Effect of partial needle lift over Diesel Spray Development and combustionand combustion

Raul PayriRaul PayriCMT Motores Termicos, Universitat Politecnica de Valencia

Collaborators:Collaborators:Jaime Gimeno, Michele Bardi, Juan Pablo Viera, Jose Enrique del Rey

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INDEX• Direct acting injector

• Hydraulic characterization• Mass flow rate measurements

• Spray momentum flux measurements

• Liquid phase visualization• Experimental methodology

• Results

• Analysis

• Vapor phase visualization• Experimental methodology

• Results

• Combustion results

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• Conclusions

The injection system

• A direct acting injector has been employed Di t dl lift t l i bl d Direct needle lift control is enabled

Piezo stack

Direct actingCommon-rail high

pressure pump

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The injection system• The injector allows the control of the needle position as a

function of the charge applied to the piezo-stack

Needle lift = f(charge)

• Main characteristics of the nozzle

Injector featuresBrand ContinentalNozzle seat type micro-sac

Injector features

Nozzle seat type micro sacN orifice 7Spray Angle 158 ºOutlet diameter 0.156 mmK factor 1.5Discharge coefficient 0 81

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Discharge coefficient 0.81

IR – Test conditions Four injection pressures (30, 90, 150 and 200 MPa) Back pressure is kept at 5 MPa Long energizing time (ET) = 3200µs Long energizing time (ET) = 3200µs 6 different lifts, more information SAE 2011-01-1827

Zone studied

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IR measurements

Linear trendHIGH CHARGE

LOW CHARGENeedle lift varies with the pressure

LOW CHARGE

It is possible to see a linear behavior of mass flow rate with the It is possible to see a linear behavior of mass flow rate with the pressure drop for larger needle lifts (throttling effect on the needle seat)

At low charge the needle position does not vary only with the charge applied to the piezo-stack injector but also with the pressure possibly due to elastic deformations

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pressure, possibly due to elastic deformations

Mass flow vs %Charge

Mass flow tends to converge to a constant constant (infinity needle lift)

The max mass flow rate for each injection pressure tends toconverge to a constant value after the max. % of charge is applied

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Spray momentum measures

Similar trend as in IR measurements

A similar trend as in mass flow rate results

Similar trend as in IR measurements

Again, the influence of needle lift as a function of charge and pressure is clearly observed

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g p y

INDEX• Direct acting injector

• Hydraulic characterization• Mass flow rate measurements

• Spray momentum flux measurements

• Liquid phase visualization• Experimental methodology

• Results

• Analysis

• Vapor phase visualization• Experimental methodology

• Results

• Combustion results

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• Conclusions

The test rig

• A novel high temperature – high pressure test rig was employed to study liquid phase penetration in real Diesel engine thermodynamic condition

Chamber diameter: 200 mm

View of the injector from lateral optical access

View of the injector fromfrontal optical access

Window diameter: 128 mm

M bi t t t 1000 KMax ambient temperature: 1000 K

Max ambient pressure: 15 Mpa Global view of the testing section withti l

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Continuous gas flow through the chamber optical accesses

Liquid determination set-up

• Mie scattering technique to detect liquid phase spray

Camera: Phantom V12

Lens: Nikkor 50 mm – f/1.8

Shutter time: 3 µs

Frame rate: 20 kfpsFrame rate: 20 kfps

pix/mm: 7.1

Field of view: ~70 x 70 mm

Repetitions: 6

Light source: Xe-arc, (double)

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Processing method• Image sectorization: each spray sector is analyzed separately

• Background correction by subtractionBackground correction by subtraction

• 3% threshold of the dynamic range for threshold calculation (SAE 980809)

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Processing method• Moving polynomial average to

avoid experimental noise•The injection event has been divided in The injection event has been divided in time step of 10s

•For each time step ti a time window of For each time step ti a time window of ±150 s has been evaluated

•A linear fit of the experimental data present ym

p pin the time window has been performed

•The value yi of the fitted curve in ti has

LLm

(θm)been calculated (θm)

ti• Parametrization of the curve on

two parameters (LLm and θm)

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150 µs

Test planDiff t i j ti t t t d t th l ith diff t dl lift• Different injection parameters were tested together along with different needle lifts

• The different charge levels are referred to in a quantitative way (low/med/high)

• The test plan is the same for liquid and vapor phase visualization experimentsp q p p p

• More details liquid penetration (Study liquid length penetration results obtained with a direct acting piezo electric injector, Applied Energy , 2013, 106, 152 - 162)

• More details Vapor penetration (Needle lift profile influence on the vapor phase penetration for aMore details Vapor penetration (Needle lift profile influence on the vapor phase penetration for a prototype diesel direct acting piezoelectric injector , Fuel, 2013, 113, 257 - 265 )

Fuel Commercial Diesel

Energizing time 3200 µs

Injector coolant temperature 343 K

Ambient gas Nitrogen

Gas pressure 5 Mpa

Gas temperature 870 – 950 K

Injection pressure 60 – 150 Mpa

Pi t k h l d hi h

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Piezo stack charge low – med – high

LL Results (1/4) Effect of temperature and injection pressure

Pinj = 150 MPa. Ch% = high Tamb = 950K, Ch% = high

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LL Results (2/4) Effect of ambient temperature and injection pressure on LLm

• Liquid length follows the general Liquid length follows the general trends described in literature• Higher LL at lower

temperaturetemperature• Small effect of injection

pressure on LL (higher LL for high injection pressurehigh injection pressure

• An important effect of piezo stack charge level is noticed. Longer liquid length at high charge

