Inlet manifold
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Aninlet manifoldorintake manifold(inAmerican English) is the part of aninternal combustion enginethat supplies thefuel/airmixture to thecylinders.[1]The wordmanifoldcomes from the Old English wordmanigfeald(from the Anglo-Saxonmanig[many] andfeald[repeatedly]) and refers to the multiplying of one (pipe) into many.[2]
In contrast, anexhaust manifoldcollects theexhaust gasesfrom multiple cylinders into a smaller number of pipes – often down to one pipe.
The primary function of the intake manifold is toevenlydistribute the combustion mixture (or just air in a direct injection engine) to each intake port in the cylinder head(s). Even distribution is important to optimize the efficiency and performance of the engine. It may also serve as a mount for the carburetor, throttle body, fuel injectors and other components of the engine.
Due to the downward movement of thepistonsand the restriction caused by the throttle valve, in a reciprocatingspark ignitionpiston engine,a partialvacuum(lower thanatmospheric pressure) exists in the intake manifold. Thismanifold vacuumcan be substantial, and can be used as a source ofautomobile ancillary powerto drive auxiliary systems: power assistedbrakes,emission control devices,cruise control,ignitionadvance,windshield wipers,power windows,ventilation system valves, etc.
This vacuum can also be used to draw any piston blow-by gases from the engine'scrankcase.This is known as a positivecrankcase ventilation system,in which the gases are burned with the fuel/air mixture.
The intake manifold has historically been manufactured fromaluminiumor cast iron, but use of composite plastic materials is gaining popularity (e.g. most Chrysler 4-cylinders,Ford Zetec2.0, Duratec 2.0 and 2.3, and GM'sEcotecseries).
Turbulence
[edit]Thecarburetoror thefuel injectorsspray fuel droplets into the air in the manifold. Due to electrostatic forces and condensation from the boundary layer, some of the fuel will form into pools along the walls of the manifold, and due to surface tension of the fuel, small droplets may combine into larger droplets in the airstream. Both actions are undesirable because they create inconsistencies in theair-fuel ratio.Turbulence in the intake helps to break up fuel droplets, improving the degree of atomization. Betteratomizationallows for a more complete burn of all the fuel and helps reduceengine knockby enlarging the flame front. To achieve this turbulence it is a common practice to leave the surfaces of the intake and intake ports in the cylinder head rough and unpolished.
Only a certain degree of turbulence is useful in the intake. Once the fuel is sufficiently atomized, additional turbulence causes unneeded pressure drops and a drop in engine performance.
Volumetric efficiency
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The design and orientation of the intake manifold is a major factor in thevolumetric efficiencyof an engine. Abrupt contour changes provoke pressure drops, resulting in less air (and/or fuel) entering the combustion chamber; high-performance manifolds have smooth contours and gradual transitions between adjacent segments.
Modern intake manifolds usually employrunners,individual tubes extending to each intake port on the cylinder head which emanate from a central volume or "plenum" beneath the carburetor. The purpose of the runner is to take advantage of theHelmholtz resonanceproperty of air. Air flows at considerable speed through the open valve. When the valve closes, the air that has not yet entered the valve still has a lot of momentum and compresses against the valve, creating a pocket of high pressure. This high-pressure air begins to equalize with lower-pressure air in the manifold. Due to the air's inertia, the equalization will tend to oscillate: At first the air in the runner will be at a lower pressure than the manifold. The air in the manifold then tries to equalize back into the runner, and the oscillation repeats. This process occurs at the speed of sound, and in most manifolds travels up and down the runner many times before the valve opens again.
The smaller the cross-sectional area of the runner, the higher the pressure changes on resonance for a given airflow. This aspect of Helmholtz resonance reproduces one result of theVenturi effect.When the piston accelerates downwards, the pressure at the output of the intake runner is reduced. This low pressure pulse runs to the input end, where it is converted into an over-pressure pulse. This pulse travels back through the runner and rams air through the valve. The valve then closes.
To harness the full power of the Helmholtz resonance effect, the opening of the intake valve must be timed correctly, otherwise the pulse could have a negative effect. This poses a very difficult problem for engines, since valve timing is dynamic and based on engine speed, whereas the pulse timing is static and dependent on the length of the intake runner and the speed of sound. The traditional solution has been to tune the length of the intake runner for a specific engine speed where maximum performance is desired. However, modern technology has given rise to a number of solutions involving electronically controlled valve timing (for exampleValvetronic), and dynamic intake geometry (see below).
