This content is not included in your SAE MOBILUS subscription, or you are not logged in.
An Innovative Solution for Two-Stroke Engines to Reduce the Short-Circuit Effects
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 16, 2012 by SAE International in United States
Annotation ability available
Two-stroke engines complete the process cycle in one crankshaft revolution: the scavenging process takes place when the piston is close to the bottom dead center, with the opportunity to open and close the cylinder ports by means of the piston motion, greatly reducing the number of moving parts. This solution however, typically used in small engines, imposes a symmetrical timing with respect to the bottom dead center, leading to a lower scavenging efficiency than a four-stroke engine.
Except for the short rpm range of dynamic tuning, two-stroke engines are affected by the short-circuit of fresh air-fuel mixture during the scavenging process: this phenomenon results in a fuel loss, subsequent lower torque and higher specific consumption, and also in an inevitable increase in pollutant emissions.
This paper presents one possible mechanical solution to reduce the short-circuit in the whole rpm engine range, to keep the typical advantages of two-stroke engines (simple construction, high specific power and working regularity for a single cylinder engine of a given displacement) and, at the same time, to avoid the usual problems of the two-stroke cycle.
An asymmetric timing of the exhaust port is certainly a benefit, and for this reason an innovative design solution was conceived: a rotating valve, directly driven from the crankshaft, was positioned in correspondence with the exhaust port. During every cycle, this valve prevents the leakage of the fresh charge from the exhaust port in the last phase of the scavenging process. At the same time, thanks to its particular geometry, it allows the exhaust flow during the discharge. In other words, the valve converts the typical fluid dynamic effect of the outlet overpressure wave into a mechanical system for all rpm range and not only for the tuning speed.
The benefits of this solution were analyzed both in terms of global performance with a 1-D simulation code, and of fluid dynamics behavior of the system through 3-D CFD simulations. The main results, presented in this paper, show significant improvements when compared to analogous traditional two-stroke engines.
|Collection||Commercial Vehicles - Drivetrain/Powertrain/Transmissions 2014|
|Collection||Thermal Systems Modeling and Simulation, 2015|
|Collection||Energy Efficiency of Thermal Systems, 2015|
CitationFerrara, G., Balduzzi, F., and Vichi, G., "An Innovative Solution for Two-Stroke Engines to Reduce the Short-Circuit Effects," SAE Technical Paper 2012-01-0180, 2012, https://doi.org/10.4271/2012-01-0180.
- Zsiga, G. Kerres, R. Bach, M. Fuoss, K. “Potential of Expansion Chamber Exhaust Pipes for Two-Stroke Powered Tools,” SAE Technical Paper 2010-32-0011 2010 10.4271/2010-32-0011
- Bell, A.G. “Two-Stroke: Performance Tuning” Haynes Publishing California USA 1999
- Clarke, M. “Motori a Due Tempi di Alte Prestazioni” Giorgio Nada Editore Milan 2003
- Heywood, J. B. “Internal Combustion Engine Fundamentals” Mc Graw Hill Book Company 1988
- Blair, G. P. “The Basic Design of Two-Stroke Engines,” SAE International Warrendale, PA 1-56091-008-9 1993 10.4271/R-104
- Hata, N. Lio, T. “Improvement of Two-Stroke Engine Performance with the Yamaha Power Valve System (YPVS),” SAE Technical Paper 810922 1981 10.4271/810922
- OpenCFD Ltd. http://www.openfoam.com 2011
- Jasak, H. Jemcov, A. Tuković, Z. “OpenFOAM: A C++ Library for Complex Physics Simulations” Proceedings of the International Workshop on Coupled Methods in Numerical Dynamics 2007 Dubrovnik, Croatia
- Jasak, H. Weller, H.G. Nordin, N. “In-Cylinder CFD Simulation Using a C++ Object-Oriented Toolkit,” SAE Technical Paper 2004-01-0110 2004 10.4271/2004-01-0110
- Lucchini, T. D'Errico, G. Jasak, H. Tukovic, Z. “Automatic Mesh Motion with Topological Changes for Engine Simulation,” SAE Technical Paper 2007-01-0170 2007 10.4271/2007-01-0170
- Versteeg, H. K. Malalasekera, W. “An introduction to computational fluid dynamics. The finite volume method” Longman England 1995
- Ferziger, J.H. Peric, M. “Computational Methods for Fluid Dynamics” 3rd rev. Springer Berlin 2002
- Hariharan, R. Mahalakshmi, N.V. Krishnamoorthy, J. “CFD Analysis of Gas Exchange Process in a Motored Small Two-stroke Engine” Journal of Applied Sciences 11 1 36 45 2011 10.3923/jas.2011.36.45
- Rinaldini, C. A. Mattarelli, E. Golovitchev, V. “CFD Analyses on 2-Stroke High Speed Diesel Engines,” SAE Technical Paper 2011-24-0016 2011 10.4271/2011-24-0016
- Ricardo Software WAVE User Manual R8.1 2009
- Schoegl, O. Schmidt, S. Abart, M. Zinner, C. Kirchberger, R. Fitl, M. Glinsner, K. Leiber, S. “Possibilities and Limits of ID CFD Simulation Methodology for the Layout of 2-Stroke GDI Combustion System,” SAE Technical Paper 2010-32-0017 2010 10.4271/2010-32-0017