Four-stroke piston engine

Four-stroke cycle engine An engine completing one cycle in four strokes of the piston or two shaft revolutions. The cyclic events are designated by the following strokes (1) induction or suction stroke, (2) compression stroke, (3) power or expansion stroke, (4) exhaust stroke. ... 

Toward the end of the nineteenth centuiy, successful two-stroke engines operating on the Otto cycle were developed by Dugald Clerk, James Robson, Karl Benz, and James Day. In this engine, the intake, combustion, expansion, and exhaust events all occur with but two piston strokes, or one crankshaft revolution. In principle this should double the output of a four-stroke engine of equal piston displacement. However, instead of the intake and exhaust events taking place during sequential strokes of the piston, they occur concurrently while the piston is near BDC. This impairs the ability of the... 

The four-stroke and two-stroke engines described above both use the slider-crank mechanism to transform piston work into crankshaft torque, but other intermittent-combustion engines have been conceived that use different kinematic arrangements to achieve this end. The only one that has realized significant commercial success is the rotary engine first demonstrated successfully in Germany by Felix Wankel in 1957. 

The four-stroke engine requires four piston strokes (or two crankshaft revolutions) for each cycle. In a downward stroke, the intake valve is opened and the combustible mixture is brought into the cylinder. In an upward stroke the fuel-air mixture is compressed and ignited near the top of the stroke. This forces the piston downward (to provide power). In the next upward stroke the exhaust valve is opened and the spent gases are forced from the cylinder. In the following downward stroke, the cycle is repeated with the opening of the intake valve. 

The most common internal-combustion engine, because of its use in automobiles, is the Otto engine. Its cycle consists of four strokes, and starts with an intake stroke at essentially constant pressure, during which a piston moving outward draws a fuel/air mixture into a cylinder. This is represented by line 0 - 1 in Fig. 8.8. During the second stroke (line 1 - 3), all valves are closed, and the fuel/air mixture is compressed, approximately adiabatically, along line 1 2. The mixture... 

In a typical four-stroke engine, when the piston descends, the air inlet valve opens and a mixture of air and petrol is sucked in through a carburettor. 

The Otto cycle is essentially the cycle describing the internal-combustion automobile engine. This is a four-stroke cycle, in contrast to the simpler two-stroke Carnot cycle and the various others, such as the Stirling and Brayton cycles, that operate on a single oscillation of the piston. The Otto cycle consists of an intake expansion, a compression, an expansion resulting from ignition... 

The four-stroke cycle spark ignition (SI) internal combustion engine (ICE) was initially proposed by Beau de Rockas in 1862 and first built by N. A. Otto in 1876. This engine has become the major piston engine in use today. The PV cycle of the engine is shown in Fig. 4.3 where the four strokes are indicated. 

The four-cycle engine takes two complete piston strokes for exhaust, scavenging, and charging. The two-cycle engine exhausts, scavenges, and charges for about 25% of its piston travel before bottom center, and until about 25% after bottom center. The two-cycle machine does not have intake and exhaust valves but uses ports. 

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