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"spray combustion chamber" facility for investigations in relation to ...


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and side w<strong>in</strong>dows. The pip<strong>in</strong>g from the <strong>in</strong>jection controlunit on the fuel rail <strong>to</strong> the <strong>in</strong>jec<strong>to</strong>r is separated by a distributionblock which is axis-symmetric <strong>to</strong> the revolvable cover.This offers the advantage <strong>to</strong> adjust the <strong>spray</strong> location directlywith the rotatable <strong>in</strong>jec<strong>to</strong>r so that the measurementposition <strong>for</strong> optical techniques can rema<strong>in</strong> fixed.Fig.4"Injec<strong>to</strong>r-<strong>in</strong>-dummy" configuration.3. OPTICAL MEASUREMENT TECHNIQUES3.1 Shadow-imag<strong>in</strong>gThe <strong>spray</strong> propagation <strong>in</strong>side the chamber has beenvisualized by means of an improved "Shadow-imag<strong>in</strong>g" (15)method. The upper sequence of Figure 5 shows a series ofimages illustrat<strong>in</strong>g the ignition process of a two <strong>spray</strong> configurationat conditions of 9 MPa and 900 K <strong>in</strong> the <strong>spray</strong><strong>combustion</strong> chamber at start of <strong>in</strong>jection. In this case, theignition is occurr<strong>in</strong>g with<strong>in</strong> the observation area at a positionrather on the lee side of the <strong>spray</strong>s and <strong>combustion</strong> isthen spread<strong>in</strong>g both <strong>to</strong>wards their tips and the <strong>in</strong>jec<strong>to</strong>r.These image series are based on a standard backgroundillum<strong>in</strong>ation with an arc lamp light source. Obviously, theflame lum<strong>in</strong>escence is dom<strong>in</strong>at<strong>in</strong>g the background illum<strong>in</strong>ationonce the <strong>combustion</strong> is fully developed. The sensorof the camera gets overexposed and this clearly represents aproblem <strong>for</strong> the visualization of the <strong>spray</strong> <strong>in</strong> the late phase.A solution <strong>for</strong> this problem has been found <strong>in</strong> apply<strong>in</strong>gan alternative illum<strong>in</strong>ation concept, consist<strong>in</strong>g <strong>in</strong> apulsed diode laser (690 nm) light source. Due <strong>to</strong> the veryshort 50 ns laser pulse with<strong>in</strong> a 1 µs exposure time of ahigh-speed CMOS-camera (20 kHz frame rate, 512x512pixel) <strong>in</strong> comb<strong>in</strong>ation with an appropriate narrow band passfilter (CWL 689.1 nm, T 60%, FWHM 10.6 nm), a highsignal-<strong>to</strong>-noise ratio <strong>in</strong> the record<strong>in</strong>gs is achieved. Due <strong>to</strong>the short exposure time, the flame light is almost completelysuppressed and <strong>spray</strong> visualization becomes feasibleeven under reactive conditions. As a consequence, considerably"sharper" images are obta<strong>in</strong>ed and it is possible <strong>to</strong>cont<strong>in</strong>ue observation of <strong>spray</strong>s even after ignition has takenplace. This is demonstrated <strong>in</strong> the lower sequence of Figure5, which refers <strong>to</strong> the same configuration and conditions as<strong>in</strong> the upper and where the propagation of the <strong>spray</strong>s rema<strong>in</strong>sclearly detectable well beyond their ignition.3.2 Mie scatter<strong>in</strong>gThe scatter<strong>in</strong>g of electromagnetic radiation by sphericalparticles is depend<strong>in</strong>g on the particle size relative <strong>to</strong> thelight wavelength λ – the term "Mie-scatter<strong>in</strong>g" is commonlyused <strong>for</strong> sizes larger than 10% of λ. In <strong>combustion</strong> diagnosticsespecially, (fuel) <strong>spray</strong>s and droplets fall <strong>in</strong><strong>to</strong> thissize range. Mie-scatter<strong>in</strong>g basically is an <strong>in</strong>verted shadow-imag<strong>in</strong>gmethod so that <strong>for</strong> the <strong>in</strong>vestigated object noillum<strong>in</strong>ated