Today, internal combustion engines The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidiser in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, that are produced by the combustion, directly apply force to a movable component of the engine, such as the pistons or turbine in cars An automobile or motor car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally for the transport, trucks A truck or lorry (British English) is a motor vehicle commonly used for carrying goods and materials. Some light trucks/lorries are similar in size to a passenger automobile. Commercial transportation trucks/lorries or fire trucks can be large and can also serve as a platform for specialized equipment, motorcycles, aircraft, construction machinery and many others, most commonly use a four-stroke cycle. The four strokes refer to intake, compression, combustion (power), and exhaust strokes that occur during two crankshaft rotations per working cycle of the Gasoline engine A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels and Diesel engine A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber during the final stage of compression. This is in contrast to a petrol engine or gas engine, which uses the Otto cycle, in which a fuel/air mixture is ignited by a spark plug.
The cycle begins at top dead center (TDC), when the piston is farthest away from the axis of the crankshaft The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to. On the intake or induction stroke of the piston, the piston descends from the top of the cylinder, reducing the pressure inside the cylinder. A mixture of fuel Fuel is any material that is burned or altered to obtain energy and to heat or to move an object. Fuel releases its energy either through a chemical reaction means, such as combustion, or nuclear means, such as nuclear fission or nuclear fusion. An important property of a useful fuel is that its energy can be stored to be released only when needed, and air The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by the Earth's gravity. It has a mass of about five quadrillion metric tons. Dry air contains roughly 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and trace amounts of other gases. Air also contains a variable amount of water vapor, on is forced (by atmospheric or greater pressure) into the cylinder through the intake (inlet) port. The intake (inlet) valve 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 shaft guides the plug portion by sliding through a valve guide. In most applications a pressure differential helps to seal the valve and in some applications also open it (or valves) then close(s), and the compression stroke compresses the fuel–air mixture.
The air–fuel mixture is then ignited near the end of the compression stroke, usually by a spark plug A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as, aerosol gasoline, Ethanol, and Liquefied petroleum gas by means of an electric spark. Spark plugs have an insulated center electrode which is connected by a heavily insulated wire to an ignition coil or (for a gasoline Gasoline or petrol is a petroleum-derived liquid mixture, primarily used as fuel in internal combustion engines. It also is used as a powerful solvent much like acetone or Otto cycle engine) or by the heat and pressure of compression (for a Diesel cycle The Diesel cycle is the thermodynamic cycle which approximates the pressure and volume of the combustion chamber of the Diesel engine, invented by Rudolph Diesel in 1897. It is assumed to have constant pressure during the first part of the "combustion" phase , v2 to v3 in the diagram . This is mostly a mathematical model: real physical or compression ignition engine Homogeneous charge compression ignition is a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction releases chemical energy into a sensible form that can be translated by an engine into work and heat). 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. The largest and intermediate size diesel engines A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber during the final stage of compression. This is in contrast to a petrol engine or gas engine, which uses the Otto cycle, in which a fuel/air mixture is ignited by a spark plug are usually two-cycle engines , requiring scavenging air pumps or blowers.
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History
The Otto cycle
Main article: Otto engine The Otto engine was a large stationary single-cylinder internal combustion four-stroke engine designed by Nicolaus Otto. It was a low-RPM machine, and only fired occasionally since it was a hit and miss engine This is a video montage of the Otto engines The Otto engine was a large stationary single-cylinder internal combustion four-stroke engine designed by Nicolaus Otto. It was a low-RPM machine, and only fired occasionally since it was a hit and miss engine running at the Western Minnesota Steam Threshers Reunion (WMSTR WMSTR , or the Western Minnesota Steam Threshers Reunion, is a nonprofit antique tractor show that draws around 50,000 visitors each year. It takes place annually on Labor Day weekend near the small town of Rollag, Minnesota. Beginning in 1954, the reunion has grown from a few farmers threshing grain as their fathers had to the largest tractor), in Rollag, Minnesota. (2min 16sec, 320x240, 340 kbit/s video)The four-stroke engine was first patented by Eugenio Barsanti Father Eugenio Barsanti , also named Nicolò, was an Italian engineer, the inventor of the Internal combustion engine and Felice Matteucci Felice Matteucci was an Italian hydraulic engineer and co-inventor, with Eugenio Barsanti, of the internal combustion engine in 1854, followed by a first prototype in 1860. It was also conceptualized by French engineer, Alphonse Beau de Rochas Alphonse Eugène Beau de Rochas was a French engineer who originated the principle of the four-stroke internal-combustion engine. His achievement lay partly in his emphasizing the previously unappreciated importance of compressing the fuel–air mixture before ignition. He publisched his results in 1861, a year after Christian Reithmann was in 1862.
