1. Auto-Ignited Kernels during Knocking Combustion in a Spark-Ignition Engine Okayama UniversityNobuyuki KAWAHARA Eiji TOMITA

2. End-gas Knocking cycle Standard cycle Okayama University Background Requirements of spark-ignition (SI) engine - Lower fuel consumption - Reduced emission of pollutants. Higher thermal efficiencies Engine knocking due to higher compression ratio

3. Heater Out Mixture tank Thermocouple Solenoid Valve-closure signal Elongated piston Electric motor Flywheel TDC signal Crank angle pulse Rotary encoder Pressure transducer Valve Valve-stopper Water In Spark electrode Bore: 78 mm Stroke: 85 mm Compression ratio: 9.02 Engine speed: 600 rpm Okayama University Compression-expansion engine

4. Bore: 78 mm Stroke: 85 mm Compression ratio: 9.0 Engine speed: 600 rpm 180 Crank angle, deg. 210240270300330360 (TDC) (BDC) Side view Top view Timing chart Valve closing Ignition In Water Out Burned gas Unburned gas Okayama University Compression-expansion engine

5. Knock intensity: K Int H.P.F 2.5kHz K Int 0 5 10 15 Time from ignition, ms Experimental condition Fuel (Octane number) Equivalence ratio, φ Initial pressure, P 0 Spark ignition timing, θ IT n-C 4 H 10 (94) 1.0 40, 50, 60kPa 335 ～ 355deg. H 2 1.0 40kPa 335 ～ 360deg. Okayama University Experimental condition Use of Ar&O 2 mixture instead of air

6. Mirror Flywheel Electric motor PC Cassegrain optics Pressure Transducer Valve Cylinder Measurement point Spark electrode Experimental methods Shimadzu Hyper vision, HPV-1 Nac Image Technology, MEMRECAM GX1 High-speed video camera

7. P 0 =50kPaΘ IT =350deg. P 0 =60kPaΘ IT =340deg.P 0 =60kPaΘ IT =345deg. Standard cycle K Int =0.434MPa n-Butane(Φ=1.0) Rec.Speed:32kf.p.s Rec.Expose:1/8 K Int =0.180MPa Okayama University Knock image (n-Butane)

8. P 0 =50kPa  IT =350deg. P 0 =60kPa  IT =345deg. Normal cycle Knocking cycle ABCDEFG abcdef g Flame front Auto-ignited kernel 350360370380 0 1 2 3 4 Pressure, MPa Crank angle, deg. 350360370380 0 1 2 3 4

9. A B C D E F G H I Rec.speed:63kfps K Int =0.491MPa 360.0deg. ～ 366.4deg. Φ=1.0 P 0 =60kPa, Θ IT =345deg. A B C E F GH I D B Flame front Auto-ignited kernel Okayama University Knock image and pressure history (n-Butane)

10. A B C D E F G H I Rec.speed:64kfps 360.0deg. ～ 366.4deg. Φ=1.0 P 0 =60kPa, Θ IT =345deg. A B C D E F GH I K Int =0.491MPa Okayama University Knock image and pressure history (n-Butane)

11. 320340360380400420 320340360380400420  = 1.0, P 0 =60kPa, T 0 =323K, Rec.speed : 20kfps. Crank angle, deg. Pressure, MPa C 4 H 10, Θ IT =345deg. K int =0.07MPa C 4 H 10, Θ IT =360deg. Non-knock condition CH 4, Θ IT =340deg. Non-knock condition 320340360380400420 4 3 2 1 0 Okayama University Knock image and pressure history (n-Butane)

12. 0 1 2 3 360365370375380 Pressure, MPa Normal cycle Crank angle, deg. H 2 -Air φ=1.0 P 0 =60kPa T 0 =323K θ i =360deg. K int =0.03MPa 1 2 3 375380 Knocking cycle 0 360365370 Crank angle, deg. H 2 -O 2 -Ar φ=1.0 P 0 =40kPa T 0 =323K θ i =360deg. K int =1.53MPa Compared normal cycle with knocking cycle Rec. speed=60,000fps Okayama University

13. Pressure wave Auto-ignition H 2 -O 2 -Ar φ=1.0 θ i =340deg. Rec. speed=250,000fps Exposure time=2  s K int =0.99MPa Knocking cycle Visualization of pressure wave and estimation of the frequency 136  s A1A1 A2A2 B1B1 B2B2 Frequency=7.35kHz Okayama University