background is required.Figure 6 shows the Mie-scatter<strong>in</strong>g setup at the <strong>spray</strong><strong>combustion</strong> chamber. In order <strong>to</strong> have sufficient illum<strong>in</strong>ationpower comb<strong>in</strong>ed with a high laser pulse frequency, aNd:YLF laser was employed. It provides a 20 kHz repetitionrate with very short laser pulses (ns) of sufficientenergy which can be synchronized with the exposure timeof the high-speed camera operat<strong>in</strong>g at the same frequency.The laser beam itself has <strong>to</strong> be aligned so that its path isadjusted <strong>to</strong> 50% beam splitters divid<strong>in</strong>g it <strong>in</strong><strong>to</strong> two beamswhich are expanded and shaped by a specific lens system <strong>to</strong>illum<strong>in</strong>ate (around the camera) the desired observation areathrough the front w<strong>in</strong>dow of the <strong>spray</strong> <strong>combustion</strong> chamberFig.6Nd:YLF laser beam alignment with front illum<strong>in</strong>ation <strong>to</strong>per<strong>for</strong>m high-speed Mie-scatter<strong>in</strong>g <strong>spray</strong> record<strong>in</strong>gs.Fig.5Shadow-imag<strong>in</strong>g record<strong>in</strong>gs with regular arc-lamp (<strong>to</strong>prow) and laser background light source (bot<strong>to</strong>m row).4. FUNDAMENTAL INVESTIGATIONSAn extensive number of systematic shadow-imag<strong>in</strong>gmeasurements <strong>for</strong> determ<strong>in</strong><strong>in</strong>g the <strong>spray</strong> evolution and ignitionbehaviour at various chamber conditions (3/6/9 MPa,930 K) and <strong>in</strong>jection parameters (nozzle tip configurationsand fuels) have been per<strong>for</strong>med (15) . The <strong>in</strong>jection pressurehas been set <strong>to</strong> 1000 bar <strong>in</strong> order <strong>to</strong> assure comparable <strong>in</strong>jectionbehaviour as <strong>in</strong> mar<strong>in</strong>e diesel eng<strong>in</strong>e applications.4.1 Qualitative <strong>spray</strong> behaviourFigure 7 shows the s<strong>in</strong>gle-hole nozzle (∅ 0.875 mm)cases with <strong>spray</strong> orientation vary<strong>in</strong>g from counter-swirl,perpendicular <strong>to</strong> the swirl, co-swirl, and a co-swirl <strong>in</strong>jec<strong>to</strong>r-co-axialorientation. The three lower left images orig<strong>in</strong>atefrom two-hole nozzle cases (counter-swirl <strong>to</strong> co-swirl)with identical orifice diameters (∅ 0.875 mm) and vary<strong>in</strong>gangles between the <strong>in</strong>dividual <strong>spray</strong>s. The lower right imagerefers <strong>to</strong> a five <strong>spray</strong> case representative of <strong>in</strong>jec<strong>to</strong>rstypically used on eng<strong>in</strong>es of similar size with pronouncedorifice size distribution (decreas<strong>in</strong>g from ∅ 0.975 mm <strong>to</strong> ∅0.675 mm with co-swirl orientation). The effect of <strong>spray</strong>

9 MPaHFOFig.11 Experimental and simulated <strong>spray</strong> evolution and density.ure 11 exemplarily gives a visual impression of an assembledmeasured <strong>spray</strong> compared <strong>to</strong> its simulated propagationand droplet shadow density (identical data process<strong>in</strong>g)along the <strong>spray</strong> evolution path.In addition <strong>to</strong> the <strong>in</strong>ert measurements <strong>for</strong> determ<strong>in</strong><strong>in</strong>g<strong>spray</strong> morphology (penetration, cone angle) at evaporat<strong>in</strong>ggas conditions, further extensive measurement campaignshave been per<strong>for</strong>med <strong>for</strong> <strong>in</strong>vestigat<strong>in</strong>g the non-evaporat<strong>in</strong>gbehavior at constant density (18) . As <strong>in</strong>dicated <strong>in</strong> Figure 12(left) the <strong>in</strong>jection <strong>spray</strong> at such conditions (non-reactive,non-evaporat<strong>in</strong>g) has been observed up <strong>to</strong> the chamber wall.On the right side of Figure 12 the deflection due <strong>to</strong> the swirlis recognizable.6 MPa9 MPaLFO6 