UTILIZATION IN DIESEL ENGINE COMBUSTION H. Dembinski, Scania AB - - PowerPoint PPT Presentation

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UTILIZATION IN DIESEL ENGINE COMBUSTION H. Dembinski, Scania AB - - PowerPoint PPT Presentation

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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,

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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

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MOTIVATION

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THE QUESTION

t = 0.2 ms aSOI

How can higher injection pressure end up with lower engine out soot ?

injection pressure / soot

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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 ?
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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

CONTENT

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  • 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 2003

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  • 1. Injection pressure - spray

Internal flow is visualized in 2D model nozzle tests. Liquid into liquid injection (Diesel) White: liquid phase (Diesel) Black: gas phase (cavitation bubbles) at Diesel vapor pressure << 1 bar

needle body 30 bar 1 bar 1 bar Pin= 400 bar needle

liquid liquid Shear layer cavitation boundary layer cavitation boundary 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

PRESSURE – GEOMETRY - FUEL FLOW - SPRAY

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  • 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 was just below cavitation limit

A B

Sharp (A) and round (B) inlet

PRESSURE – GEOMETRY - FUEL FLOW - SPRAY

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  • 1. Injection pressure - spray

Pin= 60 120 825 bar

laminar turbulent turbulent and cavitating

spray cavitation fuel 800 µm 800 µm air

Liquid into air: 2D model nozzle to see internal flow together with spray. Average of 30 events 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 Note the dimensions: 0,8 mm nozzle hole + 0,8mm free spray Conclusion: high injection pressure stabilises spray cone angle near nozzle exit.

PRESSURE – GEOMETRY - FUEL FLOW - SPRAY

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Fuel injection pressure

exit velocity: Vspray/VBernoulli ~ 0.9

1 ms 2

  • 2

2

Z = 15 mm

spray dia. - mm

1500 bar

spray diameter fluctuation Spray observation in optical Diesel research engine: Spray diameter fluctuation measurement to document spray targeting and spray fluctuation in far field

  • 2. Spray interaction with in-cylinder gas

Momentum transfer Heat transfer

PRESSURE – GEOMETRY - FUEL FLOW - SPRAY

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Length - time and Diameter - time shadow traces of Diesel sprays in an optical engine

Spray tip propagation and spray core length.

Strahlschatten

20 mm 10 1 ms 2

Start of Injection End of Injection Spray shadow 800 bar

Spray targeting and spray diameter (spray angle) fluctuations.

1 ms 2

  • 2

2

  • 2

2

  • 2

2

500 bar 800 bar 1500 bar

Z = 15 mm

Spray observation in optical Diesel research engine: 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

  • 2. Spray interaction with in-cylinder gas

Momentum transfer Heat transfer

PRESSURE – GEOMETRY - FUEL FLOW - SPRAY

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  • 2. Spray interaction with in-cylinder gas

Momentum transfer Heat transfer

Schlieren imaging in optical research engine, 500 rpm

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

PRESSURE – GEOMETRY - FUEL FLOW - SPRAY

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Prail = 300 bar Prail = 800 bar Prail = 1100 bar

Average spray contours at 0.40 ms after SOI. Nozzle: 1x 0.115 mm

  • 2. Spray interaction with in-cylinder gas

Momentum transfer Heat transfer

Schlieren imaging in optical research engine

Spray in hot compressed in-cylinder gas Heat transfer from gas into spray with resultant

  • fast expansion of spray vapor plume
  • and self ignition
  • Injection pressure enhances fuel vapor

transport

Spray core Spray vapor cloud

PRESSURE – GEOMETRY - FUEL FLOW - SPRAY

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  • 3. Ignition

Time sequence shows

  • sprays before ignition,
  • combustion of premixed fuel vapor in „blue flame“

pockets,

  • and start of diffusion combustion

Ignition and spray – flame interaction in

  • ptical engine, 85 mm bore, p = 60 bar

Combustion chamber is externally illuminated, high speed camera records of

  • ne cycle.

0 µs 50 µs 100 µs 150 µs µs

PRESSURE – GEOMETRY - FUEL FLOW – SPRAY – EVAPORATION - IGNITION

Full glass optical piston

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  • 3. Ignition

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) Ignition and spray – flame interaction in optical heavy duty engine, 127 mm bore, p = 153 bar

PRESSURE – GEOMETRY - FUEL FLOW – SPRAY – EVAPORATION - IGNITION

A

Piston bottom window

80 mm piston window dia.

