Diesel engine in the 21st century
Diesel engines in the domestic market is not as familiar to ordinary people. Dirty diesel engines because of emissions restrictions by laws and regulations, so some domestic cities such as Beijing, the capital of small diesel cars on the card against many other places can only see the use of diesel engines for trucks and buses and so on.
However, in our diesel car restrictions to take the same time, diesel engine fuel-efficient, low-speed torque output characteristics of a large, has been the preferred international depot, city life has become the most appropriate power system options. After decades of research and development, the International has developed all aspects of the depot not inferior to gasoline engine products, so that regardless of performance, emissions, etc., are equal shares with the gasoline engine.
In the case of diesel oil refining costs are lower under the diesel engines is loved by the consumers in advanced countries, and even high-priced luxury cars, but also have equipped with diesel engines, their performance of outstanding evident.
With the progress of the times, technological development, but also a practical need caused by the relevant laws and regulations impose restrictions on diesel vehicles are also being gradually refined to make diesel vehicles can be imposed in the automotive market, the long view. Whether a diesel engine and gasoline engine What’s the different?
The rise of internal combustion engine
In the definition of mechanical engineering, where the heat arising from the use of power machinery, collectively known as the heat engine (Heat Engine). The heat engine is further divided into two broad categories of internal combustion engines and external combustion engine, fuel is an internal combustion heat engine heat, then turn heat into mechanical power who are known as the internal combustion engine, such as gasoline engines, diesel engines, gas turbine engines. The fuel outside the combustion heat engine are referred to as outboard engines, such as the steam engine.
In general the common engine, is divided into the use of ignition devices (such as spark plug) ignition of the spark ignition (SI) engines, and the use of high-pressure high-temperature air combustion of fuel compression ignition (CI) engines. Gasoline engines are spark-ignition engines, diesel engines are compression-ignition engine is.
The late eighteenth century, Watt (James Watt) invented the steam engine prompted the United Kingdom the first industrial revolution, it has changed the human way of life, make people switch from their own labor or the use of mechanical power animal. Hundred years later (1876), the German Otto (Nikolaus Otto) invented the first with four-stroke internal combustion engines, and then (1887), Daimler (Daimler) will be successfully applied in four-stroke engine vehicles. AD 1892, German engineer Di Saier (Rudolf Diesel) invented a more efficient combustion of non-spark-ignition engines, and obtain the patent, which is a new milestone in the development of internal combustion engine.
The development of diesel engines
In Otto invented the first four-stroke internal combustion engines, the time many engineers are committed to the development of internal combustion engines, but mostly for the development of the direction of spark ignition engines, such as the Mercedes – the founder of Daimler-Benz, it is the ancestor of gasoline engines used in vehicles. But then the ignition technology is not mature, Di Saier it to air compression so that the theory of temperature towards the direction of compression-ignition internal combustion engine technology. That is, within the first cylinder of air compressed to high temperature, and then injected into the fuel combustion chamber, fuel and ignition due to high temperature and pressure, resulting in the engine power required
Father of diesel engines – Di Saier (Rudolf Diesel) another way, in the Otto cycle engine, the diesel engine to create a new world!
Since the delivery of air heated to ignition temperature of fuel requires a tremendous amount of pressure, then fuel – gasoline in such a high temperature and pressure will produce violent detonation, so Di Saier must develop different types of fuel, he even tried to the use of vegetable oils, while the final selection of diesel at the time received the least attention. Difficult to ignite diesel fuel can not be the result of spark-ignition engine fuel, and diesel will produce smoke upon ignition, it can not be like kerosene as a lighting fuel, so at that time not taken seriously. However, not easy to knock the stability characteristics of diesel, just as a compression-ignition engines.
After nearly two decades of research and development, first with compression-ignition engine in 1892 came the same year, Di Saier has also made this technology patents. As Di Saier diesel engine technology is not yet mature in the early stages of development, even though it has good thermal efficiency and fuel-efficient features, at that time was difficult and the technology has matured to compete for gasoline engines. Di Saier, however, it still pushed into the market, led to his sale of 20 diesel engines 11 incurred in return, and in the next period of time, people are unable to accept diesel engines. The frustrated Di Saier, also October 29, 1913 Touhai suicide.
