Muhammad Saqlain Haider 2011-ME-330

Exhaust gas recirculation and its

utilization in IC engines

1/6/20181University Of Engineering & Technology Lahore,

KSK Campus.

1/6/20182

Contents Introduction.

What are NOx?? .

Mechanism of NO and NO2 formation.

Factors affecting NO emissions.

How can NOx be reduced?.

Components of EGR system.

Working of EGR system.

EGR operation schedule.

Types of EGR control valves.

Advantages and disadvantages of EGR.

EGR feed back system.

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What are 𝑁𝑂𝑥?

Nitrogen N2 and oxygen O2 molecules are

separated into individual atoms of nitrogen and

oxygen during the combustion process.

Formation of NO and NO2.

NO and NO2 collectively known as NOx.

NO is the predominant oxide of nitrogen

produced inside the engine cylinder.

Diesel engines contain comparable amount of

nitrogen then petrol engines.

Mechanism of NO formation

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NO forms in both flame front and post flame gases.

NO formation in post flame gases always dominates.

Thermal NO: oxidation of molecular nitrogen inthe post flame zone.

Prompt NO: formation of NO in the flame zone(Fennimore mechanism).

Fuel NO: oxidation of nitrogen-containingcompounds in the fuel.

O+ N2=NO +N

N+O2=NO+O Zeldovich mechanism

N+OH=NO+H

Mechanism of 𝐍𝐎𝟐 formation

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NO formed in the flame zone rapidly converted to

NO2.

NO+ HO2=NO2 +OH

NO2+O=NO+O2

Highest NO2/NO ratio occur at light load in diesel

engine because of large cooler region.

Factor affecting NO emission

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Fuel to air equivalence ratio

Spark timing

Burned gas fraction

Residual gas fraction

Recycled exhaust gas

Change in time history of temperature

Change in oxygen concentration

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NO formation with A/F

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NO variation with spark timing

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NO variation with % EGR

How can NOx be reduced?

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NOx formation is depends upon temperature

When combustion flame front temperatures exceed

2500°F (1370°C), NOx formation increases

dramatically.

The amounts of NOx formed at temperatures below

2500°F (1370°C) can be controlled in the exhaust by

a catalyst.

To handle the amounts generated above 2500°F

(1370°C), the following are some methods that have

been used to lower NOx formation:

Enrich the air–fuel mixture.

Lower the compression ratio.

Dilute the air–fuel mixture (EGR).

NO vs temperature and ф

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High temperature and High oxygen

concentrations result in high NO formation rate.

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Components of EGR system

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Working of EGR

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EGR operating conditions

Ported EGR valve

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Consists of

Vacuum diaphragm

Stem control valve

Small pipe from the exhaust

manifold or an internal

crossover passage in the

cylinder head

Parted vacuum switch or a

computer-controlled

solenoid

Positive pressure EGR valve

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It use exhaust

backpressure to vary the

point at which they open

and their flow rates.

Inside the valve there is

a second diaphragm that

reacts to backpressure in

the exhaust system.

Second diaphragm opens

and closes bleed hole

which control main EGR

vacuum.

Negative pressure EGR valve

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It reacts to negative or decreasing pressure changes in the exhaust system to regulate EGR action.

A drop in backpressure occurs when there is less load on the engine. This causes the backpressure diaphragm to open a bleed hole and reduce EGR flow.

It has the same principle as with the positive type except that the control function occurs when backpressure goes down instead of up

Pulse width modulated EGR

valve

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Powertrain control module (PCM) cycles the EGR

vacuum control solenoid rapidly on and off.

The computer controls the flow rate by sending

electrical signals to a solenoid vacuum valve

between the PCM and the EGR valve.

The amount of "on" time versus "off" time for the

EGR solenoid ranges from 0 to 100 percent, and

the average amount of "on" time versus "off" time

at any given instant determines how much EGR

flow occurs.

Digital electronic EGR valve

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This type of valve also uses vacuum to open the valve but regulates EGR flow according to computer control.

It has three metering orifices that are opened and closed by solenoids.

To match EGR to the engine's requirements various combinations of these three solenoids can be achieved.

Linear controlled EGR valve

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It is electrically operated and uses a small computer-controlled stepper motor to open and close the EGR valve instead of vacuum.

It has a control solenoid and EGR valve position (EVP) sensor. The sensor works on the same principle as a throttle position sensor. voltage signal ranges from 0.3 volts to 5.0 volts.

The PCM controls EGR flow by pulsing the signal to the EGR solenoid.

Reduced NOx

Improved engine life through reduced cylinder

temperatures (particularly exhaust valve life)

The exhaust gas, added to the fuel, oxygen, and

combustion products, increases the specific heat

capacity of the cylinder contents, which lowers the

adiabatic flame temperature.

Reduced throttling losses in SI engine.

Reduced heat rejection.

Reduced chemical dissociation.

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Advantages of EGR

It reduces the available oxygen in the cylinder.

Reduce the peak power available from the engine.

The EGR valve can not respond instantly to

changes in demand.

Can not achieve perfect mixing in each cylinder.

Combustion contamination.

Control system stability.

Materials and durability

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Disadvantages of EGR

The PCM needs to know when and how much EGR

flow is present when commanded and not

commanded. It have sensing systems called

Feedback, which is simply some sensor used to

determine presence of flow and amount.

Types:

PFE

DPFE

EVP

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EGR Feed back

• PFE: Pressure Feedback EGR

Components:

1. PCM

2. EVR

3. EGR Valve

4. Intake

5. Exhaust

6. EGR pressure

measurement

7. PFE sensor

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PFE

• DPFE: Delta Pressure Feedback EGR

Components:

1. PCM

2. EVR

3. EGR Valve

4. Intake

5. Exhaust

6. EGR side signal

7. Exhaust side signal

8. DPFE sensor

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DPFE

EVP: EGR Valve Position

Components:

1.PCM

2.EVR

3.EVP

4.Intake

5.Exhaust

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EVP

Thank You

1/6/2018