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About the supercharging system of diesel generator set
Article source:this site | Issuing time：2019-04-18
With the continuous improvement of production needs and technological level, the requirements for diesel generator sets are getting higher and higher. The diesel engine is required to have high output power, good economy, and light weight and small size. The output power of a diesel engine depends on the amount of fuel and air entering the cylinder and the effective utilization of heat energy. It can be seen from this that the most economical and effective way to increase the output power of a diesel engine is to increase the amount of air entering the cylinder. Under the condition that the cylinder volume of the diesel engine remains unchanged, increasing the air density into the cylinder is the main means to increase the output power of the diesel engine. However, air density is proportional to pressure and inversely proportional to temperature. Therefore, increasing intake pressure and reducing intake temperature can increase intake density. Currently, turbochargers are used in diesel engines to increase pressure and intercoolers are used to reduce gas temperature.
The so-called supercharging is to use a supercharger (compressor) to compress the intake air of the diesel engine outside the cylinder and then send it to the cylinder to increase the intake air volume of the diesel engine, thereby increasing the average effective pressure and power.
Pressurization method:
According to the different energy sources used to drive the supercharger, supercharging methods can basically be divided into three categories: mechanical supercharging systems, exhaust gas turbocharging systems and composite supercharging systems. In addition to using the above three methods to increase the air pressure of the cylinder, there are also inertial supercharging systems that use the aerodynamic effect in the exhaust pipe to improve the cylinder charging efficiency and the air wave that uses the pressure exchange of intake and exhaust to increase the air pressure of the cylinder. Supercharger.
Supercharger system:
The supercharging method in which the supercharger (compressor) is directly driven by the diesel engine is called a mechanical supercharging system. It is driven by the coaxial diesel engine through gears, belts or chains and other transmission devices to drive the supercharger to rotate.
Exhaust gas turbocharging system:
Exhaust gas turbocharging is a supercharging method that uses the energy of exhaust gas discharged from a diesel engine to drive a supercharger and compress the air before sending it into the cylinder. After the diesel engine adopts exhaust gas turbocharging, the output power can be increased by more than 30% to 100%. At the same time, it can also reduce the weight of unit power, reduce the overall size, save raw materials, reduce fuel consumption, increase the torque of the diesel engine, and increase the load capacity. The advantages of reducing the pollution of the exhaust to the atmosphere, etc., have been widely used. Especially in the plateau area, the output power drops due to low air pressure and thin air. Generally, when the altitude increases by 1000m, the power will drop by 8%~10%. If the turbocharger is installed, the original output power can be restored, and its economic effect is particularly significant.
Exhaust gas turbochargers can be divided into two types: axial flow and radial flow according to the direction of air flow entering the turbine.
Radial turbocharger is mainly composed of volute, nozzle ring, turbine and rotor shaft. When the radial turbocharger is working, the exhaust gas discharged from the diesel engine enters the turbine shell of the supercharger and flows along the vertical plane of the axis of the rotor shaft of the supercharger. Most medium-sized diesel engines use radial turbochargers.
Axial turbocharger works in Bali. After the exhaust gas discharged from the diesel engine enters the turbine shell of the supercharger, the airflow flows along the axial direction of the rotor shaft of the supercharger, so it is called axial flow. Most large diesel engines use this type of supercharger.
Exhaust gas turbochargers can be divided into two types, constant pressure type and pulse type, according to whether the pulse energy of the exhaust gas in the exhaust pipe of the diesel engine is used.
The constant-pressure exhaust gas turbocharger connects the exhaust manifolds of all cylinders of a multi-cylinder diesel engine to an exhaust manifold, and then connects to the turbocharger turbine shell, and the exhaust gas follows a single unit at a certain average pressure. The inlet passage of the turbine shell leads to the entire nozzle ring. This kind of supercharger is often used in high-power and high-charge diesel engines.
The exhaust gas turbocharging of medium-sized diesel engines adopts pulse supercharger. This structure can make full use of the pulse energy of exhaust gas, and can use the instant vacuum scavenging after the pressure peak to prevent the peak of the exhaust pressure wave of a cylinder from flowing back to the inhalation Therefore, the firing interval of each cylinder in the same exhaust manifold should be greater than 180° crankshaft angle.
