Abstract: The cylindrical enclosure 12 of a recuperator 10 as in FIG. 2 contains an annular coaxial heat exchanger 50 full of cooling liquid 22 circulating therethrough. Exhaust gas from an internal combustion engine flows from an inlet end 32 through the heat exchanger 50, first in an axial region 15 via a conduit 14, then back through a surrounding annular region 18, then through tubes 37 to an outlet end 34. The inlet 30 and outlet 31 for the gas are in the side wall 40 of the cylindrical body 12, and the exhaust gas 11 enters and leaves via conduits 14 and 19 that are perpendicular to the side wall 40 at the inlet 30 and at the outlet 31. So the ends 41 and 42 of the body 12 are free of adjacent obstruction, and at least one of them is removable, as in FIG. 4 or FIG. 5 . Thus, the recuperator 10 can be opened and closed to make the interior accessible for inspection, cleaning, or other desired purpose.

Abstract: A small bore internal combustion engine our-stroke operating cycle which is adapted to function with natural gas and other gaseous fuels and which is particularly useful with residential heat pump assemblies with maximum life expectancy, high thermal efficiency, and low exhaust gas emissions, wherein provision is made for assembling the engine in a compact heat pump system with a low operating noise level and an extended engine maintenance interval.