Today internal combustion engines in cars, trucks, motorcycles, construction machinery and many others, most commonly use a four-stroke cycle. The internal combustion engine is an engine in which the Combustion of Fuel and an Oxidizer (typically air occurs in a confined space called a This article is about the semi-truck For the North American use of the word see Pickup truck. The four strokes refer to intake, compression, combustion and exhaust strokes that occur during two crankshaft rotations per working cycle of Otto Cycle and Diesel engines. A diesel engine is an Internal combustion engine which operates using the Diesel cycle (named after Dr The four steps in this cycle are often informally referred to as "suck, squeeze (or squash), bang, blow. "

The Otto cycle

Four-stroke cycle (or Otto cycle)

The Otto cycle engine was first patented by Eugenio Barsanti and Felice Matteucci in 1854 followed by a first prototype in 1860. Father Eugenio Barsanti ( October 12 1821 - April 19 1864) also named Nicolò, was the Italian inventor of the Internal Felice Matteucci ( February 12 1808 - September 13 1887) was an Italian Hydraulic Engineer and co-inventor It was also conceptualized by French engineer, Alphonse Beau de Rochas in 1862 and, independently, by the German engineer Nicolaus Otto in 1876. Alphonse Eugène Beau de Rochas (1815-1893 was a French engineer who originated the principle of the Four-stroke Internal-combustion engine. Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. Nicolaus August Otto ( June 14, 1832 Holzhausen an der Haide, Nassau - January 26, 1891 Cologne) was the German Its power cycle consists of adiabatic compression, heat addition at constant volume, adiabatic expansion and rejection of heat at constant volume, characterized by four strokes, or reciprocating movements of a piston in a cylinder:

1. intake (induction) stroke
2. compression stroke
3. power stroke
4. exhaust stroke

The cycle begins at top dead center (TDC), when the piston is furthest away from the axis of the crankshaft. This article covers adiabatic processes in Thermodynamics. For adiabatic processes in Quantum mechanics, see Adiabatic process (quantum mechanics A piston is a component of Reciprocating engines Pumps and Gas compressors It is located in a cylinder and is made gas-tight by Piston A cylinder is the central working part of a Reciprocating engine, the space in which a Piston travels A stroke is a single action of certain Engines In a steam, Otto or Diesel Piston Engine, a stroke is the action of In a Reciprocating engine, the dead center is the position of a piston in which it is farthest from or nearest to the Crankshaft. The crankshaft, sometimes casually abbreviated to crank, is the part of an Engine which translates reciprocating Linear On the intake or induction stroke of the piston, the piston descends from the top of the cylinder, reduces the pressure inside the cylinder. A mixture of fuel and air is forced (by atmospheric or greater pressure) into the cylinder through the intake (inlet) port. Fuel is any material that is burned or altered in order to obtain energy Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five The intake (inlet) valve (or valves) then close(s), and the compression stroke compresses the fuel–air mixture. 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 air–fuel mixture is then ignited near the end of the compression stroke, usually by a spark plug (for a gasoline or Otto cycle engine) or by the heat and pressure of compression (for a Diesel cycle or compression ignition engine). A spark plug (also very rarely nowadays in British English: a sparking plug) is an electrical device that fits into the Cylinder The Homogeneous Charge Compression Ignition, or HCCI, is a form of internal combustion in which well-mixed Fuel and Oxidizer (typically air are The resulting pressure of burning gases pushes the piston through the power stroke. In the exhaust stroke, the piston pushes the products of combustion from the cylinder through an exhaust valve or valves.

