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For compression ratio in data compression, see data compression ratio.

The compression ratio is a single number that can be used to predict the performance of any engine (such as an internal-combustion engine or a Stirling Engine). It is a ratio between the volume of a combustion chamber and cylinder, when the piston is at the bottom of its stroke and the volume when the piston is at the top of its stroke. The higher the compression ratio, the more mechanical energy an engine can squeeze from its air-fuel mixture. Higher compression ratios, however, also make detonation more likely. Data compression ratio is a computer term used to quantify the reduction in data quantity produced by a data compression algorithm. ... An internal combustion engine is an engine that is powered by the expansion of hot combustion products of fuel directly acting within an engine. ... A Stirling engine and generator set with 55 kW electrical output, for combined heat and power applications. ... It has been suggested that Detonation internal combustion engine be merged into this article or section. ...

The ratio is calculated by the following formula:

Failed to parse (unknown errorballs): mbox{CR} = balls { ( pi b^2 s) / 4 + V_c } {V_c}

, where

b = cylinder bore (diameter)

s = piston stroke length

V_c = volume of the combustion chamber (including head gasket). This is the minimum volume of the space into which the fuel and air is compressed, prior to ignition. Because of the complex shape of this space, it usually is measured directly rather than calculated.

• Due to pinging (detonation), the CR in a gasoline/petrol powered engine will usually not be much higher than 10:1.
• In engines running exclusively on LPG or CNG, the CR may be higher, due to the higher octane rating of these fuels.
• In engines with a 'ping' or 'knock' sensor and an electronic control unit, the CR can be as high as 13:1 (2005 BMW K1200S)
• In a turbo charged or super charged engine, the CR will be around 8.5:1
• In a diesel engine, the CR will be 14:1 and higher.

A piston and cylinder from a steam engine A cylinder in an internal combustion engine is the space within which a piston travels. ... piston + connecting rod Components of a typical, four stroke cycle, DOHC piston engine. ... A combustion chamber is part of an engine in which fuel is burned. ... Different kinds of gaskets, #4 indicating a head gasket The head gasket sits between the engine block and cylinder head in an internal combustion engine. ... The ignition system of an internal-combustion engine is an important part of the overall engine system that provides for the timely burning of the fuel mixture within the engine. ... It has been suggested that Detonation internal combustion engine be merged into this article or section. ... Gasoline, also called petrol, is a petroleum-derived liquid mixture consisting primarily of hydrocarbons and enhanced with benzenes to increase octane ratings, used as fuel in internal combustion engines. ... Gasoline, as it is known in North America, or petrol, in many Commonwealth countries (sometimes also called motor spirit) is a petroleum-derived liquid mixture consisting primarily of hydrocarbons, used as fuel in internal combustion engines. ... 45 kg LPG cylinders Liquified petroleum gas (also called liquefied petroleum gas, liquid petroleum gas, LPG, LP Gas, or autogas) is a mixture of hydrocarbon gases used as a fuel in heating appliances and vehicles, and increasingly replacing chlorofluorocarbons as an aerosol propellant and a refrigerant to reduce damage to... A CNG propelled autorickshaw on the streets of New Delhi, Delhi. ... A gas station pump offering five different octane ratings. ... It has been suggested that Detonation internal combustion engine be merged into this article or section. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... In automotive electronics, an electronic control unit (ECU) is an embedded microcomputer that controls one or more of the electrical subsystems in a vehicle. ... 2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ... BMW began as an aeroplane engine manufacturer. ... Turbocharger Cut-away A turbocharger is a device used in internal-combustion engines to increase the power output of the engine by increasing the mass of oxygen and fuel entering the engine. ... A supercharger (also known as a blower) is an air compressor used to compress air into the cylinders of an internal combustion engine. ... now. ...

Fault finding and diagnosis

Measuring the compression pressure of an engine, with a pressure gauge connected to the spark plug opening, gives an indication of the engine's state and quality. The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin, Canberra. ... Many techniques have been developed for the measurement of reduced or increased pressures. ... This article or section should include material from Spark gap A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed aerosol gasoline by means of an electric spark. ...

If the nominal compression ratio of an engine is given, e.g. as 1:10, then the measured pressure in each cylinder should be equal to or higher than 10 bar (see Boyle's law and combined gas law). If there is a significant (> 10%) difference between cylinders, that may be an indication that valves or cylinder head gaskets are leaking, piston rings are worn or that the block is cracked. The bar (symbol bar) and the millibar (symbol mbar, also mb) are units of pressure. ... Boyles law (sometimes known as the Boyle Mariotte law) is one of the gas laws. ... The ideal gas law or equation is the equation of state of an ideal gas. ... A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. ... The cylinder head from a GMC van. ... This article is about mechanical seals. ... piston + connecting rod Components of a typical, four stroke cycle, DOHC piston engine. ... The cylinder block is a machined casting (or sometimes an assembly of modules) containing cylindrically bored holes for the pistons of a multi-cylinder reciprocating internal combustion engine, or for a similarly constructed device such as a pump. ...

