Ruhr University BochumInstitute for Electrical Engineeringand Plasma TechnologyProf. Dr.-Ing. Peter Awakowicz

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Ignition of automotive HID lamps

Andre Bergnerbergner@aept.ruhr-uni-bochum.de

This work considers the ignition process of high intensity discharge (HID) lamps used for carheadlights. Due to their high background gas pressure of 15 bar xenon, ignition voltage becomesvery high. Without any ignition aid, the ignition voltage reaches values of the order of 20 kV. Currentresearch considers the possibility to reduce the ignition voltage by optimizing ignition aids, namelyantennas and the so-called outer-bulb discharge.

1 IntroductionSince many years, HID lamps are used in many fieldsof applications; one of these fields is car head lighting.A new generation of automotive HID lamps with areduced power input of 25 W helping to save energyis considered within this work. The lamps have aluminous flux of about 2000 lm to avoid automaticlevelling and headlamp wash systems. The D5 lampcombines burner, igniter and electronic controlled gear(ECG) in a compact chassis to make system small andlow in costs. This aims to bring HID head lighting tocars quipped with incandescent halogen lamps today.

Due to safety reasons, these lamps must run-upinstantaneously. Fast run-up is reached, amongstothers, with a high background gas pressure of about15 bar xenon in the cold state. The pressure is twoorders of magnitude higher than in lamps used forgeneral-lighting applications. The high filling pressurehas the disadvantage that ignition voltage increasessignificantly. Without any ignition aid, ignition voltagereaches values of about 20 kV. A high ignition voltageis disadvantageous since igniter electronics becomesmore complex and expensive. Therefore, a reductionof the ignition voltage is an aim of current research.There are several methods to reduce the ignition volt-age of HID lamps. For automotive HID lamps, weinvestigate the outer-bulb discharge, a dielectric barrierdischarge (DBD) within the outer bulb, and antennas.Antennas are conductive coatings or wires on the outerburner wall.

Figure 1: Photo of D5 lamp.

2 Investigated HID lampsThe lamps consist of an ellipsoidal shaped quartz tube,in which two tungsten electrodes are melted oppositelyto each other. The inter-electrode gap is about 4 mm,in which the light-producing arc takes place. Thelamp bulb is filled with about 15 bar xenon in the coldstate and further with a composition of metal halides,especially sodium and scandium iodine to adjust thelight properties, e.g. colour rendering index (CRI) andcorrelated colour temperature (CCT). Additionally, theyimprove the efficacy to 80-90 lm/W by inducing the

Ignition of automotive HID lamps

gas-phase emitter effect.A so-called model outer bulb is applied to vary the

inner bulb

model outer bulb

electricalcontacts

O-ring

clamping ring (PEEK)

return wire

KF 16 flange tovacuum pump andgas filling system

screw

Figure 2: Technical 3D drawing of the model outer-bulb.

gas type and gas pressure within the outer bulb. Atechnical 3D drawing of the model outer bulb is shownin figure 2. The geometry is comparable to the normalouter bulb of a commercial lamp. The model outerbulb consists of a quartz tube, having an additionalquartz pipe with a KF16 flange to connect it to apumping unit and a gas-filling system. The modelouter bulb is made of quartz to be able to withstandthe high thermal load produced by the lamp duringoperation.

3 DiagnosticsTo investigate the ignition of HID lamps used for carheadlights, several electrical and optical methods areused. The central element of the experimental setup isthe model outer bulb with the HID lamp described inthe previous section.The ignition voltage of the lamp is measured with ahigh voltage probe. It mainly consists of a capacitivevoltage divider with a division factor of 1000. Theignition current is measured with a passive currentprobe consisting of a Rogowski coil and an integratorcircuit (Pearson probe). Its conversion factor is 1 V/Aand has a rise time of 2 ns. Furthermore, the luminousflux coming from the lamp is recorded with a siliconphoto diode detecting the visible spectral range incombination with a transfer impedance amplifier witha conversion factor of 20 kV/A. The system supplies avoltage signal proportional to the detected light. Allelectrical signals are recorded with a four channel

digital oscilloscope having an analogue bandwidth of1 GHz. To observe the development of the outer bulbdischarge during ignition, an image of the lamp isfocused on an ICCD camera. By means of a trig-gered igniter and a pulse delay generator, the setupis synchronized. The pulse delay generator takes intoaccount delay times of the camera, measuring probesand cables.All measuring data, electrical signals measured withthe oscilloscope as well as the photos taken with theICCD camera are processed and saved by a PC using aLabVIEW program.