Diesel engines for some time in silence, the U.S. Cummins Inc. in 1924, it will be used in diesel engine oil injection pump, the solution to high-pressure air at the time Di Saier mode instability in oil operations, and for the first time the diesel fuel engine installed on the truck, laid the foundation for vehicles using diesel engines. In 1936, diesel engines are also equipped in the Mercedes – Benz 260D, which is the first diesel engine used in cars.
Suitable alternative sources of energy before the transition program
As the diesel engine powered large and fuel-efficient, but early because of the noise and smoke emissions, so for large-scale multi-use vehicles and construction machinery. Because of diesel engine torque characteristics of large, fuel-efficient, but also for many European efforts to improve the depot to apply for small vehicles. In the common-rail direct injection and oil can be precisely piezoelectric nozzle technology is mature, the diesel engine is more suited for a small lane to use. In the search for alternative energy sources today, diesel engines, while not the ultimate program, but the fuel-efficient diesel engine characteristics, can be used as a very appropriate transition program.
● divided into two-stroke diesel engine and four-stroke
Unlike gasoline spark ignition (SI) engines, diesel engine compression-ignition (CI) engines. The same as with gasoline engines, diesel engines operate according to their methods can be divided into four-stroke and two stroke engine. Two-stroke diesel engines and we may be more familiar with, but when readers had armor for tanks and armored vehicles used on the eight-cylinder two-stroke diesel engines, it should be a bit impressed. Used in the general vehicle diesel engines, or to four-stroke majority, the following is to introduce the four-stroke diesel engine operating principles of the main.
Four-stroke diesel engines principle of operation
Diesel engines with compression ignition, using the air temperature ignition of diesel to generate power.
Intake stroke
Exhaust valve closure of the intake valve opens. When the piston down the row from the stop point, only in the intake manifold of the air sucked into the cylinder through the intake valve in at this time is not within the fuel into the cylinder.
Compression stroke
After the end of the intake stroke, and when the piston from the bottom dead center started rising, the intake valve that is shut down and stop the intake. In the piston pressure and temperature rise at the same time they began to increase. In the diesel engine, compressed air must be heated until it reaches the ignition temperature of the above.
Doing work trip
When near the end of compression stroke when the fuel nozzle means to spray atomization, heated by the compressed air that will ignite after being atomized fuel. In this result, the cylinder pressure will increase rapidly and push the piston down, this thrust into a rotation so that the crankshaft generated power.
Exhaust stroke
In the combustion process is complete, and when the piston down just walk close to the next point, the exhaust valve will open. When the piston up again And when they exhaust through the exhaust valve, exhaust manifold, and exhaust silencers will be discharged.
● high compression ratio and compression ignition
Audi’s diesel technology is very mature, and its TDI turbo diesel engine with a power strong, fuel efficiency and emissions cleanliness of the many benefits.
Diesel engine at the institutional components are very similar to the gasoline engine, but rely mainly on the gasoline engine spark plugs to ignite the mixture, while the diesel engine into the air is pure and after a high compression ratio (16 ~ 23:1) of the cylinder volume to compressed air, so that the temperature of air compressed by the rapid increase of more than 500 ℃, and then through the nozzle into the diesel fuel to be atomized, followed by compressed air has been generated by the heat from the line of fire atomized diesel. Therefore, without the use of diesel engine ignition system, but it still needs to injection pump and injector fuel injection system composed of.
Why can rely on compressed air to ignite oil and gas, without the need for spark plugs do? The reason is when the air molecules are compressed into the cylinder, the air molecules by the collision and friction with each other, thereby rapidly increasing the speed of molecular movement. Speed up the air molecules that absorb the energy from the outside, resulting in rise in temperature. However, to be able to make the air inside the cylinder diesel ignition temperature is the need for a high compression ratio, so the high compression ratio, diesel engines must have a major feature.