If a problem is suspected then a more comprehensive test using a leak-down tester can locate the leak. There are very few or no other articles that link to this one. ...

Saab Variable Compression engine

Because cylinder bore diameter, piston stroke length and combustion chamber volume are almost always constant, the compression ratio for a given engine is almost always constant, until engine wear takes its toll.

One exception is the experimental Saab Variable Compression engine (SVC). This engine, designed by Saab Automobile, uses a technique that dynamically alters the volume of the combustion chamber (V_c), which, via the above equation, changes the compression ratio (CR). In the scientific method, an experiment (Latin: ex-+-periri, of (or from) trying), is a set of actions and observations, performed in the context of solving a particular problem or question, to support or falsify a hypothesis or research concerning phenomena. ... The Saab Variable Compression engine was a development project of Saab Automobile, for which it won and award both in 2000 and 2001. ... Saab Automobile AB is a subsidiary of General Motors. ...

To alter V_c, the SVC 'lowers' the cylinder head closer to the crankshaft. It does this by replacing the typical one-part engine block with a two-part block, with the crankshaft in the lower block and the cylinders in the upper portion. The two blocks are hinged together at one side (imagine a book, lying flat on a table, with the front cover held an inch or so above the title page). By pivoting the upper block around the hinge point, the V_c (imagine the air between the front cover of the book and the title page) can be modified. In practice, the SVC adjusts the upper block through a small range of motion, using a hydraulic actuator. The cylinder head from a GMC van. ... Crankshaft, pistons, and flywheel Continental engine marine crankshafts, 1942 For the comic strip about an old, curmudgeonly bus driver, see Crankshaft (comic strip). ... A hinge is a mechanical device that connects two solid objects, allowing rotation between them. ... Hydraulics is a branch of science and engineering concerned with the use of liquids to perform mechanical tasks. ...

The SVC project was shelved by General Motors, when it took over Saab Automobile, due to cost. General Motors Corporation (NYSE: GM), also known as GM, is an American automobile maker with worldwide operations and brands including Buick, Cadillac, Chevrolet, GMC, Holden, Hummer, Opel, Pontiac, Saturn, Saab and Vauxhall. ...

Variable Compression Ratio (VCR) Engines

The SAAB SVC is a very late addition to the world of VCR engines, the first being built and tested by Harry Ricardo in the 1920s. This work led to him devising the octane rating system that is still in use today. The company has recently been involved in working with the 'Office of Advanced Automotive Technologies', to produce a modern petrol VCR engine that showed an efficiency comparable with that of a Diesel. Many companies have been carrying out their own research in to VCR Engines, including Nissan, Volvo, PSA/Peugeot-Citroën and Renault. The Saab Variable Compression engine was a development project of Saab Automobile, for which it won and award both in 2000 and 2001. ... ira ira irsa ir air ira ira irs ira ira ira ira ira irea ira ira ira ira ira ira ira ira irs rias irsa k5tan ir4aq ira ira iora ira rika ira 9ria ira iras oira ir ri aria ria ria ira ira ira eia iea ieaiea iramieaneianieaie aieanimsnkwjijair... The 1920s was a decade sometimes referred to as the Jazz Age or the Roaring Twenties, usually applied to America. ... A gas station pump offering five different octane ratings. ... Gasoline, as it is known in North America, or petrol, in many Commonwealth countries (sometimes also called motor spirit) is a petroleum-derived liquid mixture consisting primarily of hydrocarbons, used as fuel in internal combustion engines. ... Diesel or diesel fuel is a specific fractional distillate of fuel oil (mostly petroleum) that is used as fuel in a diesel engine invented by German engineer Rudolf Diesel. ... Nissan Motor Co. ... AB Volvo (or Aktiebolaget Volvo) is a world-leading Swedish manufacturer of commercial vehicles, buses and construction equipment, drive systems for marine and industrial applications, aerospace components and services. ... Peugeot is a major French car brand, part of PSA Peugeot Citroën. ... Citroën is a French automobile manufacturer, founded in 1919 by André Citroën. ... Renault S.A. is a French vehicle manufacturer producing cars, vans, buses, tractors, and trucks. ...

The Atkinson cycle engine was one of the first attempts at variable compression. Since the compression ratio is the ratio between dynamic and static volumes of the combustion chamber the Atkinson cycle's method of increasing the length of the powerstroke compared to the intake stroke ultimately altered the compression ratio at different stages of the cycle.

External links

• SVC