4 Selected resultsFigure 3 shows a measurement example of the ignitionof an automotive HID lamp (D5 lamp). The electricalmeasurements, namely the ignition voltage Uign, theignition current Iign and the photo current, representedby 2UPD, are shown in figure 3a. Additionally, thetrigger signal for the ICCD camera Utrigger is shownindicating the beginning of the exposure time, whereasthe corresponding ICCD image is presented in figure3b.

The ignition voltage represented by the blue curvestarts to rise after triggering the igniter. At t ≈ 130 nsthe voltage slew rate decreases indicating the ignitionof the outer-bulb DBD. The ignition of the DBD iscorrelated with an increase of the electrical current(red curve) and the photo diode signal (green curve).Black arrows indicate these moments in figure 3a. Thevoltage amplitude supplied to the lamp at this momentis defined as ignition voltage of the outer-bulb DBDUign,DBD. After that, the voltage ramp increases furtherbut with a reduced slew rate until the maximum isreached at t ≈ 160 ns. The inner bulb ignites atthis moment. The maximum voltage represents theignition voltage of the lamp Uign. Shortly after thatmoment, the increasing electrical current as well asthe increasing photo current indicates the breakdownwithin the inner bulb.Figure 3b presents an ICCD photo of the outer-bulbDBD at pouter = 5mbar argon in the outer bulb. Thepowered anode is located on the left and the groundedcathode on the right side. The exposure time texp is50 ns and begins before the DBD ignites as shownby two black bars in figure 3a. Therefore, the ICCDcamera records the whole phase, in which the DBDis active, and the exposure stops before the innerbulb breaks through. However, the beginning of theignition of the inner bulb is visible in figure 3b, i.ethe initiation of surface streamers can be seen. Thesesurface streamers propagate along the inner wall of the

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Ignition of automotive HID lamps

burner and form a closed discharge channel. If thepower supply to the discharge is further increased, anlight-producing arc discharge is formed.

ReferencesThis information are mainly taken from the followingpublications, in which further information on the topiccan be found:

1. Czichy M et al, 2008, J. Phys. D: Appl. Phys. 41144027

2. Bergner A et al, 2014, J. Phys. D: Appl. Phys. 47(accepted)

3. Bergner A et al, 2014, J. Phys. D: Appl. Phys. 47(submitted)

4. Bergner A et al, 2013, Minimizing the ignitionvoltage of automotive HID lamps using a DBDwithin the outer bulb, Proceedings of the 20th Sym-posium on Physics of Switching Arc, Nové Mesto naMorave, Czech Republic, pp. 21-25

5. Bergner A et al 2013, On the Reduction ofIgnition Voltage of HID Lamps by ConductiveCoatings, Proc. 18th Plansee-Seminar (Interna-tional Conference on Refractory Metals and HardMaterials), Reutte, Austria

6. Bergner A et al 2012, Minimizing the ignitionvoltage of automotive HID lamps by an opti-mized DBD ignition, Proc. 13th Int. Symp. onthe Science and Technology of Light Sources (Troy,NY) ed R Devonshire and G Zissis CP039 173-4

0 50 100 150 200 250-5

0

5

10

15

20

25

t / ns

Uign

/kV

Iign

/A

2UPD

/V

2Utrigger

/V

exposuretime ICCD

ignitionDBD

ignitionlamp

t = 50 nsexp

luminous fluxfrom DBD

trigger ICCD

pre-currentthrough DBD

(a)

DBD

DBDouter bulb

inner bulb return wire

pumping flange

poweredanode

groundedcathode

(b)

Figure 3: Exemplary electrical measurement (a) andcorresponding ICCD image (b) of the ignitionof an automotive HID lamp with an outer-bulb pressure of 5 mbar argon

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