The Allison T56 is an American single-shaft, modular design military turboprop with a 14-stage axial flow compressor driven by a four-stage turbine. It was developed by the Allison Engine Company for the Lockheed C-130 Hercules transport entering production in 1954, it has been a Rolls-Royce product since 1995. The commercial version is designated 501-D. Over 18,000 engines have been produced since logging over 200 million flying hours; the T56 turboprop, evolved from Allison's previous T38 series, was first flown in the nose of a B-17 test-bed aircraft in 1954. One of the first flight-cleared YT-56 engines was installed in a C-130 nacelle on Lockheed's Super Constellation test aircraft in early 1954. Fitted to the Lockheed C-130 Hercules, the T56 was installed on the P-3 and E-2/C-2 aircraft, as well as civilian airliners such as the Lockheed Electra and Convair 580. A major setback occurred when a T56-A-1 engine delivered to Lockheed in May, 1953, produced only 3,000 hp, not the required 3,750 shp needed for the C-130.
A further setback occurred in August 1953 when an engine being tested failed after only 6 ½ hours run time. A redesign of the engine failed during testing in September of the same year. A second redesign was more successful. Evolution of the T56 has been achieved through increases in turbine temperature; the T56-A-14 installed on the P-3 Orion has a 4591 shp rating with a compression ratio of 9.25:1 while the T56-A-427 fitted to the E-2 Hawkeye has a 5250 shp rating and a 12:1 compression. In addition, the T56 produces 750 lbs of thrust from its exhaust. A marinised turboshaft version, the 501K engine, is used to generate electrical power for all U. S. Navy cruisers and destroyers in commission. An engine enhancement program to reduce fuel consumption and decrease temperatures was approved in 2013, the US Air Force expects to save $2 billion and extend the C-130 fleet life; the Lockheed Martin C-130J Super Hercules which first flew in 1996, has the T56 replaced by the Rolls-Royce AE 2100, which uses dual FADECs to control the engines and propellers.
It drives new six-bladed scimitar propellers from Dowty Rotol. 501-D12 501-D13 Lockheed L-188 Electra and Convair CV-580 starting December 1957 501-D13A Similar to -D13 501-D13D Similar to -D13 501-D13H Similar to -D13 501-D15 501-D22 Lockheed L-100 Hercules 501-D36A 501-D22A 501-D22C similar to -D22A 501-D22G similar to -D22A 501-M62 Company designation for the T701-AD-700 turboshaft engine to power the Boeing Vertol XCH-62 Heavy-lift helicopter XT56-A-1 XT56-A-2 proposed gas generator engines for the McDonnell XHCH-1 T56-A-3 3,250 shp XT56-A-4 proposed engines for the McDonnell XHRH-1, with propeller drive and gas generator bleed for rotor-tip pressure jets. YT56 Gas generator engines for the C-130B BLC demonstrator. T56-A-5 2,100 shp turboshaft version for the Piasecki YH-16B Transporter helicopter. T56-A-7 T56-A-8 T56-A-9 T56-A-9D Lockheed C-130A Hercules Starting December 1956 and on all Grumman E-2A Hawkeyes from 1960 T56-A-9E Similar to -A-9D T56-A-10W with water injection T56-A-7A Lockheed C-130B Hercules Starting May 1959 T56-A-7B Similar to -A-7A T56-A-10WA T56-A-14 Lockheed P-3/EP-3/WP-3/AP-3/CP-140 Aurora from August 1962 T56-A-15 Lockheed C-130H Hercules from June 1974 T56-A-16 T56-A-425 Grumman C-2A Greyhound from June 1974 T56-A-14A Fuel efficiency and reliability upgrade, Lockheed WP-3D Orion from May 2015.