Valve train

The valves are typically operated by a camshaft rotating at half the speed of the crankshaft. The camshaft is an apparatus often used in Piston engines to operate Poppet valves It consists of a cylindrical rod running the length of the Cylinder bank It has a series of cams along its length, each designed to open a valve during the appropriate part of an intake or exhaust stroke. A cam is a projecting part of a rotating Wheel or shaft that strikes a Lever at one or more points on its circular path A tappet between valve and cam is a contact surface on which the cam slides to open the valve. A tappet in Mechanical engineering is a projection which imparts a linear motion to some other component within an assembly The location of camshafts vary among engines, as does the quantity. Many engines use one or more camshafts “above” a row (or each row) of cylinders, as in the illustration, in which each cam directly actuates a valve through a flat tappet. In other engine designs the camshaft is in the crankcase, in which case each cam contacts a push rod, which contacts a rocker arm which opens a valve. For the GI Joe character see List of GI Joe ARAH characters. For the Transformers characters see Crankcase (Transformers. The overhead cam design typically allows higher engine speeds because it provides the most direct path between cam and valve. Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the

Valve clearance adjustment

Valve clearance refers to the small gap between a valve lifter and a valve stem (or between a rocker arm and a valve stem) that ensures that the valve completely closes. On engines that require manual valve adjustment, excessive clearance will cause excessive noise from the valve train (“hammering”) during operation. Improper valve clearance reduces engine performance and increases wear and noise.

Most engines have the valve clearance set by grinding the end of the valve stem during engine assembly, overhead cams not needing subsequent adjustment. All engines with poppet-type valves make some sort of allowance for maintaining this "expansion joint", while less sophisticated engines use solid, "non-adjustable” components which are simply ground off at the contact points to provide the correct clearance (though the low efficiency of this design may not be practical when the cost of labor is very high). Another method is to provide some method of manually changing the clearance with adjustable screws or shims, the implementation of which depends on and varies widely with the design of the engine. Manual valve lash adjustment is used in almost all very high performance engines because the hydraulic adjusters used in "automatic" systems are often affected by the extreme valve train accelerations of ultra high-speed engines.

Most modern production engines use some form of automatic valve adjustment (usually hydraulic) to maintain a state known as "zero lash". In pushrod and some OHC engines this adjuster is incorporated into the tappet, lash adjuster or tip of the rocker. Many DOHC engines now employ tiny hydraulic lash adjusters in the top of the cam followers to maintain "zero lash". Overhead camshaft, commonly abbreviated to OHC, Valvetrain configurations place the engine Camshaft within the Cylinder heads above the "Zero lash" is a desirable condition, since this allows for very quiet engine operation. Hydraulic lifters or lash adjusters also reduce required maintenance, reduce noise, help engines to perform at peak efficiency and minimize exhaust emissions by compensating for wear and expansion of various engine components. Earlier engines, mostly those with push rods and rocker arms, used adjustable tappets or hydraulic lifters to automatically compensate for valve train component and camshaft wear. A hydraulic lifter, also known as a hydraulic Tappet or a hydraulic Lash adjuster is a device for maintaining zero valve clearance in an internal Lack of valve clearance will prevent valve closure causing leakage and valve damage.

Valve clearance adjustment must be performed to manufacturer's specifications. It is normal that the exhaust valve will have a larger clearance. Adjustment is performed by either adjusting the rocker arm or placing shims between cam follower and valve stem. Most modern engines have hydraulic lifters and require only infrequent adjustment. A hydraulic lifter, also known as a hydraulic Tappet or a hydraulic Lash adjuster is a device for maintaining zero valve clearance in an internal

Valve clearance measurement

Valve clearance is measured with the valve closed, typically at top dead center between the compression and power strokes. In a Reciprocating engine, the dead center is the position of a piston in which it is farthest from or nearest to the Crankshaft. The tappet will be resting on the heel of the cam lobe. A feeler gauge must pass through the clearance space. A feeler gauge is a simple Tool used to measure gap-widths The feeler gauge was first patented in 1954 by Andrejs Muiza a Latvian immigrant to the United States (Nashville The feeler gauge should fit in and out with a slight drag. If the feeler gauge will not fit in, then the clearance is too small. If the blade of the feeler gauge fits in too loosely, the clearance is too large.

