Tests

Considerations on Carbon Deposit Formation in Gasoline Direct Injection Engine

2013. 09. 04

Gyu-Sob Cha

GS Caltex Corporation

Contents

Introduction

: Motivation & Objective of Research

Preliminary Test Main Tests

- Reenact IVD/CCD accumulation of GDI - Test whether PFI detergent is valid for GDI

- To find test conditions for deposit accumulation - To investigate causes of carbon deposit in GDI

Conclusion Future Plan

1 / 20

Introductions  GDI* (Gasoline Direct Injection) Technology  Gasoline is highly pressurized and injected via a common rail fuel line DIRECTLY into the combustion chamber  Concept had invented in early 20th Century, but mass production for automobiles was started in late 20th Century (by Mitsubishi Motors, 4G93 1.8L engine)  Offers better fuel economy and power output compared with PFI (Port Fuel Injection) engine → Substituting conventional PFI engines with fast speed * Also known as SIDI (Spark Ignition Direct Injection) or FSI (Fuel Stratified Injection)

 IVD (Intake Valve Deposit) and CCD (Combustion Chamber Deposit)  Carbonaceous chunk generated and accumulated while the engine is running  Could cause numerous problems in terms of exhaust emission, vehicle performance and fuel economy  For PFI engines, detergent (fuel-additive) is used to remove IVD

◀ Without detergent

With detergent ▶

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Introductions  IVD in GDI engine?  GDI engine : No direct contact between fuel spray and intake valve

Fuel injector Fuel Spray

[GDI]

[PFI]

→ Nevertheless, numerous problems with regard to intake valve deposits has been discussed in online forums

3 / 20

Introductions  Objective of Research

1. To investigate the phenomenon of carbon deposit formation in GDI engine

Conditions that carbon deposit is easily accumulated on Main cause of carbon deposit

2. To find a way to remove/mitigate carbon deposit formation(accumulation) in GDI engine

Engine hardware modification Fuel / Lubricant additives

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Preliminary Test – Objective and Test Condition  Test Objective  Reenact IVD/CCD formation(accumulation) of GDI engine in laboratory  Test whether conventional detergent for PFI engine would also be valid for GDI engine

 Test Mode/Engine  Test mode : ASTM D6201 ※ Test condition was differentiated in accordance with engine performance  Test engine : Hyundai Motor Company Theta II GDI (2.4L) / Theta II PFI (2.0L) Theta II GDI

Theta II PFI

Direct Injection

Injection type

Side

Injector mount

Multi-hole

Injector type

NA

Air charging

NA

2,359

Engine capacity (cc)

1,998

4

Number of cylinders

4

88 X 97

Stroke X Bore (mm)

86 X 86

201@6,300

Maximum Power (PS)

165@6,200

25.5@4,250

Maximum torque (kg·m)

20.2@4,600

11.3:1

Compression ratio

10.5:1

150

Maximum fuel injection pressure (bar)

3.5

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Port Injection

Preliminary Test – Objective and Test Condition  Test Apparatus  Test bed : EC-type engine dynamometer system (AVL alpha 240kW)



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Preliminary Test – Result and Conclusion  Test Result  IVD and CCD w/ or w/o detergent in GDI/PFI engines Intake Valve Deposit

Avg. mg/valve

Avg. mg/cyl.

Combustion Chamber Deposit

1200

200 161.31 160

1082.6

1100

1040.2

120 80

79.28

1000

74.37

908.9 32.65

40

877.1

900

800

0 GDI

GDI

PFI Base

w/ Detergent

PFI Base

w/ Detergent

Conclusion of Preliminary Test  Both IVD and CCD were formed in GDI engine  Absolute Amount(weight) of IVD in GDI was smaller than that in PFI engine

→ However, conventional detergent for PFI engine was ineffective for GDI engine

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Main Tests – 1) Conditions That Carbon Deposit Is Accumulated on  Test Objective  To figure out condition(in terms of engine operation) that carbon deposit is easily accumulated on

Test Mode/Engine  Test Mode : Modified ASTM D6201 (Original Test Engine : 1994 Ford Ranger 2.3L engine)  Test Engine : Hyundai Motor Company Theta II GDI (2.4L)