T56-A-15A T56-A-16A T56-A-425A Northrop Grumman E-2 Hawkeye from August 2011 T56-A-427 Northrop Grumman E-2 Hawkeye upgrades from 1972 T56-A-427A similar to the -A-427 T701-AD-700 Turboshaft engine for the Boeing Vertol XCH-62 heavy-lift helicopter. Aero Spacelines Super Guppy Boeing Vertol XCH-62 Convair 580 and Convair 5800 Grumman C-2 Greyhound Lockheed C-130 Hercules Lockheed CP-140 Aurora Lockheed L-100 Hercules Lockheed L-188 Electra Lockheed P-3 Orion Northrop Grumman E-2 Hawkeye Piasecki YH-16B Transporter Data from Rolls-Royce. Type: Turboprop Length: 146.1 in Diameter: 27 in Dry weight: 1,940 lb Compressor: 14 stage axial flow Combustors: 6 cylindrical flow-through Turbine: 4 stage Fuel type: JP8 Maximum power output: 4,350 shp limited to 4,100 Turbine inlet temperature: 860°C Fuel consumption: 2,412 pounds per hour Power-to-weight ratio: 2.75:1 Related development Allison T38 Allison T40 Comparable engines Bristol Proteus Ivchenko AI-20 Lycoming T55 Napier Eland Rolls-Royce TyneRelated lists List of aircraft engines T56 page at Rolls-Royce website
A geophone is a device that converts ground movement into voltage, which may be recorded at a recording station. The deviation of this measured voltage from the base line is called the seismic response and is analyzed for structure of the earth; the term geophone derives from the Greek word "γῆ " meaning "earth" and "phone" meaning "sound". Geophones have been passive analog devices and comprise a spring-mounted wire coil moving within the field of a case-mounted permanent magnet to generate an electrical signal. Recent designs have been based on microelectromechanical systems technology which generates an electrical response to ground motion through an active feedback circuit to maintain the position of a small piece of silicon; the response of a coil/magnet geophone is proportional to ground velocity, while MEMS devices respond proportional to acceleration. MEMS have a much higher noise level than geophones and can only be used in strong motion or active seismic applications; the frequency response of a geophone is that of a harmonic oscillator determined by corner frequency and damping.
Since the corner frequency is proportional to the inverse square root of the moving mass, geophones with low corner frequencies become impractical. It is possible to lower the corner frequency electronically, at the price of cost. Although waves passing through the earth have a three-dimensional nature, geophones are constrained to respond to single dimension - the vertical. However, some applications require the full wave to be used and three-component or 3-C geophones are used. In analog devices, three moving coil elements are mounted in an orthogonal arrangement within a single case; the majority of geophones are used in reflection seismology to record the energy waves reflected by the subsurface geology. In this case the primary interest is in the vertical motion of the Earth's surface. However, not all the waves are upwards travelling. A strong, horizontally transmitted wave known as ground-roll generates vertical motion that can obliterate the weaker vertical signals. By using large areal arrays tuned to the wavelength of the ground-roll the dominant noise signals can be attenuated and the weaker data signals reinforced.
Analog geophones are sensitive devices which can respond to distant tremors. These small signals can be drowned by larger signals from local sources, it is possible though to recover the small signals caused by large but distant events by correlating signals from several geophones deployed in an array. Signals which are registered only at one or few geophones can be attributed to unwanted, local events and thus discarded, it can be assumed that small signals that register uniformly at all geophones in an array can be attributed to a distant and therefore significant event. The sensitivity of passive geophones is 30 Volts/, so they are in general not a replacement for broadband seismometers. Conversely, some applications of geophones are interested only in local events. A notable example is in the application of Remote Ground Sensors incorporated in Unattended Ground Sensor Systems. In such an application there is an area of interest which when penetrated a system operator is to be informed by an alert which could be accompanied by supporting photographic data.
A network of geophones has been used on the moon surface too. Accelerometer Hydrophone Michelson interferometer Seismometer PSR-1 Seismic Intrusion Detector
A seismometer is an instrument that responds to ground motions, such as caused by earthquakes, volcanic eruptions, explosions. Seismometers are combined with a timing device and a recording device to form a seismograph; the output of such a device — recorded on paper or film, now recorded and processed digitally — is a seismogram. Such data is used to locate and characterize earthquakes, to study the earth's internal structure. A simple seismometer, sensitive to up-down motions of the Earth, is like a weight hanging from a spring, both suspended from a frame that moves along with any motion detected; the relative motion between the weight and the frame provides a measurement of the vertical ground motion. A rotating drum is attached to the frame and a pen is attached to the weight, thus recording any ground motion in a seismogram. Any movement of the ground moves the frame; the mass tends not to move because of its inertia, by measuring the movement between the frame and the mass, the motion of the ground can be determined.
Early seismometers used optical levers or mechanical linkages to amplify the small motions involved, recording on soot-covered paper or photographic paper. Modern instruments use electronics. In some systems, the mass is held nearly motionless relative to the frame by an electronic negative feedback loop; the motion of the mass relative to the frame is measured, the feedback loop applies a magnetic or electrostatic force to keep the mass nearly motionless. The voltage needed to produce this force is the output of the seismometer, recorded digitally. In other systems the weight is allowed to move, its motion produces an electrical charge in a coil attached to the mass which voltage moves through the magnetic field of a magnet attached to the frame; this design is used in a geophone, used in exploration for oil and gas. Seismic observatories have instruments measuring three axes: north-south, east-west, vertical. If only one axis is measured, it is the vertical because it is less noisy and gives better records of some seismic waves.
