![Kawasaki ZX-12R 071118 front](https://upload.wikimedia.org/wikipedia/commons/2/28/Kawasaki_ZX-12R_071118_front.jpg)
A ram-air intake is any
intake
An intake (also inlet) 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 ins ...
design which uses the dynamic air
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
created by vehicle motion, or
ram pressure
Ram pressure is a pressure exerted on a body moving through a fluid medium, caused by relative bulk motion of the fluid rather than random thermal motion. It causes a drag force to be exerted on the body. Ram pressure is given in tensor form as
...
, 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.
Design features
![Harley motorcycle with ram air and cold air gooseneck mounted hypercharger intake](https://upload.wikimedia.org/wikipedia/commons/e/e7/Harley_motorcycle_with_ram_air_and_cold_air_gooseneck_mounted_hypercharger_intake.jpg)
The ram-air intake works by reducing the intake air velocity by increasing the cross-sectional area of the intake ducting. When gas velocity goes down the dynamic pressure is reduced, while the static pressure is increased. The increased static pressure in the
plenum chamber
A plenum chamber is a pressurised housing containing a fluid (typically air) at positive pressure. One of its functions is to equalise pressure for more even distribution, compensating for irregular supply or demand. It is typically relatively la ...
has a positive effect on engine power, both because of the pressure itself and the increased air density that this higher pressure gives.
Ram-air systems are used on high-performance vehicles, most often on
motorcycle
A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...
s and performance cars. The 1990
Kawasaki Ninja ZX-11
The ZZ-R1100 or ZX-11 is a sport bike in Kawasaki's Ninja series made from 1990 to 2001, as the successor to the 1988–1990 Tomcat ZX-10. With a top speed of , it was the fastest production motorcycle from its introduction until 1996, surpass ...
C1 model used a ram-air intake, the very first on any production motorcycle.
Ram-air was a feature on some cars in the sixties. It fell out of favor in the seventies, but recently made a comeback. While ram-air intakes may increase the
volumetric efficiency Volumetric efficiency (VE) in internal combustion engine engineering is defined as the ratio of the mass density of the air-fuel mixture drawn into the cylinder at atmospheric pressure (during the intake stroke) to the mass density of the same volu ...
of an engine, they can be difficult to combine with carburetors, which rely on a
venturi-engineered pressure drop to draw fuel through the main jet. As the pressurised ram-air may kill this venturi effect, the carburetor needs to be designed to take this into account, or, alternatively, the engine may need
fuel-injection
Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of an injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines.
All comp ...
.
At low speeds (subsonic speeds) increases in static pressure are however limited to a few percent. Given that the air velocity is reduced to zero without losses the pressure increase can be calculated accordingly. The lack of losses also means without heating the air. Thus a ram-air intake also is a
cold air intake
A cold air intake (CAI) is usually an aftermarket assembly of parts used to bring relatively cool air into a car's internal-combustion engine.
Most vehicles manufactured from the mid-1970s until the mid-1990s have thermostatic air intake syste ...
. In some cars the intake is placed behind the radiator, where not only the air is hot, but the pressure is ''below'' ambient pressure. The ram-air intake effect may be small, but so are other mild tuning techniques to increase cylinder filling like using larger, fresh
air filter
A particulate air filter is a device composed of fibrous, or porous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. Filters containing an adsorbent or catalyst such as charcoal (carbon) may als ...
s, high flow
mass flow sensor
A mass (air) flow sensor (MAF) is a sensor used to determine the mass flow rate of air entering a fuel-injected internal combustion engine.
The air mass information is necessary for the engine control unit (ECU) to balance and deliver the corre ...
s, velocity stacks, tuned air box and large tubes from the filter to the engine.
Short ram air intake
The short ram air intake is a form of
aftermarket air intake for
automobile
A car or automobile is a motor vehicle with Wheel, wheels. Most definitions of ''cars'' say that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, pe ...
s with
internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
s.
It replaces the
OEM
An original equipment manufacturer (OEM) is generally perceived as a company that produces non-aftermarket parts and equipment that may be marketed by another manufacturer. It is a common industry term recognized and used by many professional or ...
air
intake
An intake (also inlet) 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 ins ...
with a short metal pipe and a conical
air filter
A particulate air filter is a device composed of fibrous, or porous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. Filters containing an adsorbent or catalyst such as charcoal (carbon) may als ...
inside the engine bay. A significant increase in intake air volume will only occur in an engine where the factory intake piping was designed with baffles and other sound absorbing materials (rubber, etc.).
The term ram, albeit commonly used, is somewhat a misnomer. A true ram air intake device is something that enhances intake pressure or in the case of resonant systems such as Chrysler's Sonaramic, increases the torque with a peak at a certain RPM.