 Experimental Variables  Variables : Average Engine Load, Length of the one cycle (Load change time)  Level of variables : 2 (Engine load) × 2 (Load change time) + 2 (Average of Low/High conditions) Low

High

Engine Load

Lowest engine load possible*

Low load × 2

Length of the one cycle**

24 min. (6+18)

6 min. (2+4)

* Engine load that can ensure stable engine operation ** 1) 1/3 of cycle is run at 2,000 RPM, the rest is at 2,800 RPM (ASTM D6201) 2) Total test time is same as the ASTM D6201 (Test duration : 100 hr) 8 / 20

Main Tests – 1) Conditions That Carbon Deposit Is Accumulated on  Schematic diagram for Test cycles 3)

Load change Frequency

Load

4) Load

High Load – Low Frequency

High Load – High Frequency

5)

6) Load

Load

Engine load Mid Load – Mid Frequency

Mixed Load – Mid Frequency

※ 5) & 6) Same average engine load, but 6) has wider load gaps 1)

2) Load

Load

Low Load – Low Frequency

High Load – High Frequency

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Main Tests – 1) Conditions That Carbon Deposit Is Accumulated on  IVD / CCD weight  The lower engine load, the more deposit formed → Incomplete combustion of the fuel at low load generates more deposit → Load change frequency is not important factor in IVD/ CCD formation

Combustion Chamber Deposit (avg. mg/cyl.)

 Load change frequency was less important factor on carbon deposit generation

Intake Valve Deposit (avg. mg/valve)

200

166.24 160

129.38 120

71.68

80

81.19

79.08

79.28

40

0 #1

#2

#3

#4

#5

#6

Low load conditions 10 / 20

2400

2202.5

2164.5

2000

1600

1315.8 1200

972.2

972.3

908.9

800

400

0 #1

#2

#3

#4

#5

#6

Main Tests – 1) Conditions That Carbon Deposit Is Accumulated on  Additional Finding : CCD Thickness  At the top of piston, CCD formation pattern was different from a function of engine load #1,#2 (Low Load) & #5 (Medium Load) → Fan shape

#3,#4 (High Load) & #6 (Mixed Load) → Donut shape

 It is estimated that fuel spray causes the difference in CCD formation pattern Low (Medium) Load

High Load

Unburned Hydrocarbon Forming Area 11 / 20

Accumulated CCD

Main Tests – 2) Cause of Carbon Deposit  Test Objective  To investigate cause of the carbon deposit in GDI engine (IVD and CCD)

 Test Mode/Engine  Test Mode : Modified ASTM D6201 (same as Preliminary Test)  Engine : Same as the previous test

 Experimental Variables  Choose potential causes of carbon deposit (via Literature reviews & preliminary tests) 1) Fuels 2) Lubricants (Base oil + Lubricant additives) 3) Internally trapped exhaust gases 4) Positive Crank Ventilation (Blow-by gas)

→ Need to design experimental conditions that could evaluate the contribution of each factors for the formation of carbon deposits 12 / 20

Main Tests – 2) Cause of Carbon Deposit  Experimental Set-up

Blow by gas

• Able to remove

→ Bypass crankcase ventilation

→ Make direct evaluation via engine test

Fuels

• Unable to remove

Lubricants

• Unable to remove

→ Indirect evaluation, by comparing with PFI engine test

Trapped Exhaust Gas

• Unable to remove, or control → Impossible to change unless modifying engine hardware 13 / 20

Main Tests – 2) Cause of Carbon Deposit  Test result : Effect of blow-by gas  By passing the positive crankcase ventilation lines → Blow-by gas port at the intake port was sealed by caps mg/valve

Base Test

mg/valve (mg/Cyl.)

(mg/Cyl.)

120

120 93.23 90

Excluding Blowby

90

75.03

60

60

30

30

0 IVD

80.4

85.34

0

CCD/10

IVD

CCD/10

→ No improvement in IVD formation → Blow-by gas is considered less important factor in carbon deposit formation → Nevertheless, it is still possible that contaminated lube oil (containing metals or slurry) could be the source of IVD since only fresh lube oil was used in this experiment

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Main Tests – 2) Cause of Carbon Deposit  Test result : Effect of used lubricants  Test procedure 1) Conduct ASTM D6201 test with fresh lubricant 2) Measure IVD, CCD and replace intake valves and remove CCD 3) Conduct the same test with used lubricant 4) Measure IVD, CCD and replace intake valves and remove CCD and compare with Step 2) ※ Typical 5W-30 Group 3 Lubricant was used for all tests

GDI engine

mg/valve (mg/Cyl.)

