INJECTION PRESSURE AS A MEANS TO GUIDE AIR UTILIZATION IN DIESEL ENGINE COMBUSTION

Transcription

1 INJECTION PRESSURE AS A MEANS TO GUIDE AIR UTILIZATION IN DIESEL ENGINE COMBUSTION H. Dembinski, Scania AB Sweden H.-E. Angstrom, KTH Stockholm, Sweden E. Winklhofer, AVL List GmbH, Austria London, March 10 and 11, 2015 Goteborg, November 26, th & 11th of March

2 MOTIVATION 10th & 11th of March

3 THE QUESTION How can higher injection pressure end up with lower engine out soot? injection pressure / soot t = 0.2 ms asoi 10th & 11th of March

4 THE QUESTION How can higher injection pressure end up with lower engine out soot? Can we understand the mechanisms? If so how to exploit them? Which kind of analysis would we require? 10th & 11th of March

5 CONTENT 1.Injection pressure spray at nozzle exit 2.Spray interaction with in-cylinder gas Momentum transfer Heat transfer 3.Ignition 4.Premixed and diffusion flames Soot formation Soot oxidation 5.Enhancing soot oxidation 6.How things come together pressure temperature flow 7.Summary 10th & 11th of March

6 1. Injection pressure - spray PRESSURE GEOMETRY - FUEL FLOW - SPRAY Fuel injection pressure injector internal flow Such flow is visualized in 2D model nozzle tests. E. Winklhofer et al.: Basic flow processes in high pressure fuel injection equipment, ICLASS th & 11th of March

7 1. Injection pressure - spray Internal flow is visualized in 2D model nozzle tests. Liquid into liquid injection (Diesel) PRESSURE GEOMETRY - FUEL FLOW - SPRAY liquid body 1 bar liquid needle 30 bar P in = 400 bar Shear layer cavitation boundary layer cavitation 1 bar needle Fuel flow is subject to cavitation in local shear and boundary layers. High cross flow velocity gradients force static pressure to drop below vapor pressure. Driving parameters are: Geometry Velocity gradients Pressure Vapor pressure of fuel boundary layer cavitation White: liquid phase (Diesel) Black: gas phase (cavitation bubbles) at Diesel vapor pressure << 1 bar 10th & 11th of March

8 1. Injection pressure - spray Internal flow is visualized in 2D model nozzle tests. Liquid into liquid injection (Diesel) PRESSURE GEOMETRY - FUEL FLOW - SPRAY Pressure field at inflow into nozzle hole Fuel pressure is discharged within fractions of a millimeter at the entrance to the nozzle hole. Geometry influence on local static pressure and hence on cavitation - is highest in areas of high pressure drop. A B Measurements were done as Diesel fluid was just below cavitation limit Sharp (A) and round (B) inlet 10th & 11th of March

9 800 µm 800 µm 1. Injection pressure - spray Liquid into air: 2D model nozzle to see internal flow together with spray. Average of 30 events P in = bar PRESSURE GEOMETRY - FUEL FLOW - SPRAY fuel cavitation A nozzle flow spray experiment: At high injection pressure we see Well developed cavitation down to nozzle hole exit Atomizing spray with highly stable spray cone angle spray Note the dimensions: 0,8 mm nozzle hole + 0,8mm free spray air laminar turbulent turbulent and cavitating Conclusion: high injection pressure stabilises spray cone angle near nozzle exit. 10th & 11th of March

10 spray dia. - mm 2. Spray interaction with in-cylinder gas Momentum transfer Heat transfer PRESSURE GEOMETRY - FUEL FLOW - SPRAY Fuel injection pressure exit velocity: V spray /V Bernoulli ~ 0.9 Spray observation in optical Diesel research engine: Spray diameter fluctuation measurement to document spray targeting and spray fluctuation in far field bar Z = 15 mm 0 1 ms 2 spray diameter fluctuation 10th & 11th of March

11 PRESSURE GEOMETRY - FUEL FLOW - SPRAY 2. Spray interaction with in-cylinder gas Momentum transfer Heat transfer Length - time and Diameter - time shadow traces of Diesel sprays in an optical engine Spray observation in optical Diesel research engine: Start of Injection End of Injection Strahlschatten Spray shadow 800 bar 20 mm ms 2 Spray tip propagation and spray core length ms bar 800 bar 1500 bar Z = 15 mm Spray targeting and spray diameter (spray angle) fluctuations. Spray diameter fluctuation measurement to document spray targeting and spray fluctuation in far field Conclusion: high injection pressure stabilises spray targeting. Spray diameter fluctuations appear at ever higher frequency 10th & 11th of March