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LL Results (4/4)Piezo stack charge was quantified with parameter

m

observed at different Prail

highChm

LLm observed at different Prail

Linear increase of LL with Lambda

LLm

decreases at higher charge and might bem decreases at higher charge and might be related with LL variations

m

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Discussion• From Pastor et al. (Fuel 87 pp2871-2885, 2008)

Ca: area coefficient

a

faop

C

CDKLL

tan

2 Do: orifice diameterρf: fuel densityρa: ambient densitya

mvC

2

tan ρa: ambient densityCmv: dependent on thermodynamic equilibrium between fuel and ambient gas

When needle lift is modified the parameters changing in the equation are only Ca (area coefficient) and (spray angle)only Ca (area coefficient) and (spray angle)

This theoretical equation was used to understand if variations in spray

opening angle and Ca can justify LL dependence to the charge level found experimentally

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Discussion• For each Tamb – Prail combination the high charge LL was used as

reference

• The experimental (continuous line) variations in LL were compared with the ones predicted (dashed line) by the equation using Ca and m

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INDEX• Direct acting injector

• Hydraulic characterization• Mass flow rate measurements

• Spray momentum flux measurements

• Liquid phase visualization• Experimental methodology

• Results

• Analysis

• Vapor phase visualization• Experimental methodology

• Results

• Combustion results

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• Conclusions

S hli i li ti t

Experimental methodologySchlieren visualization setup

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Sample videoShape = bootPrail = 150 MpaBp = 5 MpaBp 5 MpaT = 870 K

Frame rate = 14 834 fpsFrame rate = 14.834 fpsTime Step = 67 μsShutter time = 10 μs

10 mm

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Processing method

Each spray contour is processed separately for each time step and each sectortime step and each sector

Spray penetration (S) is calculated as the distancecalculated as the distance between the outlet orifice and the furthest point detected in the spray boundaryp y y

The spreading angle is calculated by interpolating two lines in the spray boundary, between 25% and 60% of the spray penetration, and forcing these interpolations to go through the outlet orifice

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Temperature effect

Vapor penetrationLiquid length

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Injection Pressure effect

Vapor penetrationLiquid length

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Charge effect (1/3)

Vapor penetrationVapor penetrationLiquid length

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Charge effect (2/3)

Vapor penetrationVapor penetrationLiquid length

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Charge effect (3/3)

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Charge effect (4/4)

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INDEX• Direct acting injector

• Hydraulic characterization• Mass flow rate measurements

• Spray momentum flux measurements

• Liquid phase visualization• Experimental methodology

• Results

• Analysis

• Vapor phase visualization• Experimental methodology

• Results

• Combustion results

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• Conclusions

Experimental methodologyCH*/OH* chemiluminescence imaging setup for ignition characterization

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CH*/OH* Raw images

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Experimental methodology Each spray is processed separately The maximum for each radial position is obtained

A i i fil i b i d i h An average intensity profile is obtained averaging the repetitions and the different sprays

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Experimental methodology The average intensity profile obtained from each time step is

condensed in a 3-axes contour map

In only one plot the timing, the location and the intensity of the radiation are presented

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Results (1/3) CH* location is strongly related to spray tip penetration

Oxygen concentration has a strong effect on OH* (but not on CH* )CH* OH*

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Results (2/3)

First and second stage ignition delay (SoCH and SoOH) have been measured under a wide range of test conditions

The observation of SoCH/SoOH dwell time confirms that SoCH is strictly linked with the fuel air/mixing and the thermodynamics of the mixture

The SoOH is also affected by the chemistry of the mixture (O2%)

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Results (3/3)

The second stage ignition timing (SoOH) has been compared for different injection typologies

The effect of injection pressure/needle

injection typologies

lift on ignition delay is very low

However an opposit trend can be observed when the mass flow rate is reduced either reducing the injection

th dl liftpressure or the needle lift

Thi it t d i b bl l t d This opposite trend is probably related to the increment in spreading angle related to the partial needle lift commented before

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commented before

INDEX• Direct acting injector

• Hydraulic characterization• Mass flow rate measurements

• Spray momentum flux measurements

• Liquid phase visualization• Experimental methodology

• Results

• Analysis

• Vapor phase visualization• Experimental methodology

• Results

• Combustion results

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• Conclusions

Conclusions (1/2)• Results show the effect of needle partial lift over injected mass flow

and spray momentum flux

• For large lifts the pressure drop occurs mainly in the hole while for small lifts the pressure drop occurs mainly in the needle seat

• The experimental results presented for the liquid penetration are consistent with what is found in the literature for the influence of Tamb and Pinj.

• An interesting relationship was found between steady liquid length (LLm) and charge level (needle lift)g ( )

• Possible causes for relationship between LL and needle lift: The local increase in velocity caused by the partial needle lift can change The local increase in velocity caused by the partial needle lift can changenon-axial component of the fuel velocity at the orifice outlet Increase in fuel temperature due to friction in the nozzle seat O t f it ti i th dl t

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Onset of cavitation in the needle seat

Conclusions (2/2)

• Gas temperature seems not to have an important effect on vaporpenetration (being the backpressure the same, changes in densityare very small) or spreading angle

• Partial needle lift allow to control also the vapor penetration (similarly• Partial needle lift allow to control also the vapor penetration (similarlyto injection pressure). The results also confirmed the effect of needlelift over spreading angle obtained in LL measurements.

• As the mass flow rate shows to be closely related to the spraypenetration rate the needle lift control-ability is a very powerful toolpenetration rate, the needle lift control ability is a very powerful toolto control the injection event as desired

• The modifications in the spray development are reflected in also in the combustion, showing a (slight) reduction in the ignition delay at reduced needle lift

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