Design and Simulation of Two Stroke Engines

Chapter 5 - Computer Modeling of Engines
mental evidence, there appear to be somewhat proportionately higher friction characteristics
for small industrial engines, i.e., of cylinder capacity less than 100 cm 3 , and I have never
satisfactorily resolved whether or not the bank of information which resulted in the provision
of Eq. 5.4.1 also incorporates the energy loss associated with the cooling fan normally employed
on such engines.
industrial engines fmep=150LstN (5.4.1)
motorcycles, etc. fmep = 105LstN (5.4.2)
Spark-ignition engines with plain bearings
This set of engines is normally found in prototype automobiles using direct injection of
fuel into the cylinder and with the air supply to the engine provided by a supercharger.
fmep = 25,000 + 125LstN (5.4.3)
Compression-ignition engines with plain bearings
This group of engines is normally found in prototype automobiles, and in trucks, buses
and generating sets, using direct injection of fuel into the cylinder and with the air supply to
the engine provided by a supercharger or a turbocharger. Here, there appear to be two classifications,
with somewhat lesser friction characteristics appearing in the automobile set where
the engine is more lightly constructed and runs to a higher piston speed. The breakdown point
appears to lie between engines with stroke lengths above or below 100 mm. However, diesel
engines have higher compression and combustion pressure loadings than spark-ignition engines,
and as the bearing and piston ring designs must cope with this loading, they are proportionately
greater in size or number. This gives a higher friction content for this type of engine.
automobiles fmep = 34,400 + 175LstN (5.4.4)
trucks fmep = 61,000 + 200LstN (5.4.5)
5.5 The thermodynamic and gas-dynamic engine simulation
Virtually everything written up to this point within this text has been oriented toward this
section of this chapter. The theory of unsteady gas flow in Chapter 2, the theory of scavenging
behavior in Chapter 3, and the theory of combustion and heat transfer in the engine cylinder
in Chapter 4, are all brought together into a single computational format and linked together
to simulate an engine.
For those who have studied the publications in Refs. [2.31-2.35, 2.40-2.41, 5.20-5.21]
you will realize that much has been learned, researched, and published on engine modeling
since I presented a simple engine simulation program based on Benson's publications on the
method of characteristics, together with its computer coding [3.34].
The applications selected here, to illustrate the extent of the design information that comes
from a more advanced simulation technique, are a chainsaw, a racing engine and a multicylinder
supercharged unit with direct in-cylinder fuel injection for automotive use. The simu-
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