The foundation of a seismic station is critical. A professional station is sometimes mounted on bedrock; the best mountings may be in deep boreholes, which avoid thermal effects, ground noise and tilting from weather and tides. Other instruments are mounted in insulated enclosures on small buried piers of unreinforced concrete. Reinforcing rods and aggregates would distort the pier as the temperature changes. A site is always surveyed for ground noise with a temporary installation before pouring the pier and laying conduit. European seismographs were placed in a particular area after a destructive earthquake. Today, they are concentrated in high-risk regions; the word derives from the Greek σεισμός, seismós, a shaking or quake, from the verb σείω, seíō, to shake. Seismograph is another Greek term from γράφω, gráphō, to draw, it is used to mean seismometer, though it is more applicable to the older instruments in which the measuring and recording of ground motion were combined, than to modern systems, in which these functions are separated.
Both types provide a continuous record of ground motion. The technical discipline concerning such devices is called seismometry, a branch of seismology; the concept of measuring the "shaking" of something means that the word "seismograph" might be used in a more general sense. For example, a monitoring station that tracks changes in electromagnetic noise affecting amateur radio waves presents an rf seismograph, and Helioseismology studies the "quakes" on the Sun. The first seismometer was made in China during the 2nd Century; the first Western description of the device comes from the French physicist and priest Jean de Hautefeuille in 1703. The modern seismometer was developed in the 19th century. In December 2018, a seismometer was deployed on the planet Mars by the InSight lander, the first time a seismometer was placed onto the surface of another planet. In AD 132, Zhang Heng of China's Han dynasty invented the first seismoscope, called Houfeng Didong Yi; the description we have, from the History of the Later Han Dynasty, says that it was a large bronze vessel, about 2 meters in diameter.
When there was an earthquake, one of the dragons' mouths would open and drop its ball into a bronze toad at the base, making a sound and showing the direction of the earthquake. On at least one occasion at the time of a large earthquake in Gansu in AD 143, the seismoscope indicated an earthquake though one was not felt; the available text says that inside the vessel was a central column that could move along eight tracks. The first earthquake recorded by this seismoscope was "somewhere in the east". Days a rider from the east reported this earthquake. By the 13th century, seismographic devices existed in the Maragheh observatory in Persia. French physicist and priest Jean de Hautefeuille built one in 1703. After 1880, most seismometers were descend
Blind spot monitor
The blind spot monitor is a vehicle-based sensor device that detects other vehicles located to the driver’s side and rear. Warnings can be visual, vibrating, or tactile. However, blind spot monitors are an option that may do more than monitor the sides and rear of the vehicle, they may include "Cross Traffic Alert", "which alerts drivers backing out of a parking space when traffic is approaching from the sides." If side view mirrors on a car are adjusted in a particular way, there is no blind spot on the sides. This method was first revealed by George Platzer in a 1995 paper presented to the Society of Automotive Engineers, but the method is overlooked in driver's education classes and takes some getting used to. Calculated elimination of blind spots by trained drivers is inexpensive and obviates the need for expensive technological solutions to that problem, provided drivers take the time to set up and use their mirrors properly. Platzer received a patent for his blind spot monitor, it has been incorporated into various products associated with Ford Motor Company.
The blind zone mirror has been touted as "an elegant and inexpensive solution" to this recognized problem. VolvoBLIS is an acronym for Blind Spot Information System, a system of protection developed by Volvo. Volvo's previous parent, Ford Motor Company, has since adapted the system to its Ford and Mercury brands; this system was first introduced on the redesigned 2007 Volvo S80 sedan and produced a visible alert when a car entered the blind spot while a driver was switching lanes, using two door mounted lenses to check the blind spot area for an impending collision. MazdaMazda was the first Japanese automaker to offer a blind spot monitor, which they refer to as "BSM", it was introduced on the 2008 Mazda CX-9 Grand Touring and remained limited to only that highest trim level through the 2012 model year. For 2013, BSM was standard on both the CX-9 Grand Touring models. Mazda added BSM to the redesigned 2009 Mazda 6. Blind spot monitoring was standard equipment on the 6i and 6s Grand Touring trim levels, was an available option on some lower trim levels.
