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

and side windows. The piping from the injection controlunit on the fuel rail to the injector is separated by a distributionblock which is axis-symmetric to the revolvable cover.This offers the advantage to adjust the spray location directlywith the rotatable injector so that the measurementposition for optical techniques can remain fixed.Fig.4"Injector-in-dummy" configuration.3. OPTICAL MEASUREMENT TECHNIQUES3.1 Shadow-imagingThe spray propagation inside the chamber has beenvisualized by means of an improved "Shadow-imaging" (15)method. The upper sequence of Figure 5 shows a series ofimages illustrating the ignition process of a two spray configurationat conditions of 9 MPa and 900 K in the spraycombustion chamber at start of injection. In this case, theignition is occurring within the observation area at a positionrather on the lee side of the sprays and combustion isthen spreading both towards their tips and the injector.These image series are based on a standard backgroundillumination with an arc lamp light source. Obviously, theflame luminescence is dominating the background illuminationonce the combustion is fully developed. The sensorof the camera gets overexposed and this clearly represents aproblem for the visualization of the spray in the late phase.A solution for this problem has been found in applyingan alternative illumination concept, consisting in apulsed diode laser (690 nm) light source. Due to the veryshort 50 ns laser pulse within a 1 µs exposure time of ahigh-speed CMOS-camera (20 kHz frame rate, 512x512pixel) in combination with an appropriate narrow band passfilter (CWL 689.1 nm, T 60%, FWHM 10.6 nm), a highsignal-to-noise ratio in the recordings is achieved. Due tothe short exposure time, the flame light is almost completelysuppressed and spray visualization becomes feasibleeven under reactive conditions. As a consequence, considerably"sharper" images are obtained and it is possible tocontinue observation of sprays even after ignition has takenplace. This is demonstrated in the lower sequence of Figure5, which refers to the same configuration and conditions asin the upper and where the propagation of the sprays remainsclearly detectable well beyond their ignition.3.2 Mie scatteringThe scattering of electromagnetic radiation by sphericalparticles is depending on the particle size relative to thelight wavelength λ – the term "Mie-scattering" is commonlyused for sizes larger than 10% of λ. In combustion diagnosticsespecially, (fuel) sprays and droplets fall into thissize range. Mie-scattering basically is an inverted shadow-imagingmethod so that for the investigated object noilluminated background is required.Figure 6 shows the Mie-scattering setup at the spraycombustion chamber. In order to have sufficient illuminationpower combined 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 operating at the same frequency.The laser beam itself has to be aligned so that its path isadjusted to 50% beam splitters dividing it into two beamswhich are expanded and shaped by a specific lens system toilluminate (around the camera) the desired observation areathrough the front window of the spray combustion chamberFig.6Nd:YLF laser beam alignment with front illumination toperform high-speed Mie-scattering spray recordings.Fig.5Shadow-imaging recordings with regular arc-lamp (toprow) and laser background light source (bottom row).4. FUNDAMENTAL INVESTIGATIONSAn extensive number of systematic shadow-imagingmeasurements for determining the spray evolution and ignitionbehaviour at various chamber conditions (3/6/9 MPa,930 K) and injection parameters (nozzle tip configurationsand fuels) have been performed (15) . The injection pressurehas been set to 1000 bar in order to assure comparable injectionbehaviour as in marine diesel engine applications.4.1 Qualitative spray behaviourFigure 7 shows the single-hole nozzle (∅ 0.875 mm)cases with spray orientation varying from counter-swirl,perpendicular to the swirl, co-swirl, and a co-swirl injector-co-axialorientation. The three lower left images originatefrom two-hole nozzle cases (counter-swirl to co-swirl)with identical orifice diameters (∅ 0.875 mm) and varyingangles between the individual sprays. The lower right imagerefers to a five spray case representative of injectorstypically used on engines of similar size with pronouncedorifice size distribution (decreasing from ∅ 0.975 mm to ∅0.675 mm with co-swirl orientation). The effect of spray

9 MPaHFOFig.11 Experimental and simulated spray evolution and density.ure 11 exemplarily gives a visual impression of an assembledmeasured spray compared to its simulated propagationand droplet shadow density (identical data processing)along the spray evolution path.In addition to the inert measurements for determiningspray morphology (penetration, cone angle) at evaporatinggas conditions, further extensive measurement campaignshave been performed for investigating the non-evaporatingbehavior at constant density (18) . As indicated in Figure 12(left) the injection spray at such conditions (non-reactive,non-evaporating) has been observed up to the chamber wall.On the right side of Figure 12 the deflection due to the swirlis recognizable.6 MPa9 MPaLFO6 MPaFig.13 Spray evolution with LFO and HFO at two differentchamber pressures at 900 K.5.1 Production engine fuel injectorsFigure 14 shows two exemplary images of a highspeed (20 kHz) injection recording based on front illuminationfor visualizing single sprays originating from the nozzletip of a genuine injector. The scattered light intensity isproportional to the droplet concentration and the square ofthe droplet diameter but a quantitative analysis (dropletsizes) is hardly possible. Nevertheless, the technique is ableto deliver a lot of information about the injection sprays andtheir evolution, such as penetration, cone angle, injectorquality (reproducibility, needle bouncing), and the detectionof the effective (hydraulic) injection start/end.Fig.12 Spray evolution at non-evaporating conditions.4.3 Initial studies of fuel quality impactFollowing initial experiments with HFO for validatingthe functionality and performance (e.g. reproducibility)of the setup with the separate HFO injection system, firstsets of regular measurements have been performed. In orderto allow the assessment of fuel quality effects, the spraybehavior and morphology has been investigated for thesame set of conditions – injection into air (reactive), chamberpressures 9/6/3 MPa at constant temperature (900K) –as already used in the LFO experiments. Figure 13 shows acomparison of spray propagation with the two fuel types forthe 9 and 6 MPa pressure cases. As expected, the penetrationof the sprays is largely similar; however, there seem tobe non-negligible differences in the primary breakup of thespray, leading to the establishment of a wider angle alreadyclose to the injector tip. This also has an effect on the ignitionlocation, as can be recognized from this data. It remainsto be seen if this is a general pattern or rather a consequenceof factors that are not yet entirely understood. Forthis purpose, in addition to the measurement methods usedso far, future investigations will also feature advanced techniquessuch as flame emission spectroscopy.5. COMPONENT TESTSThe versatility of the spray combustion chamber canalso be used to test components (e.g. injectors) or to investigatethe functionality of subsystems at realistic conditions.Fig.14 Preliminary front illumination visualization tests of originalinjection nozzle tips.5.2 Lubricant injectorsAnother important issue related to 2-stroke marinediesel engine operation is the performance of the cylinderlubricating system. For systems based on the injection ofthe lubricant (Figure 15), their performance is dependent ona variety of design (e.g. number of orifices, diameter in theFig.15 Scheme cylinder lubricating system (right) and preliminarylube oil visualization at different conditions (left).