Compound booster system
In some diesel engines, in addition to the exhaust gas turbocharger, a mechanical supercharger is also used. This supercharging system is called a compound supercharging system. Large two-stroke diesel engines often use a compound supercharging system. The mechanically driven supercharger in this system is used to assist the exhaust gas turbocharger to work to obtain a higher intake pressure at low load and low speed, so as to ensure that the two-stroke diesel engine is necessary at start, low speed and low load The scavenging pressure.
There are two forms of compound supercharging system: one is a series supercharging system. The exhaust gas turbine of the diesel engine drives a centrifugal compressor to increase the air pressure, and then it is sent to the mechanical supercharger and then pressurized to further increase the air pressure. Enter the combustion chamber of the diesel engine; the other is a parallel supercharging system. The exhaust gas turbocharger and the supercharger respectively increase the air pressure and enter the combustion chamber of the diesel engine.
Other boosting methods
Inertial supercharging system: This supercharging method is often used on small high-speed diesel engines, especially suitable for diesel engines with a small range of load and speed changes. Generally, it can increase power by 10% to 20% and reduce fuel consumption by about 10%. It can reduce the exhaust temperature and improve the exhaust gas exhaust. It uses the gas in the intake and exhaust pipes. Because of the certain dynamic effect during the intake and exhaust process, this kind of pressurization is released.
Air wave supercharger system: The air wave supercharger directly contacts the high-pressure exhaust gas discharged from the diesel engine with the low-pressure intake air, and uses the principle of air wave (compression wave and expansion wave) to control the high-pressure exhaust gas without mixing each other. Energy is transferred to the low-pressure intake through the pressure wave, so that the low-pressure intake is compressed and the intake pressure is increased. In fact, it is a pressure converter.
The air wave supercharger has the advantages of simple structure, convenient manufacturing, no need of heat-resistant alloy materials, good working adaptability, high low-speed torque, good acceleration performance, high maximum speed, and low environmental pollution. Suitable for small and medium diesel engines, especially automotive diesel engines. The disadvantages of the air wave supercharger are: it is a noise source in itself, and the noise is large; it needs a crankshaft to drive, and the installation position is limited; its weight and volume are large.
Intercooler:
At present, intercoolers are commonly installed in medium and high-charge diesel engines. The intercooler is essentially a heat exchanger installed between the turbocharger and the combustion chamber. When the boost pressure of the diesel engine supercharger is relatively high, the intake air temperature is also higher, which reduces the intake density. To this end, it is necessary to install an intercooler in the engine air intake system. The intercooler is used to cool the supercharged air and reduce the temperature of the supercharged intake air. The temperature drop of supercharged air in the intercooler is generally 25~60℃. On the one hand, it can increase the charge density, on the other hand, it can also reduce the cylinder temperature at the end of the intake air and the average temperature of the entire cycle.
Supercharged diesel engines for power generation generally use water-cooled intercoolers. After the turbocharger and intercooler are installed, the lubricating oil circuit and cooling water circuit of the diesel engine are also changed accordingly to meet the needs of supercharging and intercooling. The intercooler consists of a shell and an inner core. The intercooler shell is a part of the engine intake manifold. The inner core is made of tubes. Engine coolant circulates in it. Air flows through the core before entering the engine combustion chamber. Because of the application of intercooler, the intake air temperature (cooling) of the engine is better controlled, thereby improving the combustion condition of the engine.
The structure and working principle of exhaust gas turbocharger:
The exhaust gas turbocharger is composed of an exhaust gas turbine and a compressor.
Exhaust gas turbine
The exhaust gas turbine is usually composed of a turbine shell, a nozzle ring, and a working impeller. The nozzle ring is composed of nozzle inner ring, outer ring and nozzle blades. The channel formed by the nozzle vanes shrinks from the inlet to the outlet. The working impeller is composed of a turntable and an impeller, and working blades are fixed on the outer edge of the turntable. A nozzle ring and the adjacent working impeller form a "stage". A turbine with only one stage is called a single-stage turbine, and most turbochargers use a single-stage turbine.
Compressor
The compressor is mainly composed of an air inlet, a working impeller, a diffuser and a turbine shell. The compressor is coaxial with the exhaust gas turbine and is driven by the exhaust gas turbine to make the working turbine rotate at a high speed. The working turbine is the main component of the compressor, usually it is composed of a forward-curved wind guide wheel and a semi-open working wheel, and the two parts are respectively mounted on the rotating shaft. Straight blades are arranged along the radial direction on the working wheel, and an expanded air flow channel is formed between the blades. Due to the rotation of the working wheel, the intake air is compressed due to the centrifugal force, and is thrown to the outer edge of the working wheel to increase the pressure, temperature and speed of the air. When the air flows through the diffuser, the kinetic energy of the air is converted into pressure energy due to the effect of pressure diffusion. In the exhaust turbine shell, the kinetic energy of the air is gradually converted into pressure energy. In this way, the intake density of the diesel engine has been significantly improved through the compressor.