MPaFig.13 Spray evolution with LFO and HFO at two differentchamber pressures at 900 K.5.1 Production eng<strong>in</strong>e fuel <strong>in</strong>jec<strong>to</strong>rsFigure 14 shows two exemplary images of a highspeed (20 kHz) <strong>in</strong>jection record<strong>in</strong>g based on front illum<strong>in</strong>ation<strong>for</strong> visualiz<strong>in</strong>g s<strong>in</strong>gle <strong>spray</strong>s orig<strong>in</strong>at<strong>in</strong>g from the nozzletip of a genu<strong>in</strong>e <strong>in</strong>jec<strong>to</strong>r. The scattered light <strong>in</strong>tensity isproportional <strong>to</strong> the droplet concentration and the square ofthe droplet diameter but a quantitative analysis (dropletsizes) is hardly possible. Nevertheless, the technique is able<strong>to</strong> deliver a lot of <strong>in</strong><strong>for</strong>mation about the <strong>in</strong>jection <strong>spray</strong>s andtheir evolution, such as penetration, cone angle, <strong>in</strong>jec<strong>to</strong>rquality (reproducibility, needle bounc<strong>in</strong>g), and the detectionof the effective (hydraulic) <strong>in</strong>jection start/end.Fig.12 Spray evolution at non-evaporat<strong>in</strong>g conditions.4.3 Initial studies of fuel quality impactFollow<strong>in</strong>g <strong>in</strong>itial experiments with HFO <strong>for</strong> validat<strong>in</strong>gthe functionality and per<strong>for</strong>mance (e.g. reproducibility)of the setup with the separate HFO <strong>in</strong>jection system, firstsets of regular measurements have been per<strong>for</strong>med. In order<strong>to</strong> allow the assessment of fuel quality effects, the <strong>spray</strong>behavior and morphology has been <strong>in</strong>vestigated <strong>for</strong> thesame set of conditions – <strong>in</strong>jection <strong>in</strong><strong>to</strong> air (reactive), chamberpressures 9/6/3 MPa at constant temperature (900K) –as already used <strong>in</strong> the LFO experiments. Figure 13 shows acomparison of <strong>spray</strong> propagation with the two fuel types <strong>for</strong>the 9 and 6 MPa pressure cases. As expected, the penetrationof the <strong>spray</strong>s is largely similar; however, there seem <strong>to</strong>be non-negligible differences <strong>in</strong> the primary breakup of the<strong>spray</strong>, lead<strong>in</strong>g <strong>to</strong> the establishment of a wider angle alreadyclose <strong>to</strong> the <strong>in</strong>jec<strong>to</strong>r tip. This also has an effect on the ignitionlocation, as can be recognized from this data. It rema<strong>in</strong>s<strong>to</strong> be seen if this is a general pattern or rather a consequenceof fac<strong>to</strong>rs that are not yet entirely unders<strong>to</strong>od. Forthis purpose, <strong>in</strong> addition <strong>to</strong> the measurement methods usedso far, future <strong><strong>in</strong>vestigations</strong> will also feature advanced techniquessuch as flame emission spectroscopy.5. COMPONENT TESTSThe versatility of the <strong>spray</strong> <strong>combustion</strong> chamber canalso be used <strong>to</strong> test components (e.g. <strong>in</strong>jec<strong>to</strong>rs) or <strong>to</strong> <strong>in</strong>vestigatethe functionality of subsystems at realistic conditions.Fig.14 Prelim<strong>in</strong>ary front illum<strong>in</strong>ation visualization tests of orig<strong>in</strong>al<strong>in</strong>jection nozzle tips.5.2 Lubricant <strong>in</strong>jec<strong>to</strong>rsAnother important issue related <strong>to</strong> 2-stroke mar<strong>in</strong>ediesel eng<strong>in</strong>e operation is the per<strong>for</strong>mance of the cyl<strong>in</strong>derlubricat<strong>in</strong>g system. For systems based on the <strong>in</strong>jection ofthe lubricant (Figure 15), their per<strong>for</strong>mance is dependent ona variety of design (e.g. number of orifices, diameter <strong>in</strong> theFig.15 Scheme cyl<strong>in</strong>der lubricat<strong>in</strong>g system (right) and prelim<strong>in</strong>arylube oil visualization at different conditions (left).

