Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
during combustion, and in the final expansion process prior to release at exhaust port or valve
opening.
The computation time step is dt, corresponding to a crankshaft angle, d0. The notation as
used in Sec. 4.2.2 is re-employed, and Fig. 4.3 is still applicable. The crankshaft is at 61
degrees and moves to 62. All properties and values at position 1 are known, and the new
cylinder volume, V2, is known geometrically. It is assumed that the gas properties at position
1 will persist for the small time step, dt, as a function of the temperature, Ti, and purity, III,
at the beginning of the time step, using the theory of Sec. 2.1.6. These will be updated at the
end of that time step as a function of the temperature, T2, and purity, II2, to be those at the
commencement of another.
Let us deal with each phase of the closed cycle in turn in terms of the acquisition of each of
the numerical values of the terms of Eq. 4.2.8. The basic solution of the Eq. 4.2.8 is for the
new pressure, P2:
as from Sec. 2.1.3 G6 =
Y + 1
Y-l
2(5QR - 5QL - 5Qvap) + Pl(G6V! - V2)
then P2 = ~ ~ ~ ' (4.4.1)
G6V2 - Vj
Consequently, from the state equation:
and from mass continuity:
The heat transfer term, 8QL, is determined from Sec. 4.3.4.
Compression in spark-ignition engines (Eqs. 4.3.36-38)
T - P2 V 2
l 2 ~ — (4.4.2)
m2R v '
m2 = mi + dm (4.4.3)
dm = mvapd9 8Qvap = mvaphvapd9 5QR = 0
Compression in compression-ignition engines
dm = 0 5Qvap = 0 8QR = 0
Combustion in spark-ignition engines (Eqs. 4.3.23-27)
QRO, + QRG-,
dm = 0 5Qvap =0 5QR = nc -^J— 2 - d0
:vap
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