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Strategy to Meet US Standards

Engine Research Laboratory, IIT Kanpur www.iitk.ac.in/erl

Technology for Emission Reduction

Euro II, US 98

900 to 1000 bar injection pressure

Injection timing speed advance for fuel economy

Less than 0.25 g/kWh lube oil consumption

Euro III, US 2002/2004

Over 1200 bar injection pressure, electronic timer

Less than 0.15 g/kWh lube oil consumption

180 to 200 bar peak firing pressure potential

EGR

Euro 4

Exhaust after-treatment

US 2007: Most stringent legislation

Combination of all after-treatment technologies


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Effects of Higher Injection Pressure

Higher Injection Rate/ CA

Later Injection for same efficiency

More Pre-Mixture combustion

More soot formation/ CA due to higher injection rate

Higher turbulence Better oxidation of soot Reduction of Total

Particulate Emission


NOx Control

NOx reductions are as important in diesel emission control as PM.

x con ro s cu n ean con ons y 3-way ca a y c conver er(so as in diesel engines).

In stoichiometric conditions (like typical gasoline engines),

The three way catalysts takes our 98%+ of the NOx:

CO + NOx = CO2 + N2

In lean conditions, the CO prefers to react with oxygen:

CO + 1/2 O2 = CO2


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The various ways to control the formation of NOx

The most straight-forward way: Keep the temperature inside thecombustion chamber under control. This can be achieved by

nr c ng e ue a r m x ure o re uce com us on empera ures:But providing insufficient amount of air for combustion increases HCand CO emissions.

Lowering the compression ratio: But this leads to reduced performanceand a poorer fuel economy.

Spark Timing Control: When ignition timing is perfectly matched,maximum heat is generated inside the chamber. And when thetem erature exceeds the 2 000 F NO is roduced in lar e ro ortions.

Thus what we can alternatively do is to retard the spark timing slightly.The inherent disadvantage: Burning the fuel at lower temperatures /

retarding the spark timing=> inefficient combustion => fall in the fuelefficiency as well as the volumetric efficiency.So a better way has to be introduced:


Exhaust Gas Re-circulation

And what does that mean?Dilution of the incoming air-fuel mixture with a small amount of

The best inert gas available with a running automobile is i t s ow n exhaus t . i.e. to route a small fraction of the exhaust gas in a CI enginefrom the engines outlet ports back to the intake manifold. Thiseffectivel dilutes the incomin air-fuel mixture in the c linder. The

i n e r t g a s

exhaust gases have got no oxygen, thus the resulting air-fuel-exhaustmixture is not as powerful when ignited. This smarter method effectivelykeeps the temperature inside the chamber under control to minimizesthe formation of NOx (which is a result of combustion at hightemperatures).


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The Need Statement

To device a way to control the generation of Nitrogen Oxides ina CI engine without adversely affecting the engine performance

Mechanism of NOx Formation

NO and NO2 are lumped together as NOx

temperature region

The most widely accepted mechanism was suggested by Zeldovich.

N2 + O NO + N

N + O2 NO + O

The formation of NOx is almost absent at temperatures below 2000 K.

Any technique, which can keep the peak combustion temperaturesbelow 2000K will be able to reduce NOx formation.


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When peak temperatures are high enough for long enough periods of time,

the nitrogen and oxygen in the air combine to form new compounds,

primarily NO and NO2. These are normally referred to collectively as NOx.


EGR-Basic Points

EGR used to control NOx

Lower the flame temp.

Diluting the A/F mixture with non-reacting parasite gas.

Recirculating exhaust gas absorbs energy during combustion without

contributing any energy input. The net result is a lower flame temp.

No EGR is used at idle and very little at low speeds. Under these

conditions, there is already maximum exhaust residual and greater

combustion inefficiency.

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How EGR Reduces Emission

Exhaust Gas acts as diluent to the combusting mixture.

This also reduces the O2 concentration in the combustion chamber.

The specific heat of the EGR is much higher than fresh air hence EGR

increases the heat capacity (Specific heat) of the intake charge.

Thus decreasing the temperature rise for the same heat release in the

combustion chamber.

