University of Wisconsin Engine Research Center

Experimental Facilities

Objective

Injection Timing Effects

Conclusions

Effects at Varied Equivalence Ratios

Effects at Varied Fueling RatesLevel of Fuel Unmixedness

Engine Test Cell Setup

Fuel Unmixedness Effects in a Gasoline HCCI EngineFuel Unmixedness Effects in a Gasoline HCCI EngineStudents: R.E. Herold, R.J. Iverson (MS, 2004) Faculty: D.E. Foster, J.B. Ghandhi

• Quantify the effect fuel unmixedness has on gasoline HCCI combustion.

SurgeTank 2

SurgeTank 1

Inline Heater

EGR

AIR

Port Fuel Injection

Point

Exhaust

Premixed Fuel Injection

Point

Engine

To Engine

Dichroic Mirror

Pellin-Broca Prism

f = 1000 mm Plano-Convex Spherical Lens

f = -500 mm Plano-Concave

Cylindrical Lens

90° Turning Prism

Beam Stop

UG5 Schott Glass Filter

Engine Properties

CR 10.95

Bore 86 mm

Stroke 94.6 mm

EVO 131 aTDC

IVO 350 aTDC

EVC 375 aTDC

IVC 595 aTDC

Vaporized Fuel

2.3 mm ID Tube

Intake Valve Heated

Air + EGR

Port, Prevaporized Fuel Injector

Cylinder Head

Quartz Cylinder Window

Optical Engine

Sapphire Piston

Window Bowditch

Piston Extention Drop-down

Liner

Imaging Mirror

Optical Setup for PLIF Experiments

Nd:YAG Laser

• Level of fuel unmixedness created when using the port, prevaporized fuel injection was investigated optically using fuel tracer planar laser-induced fluorescence (PLIF).

• Injection crank angle locations (detailed below) corresponded to those detailed in metal engine experiments.

829° 724°

469° 364°

361° 256°

196°

140°

301°

245°IVC (855°)

IVO (358°)

IVC (135°)

= Intake Valve Open

720° (TDC – Previous Cycle)

360° (TDC Exhaust)

180° (BDC)

0° (TDC – Cycle of Interest)

Crank Angle (° bTDC)

• A significant level of unmixedness is created with prevaporized port fueling.

• Fuel unmixedness increases with retarded injection timings except for the EoPI = 256° bTDC injection timing, which is less unmixed than the EoPI = 364° bTDC injection timing.

• For the most retarded injection timing, regions exist in the cylinder with equivalence ratios that differ from the mean by +/- 50%.

25

20

15

10

5

0

PD

F

2.01.51.00.50.00

6

4

2

0

Homogeneous

Unmixed

724° bTDC 364° bTDC 256° bTDC 196° bTDC 140° bTDC

4000

3500

3000

2500

2000

Pe

ak

Pre

ssu

re (

kPa

)

151050

CA50 (° aTDC)

99

98

97

96

95

94Co

mb

ust

ion

Effi

cie

ncy

Premixed 724° bTDC 364° bTDC 256° bTDC 196° bTDC 140° bTDC

• Variations with respect to intake charge temperature due to heat transfer in intake port.• All combustion metrics investigation (i.e., peak pressure, combustion efficiency) show that

at a given combustion phasing (CA50) premixed and prevaporized port injection are indistinguishable.

• NOx emissions increase with fuel unmixedness, resulting from regions richer than the mean which burn hotter after autoignition.

• CO emissions show a slight increase with fuel unmixedness, possibly a result of regions richer than stoichiometric or quenching in regions leaner than the mean.

4000

3500

3000

2500

2000Pe

ak

Pre

ssu

re (

kPa

)

151050

CA50 (° aTDC)

100

95

90

85

Co

mb

ust

ion

Effi

cie

ncy

10 mg/cycle 7 mg/cycle 5 mg/cycle

Open = PortClosed = Premixed

200

150

100

50

0

EIC

O (

g/k

g)

151050

CA50 (° aTDC)

8

6

4

2

0

EIN

Ox

(g/k

g)

10

8

6

4

2

0

EIN

Ox

(g/k

g)

151050

CA50 (° aTDC)

30

25

20

15

10

5

0

EIC

O (

g/k

g)

• No changes in combustion observed between premixed and port fueling.• Significant NOx emissions increases only observed in 10 mg/cycle fueling. NOx

emissions were near zero for the 7 and 5 mg/cycle fueling conditions due to high EGR.• The difference in CO emissions between premixed and port fueling increases with

decreasing fueling rate.

2800

2600

2400

2200

2000

1800

Pe

ak

Pre

ssu

re (

kPa

)

151050

CA50 (° aTDC)

100

95

90

85

80Co

mb

ust

ion

Effi

cie

ncy

= 0.75 = 0.6 = 0.5

Open = PortClosed = Premixed

• No changes in combustion observed between premixed and port fueling.• NOx emissions were near zero for all conditions because of high EGR rate at the 5

mg/cycle fueling condition• Decreasing the equivalence ratio (increasing air flow, decreasing EGR at constant fueling

rate) leads to an increase in CO emissions but a decrease in the difference in CO emissions between premixed and port fueling.

• Fuel unmixedness in the absence of thermal and residual unmixedness had no effect on the HCCI combustion.

• Small changes in CO and NOx emissions were observed for the port fueling, which were attributed to the regions in the charge that were either locally richer or leaner than the mean equivalence ratio.

• At a given operating condition the CO and NOx emissions are the lowest for a fully homogeneous fuel distribution. Regions locally richer and leaner than the mean equivalence ratio lead to increases in NOx and CO and therefore should be avoiding in an HCCI engine.

• Fuel unmixedness in the absence of thermal and residual unmixedness does not appear to be a viable method for gasoline HCCI combustion control.

4000

3500

3000

2500

2000

Pe

ak

Pre

ssu

re (

kPa

)

330320310300

Intake Charge Temperature (°C)

4000

3500

3000

2500

2000

1500

Pe

ak

Pre

ssu

re (

kPa

)

375350325300

Intake Charge Temperature (°C)

250

200

150

100

50

0

EIC

O (

g/k

g)

151050

CA50 (° aTDC)

2800

2600

2400

2200

2000

1800

Pe

ak

Pre

ssu

re (

kPa

)

375350325

Intake Charge Temperature (°C)