ange of 0.2 – 1.0 mm) and operational (e.g. injection pressurebetween 20 bar and 80 bar) parameters, which alsoneed to be optimized by means of appropriate tests. For thispurpose, such prototype system has been mounted on thespray combustion chamber and first visualizations of thelube oil jet propagation have been realized (Figure 15 left).6. CONCLUSIONS AND OUTLOOKA new experimental facility allowing the investigationof spray and combustion processes at conditions typicalof large 2-stroke diesel engines has been put to productiveuse. The results yield valuable insight into the behaviourof individual as well as pairs or groups of sprays atrelevant conditions in terms of pressure, temperature andflow pattern at start of injection. With the recent addition ofa separate injection system for HFO, the impact of fuelquality, including customary marine fuels, can now be assessedin more detail. The results are thoroughly analyzedfor generating relevant reference data for CFD model developmentand the validation against these data has alreadybrought about clear improvements of the predictive qualityof CFD simulations. However, the potential of the experimentalfacility goes well beyond this classical application.It could be shown that it is equally suited for testing of keyengine components such as fuel or lube oil injectors – itshighly versatile design lends itself for a big variety of applications.Therefore, it will be employed both for morefundamental investigations, including also more advancedexperimental techniques for spray investigations, and in thecontext of product development by performing dedicatedcomponent performance and system optimization tests.ACKNOWLEDGMENTSThe present work has been conducted as part of theHERCULES-β project within EC's 7th Framework Program,Contract SCP7-GA-2008-217878. Financial 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 spray and combustion visualization in atransparent model diesel engine", SAE 1999-01-3648,(1999).(2) Balles A., Heywood J.B., "Fuel-air mixing and dieselcombustion in a rapid compression machine. SAE880206, (1988).(3) Pikett L.M., Siebers D.L., "Soot in diesel fuel jets: effectsof ambient temperature, ambient density, and injectionpressure", Combust. Flame, 138, (2004), pp.114–135.(4) Buchholz B., Pittermann R., Niendorf M., "Measuresto Reduce Smoke and Particulate Emissions from MarineDiesel Engines using Compact Common Rail Injectors"",CIMAC Congress (Vienna, Austria), (2007),No. 129.(5) Fink C., Frobenius M., Meindl E., Harndorf H., "Experimentaland Numerical Analysis of Marine Diesel EngineInjection Sprays under Cold and EvaporativeConditions ", ICLASS Conference (Vail, USA), (2009),No. 222.(6) Tajima H., Kunimitsu M., Sugiura K., Tsuru D., "Developmentof High-Efficiency Gas Engine throughObservation and Simulation of Knocking Phenomena",CIMAC Congress (Bergen, Norway), (2010), No. 213.(7) Takeda A., Nakatani H., Shimizu E., Ura T., Kato T.,Suzuki D., Miyano H., "The ignition and the combustionquality by FIA (Fuel Ignition Analyzer) of actualMFO and the countermeasure against the MFO withinferior quality", CIMAC Congress (Vienna, Austria),(2007), No. 199.(8) Tomita E., Yamaguchi A., Takeuchi T., Yamamoto Y.,Morinaka K., "Optical Combustion Analyzer (OCA)for Evaluation of Combustion Characteristics of BunkerFuel Oils", CIMAC Congress (Bergen, Norway),(2010), No. 247.(9) Fink C., Buchholz B., Niendorf M., Harndorf H., "InjectionSpray Analyses from Medium Speed Enginesusing Marine Fuels", ILASS Conference (Como, Italy),(2008), No. 102.(10) Okada H., Tsukamoto T., Ohtsuka T. 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R., "Structure of High PressureFuel Sprays", SAE 870598, (1987).(18) Von Rotz B., Herrmann K., Weisser G., Cattin M.,Bolla M., and Boulouchos K., "Impact of Evaporation,Swirl and Fuel Quality on the Characteristics of Spraystypical of Large 2-Stroke Marine Diesel Engine CombustionSystems", ILASS Conference (Estoril, Portugal),(2011).