However, the German Germany (pronounced /ˈdʒɜrməni/ ), officially the Federal Republic of Germany (German: Bundesrepublik Deutschland, pronounced [ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant] ( listen)), is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south engineer Nicolaus Otto was the first to develop a functioning four-stroke engine, which is why the four-stroke principle today is commonly known as the Otto cycle and four-stroke engines using spark plugs A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as, aerosol gasoline, Ethanol, and Liquefied petroleum gas by means of an electric spark. Spark plugs have an insulated center electrode which is connected by a heavily insulated wire to an ignition coil or often are called Otto engines. The Otto Cycle consists of adiabatic In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which no heat is transferred to or from the working fluid. The term "adiabatic" literally means impassable, coming from the Greek roots ἀ- , διὰ- ("through"), and βαῖνειν ("to pass"); this etymology corresponds compression, heat addition at constant volume, adiabatic expansion and rejection of heat at constant volume.
Design and engineering principles
Fuel octane rating
Main article: Octane rating The octane rating is a measure of the resistance of gasoline and other fuels to detonation in spark-ignition internal combustion engines. High-performance engines typically have higher compression ratios and are therefore more prone to detonation, so they require higher octane fuel. A lower-performance engine will not generally perform better withInternal combustion engine power primarily originates from the expansion of gases in the power stroke. Compressing the fuel and air into a very small space increases the efficiency of the power stroke, but increasing the cylinder compression ratio The compression ratio of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber; from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines also increases the heating of the fuel as the mixture is compressed (following Charles's law Charles's law is an experimental gas law which describes how gases tend to expand when heated. It was first published by French natural philosopher Joseph Louis Gay-Lussac in 1802, although he credits the discovery to unpublished work from the 1780s by Jacques Charles. The law was independently discovered by British natural philosopher John Dalton).
A highly flammable Flammability is defined at how easily something will burn or ignite, causing fire or combustion. The degree of difficulty required to cause the combustion of a substance is subject to quantification through fire testing. Internationally, a variety of test protocols exist to quantify flammability. The ratings achieved are used in building codes, fuel with a low self-ignition temperature can combust before the cylinder reaches top-dead-center, potentially forcing the piston backwards against rotation. Alternately, a fuel which self-ignites at top-dead-center but before the cylinder has started downwards can damage the piston and cylinder due to the extreme thermal energy concentrated into a very small space with no relief. This damage is often referred to as engine knocking Knocking in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel-air charge is meant to be ignited by the spark plug and can lead to permanent engine damage if it occurs frequently.
The octane rating is a measure of the fuel's resistance to self-ignition, by increasing the temperature at which it will self-ignite. A fuel with a greater octane rating allows for a much higher compression ratio without the risk of damage due to self-ignition.
Diesel engines rely on self-ignition for the engine to function. They solve the engine damage problem by separately injecting high-pressure fuel into the cylinder shortly before the piston has reached TDC. Air without fuel can be compressed to a very high degree without concern for self-ignition, and the highly pressurized fuel in the fuel injection Fuel injection is a system for mixing fuel with air in an internal combustion engine. It has become the primary fuel delivery system used in gasoline automotive engines, having almost completely replaced carburetors in the late 1980s system cannot ignite without the presence of air.
