D) Engine Combustion Optimization. A) Fundamentals of Sprays. B) Engine Applications of Sprays. C) Gas Injection. E) Intake Manifold Injection

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1 A) Fundamentals of Sprays / A very extensive experimental and computational project on in-cylinder injection via a liquid-only pulsating-poppet injector was completed with many new interesting developments (e.g. assessment of exciplex errors, liquid sheet computation, new way of comparing measurements and computations). The Sandia work of P. H. Paul was particularly useful. Paper A, pages 6 and 8, gives some highlights and Figure A shows a way of comparing computations with measurements by taking account in the computations of some of the limitations of the experimental technique (the figure caption is sufficiently explicative). B) Engine Applications of Sprays A detailed, space and time resolved experimental study of the equivalence ratio within the spark gap at spark time in a direct-injection engine using an air-assisted injector was completed. Among the interesting conclusions: At spark time, the ensemble-average equivalence ratio of the firing cycles is near 1, but for many combusting cycles and for some of the most efficient cycles that equivalence ratio is outside the flammability limits. Standard injection and ignition systems were used. Implication: A direct-injection stratified-charge engine can be made to ignite reliably without sophisticated ignition systems. The explanation for this behavior is the duration of the spark being longer than the space traveled by an eddy of integral scale going at the local flow velocity. The conclusion is firm because flow velocity and turbulence had previously been measured in the same engine. The exercise shows that, with systematic investigations, f m conclusions can be reached even about the difficult flow field of a direct-injection stratified-charge engine. Paper B, pages 233 and 234. Figure B. ~ C) Gas Injection Earlier computations of Diesel injection made a surprising prediction: A spray jet mixes faster than the corresponding gas jet because the former develops its turbulent boundary layer faster than the latter. A complex (dimensions of 1 pm, times.1 ms) experimental rig is still being developed. Also, an additional computational paper is being prepared. Nothing complete to report at this time. D) Engine Combustion Optimization Detailed and difficult comparisons with the incylinder data of Paper B are in progress. As always, reconciling computed with measured data in serious comparisons is always unnerving...but, ultimately, very informative. Task in progress, no results at this time. I E) Intake Manifold Injection A very nice study has been completed and a second one is in progress. In the completed study, measurements were made of UHC during the first two minutes from cold start and up to steady state. The study is unique in that a contemporary prototype engine (from Ford) was used and four fuel strategies were implemented, successively eliminating possible control processes. Thus, for the first time, we have some facts on which to base the presumed relative importance of factors such as spray

2 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government, Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty,expressor implied, or assumes any legal liabdity or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or repments that its use would not infringe privately owned rights. Reference herein to any specificcommercial product, pmcess, or service by trade name, trademark, manufacturer, or otherwise does not necessan ly constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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4 coarseness, wall wetting, mixing, wall and crevices, and oil and deposits. At this point one needs to read the abstract and/or the summary and conclusions of Paper E. As far as immediate relevance to applications is concerned, Figures El, E2 shows systematic reductions of cold start UHC emissions in going from a standard fuel-only injector to an air-forced injector and from gasoline to propane. We are now taking LIF images of gasoline on the intake-manifold walls of the same engine, from cold start to warm operation. Figures E3, E4, E5 define this task, show the engine intake, and give a set of wall liquid-fuel (first accumulating and then disappearing) using the standard fuel-only injector. We have also started with the air-forced injector. This LIF work will begin to provide some detailed information to complement the engineout measurements of Paper E. The following information may be helpful in connecting the images of Figure E4 to the engine details of Figure E5. Each of the image mosaics shows a white light image in the lower R.H comer to orient the viewer. The image is of the rear dividing wall of the port viewed through the D-shaped port from a position in the manifold slightly behind and to the right of the injector. The injector and bar are clearly visible in the detailed view of the manifold. This is the only port open during these experiments (high swirl configuration). The side-by-side pictures of the manifold are shown opened like the pages of a book. F) Advanced Experimental Techniques We are getting closer to obtaining the first quantitative exciplex vapor data in sprays from an air-assisted injector. What we learned about the limitations of the exciplex technique in the long and painful study of Chia-Fon Lee (of which Figure A is part) is being put to use in this new attempt. It is very interesting and should be completed within the next three months. We have been working for some time at making quantitative planar, single-shot Raman concentration measurements. We have made comparisons with direct numerical simulations of laminar jets. Again, we f i d that making quantitative measurements is not as easy as advertised. I am sending you some information (Figures F1, F2) and a pretty picture of a turbulent flame (Figure F3). PAPERS A. Bracco, F.V. "Transient Hollow-Cone Sprays," International Union of Theoretical and Applied Mechanics (IUTAM), 1994 Symposium on the Combustion of Droplets and Sprays, National Cheng Kung Univ., Tainan, Taiwan, December B. Ghandhi, J.B. and Bracco, F.V. "Fuel Distribution Effects on the Combustion of a Direct-Injection Stratified-Charge Engine," Societv of Automotive Engineers, 1995 Congress and Exposition, Paper 9546, February E. Fulcher, S.K., Gajdeczko, B.F., Felton, P.G. and Bracco, F.V., "The Effects of Fuel Atomization, Vaporization and Mixing on the Cold-Start UHC Emissions of a S.I. Engine with Intake-Manifold Injection," Societv of Automotive Ensineers, 1995 Fuels and Lubricants Meeting, October 1995.