12 2. Spray interaction with in-cylinder gas Momentum transfer Heat transfer PRESSURE GEOMETRY - FUEL FLOW - SPRAY Spray in hot compressed in-cylinder gas Heat transfer from gas into spray with resultant fast expansion of spray vapor plume and self ignition T = 930 K p = 53 bar Schlieren imaging in optical research engine, 500 rpm 10th & 11th of March

13 2. Spray interaction with in-cylinder gas Momentum transfer Heat transfer PRESSURE GEOMETRY - FUEL FLOW - SPRAY P rail = 300 bar P rail = 800 bar P rail = 1100 bar Spray in hot compressed in-cylinder gas Spray core Spray vapor cloud Heat transfer from gas into spray with resultant fast expansion of spray vapor plume and self ignition Injection pressure enhances fuel vapor transport Average spray contours at 0.40 ms after SOI. Nozzle: 1x mm Schlieren imaging in optical research engine 10th & 11th of March

14 3. Ignition PRESSURE GEOMETRY - FUEL FLOW SPRAY EVAPORATION - IGNITION µs 0 µs 50 µs 100 µs 150 µs Ignition and spray flame interaction in optical engine, 85 mm bore, p = 60 bar Combustion chamber is externally illuminated, high speed camera records of one cycle. Time sequence shows sprays before ignition, combustion of premixed fuel vapor in blue flame pockets, and start of diffusion combustion Full glass optical piston 10th & 11th of March

15 3. Ignition PRESSURE GEOMETRY - FUEL FLOW SPRAY EVAPORATION - IGNITION Ignition and spray flame interaction in optical heavy duty engine, 127 mm bore, p = 153 bar 80 mm piston window dia. A Piston bottom window Time sequence shows combustion of premixed fuel vapor in blue flame pockets, and start of diffusion combustion Note that blue premixed flame is only visible at ignition for up to 100 µs (0,6 deg CA at 1000 rpm) 10th & 11th of March

16 INJECTION PRESSURE COMBUSTION 4. Premixed and diffusion flames Soot formation Soot oxidation Diesel combustion movie 10th & 11th of March

17 HD DIESEL OSCE WITH PISTON BOTTOM WINDOW Fired operation for 15 cycles 10th & 11th of March

18 HD DIESEL OSCE WITH PISTON BOTTOM WINDOW Topic: 20 bar IMEP 1400 rpm Fired operation for 15 cycles 10th & 11th of March

19 total soot - KL*area 4. Premixed and diffusion flames Soot formation Soot oxidation INJECTION PRESSURE COMBUSTION AIR UTILIZATION 14 x metal engine 500 bar 1000 bar 1500 bar 2000 bar Metal engine soot measurement: Lower FSN at higher injection pressure total soot (KL*area) In optical engine 500 bar optical engine flame evaluation shows Faster soot oxidation at higher injection pressure Soot oxidation needs flame (soot) air mixing Data show that injection pressure has significant influence on air utilization = soot oxidation. Injection at 2 500bar 1000bar CAD KL is evaluated from high speed deg CA flame movies with 2-color method How can this happen? 10th & 11th of March

20 INJECTION PRESSURE COMBUSTION 4. Premixed and diffusion flames Soot formation Soot oxidation How can it be that injection pressure improves air utilization? 10th & 11th of March

21 4. Premixed and diffusion flames Soot formation Soot oxidation HOW CAN INJECTION PRESSURE IMPROVE AIR UTILIZATION? 2000 bar near end of injection 2000 bar 10 deg CA after end of injection 2000 bar At ongoing injection Backflow of flames into combustion chamber center following spray vapor - flame reflection on piston bowl wall After end of injection Speed up of swirl motion in center of piston bowl 0 m/s 55 m/s 21 10th & 11th of March

22 4. Premixed and diffusion flames Soot formation Soot oxidation HOW CAN INJECTION PRESSURE IMPROVE AIR UTILIZATION? 2000 bar near end of injection 10 deg CA after end of injection 200 bar 2000 bar 200 bar 2000 bar A comparison with very low injection pressure Spray momentum is too small for effective interaction with reflecting piston bowl wall Conclusion 1 Injection pressure drives the flame back into areas of un-used air 0 m/s 55 m/s 22 10th & 11th of March

23 INJECTION PRESSURE COMBUSTION 4. Premixed and diffusion flames Soot formation Soot oxidation How can it be that injection pressure improves air utilization? 1. It introduces flame transport into areas with un-used air 2. And further: flame transport enhances turbulent motion 10th & 11th of March

