Design and Simulation of Two Stroke Engines

Design and Simulation of Two-Stroke Engines
cylinder where the outflow is stratified, the local properties of zone CX, which are pressure,
Pcx> temperature, Tex, purity, Ilex, etc., are those that replace the mean values of pressure,
Pcx> temperature, Tex, purity, Ilex, etc In which case the solution of the continuity equation
and the First Law of Thermodynamics is as accurate and as straightforward as it was in Sec.
2.18.9 in Eqs. 2.18.44 to 2.18.49.1 provide further debate on this topic in Ref. [2.32].
The subscript notation for the properties and state conditions within the box after the time
step, dt, is CI, i.e., the new values are pressure, Pci, temperature, Tci, purity, FIci, etc.
The heat transfer, 8Qc, to or from the box in the time step is given by the local convection
heat transfer coefficient, Ch, the total surface area, Ac, and the average wall temperature of
the box, Tw.
oQc = ChAc(Tw - Tc)dt (2.18.55)
The value of the heat transfer coefficient, Ch, to be employed during the open cycle is the
subject of much research, of which the work by Annand [2.58] is noteworthy. The approach
by Annand is recommended for the acquisition of heat transfer coefficients for both the open
and the closed cycle within the engine cylinder. For all engines, it should be noted that at
some period during the closed cycle an allowance must be made for the cooling of the cylinder
charge due to the vaporization of the fuel. For spark-ignition engines it is normal to permit
this to happen linearly from the trapping point to the onset of ignition. For compressionignition
units it is conventional to consider that this occurs simultaneously with each packet
of fuel being burned during a computational time step. The work of Woschni [2.60] has also
provided significant contributions to this thermodynamic field.
The continuity equation for the process during the time step, dt, is given by:
mci = mc + dmj - drng (2.18.56)
The First Law of Thermodynamics for the cylinder or plenum system is:
5QC + dH! = dUc + dHE + ?c + ?cl dVc (2.18.57)
The work term is clearly zero for a plenum of constant volume. All of the terms except
that for the change of system state, dUc, and cylinder pressure, Pci, are already known through
the theory given above in this section. Expansion of one unknown term reveals:
This reduces to:
dUc = mciuci - mcuc
(2.18.58)
dUc = mclCVaTcl - mcCVcTc (2.18.59)
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