high-efficiency clean combustion design for …...high-efficiency clean combustion design for...

Design for Compression Ignition High-Efficiency Clean Combustion

Engines

Mike PotterRuss Durrett

General MotorsAugust 24, 2006

Overview

U.S. Heavy Duty Emission Standards

U.S. Light Duty Emission Standards

0.10 19982004

2007 2010

0.08

0.05

PM (g

/hp-

hr)

Tier 2, Bin 10 (2007-2010)

Euro 3 (2000)

Euro 4 (2005)

Euro 5 Prop

T2 Bin 5

T2 Bin 8

PM (g

/mi)

0.01 0.04

0.00 0 0.2 1 2 3 4

NOX (g/hp-hr) 0.02

0.01

0 0 0.1 0.3 0.4 0.6 0.8

NOX (g/mi)August, 2006 2

Equivalence Ratio (φ) vs T Space – Navigating the Terrain

Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

Tflame 21% O215%

10% 8%

NOX production zone

soot production

zone

CO / UHC oxidation

limit

Tcharge

fuel – charge mixing line

ignition zone

• The φ vs. T diagram is commonly used in diesel combustion discussions.

• Combustion processes pass through a particular path in this space.

• Time is not represented in the figure.

Temperature (K) August, 2006 3


Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot Tcharge effect production zone

CO / UHC oxidation

limit

Tcharge

- VVA - Tintake


ignition zone

Fuel – charge mixing line (green): As the fuel and charge mix, the temperature and equivalence ratio of the mixture will follow this line. The location of the line changes with Tcharge.

Tflame



Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot production

zone

CO / UHC oxidation

limit

Tcharge


ignition zone

fuel cetane effect

Ignition zone (grey): This is the temperature range above which a diesel fuel / air mixture will ignite rapidly.

Tflame


T flame


Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot production

zone

CO / UHC oxidation

limit

Tcharge


ignition zone

flame temperature

Flame temperature lines (red): The adiabatic flame temperature of a fuel / charge mixture at the given equivalence ratio.



Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

CO / UHC oxidation

limit

Tcharge


ignition zone

soot production

zone

Soot production zone (blue): This denotes the region where soot is formed in significant quantities.

Tflame



Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

soot production

zone

CO / UHC oxidation

limit

Tcharge


ignition zone

NOX production zone

NOx production zone (cyan): This denotes the region where NOX is formed in significant quantities.

Tflame



Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot production

zone

Tcharge


ignition zone

CO / UHC oxidation

limit

CO / UHC oxidation limit (orange): Must complete combustion above this temperature in order to consume CO and unburned HC.

Tflame


Conventional Diesel Combustion Eq

uiva

lenc

e R

atio

(φ)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot production

zone

Tcharge

ignition zone

A


Fuel mixes with charge (A) until the ignition temperature is reached.

The path shows the trajectory of a fuel parcel undergoing a conventional diesel combustion event.

Tflame

CO / UHC oxidation

limit



uiva

lenc

e R

atio

(φ)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot production

zone

Tcharge

ignition zone

A


B C

premixed

The fuel first undergoes a rich premixed reaction (B-C) in which part of the fuel energy is released.

Tflame

CO / UHC oxidation

limit



uiva

lenc

e R

atio

(φ)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot production

zone

Tcharge

ignition zone

A


B C

premixed

D

diffusion

The remainder of the fuel energy is released as the rich products continue to mix with oxygen (C-D) in a diffusion flame.

Tflame

CO / UHC oxidation

limit



uiva

lenc

e R

atio

(φ)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot production

zone

Tcharge

ignition zone

A


B C

premixed

D

diffusion

E

The combustion products continue to mix throughout the chamber (D-E).

Tflame

CO / UHC oxidation

limit


New Combustion Modes (PCCI) – Reducing NOx and Soot

Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot production

zone

Tcharge

A

B C

D’ D E

ignition zone

soot

B’ C’

NOX reduction

reduction

fuel – charge mixing line Increased mixing (lower φ at ignition)

comes from longer ignition delay via reduction in Tcharge at injection.

Flame temperature reduction comes from reduced oxygenTflame concentration via EGR.

CO / UHC oxidation

limit


zone

Soot Reduction Through Low O2 Concentration

Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot production

Tcharge

ignition zone


A

B C

D

incomplete

E

Tflame

CO / UHC oxidation

limit

soot and NOX reduction

In this scenario, soot is never formed due to the low temperature during ignition and combustion.

Difficult to avoid

combustion products (CO / UHC).


1510%

8%

Ideal Combustion Process Eq

uiva

lenc

e R

atio

(φ)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

Tflame 21% O2%combustion

NOX production zone

soot production

zone

CO / UHC oxidation

limit

Tcharge

ignition zone

takes place here


The ideal process will create the necessary conditions in which most of the energy release will take place in the region shown.


New Combustion Modes (PCCI) – Reducing NOx and Soot

Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0 500 1000 1500 2000 2500 3000

21% O215% 10%

8%

NOX production zone

soot production

zone

Tcharge

A

B C

D’ D E

ignition zone

soot

B’ C’

NOX reduction

reduction

fuel – charge mixing line Improvements in the hardware

available have improved our ability to use PCCI modes and increased their applicable range of speed and load.

Tflame

CO / UHC oxidation

limit


End of Presentation

• BackUp Material

August, 2006 18

Early vs. Late PCCI

• PCCI mode requires a longer ignition delay.

• How to lengthen the ignition delay: • Lower T at SOI • Lower [O2] at SOI

• In order to access lower temperature, the injection must move away from TDC: • Advance timing for early PCCI • Retard timing for late PCCI

• Compression ratio and charge temperature will also affect the injection range.

comp. ratio or ignition delay

too short

Late

PC

CI

Reg

ion

Ear

lyP

CC

IR

egio

n

temperature in cylinder

charge temp. variation

injection range

injection range

ignition temp.

TDC

August, 2006 19

CO / UHCoxidation

limit

Some Practical Limitations

• Impossible to achieve temperatures higher than the flame temperature – operation in the high T – high φ region is precluded.

• The ignition process must pass through the region shown (need better words here!)

• End of combustion temperature must remain high enough to insure complete oxidation of CO and UHC compounds.

Equi

vale

nce

Rat

io (φ

)

6

5

4

3

2

1

0500 1000 1500 2000 2500 3000

T flame 21% O2

15% 10%

8%

NOx production zone

soot production

zone


ignition zone

Tcharge

high T – high φ region must pass

this region

incomplete HC / CO oxidation

Temperature (K)

August, 2006 20

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