University of Wisconsin Engine Research Center

Spray Targeting to Minimize Soot & CO Formation in Premixed Compression Ignition (PCI) Combustion with a HSDI Diesel Engine

SANGSUK LEE & Rolf D. REITZMotivation

Stringent future emission regulations require low emission strategies.

PCI (Premixed Compression Ignition) is a practical way to achieve near zero levels of soot and NOx trade-off even under fairly rich conditions.

Objectives To investigate key factors which determine the

characteristics of PCI and Conventional Diesel Combustion .

To find the best way to realize low emissions.

To understand how the spray targeting affects on emission formation.

Start of Burn & Burn DurationBurn Duration (10% to 90% Burn)

2000rpm, Pin = 151kPa, Pinj = 1500bar, ~55% EGR

0

5

10

15

20

25

30

35

-45 -40 -35 -30 -25 -20 -15 -10 -5 0

SOI (deg ATDC)

Bur

n D

urat

ion

_ 10

to 9

0% (d

eg)

120' Nozzle140' Nozzle154' Nozzle50' Nozzle85' Nozzle IMEP

=5.5bar

Probably partially PCIprobably controlled by Swirl & Squish Flow

Mixing Controlled Regime(Diffusion Burn)

Burn Duration (120' Nozzle)2000rpm, Pin = 151kPa, Pinj = 1500bar, ~55% EGR

0.0

3.0

6.0

9.0

12.0

15.0

-45 -40 -35 -30 -25 -20 -15 -10 -5 0

SOI (deg ATDC)

Bur

n D

urat

ion

(deg

)

10-50%50-75%75-90%10-90%

Burn Duration 10–90 % burn durations

about 5 degree regardless of SOI and nozzle within the PCI regime.

In Conventional regime, duration increased as SOI was retarded since fuel burnt within the mixing controlled varies with SOI.

Start of Burn The Combustion starts

around -11o ATDC in PCI. ; Similar Combustion

Characteristics with different soot formation

What makes the difference in soot & CO emissions?

; Pre-ignition mixing with squish and swirl flow.

Spray Targeting

10-90% Burn Duration

Details for 120o Nozzle

Operation Conditions

Engine Speed 2000 rpm

Load 4.8bar IMEP

Boost Pressure 151 kPa

EGR about 55%

Intake Air Temp. 90oC

Injection Pressure 1500 bar

Start of Combustion (CA of 10% Burn)2000rpm, Pin = 151kPa, Pinj = 1500bar, ~55% EGR

-20

-15

-10

-5

0

5

10

15

20

-45 -40 -35 -30 -25 -20 -15 -10 -5 0

SOI (deg ATDC)

Star

t of B

urn

_ 10

% ('

ATD

C)

120' Nozzle140' Nozzle154' Nozzle50' Nozzle85' Nozzle

Start of 10% Burn

Single Injection _ Soot & COSOI Sweep (Nozzle Comparison : IMEP=4.8bar)

2000rpm, Rail P = 1500bar, Pin = 151kPa, ~55% EGR, Const IMEP Test

0.0

0.4

0.8

1.2

1.6

2.0

-45 -40 -35 -30 -25 -20 -15 -10 -5 0

SOI (deg ATDC)

Soot

(g/k

W-h

r)

Soot (154')Soot (140')Soot (130')Soot (120')Soot (85')Soot (50')

Three combustion regimes (MK, Conventional, PCI) were identified with respect to SOI.

MK (SOI > -5°) Conventional diesel

combustion

; Soot & CO increase as SOI retarded. No big difference in levels except 50 °nozzle.

PCI (SOI < -20°)

; No simple rule to describe the emission trends in PCI combustion.

No significant NOx emission difference observed under high levels of EGR.