Mazda has since expanded the availability of BSM, having added it to the feature list of the Mazda3, CX-5, MX-5 Miata, the upcoming CX-3 as part of an option package. FordFord uses the acronym BLIS for its blind spot detection; the system is active both in "drive" and "neutral" transmission gears, is turned off when in reverse or park gears. On Ford products, the system was first introduced in the spring of 2009, on the 2010 Ford Fusion and Fusion Hybrid, 2010 Mercury Milan and Milan Hybrid, 2010 Lincoln MKZ. MitsubishiMitsubishi offers a Blind Spot Warning on the Pajero Sport launched in 2016. In 2010, the Nissan Fuga/Infiniti M for the first time offered countersteering capabilities to keep the vehicle from colliding. "The danger of blind zones The area behind your vehicle can be a killing zone". Consumer Reports. Consumers Union. March 2012. Retrieved August 10, 2013
An engine or motor is a machine designed to convert one form of energy into mechanical energy. Heat engines, like the internal combustion engine, burn a fuel to create heat, used to do work. Electric motors convert electrical energy into mechanical motion, pneumatic motors use compressed air, clockwork motors in wind-up toys use elastic energy. In biological systems, molecular motors, like myosins in muscles, use chemical energy to create forces and motion; the word engine derives from Old French engin, from the Latin ingenium–the root of the word ingenious. Pre-industrial weapons of war, such as catapults and battering rams, were called siege engines, knowledge of how to construct them was treated as a military secret; the word gin, as in cotton gin, is short for engine. Most mechanical devices invented during the industrial revolution were described as engines—the steam engine being a notable example. However, the original steam engines, such as those by Thomas Savery, were not mechanical engines but pumps.
In this manner, a fire engine in its original form was a water pump, with the engine being transported to the fire by horses. In modern usage, the term engine describes devices, like steam engines and internal combustion engines, that burn or otherwise consume fuel to perform mechanical work by exerting a torque or linear force. Devices converting heat energy into motion are referred to as engines. Examples of engines which exert a torque include the familiar automobile gasoline and diesel engines, as well as turboshafts. Examples of engines which produce thrust include rockets; when the internal combustion engine was invented, the term motor was used to distinguish it from the steam engine—which was in wide use at the time, powering locomotives and other vehicles such as steam rollers. The term motor derives from the Latin verb moto which means to maintain motion, thus a motor is a device. Motor and engine are interchangeable in standard English. In some engineering jargons, the two words have different meanings, in which engine is a device that burns or otherwise consumes fuel, changing its chemical composition, a motor is a device driven by electricity, air, or hydraulic pressure, which does not change the chemical composition of its energy source.
However, rocketry uses the term rocket motor though they consume fuel. A heat engine may serve as a prime mover—a component that transforms the flow or changes in pressure of a fluid into mechanical energy. An automobile powered by an internal combustion engine may make use of various motors and pumps, but all such devices derive their power from the engine. Another way of looking at it is that a motor receives power from an external source, converts it into mechanical energy, while an engine creates power from pressure. Simple machines, such as the club and oar, are prehistoric. More complex engines using human power, animal power, water power, wind power and steam power date back to antiquity. Human power was focused by the use of simple engines, such as the capstan, windlass or treadmill, with ropes and block and tackle arrangements; these were used in cranes and aboard ships in Ancient Greece, as well as in mines, water pumps and siege engines in Ancient Rome. The writers of those times, including Vitruvius and Pliny the Elder, treat these engines as commonplace, so their invention may be more ancient.
By the 1st century AD, cattle and horses were used in mills, driving machines similar to those powered by humans in earlier times. According to Strabo, a water powered mill was built in Kaberia of the kingdom of Mithridates during the 1st century BC. Use of water wheels in mills spread throughout the Roman Empire over the next few centuries; some were quite complex, with aqueducts and sluices to maintain and channel the water, along with systems of gears, or toothed-wheels made of wood and metal to regulate the speed of rotation. More sophisticated small devices, such as the Antikythera Mechanism used complex trains of gears and dials to act as calendars or predict astronomical events. In a poem by Ausonius in the 4th century AD, he mentions a stone-cutting saw powered by water. Hero of Alexandria is credited with many such wind and steam powered machines in the 1st century AD, including the Aeolipile and the vending machine these machines were associated with worship, such as animated altars and automated temple doors.
