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A Study of Fluid Flow and Combustion with Variable Valve Timing

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A Study of Fluid Flow and Combustion with Variable Valve Timing ^9907007 INSTITUTIONEN FOR VARME- OCH KRAFTTEKNIK FORBRANNINGSMOTORER LUNDS TEKNISKA HOGSKOLA A Study of Fluid Flow and Combustion with Variable Valve Timing by Fredrik Soderberg fpp 2-5 1993 OSTI Thesis for degree of Licentiate of Engineering ISRN LUTMDN/TMHT—98/7029--SE DIVISION OF COMBUSTION ENGINES DEPARTMENT OF HEAT AND POWER ENGINEERING LUND INSTITUTE OF TECHNOLOGY P.O. BOX 118, S-221 00 LUND 1998 SWEDEN DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. A Study of Fluid Flow and Combustion with Variable Valve Timing by Fredrik Soderberg Division of Combustion Engines Department of Heat and PowerEngineering Lund Institute of Technology October 1998 List of papers The papers included in this thesis are listed in chronological order: 1. The Effect of Valve Strategy on In-Cylinder Flow and Combustion by Bengt Johansson and Fredrik Soderberg, SAE paper 960582. This paper was presented at the SAE Congress and Exposition Feb. 1996 in Detroit, Michigan by Bengt Johansson. 2. Wavelet Analysis of In-Cylinder LDV Velocity Measurements by Bengt Lindoff, Magnus Wiktorsson, Fredrik Soderberg, Bengt Johansson, SAE paper 961921. This paper was presented at the SAE Fall Fuels and Lubricants Meeting and Exposition Oct. 1996 in San Antonio, Texas by Magnus Wiktorsson. 3. Fluid Flow and Combustion with Early or Late Inlet Valve Closing by Fredrik Soderberg and Bengt Johansson, SAE paper 972937. Approved for SAE Transactions 1997. This paper was presented by Fredrik Soderberg at SAE Fall Fuels and Lubricants Meeting and Exposition Oct. 1997 in Tulsa, Oklahoma. 4. Wavelet Analysis of In-Cylinder LDV Measurements and Correlation Against Heat-Release by Fredrik Soderberg, Bengt Johansson, Magnus Wiktorsson and Bengt Lindoff, SAE paper 980483. This paper was presented by Fredrik Soderberg at the SAE Congress and Exposition Feb. 1998 in Detroit, Michigan. Magnus Wiktorsson was also a co-author but his name was unfortunately left out by the conference organizers. l Abstract The effects of variable valve timing (WT) were examined by in-cylinder Laser Doppler Velocimetry flow measurements and heat-release calculations. A single­ cylinder Volvo B5254 engine was used for all experiments and the valve timing was altered by phasing or exchanging the camshaft. Special cam lobes were developed for simulation of throttle-less operation. With the standard double camshaft, a tumbling flow was generated and with valve deactivation, a swirling flow was generated. The turbulence was increased with valve deactivation. This increased the combustion rate making lean bum possible. The standard camshaft with inlet valve deactivation and late cam phasing had a faster combustion at X - 1.8 than the standard camshaft with normal cam phasing at X = 1.0. Early and late inlet valve closing was used for enabling throttle-less operation. Early inlet valve closing (EIVC) generated a very slow tumble with low turbulence. Late inlet valve closing generated both very high and low turbulence. The net indicated efficiency was improved with up to 10%. Some reduction was observed for the gross indicated efficiency, due to a too large reduction in effective compression ratio. A very stable combustion was obtained for EIVC with gasoline, possibly due to a sheering flow over the inlet valves resulting in improved fuel-air preparation. Wavelet analysis was used for dividing LDV flow measurements into time and frequency resolved information. The technique rendered the same flow results as the moving window technique, but with a separation of the turbulence into different frequencies. The choice of wavelet was shown not to be crucial. The frequency resolved turbulence was studied for tumble and swirl. A tumbling flow had a larger transfer of energy from low frequency turbulence into high frequency turbulence than a swirling flow. This is caused by the tumble breakdown. A correlation against heat-release indicated that high frequency turbulence have a larger impact on the rate of heat-release than the low frequency turbulence. n Acknowledgement The experiments in this thesis has been performed within the Centre of Competence, Combustion Processes and I would like to thank the sponsors: Volvo Car Corporation and NUTEK, the Swedish Board for Technical Development. I would also like to thank my supervisor, Bengt Johansson, for his vast insight and patience, and Bertil Andersson for assisting in the laboratory and for keeping the engine running. The wavelet analysis in the first wavelet paper was performed at the Department of Mathematical Statistics and I would like to thank Bengt Lindoff and especially Magnus Wiktorsson for invaluable assistance concerning wavelets. I would also like to thank Krister Olsson, for making all computers working and for assisting whenever a data logging problem arose, and Patrik Einewall, for assisting in making Autocad drawings. ill Nomenclature B Cylinder bore BDC Bottom dead center, the bottom position for the piston BSA Burst Spectrum Analyzer CAD Crank angle degree Cl Compression ignition (Diesel cycle) Cp Specific heat at constant pressure cv Specific heat at constant volume EGR Exhaust gas recirculation EIVC Early inlet valve closing Y Ratio of specific heats GM General Motors IMEP Indicated mean effective pressure kHz Kilohertz, thousand times per second L Piston stroke X Air-fuel ratio divided by the stoichiometric air-fuel ratio LDV Laser Doppler velocimetry LIVC Late inlet valve closing MPa Megapascal, 106 N/m2 MPI Multipoint port fuel injection P Pressure PC Personal computer pn) Proportional, integrating and differentiating (control system) PMEP Pumping mean effective pressure R Gas constant Rc Compression ratio ROHR Rate of heat-release RPM Revolutions per minute Q Accumulated heat-release SAE Society of Automotive Engineers SI Spark ignition (Otto-cycle) T Temperature TDC Top dead center, the top position for the piston VVT Variable valve timing IV Table of contents 1 Introduction.......................................................................................................... 1 1.1 Nicolaus Otto.................................................................................................... 1 1.2 James Atkinson.................................................................................................2 2 Valves...................................................................................................................3 2.1 Definition of valve terminology......................................................................4 2.2 Push-rod valve train..........................................................................................5 2.3 Over head camshaft..........................................................................................5 2.4 Number of valves per cylinder .........................................................................5 2.5 Valve flow area.................................................................................................6 3 Camshaft design ...................................................................................................7 3.1 Three-arc cam.................................................................................................. 7 3.2 Constant velocity cam..................................................................................... 8 3.3 Constant acceleration cam............................................................................... 8 3.4 Advanced cams.................................................................................................8 3.5 Jerk-free cam................................................................................................... 8 4 Variable valve timing......................................................................................... 10 4.1 Direct acting systems..................................................................................... 10 4.2 Camshaft operated systems............................................................................ 11 4.2.1 Multi-dimensional cams........................................................................ 11 4.2.2 Variable geometry followers,fixed camshaft properties........................11 4.2.3 Variable camshaft properties,fixed geometry cam followers.................12 4.3 Other systems................................................................................................. 12 4.4 Miller cycle..................................................................................................... 12 5 Experimental setup ............................................................................................. 12 5.1 Engine............................................................................................................. 12 5.2 Engine management system.......................................................................... 13 5.3 Camshafts....................................................................................................... 13 5.4 Electric brake .................................................................................................. 14 5.5 Datalogging................................................................................................... 14 5.6 Supply systems............................................................................................... 15 5.7 Heat-release setup .................................................................. .-.......................15 5.8 LDV setup
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