1, a compression ratio of
To describe the technical parameters of an engine, it can be schematically by the magnitude of power and torque to marked, however, factors that affect the power, torque output but many, an important factor is the compression ratio of the engine, compressible than the term it seems to make a lot of maintenance personnel blur, know that it is better to know the size of the numerical value of the cylinder pressure and practical, but the engine compression ratio is indeed vital parameters.
What is the compression ratio of the engine? Regardless of the chosen this car filled with petrol engine or a diesel engine, can maintain a stable and appropriate compression ratio to make the operation of the engine is smooth and stable. Degree of compression is defined to be a mixed gas of the engine compression ratio, the cylinder volume (i.e., combustion chamber volume) of the total volume of the cylinder after compression and before the compression ratio is represented. Size of the compression ratio is represented by the piston lower dead point to the top dead point of the gas in the cylinder is compressed extent.
At present, the absolute majority of cars use so-called ‘reciprocating engines’ Simply put, that is, in the engine cylinder, a piston cycle there doing linear reciprocating motion, and has been endless loop, so in this among cycle and continuous work schedule has its movement stroke range. To a certain cylinder of the engine, when the stroke of the piston reaches the lowest point, the point will be the position at this time is called a lower dead center, the entire volume of the cylinder including a combustion chamber is formed by the maximum stroke volume, the reverse movement when the piston reaches the highest position, this position will be referred to as a top dead point, the volume of the formed condition of minimum motion of the entire piston stroke volume, which is the ratio of the maximum stroke volume and the minimum volume of the compression ratio to be calculated. To illustrate the technical parameters of an engine, can be schematically by the magnitude of power and torque to marked, however, affect the power factor, but a lot of torque output, which is an important factor in the engine compression ratio, the ratio of the compressible term seemed to make many service personnel blur, know that it is better to know the size of the numerical value of practical cylinder pressure, however, the engine compression ratio is indeed vital parameters.
2. Body
the internal combustion engineThe volume ratio of the maximum volume of the compression cylinder, the internal combustion engine is an important structural parameters (see Figure). When the piston is at the bottom dead center of the cylinder has a maximum volume, represented by Va of; piston is at top dead center in the cylinder volume of the compression volume is called, denoted by Vc. The engine compression ratio [epsilon] is the
ε is the geometric compression ratio, which represents the piston moves from the bottom dead center to top dead center when the extent of the gas within the cylinder is compressed. Piston intake valve or intake bottom dead center, exhaust ports not closed, it is sometimes required with an effective compression ratio ε0 of the concept. ε0 means the engine intake and exhaust valves (ports) all begin to close the cylinder volume of the cylinder volume of the compression ratio of the instantaneous. Where not otherwise specified refer to the geometric compression ratio compression ratio. The compression ratio has many effects on the performance of the internal combustion engine. The higher the ratio the higher the thermal efficiency of the compression, but with higher compression ratio, thermal efficiency growth rate getting smaller and smaller. Increasing the compression ratio of the compression pressure, the maximum combustion pressure are increased, so that the mechanical efficiency of the engine drops. Knock gasoline engine compression ratio is too high easy. Diesel engine compression ratio is too low will the compression end temperature becomes low, effects of cold starting performance. The compression ratio of the engine exhaust enables the harmful component (e.g., NOX, hydrocarbons, CO, etc.) content is changed. Modern diesel engine compression ratio is generally between 12 and 22, but ultra-high compression ratio turbocharged diesel engine can be as low as 8. Modern gasoline engine compression ratio is 6 to 10.
the compression ratio of the engine is generally not change, because the combustion chamber volume and working volume of the cylinder are fixed parameters, in the design has been decided on. However, in order for modern engines can play a better efficiency in various operating conditions change, to change to change to improve the operating performance of the engine. In which the variable valve drive technology has been implemented as an important parameter of the compression ratio was fixed by the attempt to “improvise”, but as it involves the compression ratio is bound to involve changing the entire structure of the engine, pull and move a hundred, is very difficult, there is no long-term progress. Now this problem has been overcome Sweden’s Saab engineers.
In recent years, Saab (Saab) developed SVC to change the compression ratio of the engine to control the engine fuel consumption. Its core technology is installed between the cylinder and the cylinder head slider wedge, the cylinder can slide along the ramp movement, so that the relative position of the combustion chamber and the top surface of the piston is changed, changed combustion chamber offProduct, thereby changing the compression ratio. Varies between 1: 1 to 14: 8 from the compression ratio range. Employed when the engine load is small in order to save fuel high compression ratio; low compression ratio when the engine load is large, and supplemented by booster to achieve high power and high torque output. Saab SVC engine of 1.6 liter five-cylinder engine, each cylinder bore 68 mm piston stroke 88 mm, the maximum power of 166 kilowatts, the maximum torque of 305 Nm, combined fuel consumption is reduced by 30 percentage than conventional engines, and to meet the European Ⅳ emission standard.
Modern vehicles are marked that it has a high compression ratio of the engine, and also shows that it is apparent to a high-performance car, the drive to meet all needs, but such terms are not to explore the full range of exactly how this alone has often been left out of the compression ratio, the fact that it represents a mature technology, is a successful author of a series of achievements related technical or theoretical, but it was a lot of people do not known, the more we need to go deep development and research. The compression ratio it? In theory, the engine is an indispensable value, a lot of maintenance staff that is just a numerical only, do not have any unit, can be seen from the above results, the performance of the engine is closely related to how much, how to maintenance personnel important.
3, with FIG.
4, the relevant connection
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