Medieval Muslim engineers employed gears in mills and water-raising machines, used dams as a source of water power to provide additional power to watermills and water-raising machines. In the medieval Islamic world, such advances made it possible to mechanize many industrial tasks carried out by manual labour. In 1206, al-Jazari employed a crank-conrod system for two of his water-raising machines. A rudimentary steam turbine device was described by Taqi al-Din in 1551 and by Giovanni Branca in 1629. In the 13th century, the solid rocket motor was invented in China. Driven by gunpowder, this simplest form of internal combustion engine was unable to deliver sustained power, but was useful for propelling weaponry at high speeds towards enemies in battle and for fireworks. After invention, this innovation spread throughout Europe; the Watt steam engine was the first type of steam engine to make use of steam at a pressure just above atmospheric to drive the piston he
A crankshaft—related to crank—is a mechanical part able to perform a conversion between reciprocating motion and rotational motion. In a reciprocating engine, it translates reciprocating motion of the piston into rotational motion. In order to do the conversion between two motions, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the connecting rods from each cylinder attach, it is connected to a flywheel to reduce the pulsation characteristic of the four-stroke cycle, sometimes a torsional or vibrational damper at the opposite end, to reduce the torsional vibrations caused along the length of the crankshaft by the cylinders farthest from the output end acting on the torsional elasticity of the metal. The earliest hand-operated cranks appeared in China during the Han Dynasty, they were used for silk-reeling, hemp-spinning, for the agricultural winnowing fan, in the water-powered flour-sifter, for hydraulic-powered metallurgic bellows, in the well windlass.
The rotary winnowing fan increased the efficiency of separating grain from husks and stalks. However, the potential of the crank of converting circular motion into reciprocal motion never seems to have been realized in China, the crank was absent from such machines until the turn of the 20th century. Al-Jazari described a crank and connecting rod system in a rotating machine in two of his water-raising machines, his twin-cylinder pump incorporated a crankshaft, including both the crank and shaft mechanisms. The 15th century saw the introduction of cranked rack-and-pinion devices, called cranequins, which were fitted to the crossbow's stock as a means of exerting more force while spanning the missile weapon. In the textile industry, cranked reels for winding skeins of yarn were introduced. Around 1480, the early medieval rotary grindstone was improved with a crank mechanism. Cranks mounted on push-carts first appear in a German engraving of 1589. Crankshafts were described by Leonardo da Vinci and a Dutch farmer and windmill owner by the name Cornelis Corneliszoon van Uitgeest in 1592.
His wind-powered sawmill used a crankshaft to convert a windmill's circular motion into a back-and-forward motion powering the saw. Corneliszoon was granted a patent for his crankshaft in 1597. From the 16th century onwards, evidence of cranks and connecting rods integrated into machine design becomes abundant in the technological treatises of the period: Agostino Ramelli's The Diverse and Artifactitious Machines of 1588 depicts eighteen examples, a number that rises in the Theatrum Machinarum Novum by Georg Andreas Böckler to 45 different machines. Cranks were common on some machines in the early 20th century. Reciprocating piston engines use cranks to convert the linear piston motion into rotational motion. Internal combustion engines of early 20th century automobiles were started with hand cranks, before electric starters came into general use; the 1918 Reo owner's manual describes how to hand crank the automobile: First: Make sure the gear shifting lever is in neutral position. Second: The clutch pedal is unlatched and the clutch engaged.
The brake pedal is pushed forward as far as possible setting brakes on the rear wheel. Third: See that spark control lever, the short lever located on top of the steering wheel on the right side, is back as far as possible toward the driver and the long lever, on top of the steering column controlling the carburetor, is pushed forward about one inch from its retarded position. Fourth: Turn ignition switch to point marked "B" or "M" Fifth: Set the carburetor control on the steering column to the point marked "START." Be sure there is gasoline in the carburetor. Test for this by pressing down on the small pin projecting from the front of the bowl until the carburetor floods. If it fails to flood it shows that the fuel is not being delivered to the carburetor properly and the motor cannot be expected to start. See instructions on page 56 for filling the vacuum tank. Sixth: When it is certain the carburetor has a supply of fuel, grasp the handle of starting crank, push in endwise to engage ratchet with crank shaft pin and turn over the motor by giving a quick upward pull.