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  • 4. Premixed and diffusion flames

Soot formation Soot oxidation

INJECTION PRESSURE – COMBUSTION

Diesel combustion movie

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HD DIESEL OSCE WITH PISTON BOTTOM WINDOW

Fired operation for 15 cycles

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Topic: 20 bar IMEP 1400 rpm

Fired operation for 15 cycles

HD DIESEL OSCE WITH PISTON BOTTOM WINDOW

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10 20 30 40 50 60 70 80 2 4 6 8 10 12 14 x 10

4

CAD total soot (KL*area) 500 bar 1000 bar 1500 bar 2000 bar

1000bar Injection at 500bar

deg CA total soot - KL*area 500 bar 1000 1500 2000

„metal engine“ In optical engine

  • 4. Premixed and diffusion flames

Soot formation Soot oxidation

„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 significant influence on air utilization = soot oxidation. How can this happen ?

KL is evaluated from high speed flame movies with 2-color method

INJECTION PRESSURE – COMBUSTION – AIR UTILIZATION

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  • 4. Premixed and diffusion flames

Soot formation Soot oxidation

How can it be that injection pressure improves air utilization ?

INJECTION PRESSURE – COMBUSTION

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2000 bar

21

2000 bar 0 m/s 55 m/s near end of injection 10 deg CA after end of injection 2000 bar

  • 4. Premixed and diffusion flames

Soot formation Soot oxidation 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

HOW CAN INJECTION PRESSURE IMPROVE AIR UTILIZATION?

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200 bar

2000 bar

22

2000 bar 0 m/s 55 m/s near end of injection 10 deg CA after end of injection 2000 bar 200 bar

  • 4. Premixed and diffusion flames

Soot formation Soot oxidation 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

HOW CAN INJECTION PRESSURE IMPROVE AIR UTILIZATION?

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  • 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

INJECTION PRESSURE – COMBUSTION

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FLAME MOTION AND TURBULENT KINETIC ENERGY

  • 5. Enhancing soot oxidation

Flame (soot) transport Flow field Turbulence: data on local turbulent kinetic energy

500 bar, FSN = 1,2 1000 bar FSN = 0,5

At 8,5 EOI 12,5 16,5 21,5 deg CA Significant rise of local turbulence with high injection pressure…

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KINETIC ENERGY RELAXATION AFTER END OF INJECTION

𝐿𝐹~ 𝑣𝑦

2 + 𝑣𝑧 2

2 . 𝐿𝐹~ 𝑣𝑦

2 + 𝑣𝑧 2

2 .

500 bar, FSN = 1,2 1000 bar FSN = 0,5 CAD

Kinetic energy vs CAD Local Turbulent Kinetic Energy

  • 5. Enhancing soot oxidation

Flame (soot) transport Flow field Turbulence

…and fast decay of turbulence at end of injection

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KINETIC ENERGY RELAXATION AFTER END OF INJECTION

𝐿𝐹~ 𝑣𝑦

2 + 𝑣𝑧 2

2 .

  • 5. Enhancing soot oxidation

2000 bar

Soot transport Turbulence is driver for soot – oxygen mixing… 𝐿𝐹~ 𝑣𝑦

2 + 𝑣𝑧 2

2 . …and results in enhanced soot oxidation

Soot formation Soot oxidation

Note: high turbulence for effective soot oxidation is only available right at the end of injection.

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„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 ?

Flame - summary

  • 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.
  • 6. How things come together

pressure temperature flow

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  • 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 ( 500 – 2500 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

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

Thank you

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6 MINUTES TO STOP THE ENGINE, CLEAN THE COMBUSTION CHAMBER AND START AGAIN

Diesel engine movie

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HD DIESEL OSCE WITH PISTON BOTTOM WINDOW

Fired operation for 15 cycles

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Topic: 20 bar IMEP 1400 rpm Fired operation for 15 cycles

HD DIESEL OSCE WITH PISTON BOTTOM WINDOW

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THE RISK OF GLASS DAMAGE

MOUNTING PRESSURE TEMPERATURE INERTIA FORCES LOCAL CONTACT UNKNOWN

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  • 1. Injection pressure - spray

Internal flow is visualized in 2D model nozzle tests. Liquid into liquid injection (Diesel) White: liquid phase (Diesel) Black: gas phase (cavitation bubbles) at Diesel vapor pressure << 1 bar

needle body 1 bar Pin= 400 bar

liquid liquid

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

PRESSURE – GEOMETRY - FUEL FLOW - SPRAY

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SLIDE 35

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  • 1. Injection pressure - spray

Internal flow is visualized in 2D model nozzle tests. Liquid into liquid injection (Diesel) White: liquid phase (Diesel) Black: gas phase (cavitation bubbles) at Diesel vapor pressure << 1 bar

needle body 30 bar 1 bar Pin= 400 bar

liquid liquid Shear layer cavitation boundary 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

PRESSURE – GEOMETRY - FUEL FLOW - SPRAY