RE500 Air Manifold

8/13/2019 RE500 Air Manifold

1/14

Intake

System

February 3

2012[Type the abstract of the document here. The abstract is typically a shortsummary of the contents of the document. Type the abstract of the

document here. The abstract is typically a short summary of the contents

of the document.]

[Type thedocument

subtitle]


2/14

THROTTLE BODY

Introduction

Throttle body regulates the amount of air entering the engine depending on the

demands of the engine. At higher speeds or while accelerating when more fuel is

burned; to yield more power throttle is opened up to increase the amount of air

entering the engine while in other conditions throttle remains closed to a degree

preventing unrestricted flow of air.

FSAE Constraints

Throttle must be actuated manually; use of electronic throttle is prohibited. The throttle actuation system must use two return springs located at

throttle body.

Positive pedal stop. Throttle must be placed upstream of the restrictor and no throttling can be

done downstream to the throttle. Also the restrictor and the throttle body

are to be separate i.e. a single body incorporating both isnt allowed.

Objectives

To maximize the volumetric air flow rate through the throttle body. To keep the weight of system as minimum as possible. Minimize the pressure drop across it. Choose the material so as to reduce the weight as well as withstand the

flow pressures.

Design the throttle body to minimize stagnation.


3/14

Design Options

Barrel Valve: It consists of a barrel like valve with a through hole, when atdefault position it completely blocks the flow of air through the pipe but as

it turns, the mouth of the hole is exposed and allows for the air to flow.However, it is used more in rally racing than FSAE (with only two positions

ON and OFF). Also, it does not allow for easy installation of the TPS. The air

flow through this valve is also less regular. It allows a faster throttle

response but at the expense of throttle control

Fluid Flow through a barrel valve:

Fig.Fluid Flow through a closed barrel valve Fig.Flow through a more open barrel valve

Fig.Flow through a wide open valve or WOT condition

Slider:It works more like a gateway than a valve. It is composed of a sliderthat slips in and out of the pipe. However, there are several problems

associated with it such as sticking. After giving throttle when we pull back


4/14

on the valve the slide might get stuck with the plate leading to an open

valve or throttling when we are actually not throttling. TPS placement is

also an issue with this design of the valve.When the driver would let off thegas at the end of the straight, the high vacuum would suck the slider

against its mating surface hard enough for it to stick at partial (but

disturbing) throttle positions in the braking zone.Hence we wont be using

this design in our car.

Butterfly Valve:Well be using this for throttling. It consists of a butterfly valvethat regulates the flow of air into the engine. The valve completely cuts off the

supply to the engine but as it turns it presents lesser and lesser area to the

incoming air and hence lesser restriction.The butterfly does obstruct airfloweven at WOT. Turbulence is bad as the air enters the restrictor. However,

turbulence is a problem with barrel valves and sliders too, because while they

don't obstruct the center of flow, it is difficult to make the sides of the walls

perfectly smooth, and in transients a 90% throttle opening on a slider or barrel

is causing a lot of turbulence too.A bigger throttle body ensures more power, but there is a restrictor of 20 mm

downstream. Thus the increased size of a throttle body has an impact only to

an extent. A 38mm valve produces much more power than a 32mm one and

only slightly less than a 50mm or 48 mm valve. The diameter of the valve

would be of 32mm and with actual testing we will improve on this with the


5/14

results of the prototype. It will be positioned at a distance of about 15 cm

above the restrictor but this too would be varied during testing to give

optimum results.

Final Design:

Stock throttle body was simulated in Ansys and an inlet pressure of 1

atmosphere was specified. Stagnation post the valve was looked into and

throttle response was mapped with varying diameters. Considering the time

constraints and the simulation results, it has been decided to go with the stock

throttle body of 34mm diameter.

CFD Analysis:


6/14

Flow simulation for angles of 300and 55

0

Simulation for 75 and

degrees


7/14

Sensors in the Intake System

The sensors associated with the intake system are MAP, TPS and Ambient

Air Temperature, lambda sensors. The outputs from these sensors are used

as inputs by the engine management unit, and this decides the amount of

fuel entering the engine, ignition timing etc. The Manifold Absolute

Pressure (MAP) sensor measures the amount of pressure or vacuum in the

manifold. This sensor tells the engine load. With more pressure, the

engine load increases. With greater load on the engine, more fuel is

required. This is an input to a microcontroller and will be a factor when

setting the voltage pulse width for the fuel injectors.

The Throttle Position Sensor (TPS) returns and senses the position of

the throttle plate. When the TPS measures a wider opening, this indicates

a greater engine load. When the TPS changes rapidly a hard acceleration is

indicated causing a need for more fuel. The TPS senses the position by

using a potentiometer that turns when the position of the throttle plate

changes. Since this is a potentiometer, there will be a change in voltage at

different positions. This voltage is then returned to the microcontroller.