ange of 0.2 – 1.0 mm) and operational (e.g. <strong>in</strong>jection pressurebetween 20 bar and 80 bar) parameters, which alsoneed <strong>to</strong> be optimized by means of appropriate tests. For thispurpose, such pro<strong>to</strong>type system has been mounted on the<strong>spray</strong> <strong>combustion</strong> chamber and first visualizations of thelube oil jet propagation have been realized (Figure 15 left).6. CONCLUSIONS AND OUTLOOKA new experimental <strong>facility</strong> allow<strong>in</strong>g the <strong>in</strong>vestigationof <strong>spray</strong> and <strong>combustion</strong> processes at conditions typicalof large 2-stroke diesel eng<strong>in</strong>es has been put <strong>to</strong> productiveuse. The results yield valuable <strong>in</strong>sight <strong>in</strong><strong>to</strong> the behaviourof <strong>in</strong>dividual as well as pairs or groups of <strong>spray</strong>s atrelevant conditions <strong>in</strong> terms of pressure, temperature andflow pattern at start of <strong>in</strong>jection. With the recent addition ofa separate <strong>in</strong>jection system <strong>for</strong> HFO, the impact of fuelquality, <strong>in</strong>clud<strong>in</strong>g cus<strong>to</strong>mary mar<strong>in</strong>e fuels, can now be assessed<strong>in</strong> more detail. The results are thoroughly analyzed<strong>for</strong> generat<strong>in</strong>g relevant reference data <strong>for</strong> CFD model developmentand the validation aga<strong>in</strong>st these data has alreadybrought about clear improvements of the predictive qualityof CFD simulations. However, the potential of the experimental<strong>facility</strong> goes well beyond this classical application.It could be shown that it is equally suited <strong>for</strong> test<strong>in</strong>g of keyeng<strong>in</strong>e components such as fuel or lube oil <strong>in</strong>jec<strong>to</strong>rs – itshighly versatile design lends itself <strong>for</strong> a big variety of applications.There<strong>for</strong>e, it will be employed both <strong>for</strong> morefundamental <strong><strong>in</strong>vestigations</strong>, <strong>in</strong>clud<strong>in</strong>g also more advancedexperimental techniques <strong>for</strong> <strong>spray</strong> <strong><strong>in</strong>vestigations</strong>, and <strong>in</strong> thecontext of product development by per<strong>for</strong>m<strong>in</strong>g dedicatedcomponent per<strong>for</strong>mance and system optimization tests.ACKNOWLEDGMENTSThe present work has been conducted as part of theHERCULES-β project with<strong>in</strong> EC's 7th Framework Program,Contract SCP7-GA-2008-217878. F<strong>in</strong>ancial support by theSwiss Federal Office of Energy SFOE Contract 154269,Project 103241) is gratefully acknowledged.REFERENCES(1) Bruneaux G., Verhoeven D., Baritaud T., "High pressurediesel <strong>spray</strong> and <strong>combustion</strong> visualization <strong>in</strong> atransparent model diesel eng<strong>in</strong>e", SAE 1999-01-3648,(1999).(2) Balles A., Heywood J.B., "Fuel-air mix<strong>in</strong>g and diesel<strong>combustion</strong> <strong>in</strong> a rapid compression mach<strong>in</strong>e. SAE880206, (1988).(3) Pikett L.M., Siebers D.L., "Soot <strong>in</strong> diesel fuel jets: effectsof ambient temperature, ambient density, and <strong>in</strong>jectionpressure", Combust. Flame, 138, (2004), pp.114–135.(4) Buchholz B., Pittermann R., Niendorf M., "Measures<strong>to</strong> Reduce Smoke and Particulate Emissions from Mar<strong>in</strong>eDiesel Eng<strong>in</strong>es us<strong>in</strong>g Compact Common Rail Injec<strong>to</strong>rs"",CIMAC Congress (Vienna, Austria), (2007),No. 129.(5) F<strong>in</strong>k C., Frobenius M., Me<strong>in</strong>dl E., Harndorf H., "Experimentaland Numerical Analysis of Mar<strong>in</strong>e Diesel Eng<strong>in</strong>eInjection Sprays under Cold and EvaporativeConditions ", ICLASS Conference (Vail, USA), (2009),No. 222.(6) Tajima H., Kunimitsu M., Sugiura K., Tsuru D., "Developmen<strong>to</strong>f High-Efficiency Gas Eng<strong>in</strong>e throughObservation and Simulation of Knock<strong>in</strong>g Phenomena",CIMAC Congress (Bergen, Norway), (2010), No. 213.(7) Takeda A., Nakatani H., Shimizu E., Ura T., Ka<strong>to</strong> T.,Suzuki D., Miyano H., "The ignition and the <strong>combustion</strong>quality by FIA (Fuel Ignition Analyzer) of actualMFO and the countermeasure aga<strong>in</strong>st the MFO with<strong>in</strong>ferior quality", CIMAC Congress (Vienna, Austria),(2007), No. 199.(8) Tomita E., Yamaguchi A., Takeuchi T., Yamamo<strong>to</strong> Y.,Mor<strong>in</strong>aka K., "Optical Combustion Analyzer (OCA)<strong>for</strong> Evaluation of Combustion Characteristics of BunkerFuel Oils", CIMAC Congress (Bergen, Norway),(2010), No. 247.(9) F<strong>in</strong>k C., Buchholz B., Niendorf M., Harndorf H., "InjectionSpray Analyses from Medium Speed Eng<strong>in</strong>esus<strong>in</strong>g Mar<strong>in</strong>e Fuels", ILASS Conference (Como, Italy),(2008), No. 102.(10) Okada H., Tsukamo<strong>to</strong> T., Ohtsuka T. 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