Power output limit
The four-stroke cycle 1=TDC 2=BDC A: Intake B: Compression C: Power D: ExhaustThe maximum amount of power generated by an engine is determined by the maximum amount air ingested. The amount of power generated by a piston engine is related to its size (swept cilinder volume) and speed (RPM Revolutions per minute is a unit of frequency: the number of full rotations completed in one minute around a fixed axis. It is most commonly used as a measure of rotational speed or angular velocity of some mechanical component).The speed is ultimately limited by material strength and lubrication Lubrication is the process, or technique employed to reduce wear of one or both surfaces in close proximity, and moving relative to each another, by interposing a substance called lubricant between the surfaces to carry or to help carry the load between the opposing surfaces. The interposed lubricant film can be a solid, (eg graphite, MoS2) a. Valves, pistons and connecting rods suffer severe acceleration forces. At high engine speed, physical breakage and piston ring 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 engine or steam engine flutter can occur, resulting in power loss or even engine destruction. Piston ring flutter occurs when the rings oscillate vertically within the piston grooves they reside in. Ring flutter compromises the seal between the ring and the cylinder wall which results in a loss of cylinder pressure and power. If an engine spins too quickly, valve springs cannot act quickly enough to close the valves. This is commonly referred to as 'valve float Valve float is an adverse condition which occurs when the poppet valves on an internal combustion engine valvetrain do not remain in contact with the camshaft lobe during the valve closure phase of the cam lobe profile. This reduces engine efficiency and performance and potentially increases engine emissions', and it can result in piston to valve contact, severely damaging the engine. At high speeds the lurbication of piston cilinder wall interface tends to break down. This limits the piston speed for industrial engines to about 10 m/sec.
Intake/Exhaust 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 above the cylinders and consists of a platform containing part of the combustion chamber and the location of the valves and spark plugs. In a flathead engine, the mechanical parts of the valve train are all contained within the block, and the head is essentially a flat plate of metal bolted. 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 The valve seat in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed. The valve seat is a critical component of an engine in that if it is improperly positioned, oriented, or formed during manufacture, valve configuration can be modified to reduce resistance. This process is called porting 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. Cylinder heads, as manufactured, are usually suboptimal due to design and manufacturing constraints. Porting the heads provides the finely detailed attention required to bring, and it can be done by hand or with a CNC Numerical control refers to the automation of machine tools that are operated by abstractly programmed commands encoded on a storage medium, as opposed to manually controlled via handwheels or levers or mechanically automated via cams alone. The first NC machines were built in the 1940s and 50s, based on existing tools that were modified with machine..
Supercharging
One way to increase engine power is to force more air into the cylinder so that more power can be produced from each power stroke. This was originally done using a type of air compression device known as a Supercharger A supercharger is an air compressor used for forced induction of an internal combustion engine. The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally-aspirated engine, which allows more fuel to be provided and more work to be done per cycle, increasing the power output of the engine which is powered by the engine crankshaft.
Supercharging increases the power output limits of four-stroke engine, but the supercharger is always running. Continuous compression of the intake air requires some mechanical energy to accomplish, so the supercharger has a cost of reduced fuel efficiency when the engine is operating at low power levels or when the engine is simply unloaded and idling.
Turbocharging
The Turbocharger A turbocharger, or turbo, is a gas compressor used for forced-induction of an internal combustion engine. Like a supercharger, the purpose of a turbocharger is to increase the density of air entering the engine to create more power. However, a turbocharger differs in that the compressor is powered by a turbine driven by the engine's own exhaust was designed as a part-time method of compressing more air into the cylinder head. It consists of a two piece, high-speed turbine assembly with one side that compresses the intake air, and the other side that is powered by the exhaust gas outflow.
When idling, and at low-to-moderate speeds, the turbocharger is not engaged and the engine operates in a naturally-aspirated manner. When much more power output is required, the engine speed is increased until the exhaust gases are sufficient to 'spin up' the turbocharger's turbine to start compressing much more air than normal into the intake manifold.
