When the turbocharger compresses the fresh air through the middle cooler for cooling, it flows to the cylinder combustion chamber through the intake manifold and intake valve
Supercharging and intercooling technologyTurbochargerCompress fresh air through the middle sectioncoolerAfter coolingIntake manifoldInlet valve flows to cylindercombustion chamber。The effective intercooling technology can reduce the pressurization temperature to below 50 ℃, which helps to reduce the exhaust emissions and improve theFuel economy。
waste gasTurboThe technology has been applied to diesel engines since the 1950s and has developed rapidly over the past 40 years.Diesel engine since 1960sAverage effective pressureandpistonIncrease in average speed.During this period, the latter increased by about one third, while the former nearly tripled.The intercooling supercharging system does not work normally. Only when the vehicle is fully loaded or reaches a certain speed,Intercooling superchargingThe superiority of can really reflect that it is actually a kind ofAir compressor, increase the air intake through compressed air.It uses the inertia impulse of exhaust gas discharged from the engine to drive the turbine in the turbine chamber, and the turbine drives the coaxial impeller, which is pressed byAir filterThe air sent is pressurized into the cylinder.When the engine speed increases, the exhaust gas discharge speed increases synchronously with the turbine speed, the impeller compresses more air into the cylinder, and the increase of air pressure and density can burn more fuel. The engine speed can be increased by increasing the fuel and adjusting the engine speed accordinglyoutput power。The fact shows that increasing the mean effective pressure is the main way to increase the specific power of the internal combustion engine, and increasing the mean effective pressure.The specific measure is to increase the boost pressure and the maximum burst pressure.With the continuous development of internal combustion engine towards high supercharging, its thermal load problem becomes more prominent. If no measures are taken, the diesel engine will often suffer from cylinder head "nose bone" fracture, combustion chamber insert burning crack, piston ring sintering seizure, piston burning crack and other phenomena. As for the turbine rotor, it is also often damaged due to excessive thermal load, such as seal ring sintering, blade deformation and so on.It can be seen that single-stage turbocharging should reach a high turbocharging pressurethermal loadIs a very critical issue.Supercharged intercooling is a good solution. According to the calculation, the compressed air Tk can be reduced by 1 ℃, the maximum combustion temperature and exhaust temperature can be reduced by 2 and 3 ℃, which can effectively relieve the heat load.Therefore, turbocharging and intercooling are almost essential, especially for turbocharging systems with medium turbocharging degree or above.In addition, turbocharging and intercooling can further improve the intake air density, increase the power by 15% - 20% without increasing the heat load, reduce the NOx content in emissions and improve the environment.
Supercharged intercooling theory
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aboutautomobile engineWe always hope that its power per unit volume and weight is as high as possible.In order to increase the power, it is necessary to increase the amount of fuel burned per unit time, that is, it is required to increase the amount of fuel entering per unit timeCylinderAir volume of.To this end, one measure is to increase the speed, that is, increase the number of cycles per unit time;Another measure is to increase the air intake of each cycle.The so-called supercharging is a technology that pre compresses the air before entering the cylinder to improve the air density and increase the air intake.By addingIntake volumeIt is an important way to increase the engine power by increasing the circulating fuel supply accordingly.Same powerNon supercharged engineCompared with turbocharged engines, turbocharged engines not only have small size, light weight and large power, but also reduce the cost of unit power and improve fuel economy.At the same time, turbocharging and intercooling can also reduce the heat load of the engine and improve the emissions of pollutants.Therefore, turbocharging and intercooling technology is not only widely used in diesel engines, but also extended to gasoline engines.It is improvementengine performance Important technical means.Supercharging includes turbochargingSuperchargingAnd gas wave pressurization. The corresponding supercharger is calledTurbocharger、SuperchargerandGas wave supercharger。staySupercharged engineThe power is proportional to the boost pressure and inversely proportional to the boost temperature.However, according to the thermodynamic principle, the charge air is compressed in the supercharger according toPolytropic processConducted.In order to make the supercharged air have the greatest density and lower temperature, a cooler (intercooler) needs to be set between the supercharger and the engine to cool the supercharged air, which is called intercooling.All engine manufacturers have strict regulations on this. For example, the WD615 series diesel engine produced by Weichai requires that the intake air temperature after intercooling should not exceed 55 ℃ when the atmospheric temperature is 25 ℃.
Reasons for technology
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Diesel cars are common in Europe.After years of research and application,Hyundai MotorThe diesel engine adopts electronic control injectionCommon rail, turbocharging and intercooling and other technical means have made significant achievements in weight, noise, smoke and other aspects, reaching the level of gasoline engines.Supercharging can increase the output power of the diesel engine with the same displacement and weight.Compared with the non supercharged diesel engine with the same power, the supercharged diesel engine is not only small in size, light in weight and large in power, but also reduces the cost per unit power.Therefore, turbocharging technology is widely used in diesel engines, but also extended to gasoline engines, which is an important technical means to improve internal combustion engines.