Valve clearance too wide

A too-wide valve clearance causes excessive wear of the camshaft and valve lifter contact areas, and noise. The camshaft is an apparatus often used in Piston engines to operate Poppet valves It consists of a cylindrical rod running the length of the Cylinder bank Should the clearance become wide enough, valve timing is significantly affected, resulting in poor performance. In a Piston engine, the valve timing is the precise timing of the opening and closing of the valves

Valve clearance too narrow

A too-narrow valve clearance does not allow for heat expansion and results in the failure of the valve to fully close. The combustion chamber does not seal properly, resulting in poor compression, which reduces performance. The valve can also overheat and even melt.

Port flow

The output power of an engine is dependent on the ability of intake (air–fuel mixture) and exhaust matter to move quickly through valve ports, typically located in the cylinder head. In an Internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the Combustion chamber and the To increase an engine’s output power, irregularities in the intake and exhaust paths, such as casting flaws, can be removed and, with the aid of an air flow bench, the radii of valve port turns and valve seat configuration can be modified to reduce resistance. An air flow bench is a device used for testing the internal Aerodynamic qualities of an Engine component and is related to the more familiar Wind tunnel The valve seat in an internal combustion gasoline or Diesel engine is the surface against which an Intake or an exhaust This process is called porting, and it can be done by hand or with a CNC machine. Cylinder head porting refers to the process of modifying the intake and exhaust ports of an Internal combustion engine to improve the quality and quantity of the gas flow The abbreviation CNC stands for computer numerical control, and refers specifically to a computer "controller" that reads G-code

Output limit

The amount of power generated by a four-stroke engine is related to its speed. The speed is ultimately limited by material strength. Valves, pistons and connecting rods (where applicable) suffer severe forces and severe acceleration, and physical breakage and piston ring flutter can occur, resulting in power loss or even engine destruction. A piston ring is an open-ended ring that fits into a groove on the outer diameter of a Piston in a Reciprocating engine such as an Internal combustion Piston ring flutter occurs are dislodged, resulting in a loss of cylinder seal and power. If an engine spins too quickly, valves cannot close quickly enough, and this can result in contact between a valve and a piston, severely damaging the engine.

Rod/stroke ratio, an important factor in engine design, is the ratio of the length of the connecting rod to the length of the crankshaft's (or piston's) stroke. In a reciprocating Piston engine, the connecting rod or conrod connects the Piston to the crank or Crankshaft. An increase in the rod/stroke ratio (a longer rod, a shorter stroke or both) results in a lower piston speed. A longer rod (and consequently, higher rod/stroke ratio,) can potentially create more power, due to the fact that with a longer connecting rod, more force from the piston is delivered tangentially to the crankshaft's rotation, delivering more torque. A shorter rod/stroke ratio creates higher piston speeds, but this can be beneficial depending on other engine characteristics. Increased piston speeds can create tumble or swirl within the cylinder and reduce detonation. Increased piston speeds can also draw fuel-air mixture into the cylinder more quickly through a larger intake runner, promoting good cylinder filling.

Rod length and stroke length are independent variables. Rod length is expressed as center-to-center (c/c) length. An engine with a particular stroke can be fitted with rods of several c/c lengths by changing the piston pin location or block deck height. A rod that is longer in relation to stroke causes the piston to dwell a longer time at top dead center and causes the piston to move toward and away from TDC more slowly. Long rod engines with a particular stroke also build suction above the piston with less force, since the piston moves away from TDC more slowly. Consequently, long rod engines tend to produce a lower port air velocity, which also reduces low speed torque. Long rods place less thrust load on the cylinder walls, thus generate less parasitic drag and result in less frictional losses as engine revolutions rise. A "short rod" engine has the opposite characteristics. “The short rod exerts more force to the crank pin at any crank angle that counts i. e. --20° ATDC to 70° ATDC” (Jere Stahl [1]). Short rod engines tend develop more torque at lower engine speeds with torque and horsepower falling off quickly as engine RPM rises to high levels. Long rod engines generally produce more power due to reduced engine drag, especially as engine RPM increases. Regardless of rod length for a given stroke, the average piston speed (usually expressed in ft/s or m/s) remains the same. What changes as the rod length becomes shorter or longer in relation to the stroke, is the RATE of motion as the piston rises and falls in relation to the crankshaft. A long rod fitted to a given stroke generates less stress on the component parts due to the lower rate of acceleration away from and toward TDC. The average piston speed is the same; however, the peak piston speed is lower with long rods.