As a result of "resonance tuning", some naturally aspirated intake systems operate at a volumetric efficiency above 100%: the air pressure in the combustion chamber before the compression stroke is greater than the atmospheric pressure. In combination with this intake manifold design feature, the exhaust manifold design, as well as the exhaust valve opening time can be so calibrated as to achieve greater evacuation of the cylinder. The exhaust manifolds achieve a vacuum in the cylinder just before the piston reaches top dead center.[citation needed]The opening inlet valve can then—at typical compression ratios—fill 10% of the cylinder before beginning downward travel.[citation needed]Instead of achieving higher pressure in the cylinder, the inlet valve can stay open after the piston reaches bottom dead center while the air still flows in.[citation needed][vague]
In some engines the intake runners are straight for minimal resistance. In most engines, however, the runners have curves, some very convoluted to achieve desired runner length. These turns allow for a more compact manifold, with denser packaging of the whole engine, as a result. Also, these "snaked" runners are needed for some variable length/ split runner designs, and allow the size of theplenumto be reduced. In an engine with at least six cylinders the averaged intake flow is nearly constant and the plenum volume can be smaller. To avoid standing waves within the plenum it is made as compact as possible. The intake runners each use a smaller part of the plenum surface than the inlet, which supplies air to the plenum, for aerodynamic reasons. Each runner is placed to have nearly the same distance to the main inlet. Runners whose cylinders fire close after each other, are not placed as neighbors.
In180-degree intake manifolds,originally designed for carburetor V8 engines, the two plane, the split plenum intake manifold separates the intake pulses which the manifold experiences by 180 degrees in the firing order. This minimizes interference of one cylinder's pressure waves with those of another, giving better torque from smooth mid-range flow. Such manifolds may have been originally designed for either two- or four-barrel carburetors, but now are used with both throttle-body andmulti-point fuel injection.An example of the latter is theHonda J enginewhich converts to a single plane manifold around 3500 rpm for greater peak flow and horsepower.
Olderheat risermanifolds with 'wet runners' for carbureted engines used exhaust gas diversion through the intake manifold to provide vaporizing heat. The amount of exhaust gas flow diversion was controlled by a heat riser valve in the exhaust manifold, and employed abi-metallic springwhich changed tension according to the heat in the manifold. Today's fuel-injected engines do not require such devices.
Variable-length intake manifold
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Avariable-length intake manifold(VLIM) is aninternal combustion enginemanifold technology. Four common implementations exist. First, two discrete intake runners with different length are employed, and a butterfly valve can close the short path. Second the intake runners can be bent around a common plenum, and a sliding valve separates them from the plenum with a variable length. Straight high-speed runners can receive plugs, which contain small long runner extensions. The plenum of a 6- or 8-cylinder engine can be parted into halves, with the even firing cylinders in one half and the odd firing cylinders in the other part. Both sub-plenums and the air intake are connected to an Y (sort of main plenum). The air oscillates between both sub-plenums, with a large pressure oscillation there, but a constant pressure at the main plenum. Each runner from a sub plenum to the main plenum can be changed in length. For V engines this can be implemented by parting a single large plenum at high engine speed by means of sliding valves into it when speed is reduced.
As the name implies, VLIM can vary the length of the intake tract in order to optimizepowerandtorque,as well as provide betterfuel efficiency.
There are two main effects of variable intake geometry:
- Venturi effect:At lowrpm,the speed of the airflow is increased by directing the air through a path with limited capacity (cross-sectional area). The larger path opens when the load increases so that a greater amount of air can enter the chamber. Indual overhead cam(DOHC) designs, the air paths are often connected to separateintake valvesso the shorter path can be excluded by deactivating the intake valve itself.
- Pressurization:Atunedintake path can have a light pressurizing effect similar to a low-pressuresuperchargerdue to Helmholtz resonance. However, this effect occurs only over a narrow engine speed range which is directly influenced by intake length. A variable intake can create two or more pressurized "hot spots." When the intake air speed is higher, the dynamic pressure pushing the air (and/or mixture) inside the engine is increased. The dynamic pressure is proportional to the square of the inlet air speed, so by making the passage narrower or longer the speed/dynamic pressure is increased.
