25]FIG. 2B is a simplified vertical cross sectional view similar to FIG. 2 but showing a second modification of the thermal engine plant first embodiment. [0026]FIGS. 3 and 4 are simplified fragmentary perspective and vertical cross sectional views respectively similar to FIGS. 1 and 2 but illustrating a second embodiment thermal engine plant utilizing a ???negative??? air flow system. [0027]FIG.