Turbocharging allows for more efficient engine operation at low-to-moderate speeds, but there is a design limitation known as turbo lag A turbocharger, or turbo, is a gas compressor used for forced-induction of an internal combustion engine. Like a supercharger, the purpose of a turbocharger is to increase the density of air entering the engine to create more power. However, a turbocharger differs in that the compressor is powered by a turbine driven by the engine's own exhaust. The increased engine power is not immediately available, due to the need to sharply increase engine RPM to spin up the turbo, before the turbo starts to do any useful air compression.
Rod and Piston-to-Stroke ratio
The rod-to-stroke ratio is the ratio of the length of the connecting rod In a reciprocating piston engine, the connecting rod or conrod connects the piston to the crank or crankshaft to the length of the piston stroke. A longer rod will reduce the sidewise pressure of the piston on the cylinder wall and the stress forces, hence increasing engine life. It also increases cost and engine height and weight.
A "square engine" is an engine with a bore diameter equal to its stroke length. An engine where the bore diameter is larger than its stroke length is an oversquare 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 piston is at the bottom dead center point. The stroke ratio also gives a general direction of the engines characteristics. The bore is the diameter of the cylinder and the stroke is the length that piston engine, conversely, an engine with a bore diameter that is smaller than its stroke length is an undersquare engine.
Valve train
The valves are typically operated by a camshaft 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 with a number of oblong lobes or cams protruding from it, one for each valve. The cams force the valves open by pressing on the valve, or on some intermediate mechanism, as they rotate rotating at half the speed of the crankshaft The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to. It has a series of cams 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. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shape that produces a smooth reciprocating motion in the follower which is a lever making contact along its length, each designed to open a valve during the appropriate part of an intake or exhaust stroke. A tappet A tappet in mechanical engineering is a projection which imparts a linear motion to some other component within an assembly. Properly speaking, a tappet is only that part of a rocker arm which makes contact with an intake or exhaust valve stem above the cylinder head of an internal combustion engine. As the cam rotates it creates both a sideways between valve and cam is a contact surface on which the cam slides to open the valve. 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 an internal combustion engine, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder block, in which case each cam contacts a push rod An overhead valve engine, also called pushrod engine or I-head engine is a type of piston engine that places the camshaft in the cylinder block (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to actuate rocker arms above the cylinder head to, which contacts a rocker arm Generally referred to within the internal combustion engine of automotive, marine, motorcycle and reciprocating aviation engines, the rocker arm is a reciprocating lever that conveys radial movement from the cam lobe into linear movement at the poppet valve to open it. One end is raised and lowered by the rotating lobes of the camshaft (either which opens a valve. The overhead cam Overhead camshaft, commonly abbreviated to OHC, valvetrain configurations place the engine camshaft within the cylinder heads, above the combustion chambers, and drive the valves or lifters in a more direct manner compared to overhead valves and pushrods design typically allows higher engine speeds because it provides the most direct path between cam and valve.
Valve clearance
Valve clearance refers to the small gap between a valve lifter and a valve stem that ensures that the valve completely closes. On engines with mechanical valve adjustment excessive clearance will cause noise from the valve train. Typically the clearance has to be readjusted each twenty thousand miles with a feeler gage.
Most modern production engines use hydraulic lifters to automatically compensate for valve train component wear. Dirty engine oil may cause lifter failure.
Energy Balance
Otto engines are about 35% efficient - 35% of fuel energy arises at the output shaft, the remainder appears as waste heat.[citation needed]A six stroke engine uses more than 50% of the energy.
Starting position, intake stroke, and compression stroke. Ignition of fuel, power stroke, and exhaust stroke.
See also
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References
- Hardenberg, Horst O., The Middle Ages of the Internal combustion Engine, Society of Automotive Engineers (SAE), 1999
- scienceworld.wolfram.com/physics/OttoCycle.html
External links
- four stroke cycle animation and video
- U.S. Patent 194,047
- Detailed Engine Animations
- How Car Engines Work
- Animated Engines, four stroke another explanation of the four-stroke engine
- CDX eTextbook – some videos of car components in action
- Video from inside a four-stroke engine cylinder.
Categories: Internal combustion piston engines | 1854 introductions
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