Considerations on Carbon Deposit Formation in Gasoline Direct Injection Engine

Transcription

1 Considerations on Carbon Deposit Formation in Gasoline Direct Injection Engine Gyu-Sob Cha GS Caltex Corporation

2 Contents Introduction : Motivation & Objective of Research Preliminary Test - Reenact IVD/CCD accumulation of GDI - Test whether PFI detergent is valid for GDI Main Tests - To find test conditions for deposit accumulation - To investigate causes of carbon deposit in GDI Conclusion Future Plan 1 / 20

3 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 20 th Century, but mass production for automobiles was started in late 20 th 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 2 / 20

4 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

5 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 4 / 20

6 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 Port Injection 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 @6,300 Maximum Power (PS) 165@6, @4,250 Maximum torque (kg m) 20.2@4, :1 Compression ratio 10.5:1 150 Maximum fuel injection pressure (bar) / 20

7 Preliminary Test Objective and Test Condition Test Apparatus Test bed : EC-type engine dynamometer system (AVL alpha 240kW) <Schematic diagram for experimental set-up> 6 / 20

8 Preliminary Test Result and Conclusion Test Result IVD and CCD w/ or w/o detergent in GDI/PFI engines Avg. mg/valve Intake Valve Deposit Avg. mg/cyl. Combustion Chamber Deposit GDI PFI 800 GDI PFI Base w/ Detergent 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 7 / 20

9 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

10 Main Tests 1) Conditions That Carbon Deposit Is Accumulated on Schematic diagram for Test cycles 3) Load Load change Frequency 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 9 / 20

11 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 Load change frequency was less important factor on carbon deposit generation Intake Valve Deposit (avg. mg/valve) Combustion Chamber Deposit (avg. mg/cyl.) #1 #2 #3 #4 #5 #6 #1 #2 #3 #4 #5 #6 Low load conditions 10 / 20

12 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 11 / 20 Unburned Hydrocarbon Forming Area Accumulated CCD

13 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

14 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

15 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 (mg/cyl.) 120 Base Test mg/valve (mg/cyl.) 120 Excluding Blowby IVD CCD/10 0 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 14 / 20

16 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 mg/valve (mg/cyl.) GDI engine mg/valve (mg/cyl.) PFI engine 4.2% % IVD Fresh Lubricant CCD/10 Used Lubricant 80 IVD 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

17 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/cyl.) 110 Intake Valve Deposit mg/valve (mg/cyl.) 1100 Combustion Chamber Deposit Group 2 Group 3 Group Group 2 Group 3 Group 4 Fresh Lubricant Used Lubricant Fresh Lubricant 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

18 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 wt.% 100% Portion of unburned carbon residue GDI PFI 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

19 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 The weight of carbon deposit was much smaller than that in PFI engine Conventional detergent was unable to reduce IVD formation CCD 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. 18 / 20

20 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

21 Question & Answer 20 / 20