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A hood scoop (North American English) or bonnet scoop (Commonwealth English), sometimes called bonnet airdam and air dam, is an upraised component on the hood of a motor vehicle that either allows air to directly enter the engine compartment or appears to do so. It has only one opening and is closed on all other sides. Its upraised design allows it to effectively channel air directly into the engine compartment without the need to pass through the normal intake ducting. [1] Some hood scoops are always closed and serve as decoration rather than performance.
In most modern vehicles, internal combustion engines "breathe" under-hood air or air ducted from under the front bumper through plastic and rubber tubing. The high operating temperatures in the engine compartment result in intake air that is 28°C (82°F) or warmer than the ambient temperature and consequently, less dense. A hood scoop can provide the engine with cooler, denser outside air, increasing power.
At higher road speeds, a properly designed hood scoop known as ram-air intake can increase the speed and pressure with which air enters the engine's intake, creating a resonance supercharging effect. Such effects are typically only felt at very high speeds, making ram air primarily useful for racing, not street performance.
Pontiac used the trade name Ram Air to describe its engines equipped with functional scoops. Despite the name, most of these systems only provided cool air, with little or no supercharging effect. [2]
Some engines with turbochargers or superchargers are also equipped with top mounted intercoolers to reduce the temperature and increase the density of the high-pressure air produced by the compressor. Channeling outside air to the intercooler (which is a heat exchanger similar to a radiator) increases its effectiveness, providing a significant improvement in power.
To be effective, a functional scoop must be located at a high-pressure area on the hood. For that reason, some functional scoops are located at the rear of the hood, near the vehicle's cowl, where the curvature of the windshield creates such a high-pressure zone and may be placed so that their opening faces the windshield (a reversed scoop).
The scoop will be most effective if it is either mounted high enough to clear the boundary layer (the slow-moving air that clings to the surface of a moving object) or if it is a NACA duct, mounted below the surface and designed to draw the faster-moving air outside of the boundary layer into the duct. A shallow scoop that is not a NACA duct may not admit a useful amount of air even if it is open.
Under the hood, an effective scoop must funnel air into the engine's intake in as short and direct a path as possible, preferably through a tube or channel that is insulated against underhood heat.
A scoop may be part of the hood or may be part of the engine's air cleaner assembly, protruding through a hole cut into the bonnet. Such a scoop is called a shaker hood, because the scoop vibrates noticeably when the engine is running, especially under power.
A hood scoop/top mounted intercooler can be beneficial, especially during an off-road rally race. Rocks and debris can be kicked up by a car in front, and those objects can damage a front-mounted intercooler. However, rock guards can be installed to prevent this problem.
A ramjet is a form of airbreathing jet engine that requires forward motion of the engine to provide air for combustion. Ramjets work most efficiently at supersonic speeds around Mach 3 and can operate up to Mach 6.
In engineering, the Miller cycle is a thermodynamic cycle used in a type of internal combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, U.S. patent 2,817,322 dated Dec 24, 1957. The engine may be two- or four-stroke and may be run on diesel fuel, gases, or dual fuel. It uses a supercharger or a turbocharger to offset the performance loss of the Atkinson cycle.
Air-augmented rockets use the supersonic exhaust of some kind of rocket engine to further compress air collected by ram effect during flight to use as additional working mass, leading to greater effective thrust for any given amount of fuel than either the rocket or a ramjet alone.
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Volumetric efficiency (VE) in internal combustion engine engineering is defined as the ratio of the equivalent volume of the fresh air drawn into the cylinder during the intake stroke to the volume of the cylinder itself. The term is also used in other engineering contexts, such as hydraulic pumps and electronic components.
A shaker scoop is an automobile term for an air intake for combustion air that is mounted directly on top of the engine's air cleaner and protrudes through a hole in the hood. Since it is fastened directly to the engine, it moves with the engine's movement and vibration on its mountings, thus the 'shaker' name.
A ram-air intake is any intake design which uses the dynamic air pressure created by vehicle motion, or ram pressure, to increase the static air pressure inside of the intake manifold on an internal combustion engine, thus allowing a greater massflow through the engine and hence increasing engine power.
An intake is an opening, structure or system through which a fluid is admitted to a space or machine as a consequence of a pressure differential between the outside and the inside. The pressure difference may be generated on the inside by a mechanism, or on the outside by ram pressure or hydrostatic pressure. Flow rate through the intake depends on pressure difference, fluid properties, and intake geometry.
A NACA duct, also sometimes called a NACA scoop or NACA inlet, is a common form of low-drag air inlet design, originally developed by the U.S. National Advisory Committee for Aeronautics (NACA), the precursor to NASA, in 1945.
A glossary of terms relating to automotive design.
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In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement.
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The Meredith effect is a phenomenon whereby the aerodynamic drag produced by a cooling radiator may be offset by careful design of the cooling duct such that useful thrust is produced by the expansion of the hot air in the duct. The effect was discovered in the 1930s and became more important as the speeds of piston-engined aircraft increased over the next decade.
The Lamborghini Essenza SCV12 is a track-only car produced by the Italian automobile manufacturer Lamborghini under their Squadra Corse racing division. Introduced on 29 July 2020, it was the most powerful and the last purely naturally-aspirated car built by the brand at the time.