EGR Ratio

100EGRof

% = Volume

EGRcy n er t entoc argenta eota

( ) 100M

M%EGR

i

EGR=

[ ] [ ][ ] [ ]

ambientexhaust

ambientakeEGR

22

2int2

CO-CO

CO-COratio =

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Soot NOx

Trade-Off

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The TechnologyThe Technology

The Theory:

valve re-circulates exhaust into

the intake stream. Exhaust gases

have already combusted, so they

do not burn again when they are

re-circulated. These gases displace

.

This chemically slows and cools

the combustion process by severalhundred degrees, thus reducing

NOx formation.


Exhaust Gas Recirculation


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Classification of EGR Systems

i) Classification Based on Temperature

1. Hot EGR: Exhaust gas is re-circulated without being cooled, resulting in

the increased intake charge temperature.

2. Fully cooled EGR: Exhaust gas is cooled before re-circulation in to the

combustion chamber by a water-cooled heat exchanger. In this case,

condensed water enters the cylinder and produces undesirable effects.

3. Partly cooled EGR: To avoid the water condensation, the temperature of

exhaust gas is kept just above its dew point temperature.

(ii) Classification Based on Configuration


1. Long Route System (LR): In LR system the pressure drop across the air

intake and the stagnation pressure in the exhaust gas stream cause the EGR

possible.

2. Short Route System (SR): These systems differed mainly in the method

used to set up a positive pressure difference across the EGR circuit.

Another way of controlling the EGR-rate is to use Variable Nozzle Turbine

(VNT). Most of the VNT systems have single entrance, which reduce the

efficiency of the system by exhaust pulse separation.

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(iii) Classification Based on Pressure


Two different routes for EGR, namely low-pressure route system and high-

pressure route system may be used.

1. Low Pressure Route System: The passage for EGR was provided from

downstream of the turbine to upstream side of the compressor.

2. High Pressure Route System: The EGR is passed from upstream of the

turbine to the downstream of the compressor.

Cooled EGR

Cooled Exhaust Gas Recirculation (EGR) technology was introduced for U.S. on-highwaymarkets in 2002 to meet the 2.5-g/hp-hr NOx + NMHC EPA automotive standards.

Cooled EGR is a very effective NOx control.

,mixing it with the incoming air charge to the cylinder.

The EGR reduces oxygen concentration in the combustion chamber by diluting theincoming ambient air with exhaust gases.

During combustion, the lower oxygen content has the effect of reducing flametemperatures, which in turn reduces NOx since NOx production is exponentiallyproportional to flame temperature.

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Internal EGR or Un-Cooled EGR

As with cooled EGR, the EGR reduces oxygen concentration in the combustion chamber bydiluting the incoming ambient air with exhaust gases.

which in turn reduces NOx production since NOx is exponentially proportional to flame

temperature.

However, since the exhaust gas is quite hot when directly recalculated back into the

combustion chamber, the benefits are limited.

The air/fuel ratios are also reduced, resulting in increased smoke and fuel consumption.

This technology will limit power density and will likely be used only in low BMEP

applications.

Cooled v/s Uncooled EGR

At higher exhaust recirculationrates, the fuel consumption can bemprove y coo ng e ,

while the smoke numbers can bereduced simultaneously by increasing the oxygen contentinside the combustion chamberdue to limited thermal throttling.

Since both the NOx formation

reaction and soot formationmechanism are heavily influenced

by temperature, the application ofcooled EGR supports the reductionof both species.

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Low Pressure Loop EGR High Pressure Loop EGR

High Pressure Venturi EGR System

Advantages

Problems

System contamination

Increased soot in oil

Transport losses increase

VTG-EGR control

Requirements

Good Oil Control


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Clean Low Pressure EGR System

Advantages

Reduced control com lexit

Fuel economy

Problems

Reliability of particulate filter

Re-circulated NO2 may formcorrosive nitrous acid

Requirement

Low sulfur fuel (Less than 50PPM S)

Durable particulate filter withreliable regeneration


Design Specifications and Constraints

The whole system (including the mechanism and the controls) should

.

The accuracy of controlling the fraction of EGR should be as high as 1%,

because we have to precisely monitor and route the EGR into the system

(standard EGR is around 5-7%).


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How Does EGR Work?


How Does EGR Work?


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Exhaust Gas Recirculation Valve

The EGR Valve is just above the exhaust pipe in the middle of the engine.