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6 Equivalence Ratio I.O.5 Figure 8 Ensemble average fuel distribution, 3-pentanone fluorescence. Equivalence Ratio ~ 1..5 Figure 11 Laser-induced fluorescence images for six cycles displaying a lean mixture, but did combust. I. I Equivalence Ratio I.5 Figure 1 Laser-induced fluorescence images for the seven highest lmep cycles. 1.o.5 FM,

7 oo -8 6 so 86 4 Y 'Ooo 2 IO SO 5soo SO 6 Time (s) I1 12 Figure 15: E F K V injection UHC concentrations by class measured with FT-IR tn g IS SO Time (s) 35 E, 3C 1h r 1 1 I I I ' 4ooo 35 3 zsoo 3 4 SO 6 Time (s) = A 12. AcaylawMahanc zsoo V 2 e. Y 5 2 Figure 17: AFI/OV injection UHC concentfations by class measured with IrT-IR Figure 16: AFYCV injection UHC concentrations by class measured with FT-IR so IO SO 6 Time (s) 7 8 YO 1 11 Figure 19: Premixed propane UHC concentrations by class measured with FT-IR u SO 6 7 Timc (s) 8 YO 1 11.Figure 18: PM/OV injection UHC concentrations by class measured with FT-IR E( FIG, 12

8 EFUCV inj. A W V hj. AFWV in]. Fuel sysrun P W P V inj. Premixed Figure 14: Ratio of aye. UHC concentrations over the first 2 min. to warm engine concentrations (+5% uncertainty) sa 6 7.z3E n 6 3 g 2 6 % 1 W C V ij. A F K V inj. AFUoV bj. Fuucl S y S L a n Pfi'/oV inj. Prcdrul Figure 2: Cold-start BSHC by class measured with F'T-IR 13 WCVinj. AFUCVinj. AWVinj. Fuel systan PWtOVbj. Prunixsd Figure 21: Cold-start BSOFP by class measured with FT-IR

9 L.I.F. studv of liquid fuel in the intake manifold durinu cold-start Liquid fuel films in the intake manifold are excited using the third harmonic of the Nd:YAG laser (355nm). Fluorescence from a dye in the gasoline is imaged via a fiber-optic probe and recorded on a VCR during cold-start. The build-up of a liquid film during the first 25secs of the cold-start is observed followed by its disappearance after about 1 minutes as the engine warms up. Results have been obtained using conventional pintle-type port fuel injection. Further work is underway with Air-forced injection (AFI) which gives much better atomization, with a view to comparing the manifold wetting behavior of the two injection systems. These results will be used to interpret the UHC emissions measured on the same engine.

10 Manifold confiquration Side-view of manifold. Detail of split port in head. Detail of port in manifold.

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12 Planar, Single-Shot Raman Concentration Measurements Has the potential for 24 mapping of gas concentration. Unlike L.I.F., in the temperature range of interest for combustion, the Raman signal is proportional to concentration. Also has the potential for mapping the temperature field via the ratio of Stokes/Anti-Stokes signals. Due to low cross-section requires high laser pulse energy and an intensified camera. The ultimate application is a quantitative investigation of the spatial distribution of the charge in I.C. engines: - Charge stratification in direct injection engines. - Charge homogeneity in port injected engines.

13 t Current work Setup an experimental apparatus for 2D imaging employing no multipass cells. (Multipass configurations cannot be used for engine applications due to losses introduced by the e ng i ne w i ndo w s). To fully characterize the method for quantitative 2D imaging of fluid flow (sensitivity thresholds, dynamic range, S/N etc), laminar jet flow was imaged. The results were compared with DNS computations. The limitations of the method concerning the resolution of the structure in a turbulent reacting flow were evaluated. In particular the properties of the intensified cameras were investigated.

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