There is no "Ideal" rod to stroke ratio, however a ratio of about 2 to 1 seems to be the upper practical limit and 1. 5 to 1 the lower limit in general practice. The Chevrolet 350 engine with a 3. 48" stroke and a 5. 7-inch (140 mm) c/c rod has a rod/stroke ratio of 1. 638 to 1. The durability and longevity of this engine seems to prove that this is a “acceptable” figure for a rod/stroke ratio number. The "small block 400" used a 3. 75" stroke and a rod c/c of 5. 565" for a ratio of 1. 484. The SB 400 was known for torque and "running out of breath" at high engine speeds. Even with large port heads and high lift camshaft, the S/B 400 ran into a "wall" of friction when engine speeds climbed above 5000 rpm. S/B 400s we also know for wearing piston skirts and cylinder walls at a faster rate than their smaller brothers. Many people that race the S/B 400 convert the engine to 5. 7 or 6. 0 rods to reduce the effects of the long-stroke crankshaft and lower friction within the engine. The 1967–1969 Z-28 302 engine was fitted with a 3. 0" stroke crank and in some racing applications used up to a 6. 0" rod, resulting in a 2 to 1 rod/stroke The 302 Chevrolet V-8 was famous for phenomenal power in the upper RPM range while it sacrificed low speed torque to gain the high RPM power and reliability.

Honda's B16A/B16B is considered ideal in high revolution and high durability applications and it is, not coincidentally, right in between the 1. 5:1 and 2:1 ratios, with a 1. 75:1 ratio. Although this gives it relative low power at lower engine speeds, it also gives it a rev-happy nature that is durable beyond its factory rev limit. Some sport bikes surpass the 1. 75:1 ratio, but the lower torque at less engine speed becomes evident for practical applications such as cars(where power/weight ratio is important).

A "square engine" is an engine with a bore equal to its stroke. An engine where the bore dimension is larger than the stroke is commonly known as an oversquare engine; such engines have the ability to attain higher rotational speed since the pistons do not travel as far. Stroke ratio, bore/stroke ratio and stroke/bore ratio are terms that are used to describe the form of a piston engine's cylinder when the Conversely, an engine with a bore that is smaller than its stroke is known as an undersquare engine; such engines cannot rotate as quickly, but are able to generate more torque at lower rotational speeds. Stroke ratio, bore/stroke ratio and stroke/bore ratio are terms that are used to describe the form of a piston engine's cylinder when the

Bibliography

• Hardenberg, Horst O. , The Middle Ages of the Internal combustion Engine, Society of Automotive Engineers (SAE), 1999

See also

• Four-stroke power valve system
• Atkinson cycle
• Desmodromic valve
• Six stroke engine

External links

• Detailed Engine Animations
• How Cars Work – lots of general and specific car information, with forums
• U.S. Patent 194,047 
• How Four-stroke Small Engines Work
• How Car Engines Work
• Barsanti & Matteucci Foundation – "fathers of the internal combustion engine"
• Animated Engines: another explanation of the four-stroke engine
• New 4 Stroke
• The Fuel and Engine Bible – A good resource for comparing different engine types, fuels, and engine components
• CDX eTextbook – some videos of car components in action
• View from a camera mounted inside a four-stroke engine cylinder. The Atkinson-cycle engine is a type of Internal combustion engine invented by James Atkinson in 1882. In general mechanical terms the word desmodromic is used to refer to mechanisms that have different controls for their actuation in different directions The term six stroke engine describes two different approaches in the Internal combustion engine, developed since the 1990s to improve its efficiency and reduce emissions