However, there are always contradictions. The increase of air pressure is the increase of air density. The increase of air density will inevitably increase the air temperature at the same time, just as the pump will heat up when inflating the tire.The outlet temperature of the engine turbocharger will also increase with the increase of pressure, which in turn will limit the increase of air density. To further increase the air density, it is necessary to reduce the temperature of the charge air.According to the experiment, under the same air-fuel ratio, the diesel engine power can be increased by 3% - 5% every time the charge air temperature drops by 10 ℃, and it can also reduce theNitrogen oxides(NOx) to improve the low-speed performance of the engine.Therefore, intermediate cooling technology is also produced.
Principle of intercooling technology
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For medium and high boost pressureSupercharged engine, generally requires devicesIntercooler, this is becauseTurbochargerThe temperature of the air sucked in will rise after being compressed, and the air will further rise due to friction with the pipe wall during the flow process, which will not only affect the inflation efficiency, but also easily causeDeflagration。Effective power of engine PeIt is proportional to the gas density charged into the cylinder. The higher the density is, the greater the power is. The charge air density is determined by the gas state equation.
I.e
Where: p is the boost pressure, Pa（Absolute pressure)；T is the absolute temperature of air at the time of pressurization, K; R isGas constant(287.14/JkgK)。
Supercharged engineThe power is proportional to the boost pressure and inversely proportional to the boost air temperature.Only when the air temperature T remains constant, the effective power P of the engineeIs linear with p.It can be seen that intermediate cooling of the charge air is very important.Generally, supercharging can increase the power of high-speed diesel engines by 30%, and intercooling technology can further increase the power by 50% - 60%.
The high pressure hot air of the supercharger flows through the cooling pipe of the intercooler to transfer the heat to the cooling pipe and the heat sink attached to the pipe. The outside cold air flows through the cooling pipe and the heat sink attached to the pipe to take away the heat above.In this way, the heat of the hot air is transferred to the outside cold air through the pipes and the heat sink, and the temperature of the pressurized hot air is reduced.
Intercooling technology type
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There are two types of diesel engine intermediate cooling technologyCirculating cooling waterThe intercooler is cooled by radiator, that is, external air.When using cooling water for cooling, it is necessary to add an auxiliary system of independent circulating water to achieve better cooling effect, which is costly and complex.Therefore, air cooled intercoolers are mostly used in automobile diesel engines.The air cooled intercooler uses pipes to send compressed air to radiators, and uses the cooling air provided by the fan for forced cooling.Air cooled intercooler.It can be installed in front of or beside the engine water tank or in an independent position. Its corrugated aluminum fins and pipes are similar to the structure of the engine water tank, with high heat conduction efficiency, and can cool the temperature of the pressurized air to 50 to 60 degrees Celsius.
Applications on automobiles
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Sedan
An air air cooling system is used in a car. The intercooler is usually cooled by the headwind when driving. That is to say, the effect of the intercooler mainly depends on the driving speed of the car. The higher the flow rate of cooling air in the cooling core, the better the cooling effect. Therefore, in order to make the cooling air flow rate in the core as high as possible, the intercooler with lower resistance on the air side must be selectedCooling system。The intercooler shall be arranged at the position with high dynamic pressure head to ensure that the cooling air can flow in and out smoothly.When the intercooler is installed far away from the engine, most of the intercoolers are placed in the front of the carradiator(Water tank) before or beside it, as far as possible, it should be placed in the range with high dynamic head.However, its disadvantage is that the charge air pipe is long, and most of them are curved, with radian and cross section changes, which will cause pressure loss, so that the cooling efficiency and the response characteristics of exhaust gas turbocharging will deteriorate. When the engine is installed close to the engine, if due to structural constraints, the intercooler can also be placed on the engine, so that the air side path is shorter,Therefore, the pressure loss is small.However, this arrangement has high requirements for cooling air channel and sealing.[1]
truck
The truck mainly adopts air air cooling system.Due to the requirements of the working conditions of the truck, it is not enough to rely only on the headwind cooling when driving, soIntercoolerIt is installed in front of or beside the radiator (water tank) and cooled by the fan.Because the total width of the cooling device is limited by the installation space.The scheme that the intercooler is installed next to the radiator is seldom considered. When the intercooler front scheme is adopted, sometimes other coolers (such asAir conditioning condenser, oil cooler of transmission or hydraulic device, etc.), these coolers cover part of the radiator windward area.The inlet temperature of cooling air increases, which greatly increases the heat load of the radiator placed behind. Therefore, the radiator must be designed accordingly.[1]