The so-called supercharging is to use a supercharger (compressor) to compress the intake air of the diesel engine outside the cylinder and then send it to the cylinder to increase the intake air volume of the diesel engine, thereby increasing the average effective pressure and power.
Pressurization method:
According to the different energy sources used to drive the supercharger, supercharging methods can basically be divided into three categories: mechanical supercharging systems, exhaust gas turbocharging systems and composite supercharging systems. In addition to using the above three methods to increase the air pressure of the cylinder, there are also inertial supercharging systems that use the aerodynamic effect in the exhaust pipe to improve the cylinder charging efficiency and the air wave that uses the pressure exchange of intake and exhaust to increase the air pressure of the cylinder. Supercharger.
Supercharger system:
The supercharging method in which the supercharger (compressor) is directly driven by the diesel engine is called a mechanical supercharging system. It is driven by the coaxial diesel engine through gears, belts or chains and other transmission devices to drive the supercharger to rotate.
Exhaust gas turbocharging system:
Exhaust gas turbocharging is a supercharging method that uses the energy of exhaust gas discharged from a diesel engine to drive a supercharger and compress the air before sending it into the cylinder. After the diesel engine adopts exhaust gas turbocharging, the output power can be increased by more than 30% to 100%. At the same time, it can also reduce the weight of unit power, reduce the overall size, save raw materials, reduce fuel consumption, increase the torque of the diesel engine, and increase the load capacity. The advantages of reducing the pollution of the exhaust to the atmosphere, etc., have been widely used. Especially in the plateau area, the output power drops due to low air pressure and thin air. Generally, when the altitude increases by 1000m, the power will drop by 8%~10%. If the turbocharger is installed, the original output power can be restored, and its economic effect is particularly significant.
Exhaust gas turbochargers can be divided into two types: axial flow and radial flow according to the direction of air flow entering the turbine.
Radial turbocharger is mainly composed of volute, nozzle ring, turbine and rotor shaft. When the radial turbocharger is working, the exhaust gas discharged from the diesel engine enters the turbine shell of the supercharger and flows along the vertical plane of the axis of the rotor shaft of the supercharger. Most medium-sized diesel engines use radial turbochargers.
Axial turbocharger works in Bali. After the exhaust gas discharged from the diesel engine enters the turbine shell of the supercharger, the airflow flows along the axial direction of the rotor shaft of the supercharger, so it is called axial flow. Most large diesel engines use this type of supercharger.
Exhaust gas turbochargers can be divided into two types, constant pressure type and pulse type, according to whether the pulse energy of the exhaust gas in the exhaust pipe of the diesel engine is used.
The constant-pressure exhaust gas turbocharger connects the exhaust manifolds of all cylinders of a multi-cylinder diesel engine to an exhaust manifold, and then connects to the turbocharger turbine shell, and the exhaust gas follows a single unit at a certain average pressure. The inlet passage of the turbine shell leads to the entire nozzle ring. This kind of supercharger is often used in high-power and high-charge diesel engines.
The exhaust gas turbocharging of medium-sized diesel engines adopts pulse supercharger. This structure can make full use of the pulse energy of exhaust gas, and can use the instant vacuum scavenging after the pressure peak to prevent the peak of the exhaust pressure wave of a cylinder from flowing back to the inhalation Therefore, the firing interval of each cylinder in the same exhaust manifold should be greater than 180° crankshaft angle.
Compound booster system
In some diesel engines, in addition to the exhaust gas turbocharger, a mechanical supercharger is also used. This supercharging system is called a compound supercharging system. Large two-stroke diesel engines often use a compound supercharging system. The mechanically driven supercharger in this system is used to assist the exhaust gas turbocharger to work to obtain a higher intake pressure at low load and low speed, so as to ensure that the two-stroke diesel engine is necessary at start, low speed and low load The scavenging pressure.