The ambient air temperature is measured using a thermistor. A

thermistor is a variable resistor that varies with temperature. If a voltage is

applied to this thermistor in series with another resistor the voltage

between the two will change as temperature changes according to the

voltage divider rule.


8/14

MAP Sensor:The MAP sensor detects the pressure in the intake manifold. Knowledge of

this pressure is vital for proper engine performance since the amount of

fuel necessary for any given engine load is determined by the pressure in

the intake manifold. The MAP sensors output is a voltage whose level

depends on the manifold pressure in the engine. As engine load increases,

the MAP voltage will decrease. The MAP sensors outputvoltage range is

1V - 6V for an 8V supply.

Based on the voltage present at the MAP sensor, the corresponding

pressure can be deduced by means of a pressure-voltage graph exclusive to

the particular MAP sensor being used

The MAP sensor signal is proportional to the fuel that is necessary at any

given engine speed. The MAP sensor operates as follows:

Light load (cruise): Low manifold pressure, high voltage at MAP sensor

reference (5V)

Heavy load (wide open throttle): High manifold pressure, low voltage at

MAP sensor reference (1V)

High voltage: Smaller fuel pulse width and advance spark timing

Low voltage: Larger fuel pulse width and retard spark timing

The previous relationships depict how intake manifold pressure and load

affect the MAP sensor output. The spark timing is varied based on the

engine speed and the pressure in the intake manifold. The intake manifold

pressure and MAP sensor voltage have a linear relationship. Using the


9/14

pressure-voltage relationship of our sensor, the pressure in the intake

manifold can be determined by the MAP sensor voltage. This pressure

along with the RPM of the engine is used to determine a parameter known

as the spark-angle (spk). Spark-angle is determined from the spkvs. RPM

graph or from look-up tables developed by the ME team during

dynamometer testing. Spark-angle is simply the number of degrees of

rotation left in the crankshaft before the piston gets to the top of the

cylinder.

Manifold Absolute Pressure (MAP) Sensor Circuit

Manifold Absolute Pressure (MAP) Sensor Circuit


10/14

The MAP sensor returns a voltage between 1V and 6.2V DC depending on

manifold pressure. Therefore, a voltage divider is needed to provide the

microcontroller with a voltage less than or equal to 5V DC.

Rich/Lean Adjustment Circuit:

Rich/Lean Adjustment Circuit


11/14


12/14

determine the position of the plate. During a hard acceleration, there can

be a delay if the MAP sensor is not quick enough to pick up the pressure

change in the intake. The TPS voltage is used by the microcontroller to

improve the throttle response.

Lambda Sensor:

They help determine, in real time, if theair fuel ratio of a combustion

engine is rich or lean. Since oxygen sensors are located in the exhaust

stream, they do not directly measure the air or the fuel entering the

engine. But when information from oxygen sensors is coupled with

information from other sources, it can be used to indirectly determine the

air-to-fuel ratio.Closed-loop feedback-controlled fuel injection varies the

fuel injector output according to real-time sensor data rather than

operating with a predetermined (open-loop) fuel map. In addition to

enabling electronic fuel injection to work efficiently, this emissions control

technique can reduce the amounts of both unburnt fuel and oxides of

nitrogen entering the atmosphere. The sensor does not actually measure

oxygen concentration, but rather the difference between the amount of

oxygen in the exhaust gas and the amount of oxygen in air. Rich mixture

causes an oxygen demand. This demand causes a voltage to build up, due

to transportation of oxygen ions through the sensor layer. Lean mixture

causes low voltage, since there is an oxygen excess.

Engine fuel mapping can be done by using TPS or MAP sensors, with naturally

aspirated engines TPS fuel mapping is preferred over MAP based mapping,

primarily because TPS is easier to implement with easy installation on the throttle

body. MAPs give us a curve where interpolation is required to consider a point on
http://en.wikipedia.org/wiki/Air_fuel_ratiohttp://en.wikipedia.org/wiki/Closed-loophttp://en.wikipedia.org/wiki/Closed-loophttp://en.wikipedia.org/wiki/Air_fuel_ratio


13/14

the curve whereas no such trouble exists with TPS. MAP is more accurate but its

placement in the intake is tricky with the pressure currents leading to some errors

in the readings, hence an iterative method is required for its correct placement.

Measured in degrees of throttle position. When the throttle is closed, it defaults

to the top row of the map, but even at idle throttle is at usually 5% with the

corresponding pressures being shown.


14/14

This is how the generated plot looks like with manifold pressure and RPM being

the parameters.

Documents

RE500 Air Manifold