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, 2015 | | 10th & 11th of March 2015| 1
MOTIVATION | | 10th & 11th of March 2015| 2
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 2015| 3
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 2015| 4
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 2015| 5
PRESSURE – GEOMETRY - FUEL FLOW - SPRAY 1. Injection pressure - 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 2003 | | 10th & 11th of March 2015| 6
PRESSURE – GEOMETRY - FUEL FLOW - SPRAY 1. Injection pressure - spray Internal flow is visualized in 2D model nozzle tests. Liquid into liquid injection (Diesel) P in = 400 bar liquid Fuel flow is subject to cavitation in local shear and boundary layers. needle needle High cross flow velocity gradients force static pressure to drop below vapor pressure. boundary layer Shear layer body cavitation cavitation Driving parameters are: Geometry • Velocity gradients • 1 bar 1 bar Pressure • liquid Vapor pressure of fuel • 30 bar boundary layer cavitation White: liquid phase (Diesel) Black: gas phase (cavitation bubbles) at Diesel vapor pressure << 1 bar | | 10th & 11th of March 2015| 7
PRESSURE – GEOMETRY - FUEL FLOW - SPRAY 1. Injection pressure - spray Internal flow is visualized in 2D model nozzle tests. Liquid into liquid injection (Diesel) 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. Measurements were done as Diesel fluid A B was just below cavitation limit Sharp (A) and round (B) inlet | | 10th & 11th of March 2015| 8
PRESSURE – GEOMETRY - FUEL FLOW - SPRAY 1. Injection pressure - spray Liquid into air: 2D model nozzle to see internal flow together with spray. Average of 30 events P in = 60 120 825 bar A nozzle flow – spray experiment: fuel 800 µm At high injection pressure we see Well developed cavitation down to nozzle hole exit • cavitation Atomizing spray with highly stable spray cone • angle 800 µm Note the dimensions: 0,8 mm nozzle hole + 0,8mm free spray spray air Conclusion: high injection pressure stabilises spray laminar cone angle near nozzle exit. turbulent turbulent and cavitating | | 10th & 11th of March 2015| 9
PRESSURE – GEOMETRY - FUEL FLOW - SPRAY 2. Spray interaction with in-cylinder gas Momentum transfer Heat transfer Fuel injection pressure Spray observation in optical Diesel research engine: exit velocity: V spray /V Bernoulli ~ 0.9 Spray diameter fluctuation measurement to document spray targeting and spray fluctuation in far field spray dia. - mm 1500 bar 2 0 Z = 15 mm -2 0 1 ms 2 spray diameter fluctuation | | 10th & 11th of March 2015| 10
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 Spray observation in optical an optical engine Diesel research engine: 2 500 bar Spray diameter fluctuation Start of Injection End of Injection 0 measurement to document spray 20 mm targeting and spray fluctuation in -2 far field 2 800 bar 0 10 -2 Conclusion: 1500 bar 2 Strahlschatten Spray shadow 800 bar 0 high injection pressure • 0 stabilises spray targeting. Z = 15 mm -2 Spray diameter fluctuations • 0 1 ms 2 0 1 ms 2 appear at ever higher frequency Spray tip propagation and spray core length. Spray targeting and spray diameter (spray angle) fluctuations. | | 10th & 11th of March 2015| 11
PRESSURE – GEOMETRY - FUEL FLOW - SPRAY 2. Spray interaction with in-cylinder gas Momentum transfer Heat transfer 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 2015| 12
PRESSURE – GEOMETRY - FUEL FLOW - SPRAY 2. Spray interaction with in-cylinder gas Momentum transfer Heat transfer P rail = 300 bar P rail = 800 bar P rail = 1100 bar Spray in hot compressed in-cylinder gas Heat transfer from gas into spray with Spray resultant core fast expansion of spray vapor plume • and self ignition • Injection pressure enhances fuel vapor • transport Spray vapor cloud Average spray contours at 0.40 ms after SOI. Nozzle: 1x 0.115 mm Schlieren imaging in optical research engine | | 10th & 11th of March 2015| 13
PRESSURE – GEOMETRY - FUEL FLOW – SPRAY – EVAPORATION - IGNITION 3. Ignition 0 µs 50 µs 100 µs 150 µs µs Time sequence shows Ignition and spray – flame interaction in sprays before ignition, • optical engine, 85 mm bore, p = 60 bar combustion of premixed fuel vapor in „ blue flame “ • Combustion chamber is externally pockets, illuminated, high speed camera records of and start of diffusion combustion one cycle. • Full glass optical piston | | 10th & 11th of March 2015| 14
PRESSURE – GEOMETRY - FUEL FLOW – SPRAY – EVAPORATION - IGNITION 3. 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 2015| 15
INJECTION PRESSURE – COMBUSTION 4. Premixed and diffusion flames Soot formation Soot oxidation Diesel combustion movie | | 10th & 11th of March 2015| 16
HD DIESEL OSCE WITH PISTON BOTTOM WINDOW Fired operation for 15 cycles | | 10th & 11th of March 2015| 17
HD DIESEL OSCE WITH PISTON BOTTOM WINDOW Topic: 20 bar IMEP Fired operation for 1400 rpm 15 cycles | | 10th & 11th of March 2015| 18
INJECTION PRESSURE – COMBUSTION – AIR UTILIZATION 4. Premixed and diffusion flames Soot formation Soot oxidation 4 x 10 14 „ metal engine “ 500 bar 1000 bar „ Metal engine “ soot measurement: 12 1500 bar Lower FSN at higher injection pressure • 2000 bar total soot - KL*area 10 „ optical engine “ flame evaluation shows total soot (KL*area) Faster soot oxidation at higher injection • pressure 8 6 Soot oxidation needs flame (soot) – air mixing In optical engine 1500 Data show that injection pressure has significant 4 influence on air utilization = soot oxidation. 500 bar 2000 1000 Injection at 2 How can this happen ? 500bar 1000bar 0 0 10 20 30 40 50 60 70 80 CAD deg CA KL is evaluated from high speed flame movies with 2-color method | | 10th & 11th of March 2015| 19
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 2015| 20
HOW CAN INJECTION PRESSURE IMPROVE 2000 bar AIR UTILIZATION? 4. Premixed and diffusion flames Soot formation Soot oxidation 10 deg CA after end of injection near end of injection 2000 bar 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 2015| 21
HOW CAN INJECTION PRESSURE IMPROVE 2000 bar AIR UTILIZATION? 4. Premixed and diffusion flames Soot formation Soot oxidation 10 deg CA after end of injection near 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 2015| 22
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 2015| 23
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