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Diesel engine and gasoline engine applications and development, and has been more than a century, two kinds of engines have their own market, but also have their own applications. In general, diesel engines because it produces more power, but running low, and mostly used in ships, heavy-duty vehicles and heavy machinery; while the gasoline engine because of its size and weight is small, delicate and suitable for high speed operation can be used cars, mowers and other small-scale machinery and small propeller aircraft.
The mainstream four-stroke diesel engine (Figure right) and four-stroke gasoline engine (left) is similar in design, the main difference is that compression ignition and spark ignition. Most of the new generation of diesel engines with common-rail direct-injection technology, and towards the cylinder gasoline engine is the fuel injection direction.
As the diesel engine technology, continuously updated, more and more business travel cars and diesel cars with small displacement engines, in the end diesel engine cars and gasoline-powered vehicles What is different? The following will report on its mechanical properties and the driving characteristics of diesel and gasoline engines for comparison, while diesel engines are widely used in the current common-rail direct-injection engines of small cars to compare objects.
● Mechanical Properties
Diesel engine and gasoline engine in the differences in mechanical properties
Gasoline engine diesel engine (common rail direct injection type)
Fuel gasoline, liquefied petroleum gas from diesel
Intake mixture / pure air pure air
Spark ignition mode ignition (spark plug) compression ignition
6 ~ 11:1 compression ratio of 16 ~ 23:1
Load control the amount of control the fuel mixture ratio control
Air-fuel ratio 13 ~ 17 (mixing ratio concentration) of 16:1 or more (air over the fuel lean-burn)
Combustion Pressure 50 ~ 70bar 60 ~ 90bar
Thermal efficiency of 25 ~ 30% 35 ~ 40%
The use of vacuum or high-pressure fuel spray nozzle to enable the use of high-pressure gas atomization spray nozzle to make diesel
The higher the better burning of fuel ignition characteristics of the lower the better
Combustion of the combustion process (flame propagation) expansion of combustion flame
The maximum speed of around 7500rpm and above 4500rpm
Exhaust gas temperature high and low
Engine light and heavy weight of
Front we’ve described in detail the history of diesel engines, development and the basic principles of its work, the next we will be in-depth description of diesel engine fuel supply system, including direct injection and indirect injection VS Piston VS injection common rail injection pump system system.
● a systematic comparison of various diesel: direct injection Indirect injection VS
Different types of diesel engines among the different displacement, the biggest difference lies in its combustion chamber and fuel supply system design. Diesel engine combustion chamber in accordance with different design can be divided into direct injection (DI)-type and indirect injection (IDI) type two kinds of indirect injection can be divided into pre-combustion chamber type and vortex type two broad categories.
Direct injection type:
Direct injection engine cylinder head combustion chamber design is flat, the main combustion chamber located at the top forged pistons into the hollow of a special space, and have been in a pit of the Central Office of porous injector to complete the fast jet fuel purposes.
Direct injection diesel engines the fuel directly into the cylinder in the
Benefits:
Structure is simple and relatively small surface area of the combustion chamber, heat loss and fuel consumption is low;
Cylinder head simple in structure, heat distortion opportunity small;
The engine starts easily and without preheating plug;
Combustion chamber surface area of the floor area ratio is small, the cooling loss is also small.
Disadvantages:
The flammability of the fuel requirements of the higher series;
Require a higher fuel injection pressure;
Of porous-type injector used in higher prices;
Nozzle small recession would significantly affect the engine performance;
Because of air eddy is weak, poor utilization of the air is not suitable for high speed operation.
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Pre-combustion chamber indirect injection:
Pre-combustion chamber is located in the main combustion chamber above the combustion stroke in the early stage of fuel spray nozzle into the combustion chamber pre-generated partial combustion, resulting in high temperature and pressure of gas. With this pressure, the remaining fuel emitted by the nozzle of the hole and into the main combustion chamber, and then with the whirl of the air mixture for complete combustion. Pre-combustion chamber engine, its combustion process in two stages, the difference is in the fuel and air mixture is to use pre-combustion chamber from the exhaust air to complete.
