This content is not included in your SAE MOBILUS subscription, or you are not logged in.
Simulation of a Crankcase Scavenged, Two-Stroke, SI Engine and Comparisons with Experimental Data
ISSN: 0148-7191, e-ISSN: 2688-3627
Published February 01, 1969 by SAE International in United States
Annotation ability available
A detailed mathematical model of the thermodynamic events of a crankcase scavenged, two-stroke, SI engine is described. The engine is divided into three thermodynamic systems: the cylinder gases, the crankcase gases, and the inlet system gases. Energy balances, mass continuity equations, the ideal gas law, and thermodynamic property relationships are combined to give a set of coupled ordinary differential equations which describe the thermodynamic states encountered by the systems of the engine during one cycle of operation. A computer program is used to integrate the equations, starting with estimated initial thermodynamic conditions and estimated metal surface temperatures. The program iterates the cycle, adjusting the initial estimates, until the final conditions agree with the beginning conditions, that is, until a cycle results.
The combustion process is described by dividing the cylinder gases into two systems, one corresponding to the burned region and the other to the unburned region. As combustion takes place, the boundary between the two systems moves, and mass is transferred from the unburned system to the burned system. The effects of dissociation of the combustion products are included by using empirical curve fits for the equilibrium thermodynamic properties of the combustion products of air and CnH2n fuel.
The instantaneous mass flow through the engine is computed from stagnation conditions upstream and downstream of each flow restriction using steady flow coefficients. The motion of the reed is described by the solution of an equivalent spring-mass system.
A theoretical relationship between scavenging efficiency and delivery ratio assuming perfect mixing is employed. The delivery ratio actually used in this expression is multiplied by a factor chosen to give the best agreement between computed and experimental BHP.
An arbitrary model which has characteristics in common with the real process is used to compute the vaporization rates during the cycle.
The heat transfer surfaces for each system are divided into several different areas, each considered to be at one uniform temperature for the cycle. At the end of each iteration, a one-dimensional heat transfer rate balance is performed on each surface to obtain better estimates of the metal temperatures for the next cycle.
Experimental data from the simulated engine are compared with the computed results.
CitationKrieger, R., Booy, R., Myers, P., and Uyehara, O., "Simulation of a Crankcase Scavenged, Two-Stroke, SI Engine and Comparisons with Experimental Data," SAE Technical Paper 690135, 1969, https://doi.org/10.4271/690135.
- Alyea J. “The Development and Evaluation of an Electronic Indicated Horsepower Meter.” Univeristy of Wisconsin 1968
- Bishop, I. N. “Effect of Design Variables on Friction and Economy.” Paper 812A presented at SAE Annual meeting Jan. 13–17 1964
- Booy, R. R. “Evaluating Scavenging Efficiency of Two-Stroke Cycle Gasoline Engines.” SAE Paper 670029 Jan. 9–13 1967
- Borman G. L. “Mathematical Simulation of Internal Combustion Engine Processes and Performance Including Comparisons with Experiment.” University of Wisconsin 1964
- Chen Yu “Vibrations: Theoretical Methods.” Reading Mass Addison-Wesley Publishing Co., Inc. 1966
- Cook, H. A. “Digital Computer Analysis and Interpretation of Turbocharged Diesel Engine Performance.” SAE Trans 67 1959
- Costagliola M. “Dynamics of a Reed Type Valve.” M.I.T. 1949
- Edson, M. H. “The Influence of Compression Ratio and Dissociation on Ideal Otto Cycle Engine Thermal Efficiency.” SAE Trans 70 1962 665
- Eichelberg, G. “Some New Investigations of Old Internal Combustion Engine Problems.” Engineering 148 1939 463 466 547 550 603 605 149 1939 297 299
- Greenspan D. Private Communication University of Wisconsin 1968
- Huber P. Brown, J. R. “Computation of Instantaneous Air Flow and Volumetric Efficiency.” SAE Paper 812B 1964
- Krieger R. B. Borman, G. L. “The Computation of Apparent Heat Release for Internal Combustion Engines.” ASME Paper No. 66-WA/DGP-4 1966
- Mariotti J. “An Analysis of Outboard Engine Reed Valves.” University of Wisconsin 1964
- McAulay, K. J. Wu, T. Chen, S. K. Borman, G. L. Myers P. S. Uyehara, O. A. “Development and Evaluation of the Simulation of the Compression-Ignition Engine.” SAE Transactions 74
- Patterson, D. J. “Cylinder Pressure Variations, A Fundamental Combustion Problem.” SAE Paper 660129 1966
- Patterson, D. J. Van Wylen, G. “Digital Computer Simulation for Spark Ignition Engine Cycles.” SAE Paper 633F Jan. 14–18 1962
- Powell, H. N. “Applications of an Enthalpy-Fuel/Air Ratio Diagram to ‘First Law’ Combustion Problems.” Trans. ASME 79 1957 1129 1142
- Strange, F. M. “An Analysis of Ideal Otto Cycle Including Effects of Heat Transfer, Finite Combustion Rates, Chemical Dissociation and Mechanical Losses.” SAE Paper 633D Jan. 14–18 1963
- Taylor, C. F. Rogowski, A. R. “Scavenging the 2-Stroke Engine.” SAE Trans 62 1954 487
- Taylor, C. F. Rogowski, A. R. Hagen, A. L. Koppernaes, J. D. “Loop Scavenging Versus Through Scavenging of 2 Cycle Engines.” SAE Trans 66 1958 444
- Tsu, T. C. “Theory of Inlet and Exhaust Processes of Internal Combustion Engines.” NACA, TN 1446 1949
- Walker, G. “Effect of Rate of Combustion on Gasoline Engine Performance.” Inst. Fuel J 37 No. 281 June 1964 228 233
- Walker J. W. “Piston Temperature Measurements in a Watercooled Two Stroke Cycle Spark Ignition Engine.” University of Wisconsin 1966
- Wambsganss, M. “Simulation of Reciprocationg Gas Compressors with Automatic Reed Valves.” Simulation 8 No. 4 April 1967 209 214