Many automobile manufacturers use similar technology with different names. Another common term for this technology isvariable resonance induction system(VRIS).
- Audi:2.8-liter V6 gas engine (1991–98); 3.6- and 4.2-liter V8 engines, 1987–present
- Alfa Romeo:2.0 TwinSpark 16v - 155 ps(114 kW)
- BMW:DISAandDIVAsystems
- Dodge:2.0 A588 – ECH (2001–2005) used in the 2001–2005 model year Dodge Neon R/T
- Ferrari:360 Modena,550 Maranello
- FordVIS(Variable-resonance Intake System): on their 2.9-liter 24V Cosworth (BOB) based on theFord Cologne V6 enginein the later modelFord Scorpio
- FordDSI(dual-stage intake): on theirDuratec2.5- and 3.0-liter V6s and it was also found on theYamahaV6 in theTaurus SHO
- Ford: TheFord Modular V8 enginessport either the Intake Manifold Runner Control (IMRC) for 4V engines, or the Charge Motion Control Valve (CMCV) for 3V engines.
- Ford: The2.0L Split Portengine in the Ford Escort and Mercury Tracer feature an Intake Manifold Runner Control variable geometry intake manifold.
- General Motors:3.9LLZ8/LZ9V6, 3.2LLA3V6, and the 4.3LLF4V6 in some second generation S10s and Sonomas
- GM Daewoo:DOHC versions ofE-TEC IIengines
- Holden:Alloytec
- Honda:Integra,Legend,NSX,Prelude
- Hyundai:XGV6
- Isuzu:Isuzu Rodeo,used in the second generation V6, 3.2L (6VD1) Rodeos
- Jaguar:AJ-V6
- Lancia:VIS
- Mazda:VICS(variable inertia charging system) is used on theMazda FE-DOHC engineandMazda B enginefamily ofstraight-4s,and VRIS (variable resistance induction system) in theMazda K enginefamily ofV6engines. An updated version of this technology is employed on the newMazda Z engine,which is also used by Ford as theDuratec.
- Mercedes-Benz
- MG:MG ZS 180MG ZT160, 180 and 190
- Mitsubishi:Cycloneis used on the 2.0L I44G63engine family.
- Nissan:I4, V6, V8
- Opel(or Vauxhall):TwinPort– modern versions ofEcotec Family 1andEcotec Family 0straight-4 engines; a similar technology is used in3.2 L 54° V6engine
- Peugeot:2.2 L I4, 3.0 L V6
- Porsche:VarioRam–964,993,996,Boxster
- Proton:Campro CPS and VIM–Proton Gen-2 CPSandProton Waja CPS;ProtonCampro IAFM– 2008Proton Saga1.3
- Renault:Clio 2.0RS
- Rover:Rover 623,Rover 825,Rover 75v6,Rover 45v6
- Subaru Legacy1989–1994JDMEJ20 2.0-liter naturally aspirated DOHC 16-valve flat-4
- Subaru SVX1992–1997 EG33 3.3-liter naturally aspirated DOHC 24-valve flat-6
- Subaru LegacyandSubaru Impreza1999–2001JDMEJ20 2.0-liter naturally aspirated DOHC 16-valve flat-4
- Toyota:T-VIS– (Toyota Variable Induction System) used in the early versions of the3S-GE,7M-GE,and4A-GEengines, andACIS(acoustic control induction system)
- Volkswagen:1.6 L I4,VR6,W8
- Volvo:VVIS(Volvo variable induction system) –Volvo B5254S and B5204S enginesas found on theVolvo 850vehicles. Longer inlet ducts used between 1500 and 4100 rpm at 80% load or higher.[3]
See also
[edit]References
[edit]![](https://upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)
- ^"What Is an Intake Manifold? • STATE OF SPEED".STATE OF SPEED.2018-11-10.Retrieved2022-02-03.
- ^manifold, (adv.) "in the proportion of many to one, by many times". AD1526Oxford English Dictionary,
- ^Volvoclub UK: 850GLT Engine Info