Pre-ignition-type indirect injection diesel engine, first in the pre-ignition combustion room, and then ignite the main combustion chamber
Benefits:
Due to the relatively low fuel injection pressure (80 ~ 150bar), fuel system failure rate is low and the longer life span than;
A lower requirement for fuel flammability series;
Running in a quieter and less prone to detonation;
Status of air and fuel mixture better.
Disadvantages:
Cylinder Head complex structures;
Pre-combustion chamber surface area due to large capacity, so the cooling will incur greater losses;
Difficulties and the need to start the engine preheating system;
Needs more torque to start, that is, require high power to start the motor;
Higher fuel consumption than the direct injection.
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Vortex-type indirect injection:
During the compression stroke swirl-type air into the swirl chamber, when the fuel spray Pops will have a strong eddy effects, and then to the combustion chamber. Fuel ignition is sprayed into the swirl chamber through the fuel mixed with air produced a strong cycle occurs. In the pre-combustion chamber type, the fuel is only partially lit, but the vortex on the room type, all of the fuel were ignited. Therefore, the swirl chamber combustion chamber volume of the total volume of 70 ~ 80%. Swirl chamber type combustion characteristics between direct injection and pre-combustion chamber between the types.
Vortex-type direct injection Indirect injection is between the pre-combustion chamber and between the design of an indirect injection
Benefits:
The fuel mixed with air condition better, the engine speed and mean effective pressure can improve;
With lower injection pressure;
Broader due to engine speed, engine run more smoothly.
Disadvantages:
Cylinder Head complex structures;
Thermal efficiency than the direct injection type is low;
Prone to knock at low speeds;
Need to preheat the engine during start-up plug.
A systematic comparison of various diesel: plunger-type injection pump system, common rail injection system VS
Diesel engine combustion is the fuel injected into the combustion chamber, and in the air mixture in the combustion chamber to produce spontaneous combustion. Therefore, In order to achieve maximum performance and smooth operation of the case, there must be appropriate fuel injection quantity and injection timing. Meanwhile, when injected into the fuel must be allowed to form atomized spray of fuel in order to obtain smooth combustion. Simply put, diesel engine fuel injection fuel supply system must be in the volume, injection time and fuel atomization three have accurate control.
Now we will introduce the plunger-type injection pump systems and common rail injection system of diesel engines of the two different fuel supply system.
Plunger-type jet pump system:
Plunger-type injection pump system used in conventional diesel engines the fuel supply system, because of its low cost manufacturing technology is mature and is still widely used in large diesel engines.
Their modes of operation is for the pump-priming the fuel from the tank to the jet pump, jet pump has a cam shaft, camshaft driven by the engine. In accordance with the engine camshaft rotation makes the rotation of cam timing to control the pressure moving the piston of each cylinder injection pressure to build fuel pressure and fuel delivery by high-pressure tubing to the nozzle of each cylinder and fuel injected into the cylinder, while the The open and close nozzle is controlled by the engine camshaft. Because it is run by the engine to drive the jet pump, so the fuel pressure difference as the engine speed change.
Although the plunger-type injection pump systems for diesel engines widely used, but because of its jet pump is a mechanically-driven, not based on engine load conditions to provide accurate fuel supply; and jet pump to each cylinder as the distance is not the same, making delivered to each cylinder of the fuel pressure is different. Such defects will reduce the delicate nature of the engine operation and increased noise, emissions and fuel consumption.
Common-rail injection system:
『The new common-rail diesel engine, with precise control of light weight advantages, can effectively control the emission』
Common-rail injection system is pressurized by the high-pressure fuel pump, and transported to share with a relief valve in the oil rail, and then from the oil nozzle in the fuel rail into the cylinder. Currently for use in small cars and business travel common-rail direct-injection engine vehicle is determined by the engine control system (ECU) to control the high-pressure pump, pressure regulating valve and the nozzle and other components of the operation, making the fuel at very high pressure, still can be based on the time of the engine load and speed to accurately adjust the fuel injection quantity, so that engine running smoothly, and the operation noise and emissions than conventional diesel engines are much smaller. And the injection pump volume and weight than the plunger-type injection pump is small, to reduce the weight of a lot of the engine.
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