PFI engine

mg/valve (mg/Cyl.)

240

120

207.01 200

100

93.23

75.03

↑ 4.2%

90.34 160

84.2 80

215.74

↑ 12.2%

120

101.3

102.2

80

60 IVD Fresh Lubricant

IVD

CCD/10 Used Lubricant

Fresh Lubricant

CCD/10 Used Lubricant

→ IVD formation in GDI engine was more sensitive to “Freshness of Lubricant” → Using used lubricant does not deteriorate CCD formation for both types of engines 15 / 20

Main Tests – 2) Cause of Carbon Deposit  Test result : Effect of used lubricants – additional test  Quantifying amount of metallic compound in carbon deposit  Use different types of lubricants : Group II(7.5w-30), III(5w-30), IV(0w-30) ※ Test procedure was same as the previous tests mg/valve

mg/valve

Intake Valve Deposit

(mg/Cyl.)

1067

1100

110 92.7 90

68.6 68.8

69.6

1034.5

1000 900

79.1 70

Combustion Chamber Deposit

(mg/Cyl.)

924.1

885.1

964.5

823.7

800 57.8

50

700 600

Group 2

Group 3 Fresh Lubricant

Group 2

Group 4 Used Lubricant

Group 3

Fresh Lubricant

Group 4

Used Lubricant

→ For high quality lubricants, increase of IVD due to larger aging of lubricant → It is assumed that higher contents of additives in high quality lubricants might have caused this phenomenon (Base Oil : Additive = 84:16(Group II), 82:18(Group III), 74:26(Group IV)) → However, further experiments (repeatability check, detail analysis on additive)are needed to prove this rationale due to lacking of experimental data 16 / 20

Main Tests – 2) Cause of Carbon Deposit  Thermo Gravimetric Analysis (TGA)  Quantifying amount of metallic compound in carbon deposit  Metallic components are only contained in Lubricants additives

→ More metallic compounds may imply when contribution of lubricant (additive) was larger  TGA result : Comparison of carbon deposit between GDI and PFI engine Portion of unburned carbon residue

wt.% 100%

GDI

75%

63.60%

50% 25%

24.09%

22.34%

16.69%

0% IVD

CCD

→ In GDI engine (compared with PFI engine), 1) Lubricant oil could be an important source of IVD 2) CCD mainly comes from unburned fuel 17 / 20

PFI

Conclusions  Conclusions 

Both IVD and CCD were formed in GDI engine, although fuel spray did not make any contact with the intake valves. More carbon deposits were accumulated when the average engine load was low

※ Characteristics of IVD and CCD are given below IVD

CCD

• The weight of carbon deposit was much smaller than that in PFI engine • Conventional detergent was unable to reduce IVD formation • The weight was comparable to that of PFI engine • Shape of accumulated deposit was different by the engine load → It is estimated that the difference in fuel injection quantity and timing caused different shape



Positive crankcase ventilation(Blow-by) was not related to carbon deposit formation



The TGA results showed that, in GDI engines, lubricants might be an important source of IVD while CCD mainly come from unburned fuel.

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Future Work  Future work 1. To Investigate phenomenon of carbon deposit formation in Gasoline Direct Injection Engine Condition that carbon deposit is easily accumulated in Main cause of the carbon deposit Quantify contribution of each factors • Fuel composition (Aromatic / Olefin contents ) effect • Lubricants effect – Base oil and lubricant additives • Find / Test of other hidden factors • Development/modification in-house test procedure • Correlation between IVD/CCD and engine performance

2. To Find a way to remove/mitigate carbon deposit formation (accumulation) in Gasoline Direct Injection Engine Fuel / Lubricant Additives • Development of fuel/lubricant additive that can remove intake valve deposit in GDI engines 19 / 20

Question & Answer

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