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The manifold absolute pressure sensor (MAP sensor) is one of the sensors used in an internal combustion engine's electronic control system. Engines that use a MAP sensor are typically fuel injected. The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine's electronic control unit (ECU).
This requires the use of an alternative method of calculating airflow into the engine, which is also referred to as 'Speed-Density' system, as opposed to a MAF system. On vehicles so equipped, this alternative involves the use of a manifold absolute pressure, or MAP, sensor. The MAP sensor measures pressure in the engine's inlet manifold.
Manifold absolute pressure is one of a multitude of parameters used by the engine control unit (ECU) to optimize engine operation. It is important to differentiate between absolute and gauge pressure when dealing with certain applications, particularly those that experience changes in elevation during normal operation.
Absolute cylinder pressure is used to calculate the dynamic compression ratio, using the following formula: = where is a polytropic value for the ratio of specific heats for the combustion gases at the temperatures present (this compensates for the temperature rise caused by compression, as well as heat lost to the cylinder)
Manifold pressure (MP) gauge - Indicates the absolute pressure in the intake manifold. For an aircraft equipped with a constant speed propeller, this is the most direct indication of the engine's operating power.
The ratios were obtained using the criterion that choked flow occurs when the ratio of the absolute upstream pressure to the absolute downstream pressure is equal to or greater than ([+] /) / (), where is the specific heat ratio of the gas. The minimum pressure ratio may be understood as the ratio between the upstream pressure and the pressure ...
An Eaton M62 Roots-type supercharger is visible at the front of this Ecotec LSJ engine in a 2006 Saturn Ion Red Line.. The Roots-type blower is simple and widely used. It can be more effective than alternative superchargers at developing positive intake manifold pressure (i.e., above atmospheric pressure) at low engine speeds, making it a popular choice for passenger automobile applications.
A typical nominal regulated gauge pressure from a medical oxygen regulator is 3.4 bars (50 psi), for an absolute pressure of approximately 4.4 bar and a pressure ratio of about 4.4 without back pressure, so they will have choked flow in the metering orifices for a downstream (outlet) pressure of up to about 2.3 bar absolute.