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Problems with EGR

Due to the high temperature of the exhaust gas and its anticipated effect

, -

exhaust gas is typically cooled to maintain high volumetric efficiency as

well as avoid excessive increase in heat loss.

A problem unique to CI engines when using EGR is the solid carbon soot

n t e ex aust. e soot acts as an a ras ve an rea s own t e

lubricant. Greater wear on the piston rings and valve train, results.


Solution

Studies have shown that EGR coupled with a high collection efficiency particulate trap,

, x .

The particulate trap, however, need to be regenerated since its pores are clogged by

the soot particles trapped.

Clogged soot traps increases backpressure to the engine exhaust, thus affecting

engine performance.


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Treatment of EGR

x a on a a y c pera on ue e ormer

1. Intake Manifold

2. Throttle Body

EGR System with Catalytic Converter

3. Air Filter

4. Electrical Vacuum

Modulator

5. Control Unit

6. EGR Valve with

emperature ro e7. Exhaust Gas

Manifold

8. Catalytic Converter

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ExhaustMuffler

Orifice

EGR Loop

Air Box and

Diaphragm

TC-4

Back Pressure Valve

arFlow

ment

Smoke Opacity Meter

EGR Control Valve

Exhaust

Gas

TC1

TC2

TC3

TC5

Schematic Diagram of Experimental Setup

Lamin

Equip

FreshAir

AC

Generator

Load

Bank

V

A

Exhaust Gas Temperature Vs Load

350

EGR 0%

EGR 7 75%

200

250

300

TEMP(C)

.

EGR 10.4%

EGR 12.5%

100

150

0 2 4 6 8

LOAD (KW)


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260

280

300

320

Temp(0C)

0%EGR

10%EGR20

25

30

35

iciency(%)

0%EGR

Effect of EGR on Engine Performance

160

180

200

220

240

0 20 40 60 80 100

% of Rated Load

ExhaustGa

20%EGR

0

5

10

15

0 20 40 60 80 100

% of Rated Load

ThermalEffi

10%EGR

15%EGR

20%EGR

0.4

0.45

-hr)

0%EGR

10%EGR

Exhaust Gas Temperature for Different EGR Rates Thermal Efficiency for Different EGR Rates

60

80

100

(%) 0%EGR

10%EGR

0.25

0.3

0.35

0 20 40 60 80 100

% of Rated Loa d

BSFC(kg/k

15%EGR

20%EGR

BSFC for Different EGR Rates

0

20

40

0 20 40 60 80 100

% of Rated L oad

Opacity

15%EGR

20%EGR

Opacity for Different EGR Rates

50

100

150

200

250

NOx(ppm) 0%EGR

10%EGR

15%EGR

20%EGR

1100

1600

2100

2600

3100

3600

HC(ppm)

0%EGR

10%EGR

15%EGR

20%EGR

% of Rated L oad % of Rated Load

450

600

750

(ppm)

0%EGR

10%EGR

15%EGR

20%EGR

Hydrocarbons for Different EGR RatesNOx for Different EGR Rates

150

300

0 20 40 60 80 100

% of Rated Load

C

Carbon Monoxide for Different EGR Rates


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Lubricating Oil Tribology of EGROperated Engine

Carbon Deposits on Cylinder Head Using EGR Carbon Deposits on Cylinder Head without EGR

Carbon Deposits on Injector Tip Using EGR Carbon Deposits on Injector Tip without EGR

Lubricating Oil Tribology of EGR

Operated Engine

Carbon Deposits on Piston Crown Using EGR Carbon Deposits on Piston Crown without EGR

5

6

7

rbon

Without EGR

/g) 160

200

With EGR

Without EGR

0

1

2

3

4

24 48 72 96Time (hrs)

%C

hangeinCa With EGR

% Change in Carbon as Function of Lubricating Oil Usage

Time (hrs)

0 24 48 72 96

FeConcentration

(

0

40

80

120

Fe Concentration as a Function of Lubricating Oil Usage


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ration(g/g)

20

30

40

With EGR

Without EGR

ration(g/g)

3

4

5

6

With EGR

Without EGR

Lubricating Oil Tribology of EGROperated Engine

Time (hrs)

0 24 48 72 96

CuConcent

0

10

Cu Concentration as a Function of Lubricating Oil Usage

Time (hrs)

0 24 48 72 96

CrConcent

0

1

2

Cr Concentration as a Function of Lubricating Oil Usage

(g

/g)