Never push down, because if for any reason the motor should kick back, it would endanger the operator. Large engines are multicylinder to reduce pulsations from individual firing strokes, with more than one piston attached to a complex crankshaft. Many small engines, such as those found in mopeds or garden machinery, are single cylinder and use only a single piston, simplifying crankshaft design. A crankshaft is subjected to enormous stresses equivalent of several tonnes of force; the crankshaft is connected to the fly-wheel, the engine block, using bearings on the main journals, to the pistons via their respective con-rods. An engine loses up to 75% of its generated energy in the form of friction and vibration in the crankcase and piston area; the remaining losses occur in blow by. The crankshaft has a linear axis about which it rotates with several bearing journals riding on replaceable bearings held in the engine block; as the crankshaft undergoes a great deal of sideways load from each cylinder in a multicylinder engine, it must be supported by several such bearings, not just one at each end
Internal combustion engine cooling
Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and simple system. Watercraft can use water directly from the surrounding environment to cool their engines. For water-cooled engines on aircraft and surface vehicles, waste heat is transferred from a closed loop of water pumped through the engine to the surrounding atmosphere by a radiator. Water has a higher heat capacity than air, can thus move heat more away from the engine, but a radiator and pumping system add weight and cost. Higher-power engines generate more waste heat, but can move more weight, meaning they are water-cooled. Radial engines allow air to flow around each cylinder directly, giving them an advantage for air cooling over straight engines, flat engines, V engines. Rotary engines have a similar configuration, but the cylinders continually rotate, creating an air flow when the vehicle is stationary.
Aircraft design more favors lower weight and air-cooled designs. Rotary engines were popular on aircraft until the end of World War I, but had serious stability and efficiency problems. Radial engines were popular until the end of World War II, until gas turbine engines replaced them. Modern propeller-driven aircraft with internal-combustion engines are still air-cooled. Modern cars favor power over weight, have water-cooled engines. Modern motorcycles are lighter than cars, both cooling fluids are common; some sport motorcycles were cooled with both oil. Heat engines generate mechanical power by extracting energy from heat flows, much as a water wheel extracts mechanical power from a flow of mass falling through a distance. Engines are inefficient, so more. Internal combustion engines remove waste heat through cool intake air, hot exhaust gases, explicit engine cooling. Engines with higher efficiency less as waste heat; some waste heat is essential: it guides heat through the engine, much as a water wheel works only if there is some exit velocity in the waste water to carry it away and make room for more water.
Thus, all heat engines need cooling to operate. Cooling is needed because high temperatures damage engine materials and lubricants and becomes more important in hot climates. Internal-combustion engines burn fuel hotter than the melting temperature of engine materials, hot enough to set fire to lubricants. Engine cooling removes energy fast enough to keep temperatures low; some high-efficiency engines run without explicit cooling and with only incidental heat loss, a design called adiabatic. Such engines can achieve high efficiency but compromise power output, duty cycle, engine weight and emissions. Most internal combustion engines are fluid cooled using either air or a liquid coolant run through a heat exchanger cooled by air. Marine engines and some stationary engines have ready access to a large volume of water at a suitable temperature; the water may be used directly to cool the engine, but has sediment, which can clog coolant passages, or chemicals, such as salt, that can chemically damage the engine.
Thus, engine coolant may be run through a heat exchanger, cooled by the body of water. Most liquid-cooled engines use a mixture of water and chemicals such as antifreeze and rust inhibitors; the industry term for the antifreeze mixture is engine coolant. Some antifreezes use no water at all, instead using a liquid with different properties, such as propylene glycol or a combination of propylene glycol and ethylene glycol. Most "air-cooled" engines use some liquid oil cooling, to maintain acceptable temperatures for both critical engine parts and the oil itself. Most "liquid-cooled" engines use some air cooling, with the intake stroke of air cooling the combustion chamber. An exception is Wankel engines, where some parts of the combustion chamber are never cooled by intake, requiring extra effort for successful operation. There are many demands on a cooling system. One key requirement is to adequately serve the entire engine, as the whole engine fails if just one part overheats. Therefore, it is vital.
Liquid-cooled engines are able to vary the size of their passageways through the engine block so that coolant flow may be tailored to the needs of each area. Locations with either high peak temperatures or high heat flow may require generous cooling; this reduces the occurrence of hot spots. Air-cooled engines may vary their cooling capacity by using more spaced cooling fins in that area, but this can make their manufacture difficult and expensive. Only the fixed parts of the engine, such as the block and head, are cooled directly by the main coolant system. Moving parts such as the pistons, to a lesser extent the crank and rods, must rely on the lubrication oil as a coolant, or to a limited amount of conduction into the block and thence the main coolant. High performance engines have additional oil, beyond the amount needed for lubrication, sprayed upwards onto the bottom of the piston just for extra cooling. Air-cooled motorcycles rely on oil-cooling in addition to air-cooling of the cylinder barrels.
Liquid-cooled engines have a circulation pump. The first engines relied