaller the surface area, the less heat will be consumed. The heat generated by combustion is used to do work. The more heat is lost, the lower the power of the engine. Therefore, minimizing the heat loss is helpful to improve the engine efficiency of the vehicle.

The goal of HEMI is to reduce heat loss and make it stronger. In addition, Hermione's spark plug is placed at the top of the hemisphere, which will make the engine burn better. But low compression ratio is the disadvantage of HEMI engine, and high compression ratio is the necessary condition for efficient engine. Therefore, engineers transformed the piston top into a hemisphere to conform to the design of the combustion chamber. However, this will make the piston heavier, and the crankshaft needs to overcome the extra weight to generate extra force during operation, so this design is not a good one. Therefore, with the development of technology, engineers constantly improve the design of HEMI engine.

The curve at the top of the piston in today's HEMI engine becomes more gentle. The main reason for this is to overcome: after the spark plug is ignited, the flame gradually spreads to all corners. For the traditional HEMI engine, the long propagation distance takes longer, so a more compact combustion chamber will make the combustion effect better.

At present, the top of the cylinder of most cars is roof-shaped. The roof-shaped cylinder head looks like a triangle from the side, and it can install four valves in one cylinder. Think about it. If the top of the cylinder head of HEMI engine is hemispherical, it will be more difficult to arrange four valves, but the design of the roof shape is much simpler. Just simply divide the four valves into two rows, and a four-valve cylinder will have better intake and exhaust airflow. Another advantage of the roof design is that the overhead camshaft can be arranged. HEMI engine will use push rod, and the design of push rod camshaft needs to overcome more inertia problems.

Now the HEMI engine will have two spark plugs, because it is difficult to meet the strict emission requirements by using only one spark plug, so the two spark plugs will have two ignition points, which will spread the flame faster than one ignition point and accelerate the combustion speed.

Generally speaking, the main feature of HEMI engine is its hemispherical combustion chamber.

The main difference between a two-stroke engine and a four-stroke engine is that the crankshaft of a two-stroke engine is ignited once every revolution, while the crankshaft of a four-stroke engine is ignited once every revolution. According to the above, we can know the working principle of four-stroke engine. For a two-stroke engine, it combines four strokes, but the piston will only move up and down once. When the piston goes up, that is, the compression stroke, it will ignite when it reaches the top dead center; When the piston descends, work, suction and exhaust will be completed in this step.

Two-stroke engines have no valves and camshafts that control the valves. There is a hole in the engine, which is equivalent to the intake and exhaust valve. This hole is controlled by a piston. When the piston goes down, the exhaust hole will be opened first, and the burnt gas will be discharged. When the piston continues to descend, it will compress the gas in the crankcase and the oil-gas mixture in the crankcase. When the piston continues to descend, it will open the air inlet, so the oil-gas mixture enters the cylinder, and then the piston rises, compressing the sucked oil-gas mixture upward. When the piston starts to rise, because the pressure in the lower crankcase becomes smaller, a small one-way valve next to the crankcase will open, allowing the oil-gas mixture to enter the lower crankcase.

It is worth noting that the air inlet and air outlet will be opened at the same time. Although engineers prevent combustible gas from flowing directly to the exhaust by some means, it cannot be completely avoided. One method is loop scavenging, and the other method is to design a special exhaust to generate pressure and send it back. When part of the oil-gas mixture reaches the exhaust port, the previously combusted gas will expand in the expansion chamber and then bounce back, so that the unburned combustible oil-gas mixture is sent back to the cylinder for compression combustion.

In addition, there will be oil-gas mixture in the crankcase of two-stroke engine, including crankshaft and connecting rod, while the crankcase of four-stroke engine is closed and full of engine oil, so the lubrication effect is better, so the life of four-stroke engine is longer. The crankcase of two-stroke engine is an oil-gas mixture, so it is necessary to add engine oil to gasoline to lubricate the moving parts in the crankcase. Adding oil means that the emission of two-stroke engine will be poor, which is also one of the disadvantages of two-stroke engine.

Engine or internal combustion engine is one of the most important tools to promote human progress. A better understanding of this tool will help us to know more about the world and your car. If you think about it carefully, you will find the beauty of internal combustion engine. The above is the first article in the teaching series of engine science, which may be longer. Friends who see here must also like the mechanical principle. If you have anything to say, you can leave a message below, and the professor will listen to it one by one and make improvements.

This article comes from car home, the author of the car manufacturer, and does not represent car home's position.