24 5. Enhancing soot oxidation FLAME MOTION AND TURBULENT KINETIC ENERGY Flame (soot) transport Turbulence: data on local turbulent kinetic energy At 8,5 EOI 12,5 16,5 21,5 deg CA Flow field 500 bar, FSN = 1, bar FSN = 0,5 Significant rise of local turbulence with high injection pressure 10th & 11th of March

25 1000 bar FSN = 0,5 500 bar, FSN = 1,2 5. Enhancing soot oxidation Flame (soot) transport KINETIC ENERGY RELAXATION AFTER END OF INJECTION KE~ u x u y. 2 Flow field KE~ u x u y. 2 Kinetic energy vs CAD CAD Local Turbulent Kinetic Energy Turbulence and fast decay of turbulence at end of injection 10th & 11th of March

26 5. Enhancing soot oxidation KINETIC ENERGY RELAXATION AFTER END OF INJECTION KE~ u x u y bar KE~ u x 2 2 Soot + u y. formation2 Soot oxidation Turbulence is driver for soot oxygen mixing Soot transport and results in enhanced soot oxidation Note: high turbulence for effective soot oxidation is only available right at the end of injection. 10th & 11th of March

27 Flame - summary 6. How things come together pressure temperature flow Metal engine soot measurement: Lower FSN at higher injection pressure optical engine flame evaluation shows Faster soot oxidation at higher injection pressure Soot oxidation needs flame (soot) air mixing Data show that injection pressure has singificant influence on air utilization = soot oxidation. How can this happen? 1. Transport soot to meet with air 2. Use turbulence for fast soot air mixing Examples have shown that and how both, transport and turbulence, are controlled by fuel injection and spray momentum reflection on piston bowl walls. Effective soot oxidation must happen close to the end of injection to benefit from high temperature oxidation rates. 10th & 11th of March

28 7. Summary INJECTION PRESSURE AS A MEANS TO GUIDE AIR UTILIZATION IN DIESEL ENGINE COMBUSTION Spray: Spray turbulence and atomizaton are driven by cavitation Cavitation is controlled by shear and boundary layer flow under influence of local spray hole geometry At usual temperatures ( 100 C) and injection pressures ( bar) normal behaviour of Diesel sprays: liquid spray core of droplets and ligaments, fuel vapor and diffusion flame Flame: Temperature and pilot injection control ignition, soot formation in diffusion flame, Soot oxidation: Injection pressure is most effective to control flame transport and turbulent mixing for fast oxidation Analysis: in optical Diesel engines with realistic temperature, pressure and geometry parameters 10th & 11th of March

29 INJECTION PRESSURE AS A MEANS TO GUIDE AIR UTILIZATION IN DIESEL ENGINE COMBUSTION Thank you 10th & 11th of March

30 6 MINUTES TO STOP THE ENGINE, CLEAN THE COMBUSTION CHAMBER AND START AGAIN Diesel engine movie 10th & 11th of March

31 HD DIESEL OSCE WITH PISTON BOTTOM WINDOW Fired operation for 15 cycles 10th & 11th of March

32 HD DIESEL OSCE WITH PISTON BOTTOM WINDOW Topic: 20 bar IMEP 1400 rpm Fired operation for 15 cycles 10th & 11th of March

33 THE RISK OF GLASS DAMAGE MOUNTING PRESSURE TEMPERATURE INERTIA FORCES LOCAL CONTACT UNKNOWN 10th & 11th of March

34 1. Injection pressure - spray Internal flow is visualized in 2D model nozzle tests. Liquid into liquid injection (Diesel) PRESSURE GEOMETRY - FUEL FLOW - SPRAY liquid body 1 bar liquid P in = 400 bar needle Fuel flow is subject to cavitation in local shear and boundary layers. High cross flow velocity gradients force static pressure to drop below vapor pressure. Driving parameters are: Geometry Velocity gradients Pressure Vapor pressure of fuel White: liquid phase (Diesel) Black: gas phase (cavitation bubbles) at Diesel vapor pressure << 1 bar 10th & 11th of March

35 1. Injection pressure - spray Internal flow is visualized in 2D model nozzle tests. Liquid into liquid injection (Diesel) PRESSURE GEOMETRY - FUEL FLOW - SPRAY liquid body 1 bar liquid needle 30 bar P in = 400 bar Shear layer cavitation Fuel flow is subject to cavitation in local shear and boundary layers. High cross flow velocity gradients force static pressure to drop below vapor pressure. Driving parameters are: Geometry Velocity gradients Pressure Vapor pressure of fuel boundary layer cavitation White: liquid phase (Diesel) Black: gas phase (cavitation bubbles) at Diesel vapor pressure << 1 bar 10th & 11th of March