within the air concentrated mixture the second embodiment may also contain several features of the first embodiment including system chamber insulation 114 a center or near center compact combustion chamber location for example 110 within the piston and high temperature combustion chamber insulating insert 120 since the second embodiment allows much higher overall system dilution and in particular the outer ring of gases being composed primarily of remaining spent system gases system chamber walls 101 and 103 can be maintained at lower temperatures such that high temperature liquid lubricants can be used to lubricate the piston rings 116 and 117 certain piston ring and system chamber wall materials may also be utilized if sufficient durability is attained without liquid lubrication in this embodiment side forces on the piston 100 are substantially reduced and therefore the guiding mechanism 48 50 in the first embodiment may be deleted the second embodiment provides higher specific power than the first but requires a separate pressurized air supply system the second embodiment allows a greater expansion ratio than compression ratio by adjusting the quantity of remaining spent system gases and the quantity of injected air this feature provides a lower system pressure and temperature at the end of expansion and thus improves thermodynamic efficiency as discussed previously a lower temperature for the remaining spent system gases also reduces the temperature of the system chamber walls other embodiments of the invention flow logically from the two specific designs described for example the first embodiment described may retain a more conventional piston design with the piston rings near the top of the piston e g as described in the second embodiment while still incorporating air insulation and radiant heat shields however rings in the top of the piston will need to be dry lubricated.