There are two forms of compound supercharging system: one is a series supercharging system. The exhaust gas turbine of the diesel engine drives a centrifugal compressor to increase the air pressure, and then it is sent to the mechanical supercharger and then pressurized to further increase the air pressure. Enter the combustion chamber of the diesel engine; the other is a parallel supercharging system. The exhaust gas turbocharger and the supercharger respectively increase the air pressure and enter the combustion chamber of the diesel engine.
Other boosting methods
Inertial supercharging system: This supercharging method is often used on small high-speed diesel engines, especially suitable for diesel engines with a small range of load and speed changes. Generally, it can increase power by 10% to 20% and reduce fuel consumption by about 10%. It can reduce the exhaust temperature and improve the exhaust gas exhaust. It uses the gas in the intake and exhaust pipes. Because of the certain dynamic effect during the intake and exhaust process, this kind of pressurization is released.
Air wave supercharger system: The air wave supercharger directly contacts the high-pressure exhaust gas discharged from the diesel engine with the low-pressure intake air, and uses the principle of air wave (compression wave and expansion wave) to control the high-pressure exhaust gas without mixing each other. Energy is transferred to the low-pressure intake through the pressure wave, so that the low-pressure intake is compressed and the intake pressure is increased. In fact, it is a pressure converter.
The air wave supercharger has the advantages of simple structure, convenient manufacturing, no need of heat-resistant alloy materials, good working adaptability, high low-speed torque, good acceleration performance, high maximum speed, and low environmental pollution. Suitable for small and medium diesel engines, especially automotive diesel engines. The disadvantages of the air wave supercharger are: it is a noise source in itself, and the noise is large; it needs a crankshaft to drive, and the installation position is limited; its weight and volume are large.
Intercooler:
At present, intercoolers are commonly installed in medium and high-charge diesel engines. The intercooler is essentially a heat exchanger installed between the turbocharger and the combustion chamber. When the boost pressure of the diesel engine supercharger is relatively high, the intake air temperature is also higher, which reduces the intake density. To this end, it is necessary to install an intercooler in the engine air intake system. The intercooler is used to cool the supercharged air and reduce the temperature of the supercharged intake air. The temperature drop of supercharged air in the intercooler is generally 25~60℃. On the one hand, it can increase the charge density, on the other hand, it can also reduce the cylinder temperature at the end of the intake air and the average temperature of the entire cycle.
Supercharged diesel engines for power generation generally use water-cooled intercoolers. After the turbocharger and intercooler are installed, the lubricating oil circuit and cooling water circuit of the diesel engine are also changed accordingly to meet the needs of supercharging and intercooling. The intercooler consists of a shell and an inner core. The intercooler shell is a part of the engine intake manifold. The inner core is made of tubes. Engine coolant circulates in it. Air flows through the core before entering the engine combustion chamber. Because of the application of intercooler, the intake air temperature (cooling) of the engine is better controlled, thereby improving the combustion condition of the engine.
The structure and working principle of exhaust gas turbocharger:
The exhaust gas turbocharger is composed of an exhaust gas turbine and a compressor.
Exhaust gas turbine
The exhaust gas turbine is usually composed of a turbine shell, a nozzle ring, and a working impeller. The nozzle ring is composed of nozzle inner ring, outer ring and nozzle blades. The channel formed by the nozzle vanes shrinks from the inlet to the outlet. The working impeller is composed of a turntable and an impeller, and working blades are fixed on the outer edge of the turntable. A nozzle ring and the adjacent working impeller form a "stage". A turbine with only one stage is called a single-stage turbine, and most turbochargers use a single-stage turbine.
Compressor
The compressor is mainly composed of an air inlet, a working impeller, a diffuser and a turbine shell. The compressor is coaxial with the exhaust gas turbine and is driven by the exhaust gas turbine to make the working turbine rotate at a high speed. The working turbine is the main component of the compressor, usually it is composed of a forward-curved wind guide wheel and a semi-open working wheel, and the two parts are respectively mounted on the rotating shaft. Straight blades are arranged along the radial direction on the working wheel, and an expanded air flow channel is formed between the blades. Due to the rotation of the working wheel, the intake air is compressed due to the centrifugal force, and is thrown to the outer edge of the working wheel to increase the pressure, temperature and speed of the air. When the air flows through the diffuser, the kinetic energy of the air is converted into pressure energy due to the effect of pressure diffusion. In the exhaust turbine shell, the kinetic energy of the air is gradually converted into pressure energy. In this way, the intake density of the diesel engine has been significantly improved through the compressor.
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