  We present theoretical results of a piecewise isothermal shock wind model
devised for predicting the luminosity and surface brightness profile of diffuse
X-ray emissions primarily from the inner shocked downstream wind zone of a
planetary nebula (PN) surrounded by self-similar shocked dense shell and outer
slow AGB wind envelope involving self-gravity and compare/fit our computational
model results with available observations of a few grossly spherical X-ray
emitting PNe. Matching shocked piecewise isothermal self-similar void (ISSV)
solutions with self-gravity of Lou & Zhai (LZ) for the outer zone and a
stationary isothermal fast tenuous wind with a reverse shock for the inner zone
across an expanding contact discontinuity, we can consistently construct
dynamic evolution models of PNe with diffuse X-ray emissions. On the basis of
such a chosen dynamic wind interaction model, both X-ray luminosity and radial
X-ray brightness profile are determined by three key parameters, namely the
so-called X-ray parameter $X$, two radii $R_{rs}$ and $R_c$ of the reverse
shock and the contact discontinuity. We find that morphologies of X-ray
emissions would appear in the forms of either a central luminous sphere or a
bright ring embedded within optically bright shells. In contrast to previous
adiabatic models, the X-ray brightness peaks around the reverse shock, instead
of the contact discontinuity surface just inside the outer shocked dense shell.
Diffuse X-ray emissions of a few observed PNe appear to support this wind-wind
dynamic interaction scenario.
