Combustion cylinder air supply intake
Simscape / Driveline / Engines & Motors / Engine Subcomponents
The Air Intake block represents an abstract air intake system that computes lumped-parameter air flow dynamics. This block is suitable for internal combustion engines. The block computes the intake manifold pressure from the throttle and engine speed.
The Air Intake block computes the intake manifold pressure as
Rair is the Dry air specific gas constant parameter.
Tamb is the Ambient temperature parameter.
Vim is the Intake manifold volume parameter.
The block calculates the combustion cylinder mass flow rate, ṁcyl, as
which is a time derivative formulation of the ideal gas law. ω is the engine speed the block receives from port EngSpd, and Vd is the Engine displacement volume parameter.
The block calculates the throttle mass flow rate, ṁthr as
depending on the flow conditions. In this equation, Sthr is the area of the throttle opening, and Pamb is the ambient pressure. The block defines the equation constants as
κ is the Dry air specific heat ratio parameter.
Πlam is the laminar flow threshold constant.
Πcr is the critical pressure ratio.
The block finds Πcr as
The block treats the throttle open area, Sthr, as a third-order polynomial that functions with respect to the throttle angle, θ. This method simplifies the block computation to improve performance. The block computes the throttle open area as
where the block derives the coefficients, ki, using these quantities:
Dplate — Throttle plate diameter parameter
Arest — Throttle rest angle parameter
Apeak — 85°
Sleak — Throttle leakage area parameter
The throttle open area uses these constraints:
where Seng is the engineering formula for the throttle open area, such that
This figure shows a comparison of the polynomial result and the engineering result.
Thr — Throttle command input, unitless
Physical signal input associated with the normalized throttle command,
0 represents a fully closed throttle, and
1 represents a fully open throttle. The block
maps this input to a throttle-open angle between
EngSpd — Rotational engine speed, rad/s
Physical signal input associated with the rotational speed, in rad/s.
Pim — Intake manifold pressure input, kPa
Physical signal input associated with the intake manifold, in kPa.
Dry air specific gas constant — Dry air specific gas constant
J/(K*kg) (default) | positive scalar
Specific gas constant of dry air.
Dry air specific heat ratio — Dry air specific heat ratio
1.4 (default) | positive scalar
Specific heat ratio of dry air.
Ambient pressure — Reference air pressure
kPa (default) | positive scalar
Pressure of the air entering the intake.
Ambient temperature — Reference temperature
K (default) | positive scalar
Temperature of the air entering the intake.
Throttle rest angle — Released throttle position
deg (default) | positive scalar
Radial distance from the resting throttle position to
Throttle plate diameter — Throttle plate diameter
cm (default) | positive scalar
Diameter of the butterfly valve disc in the throttle body.
Throttle leakage area — Throttle leakage area
cm^2 (default) | nonnegative scalar
Cumulative area of throttle leakage.
Intake manifold volume — Intake manifold volume
cm^3 (default) | positive scalar
Volumetric capacity of the intake manifold.
Engine displacement volume — Engine displacement volume
cm^3 (default) | positive scalar
Combined displacement of all engine pistons.
Throttle response time constant — Throttle response time constant
s (default) | positive scalar
Time constant associated with the response rate of the engine to the throttle command.
Introduced in R2022a