0.8

1.0

With EGR

Without EGR

n(g/g)

12

16

With EGR

Without EGR

Time (hrs)

0 24 48 72 96

N

iConcentration

0.2

0.4

0.6

Ni Concentration as a Function of Lubricating Oil Usage

Time (hrs)

0 24 48 72 96

AlConcentratio

0

4

8

Al Concentration as a Function of Lubricating Oil Usage


ion(g/g)

1.5

2.0

ion(g/g)

20

25

30

With EGR

Without EGR

Lubricating Oil Tribology of EGR

Operated Engine

Time (hrs)

0 24 48 72 96

MnConcentrat

0.0

0.5

1.0

With EGR

Without EGR

Mn Concentration as a Function of Lubricating Oil Usage

Time (hrs)

0 24 48 72 96

PbConcentrat

5

10

15

Pb Concentration as a Function of Lubricating Oil Usage

(g/g)

24

26

With EGR

Without EGR

/g)

600

620

Time (hrs)

0 24 48 72 96

MgConcentration

20

22

Mg Concentration as a Function of Lubricating Oil Usage

Time (hrs)

0 24 48 72 96

ZnConcentration(g

480

500

520

540

560

580 With EGR

Without EGR

Zn Concentration as a Function of Lubricating Oil Usage


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EGR System Issues

Two-Stage Turbocharger Diesel Engine set up fitted with HP EGR

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Effect of EGR on Peak Flame Temperature

Effect of EGR on Particulate Formation

High % of EGR adversely reduces combustion quality results in PM formation. High % EGR suppresses flame speed sufficiently leads to incomplete combustion. Efficient Particulate trap are bound to be used.

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COOLED EGR

Cooling EGR gases is essential for emissions control and to avoid

re uc ng n-cy n er mass t roug t erma t rott ng

Very cold EGR gases have shown further improvements but these

systems will ultimately only be achieved on vehicle through the thermal

management system.


Effect of EGR cooling on NOx reduction


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EGR Effect on Diesel Engine Wear

Oil Ageing due to EGR

Increase in soot and viscosity level

Depends on speed, load, EGR rate

& running time.

In cylinder effects of EGR

Soot absorbs anti-wear additivesand inhibits protective layerformation. Soot has an abrasive

.Corrosion enhanced wear due to oilageing.

Above wear mechanisms are

more severe at high engine loads.


50

60

r[%]

Change in Cooling Power

EFFECT OF EGR ON HEAT IN COOLANT

10

20

30

40

hangeinCoolingPow

-10

0

NO NO HP Loop LP Loop HP Loop LP Loop HP Loop

6.9 4.8 3.5 3.5 2.0 2.0 1.4 before

SCR

EURO II EURO III EURO IV EURO IV EURO V EURO V US/2007

CEGRBSNOx

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Summery effects of EGR on various parameters

PARAMETERS Effect of EGR

Air-Fuel-Ratio Reduces

Oxygen Concentration Reduces

Water Content in Inlet Charge Increases

Ignition delay Increases

Specific Heat of the Inlet Charge Increases

Rate of Combustion Reduces

Pre-mixed Combustion Increases

Peak Flame Temperature Reduces

Spray-Flame Volume Increases

Peak Pressure Reduces

BSFC Increases

Knock Reduces

Nox Reduces

HC Increases

PM & Soot Increases

CO No Significant Increase

Aldehydes Increases

Lubrication Contamination

Engine Wear Increases

EGR cooler


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Multitube EGR cooler


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Factors Contributing to EGR Cooler Fouling

Two particle deposition mechanisms for EGR cooler fouling:

S ecific article size de osition

Thermophoretic deposition

Thermal gradient is the key!

Four factors that increase EGR cooler fouling:

Hi h PM number (or mass) concentration

High gas temperature gradient across the cooler

Low gas outlet temperature to enhance condensation inside cooler

Wet particle composition (soluble organic fraction SOF)


EGR System Fouling high at higher loads


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Effect of Diesel Particulate Matter (PM)

Effect on EGR Cooler

g rate o eros ve an a ras ve wear

-Mechanical durability

Deposit and fouling of PM

-Pressure Drop

-Heat transfer efficiency

Washcoat powder & fuel soleplates

major reasons of EGR valve fouling

%

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