Design and Simulation of Two Stroke Engines

Chapter 4 - Combustion in Two-Stroke Engines
a chamber be tried experimentally and fail to provide an instant improvement to the engine
performance characteristics, the designer should always remember that the scavenging behavior
of the engine is also being altered by this modification.
For combustion of other fuels, such as kerosene or natural gas, which are not noted for
having naturally high flame speed capabilities, the creation of turbulence by squish action
will speed up the combustion process. In this context, earlier remarks in the discussion on
stratified charge combustion become applicable in this homogeneous charge context.
Combustion chambers for cross-scavenged engines
For conventional cross-scavenged engines, it is regretted that little direct advice can be
given on this topic, for the simple truth is that the complex shapes possible from the deflector
design are such that universal recommendations are almost impossible. Perhaps the only common
thread of information which has appeared experimentally over the years is that combustion
chambers appear to perform most efficiently when placed over the center of the cylinder,
with just a hint of bias toward the exhaust side, and with very little squish action designed to
come from either the scavenge side or the exhaust side of the piston. Indeed, some of the best
designs have been those which are almost quiescent in this regard.
For unconventional cross-scavenged engines, as discussed in Sec. 3.5.3, the associated
computer program, Prog.3.3(a), includes a segment for the design of a combustion chamber
which is central over the flat top of the piston and squishes from the deflector areas. It is also
possible to squish on the flat top of the piston over the edges of the deflector, although no
experimental data exist to confirm that would be successful.
References for Chapter 4
4.1 B. Lewis, G. Von Elbe, Combustion. Flames and Explosions of Gases. Academic
Press, 1961.
4.2 N.C. Blizard, J.C. Keck, "Experimental and Theoretical Investigation of Turbulent
Burning Model for Internal Combustion Engines," SAE Paper No. 740191, Society
of Automotive Engineers, Warrendale, Pa., 1974.
4.3 T. Obokata, N. Hanada, T. Kurabayashi, "Velocity and Turbulence Measurements in
a Combustion Chamber of SI Engine under Motored and Firing Conditions by LD A
with Fibre-Optic Pick-up," SAE Paper No. 870166, Society of Automotive Engineers,
Warrendale, Pa., 1987.
4.4 W.G. Agnew, "Fifty Years of Combustion Research at General Motors," Prog.Energy
Combust.ScL, Vol 4, ppl 15-155, 1978.
4.5 R.J. Tabaczynski, "Turbulence and Turbulent Combustion in Spark-Ignition Engines,"
Prog.Energy Combust.ScL, Vol 2, pl43, 1977.
4.6 M.S. Hancock, D.J. Buckingham, M.R. Belmont, "The Influence of Arc Parameters
on Combustion in a Spark-Ignition Engine," SAE Paper No. 860321, Society of Automotive
Engineers, Warrendale, Pa., 1986.
4.7 G.M. Rassweiler, L. Withrow, "Motion Pictures of Engine Flames Correlated with
Pressure Cards," SAE Paper No. 800131, Society of Automotive Engineers,
Warrendale, Pa., 1980.
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