There is still some open debate on this issue, but some believe that a problem with short ram air intakes is that the air entering the intake is at a higher temperature due to the proximity of the engine, which may reduce some power. This may be partially offset by an increase in the volume of air entering the engine. To counter intake heat problems, many short ram intakes include some form of heat shield. Moving the intake inlet port further away from the engine block will also help to alleviate the problem and some users use a
cold air intake
A cold air intake (CAI) is usually an aftermarket assembly of parts used to bring relatively cool air into a car's internal-combustion engine.
Most vehicles manufactured from the mid-1970s until the mid-1990s have thermostatic air intake syste ...
where the inlet air is at or close to ambient temperature. However, others claim that Short Ram Intakes (SRIs) or similar Warm Air Intakes (WAIs) offer benefits over Cold Air Intakes (CAIs) which include better MPG due to a more complete burning of fuel. Users with
forced induction
In an internal combustion engine, forced induction is where turbocharging or supercharging is used to increase the density of the intake air. Engines without forced induction are classified as naturally aspirated.
Operating principle Overvi ...
engines often opt for short ram intakes because
compressors
A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps: both increase the pressure on a fluid and both can transp ...
adjacent to the engine, especially
turbocharger
In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...
s, heat the incoming air and negate much of the benefits of a cold air intake. Additional problems can result from using a short ram intake in cars utilizing a
mass airflow sensor
A mass (air) flow sensor (MAF) is a sensor used to determine the mass flow rate of air entering a fuel-injected internal combustion engine.
The air mass information is necessary for the engine control unit (ECU) to balance and deliver the corre ...
though most of today's sensors automatically adjust without issue.
Turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
in the intake airflow produced by the filter or piping, or a change in intake diameter at the point where the airflow is measured can produce inaccurate airflow readings. The error in airflow then translates to an error in the amount of added fuel. In the worst case, the
air-fuel ratio can run lean, causing
detonation
Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with ...
and possibly engine failure although the airflow sensor will generally detect and correct the throttle to compensate for the warmer air. This can also be solved by modifying/elongating the intake piping, replacing the airflow meter, or by replacing/remapping the engine control computer to provide the correct amount of fuel for the intake airflow at all engine speeds.
A harmless but noticeable result of using a short ram air intake is an increase in intake noise, which may manifest as a sucking sound, and the loss of any silencing properties that the factory intake had.
Aircraft
Pitot sensors are used to measure ram pressure which, along with static pressure, is used to estimate the
airspeed
In aviation, airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are:
* Indicated airspeed ("IAS"), what is read on an airspeed gauge connected to a Pitot-static system;
* Calibrated a ...
of an aircraft.
File:TA-4SU Skyhawk cockpits.jpg, TA-4SU Super Skyhawk
The ST Aerospace A-4SU Super Skyhawk is a major upgrade project of the Douglas A-4S Skyhawk attack aircraft undertaken by Singapore Aircraft Industries (SAI, now ST Aerospace) in the 1980s. It was used exclusively by the Republic of Singapor ...
, note the ram-air intake mounted on the portside air intake for cooling the jet engine.
Image:MiG-15 RB2.jpg, Mikoyan-Gurevich MiG-15
Image:Piston engine breathing.svg, Diagram of piston engine with (from left to right):
See also
*
Air filter
A particulate air filter is a device composed of fibrous, or porous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. Filters containing an adsorbent or catalyst such as charcoal (carbon) may als ...
*
Booster
Booster may refer to:
Amusement rides
* Booster (Fabbri ride), a pendulum ride
* Booster (HUSS ride), an evolution of the Breakdance ride
* Booster (KMG ride), a pendulum ride
Arts, entertainment, and media Fictional characters
*Booster, a char ...
*
Ramjet
A ramjet, or athodyd (aero thermodynamic duct), is a form of airbreathing jet engine that uses the forward motion of the engine to produce thrust. Since it produces no thrust when stationary (no ram air) ramjet-powered vehicles require an ass ...
*
Supercharger
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.
The current categorisation is that a supercharger is a form of forced induct ...
*
Turbocharger
In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...
*
Warm air intake
A warm air intake (WAI) also known as a hot air intake (HAI), is a system to decrease the amount of the air going into a car for the purpose of increasing the fuel economy of the internal-combustion engine.
This term is sometimes used erroneousl ...
*
Short ram air intake
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 massf ...
*
Diffuser (automotive)
A diffuser, in an automotive context, is a shaped section of the car rear which improves the car's aerodynamic properties by enhancing the transition between the high-velocity airflow underneath the car and the much slower freestream airflow of th ...
References
{{Automotive engine , collapsed
Engine technology
Automotive technologies
Motorcycle engines