Exhaust gas Re circulation Systems
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Transcript of Exhaust gas Re circulation Systems
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