SOI Sweep (Nozzle Comparison : IMEP=4.8bar)2000rpm, Rail P = 1500bar, Pin = 151kPa, ~55% EGR, Const IMEP Test

0

50

100

150

200

250

300

-45 -40 -35 -30 -25 -20 -15 -10 -5 0

SOI (deg ATDC)

CO

(g/k

W-h

r)

CO (154')CO (140')CO (120')CO (85')CO (50')

CO

Soot

Split Injections

Effect of Fueling Distribution in Split Injections 2000rpm, IMEP=4.8bar, Rail P = 1500bar, SOI_1=-31', SOI_2=-19', 50% EGR

0.0

0.1

0.2

0.3

0.0 0.2 0.4 0.6 0.8 1.0

NOx (g/kw-hr)

Soot

(g/k

W-h

r)

1st = 75% 1st = 55%

1st = 30%

1st = 10%

1st = 0% (Single)

Comparison between Single and Split (85' Nozzle)2000rpm, IMEP=4.8bar, Rail P = 1500bar, Pin = 151kPa, ~55% EGR

0.0

0.4

0.8

1.2

1.6

2.0

-40 -35 -30 -25 -20 -15 -10 -5 0

SOI (deg ATDC)

Soot

(g/k

W-h

r)

Soot (Single)Soot (Split : SOI_1 = -52')Soot (Split : SOI_1 = -43')Soot (Split : SOI_1 = -35')Soot (Split : SOI_1 = -31')Soot (Split : SOI_1 = -27')

Hard to find an advantage of split injections compared to single injection optimum in PCI.

Results of Pickett (SAE2005-01-0921) explained that soot emission increased when the spray interacted with the burnt gas due to a shortened lift-off length.

CO & Spray Targetting

-16

-14

-12

-10

-8

-6

-4

-2

0

0 2 4 6 8 10 12 14 16 18 20 22 24 26

X (mm)

Y (m

m)

Piston120' Nozzle85' Nozzle50' Nozzle

-25'

-30'

-35'

-40'

-20' -25' -30'-35'

SOI=-40'

-20'

-30'

SOI=-35'

SOI=-43

-25'-20'-15'-10'

Spray Targeting

Soot & Spray Targetting

-16

-14

-12

-10

-8

-6

-4

-2

0

0 2 4 6 8 10 12 14 16 18 20 22 24 26

X (mm)

Y (m

m)

Piston120' Nozzle85' Nozzle50' Nozzle

-25'

-30'

-35'

-40'

-20' -25' -30'-35'

SOI=-40'

-20'

-30'

SOI=-35'

SOI=-43

-25'-20'

Soot

CO

Spray Targeting at a piston bowl edge gave the minimum emissions both soot and CO.

Soot was minimized when the spray was targeted at the bottom of the piston bowl.

Targeting at the inner surface of the piston gave optimized CO emissions.

CO & Spray Targetting (wider Nozzles)

-16

-14

-12

-10

-8

-6

-4

-2

0

15 17 19 21 23 25

X (mm)

Y (m

m)

Piston120' Nozzle130' Nozzle140' Nozzle154' Nozzle

Spray Targeting _ Squish Flow

Soot & Spray Targetting (wider Nozzles)

-16

-14

-12

-10

-8

-6

-4

-2

0

15 17 19 21 23 25

X (mm)

Y (m

m)

Piston120' Nozzle130' Nozzle140' Nozzle154' Nozzle

Soot

CO

Optimum spray targeting near the edge of the piston bowl was observed regardless of spray angles.

Optimum spray targeting moved up piston bowl as spray angle became narrower.

Conclusions

Burn durations are good indicator to classify the PCI combustion in diesel engines.

Spray Targeting at the edge of the piston bowl is a key factor to minimize emissions in PCI combustion.

Soot could be optimized when spray was targeted at the bottom of piston which provided the longest spray travel distance. However, CO emission increased.

CO was significantly reduced when spray was targeted at the inner surface of the bowl, with a corresponding increase in soot emission.

SOI Sweep (Nozzle Comparison : IMEP=4.8bar)2000rpm, Rail P = 1500bar, Pin = 151kPa, ~55% EGR, Const IMEP Test

0.0

0.4

0.8

1.2

1.6

2.0

-40 -35 -30 -25 -20 -15 -10 -5 0

SOI (deg ATDC)

NO

x (g

/kW

-hr)

NOx (154')NOx (140')NOx (120')NOx (85')NOx (50')

NOx

Why Targeting?

Optimum Targeting (SOI = - 43o )

Fuel can be dispersed more effectively when the spray is targeted at a spot where the interaction between the spray and the squish flow is enhanced.

Worst Targeting (SOI = - 30o )

120° Nozzle120° Nozzle