Abstract: A piston engine may include a clearance gap between a piston assembly and a cylinder. The piston may be configured to translate in a bore of the cylinder. The clearance gap between the piston assembly and the bore may be actively or passively controlled. A control system may provide one or more adjustments based on, for example, a detected temperature, pressure, flow rate, work metric, and/or other indicator. The adjustments may include, for example, adjusting a cylinder liner, adjusting a flow through a bearing element, adjusting a coolant flow, adjusting a heat pipe property, and/or other adjustments. One or more auxiliary systems may be used to provide the adjustments.

Abstract: A piston engine may include a heat pipe capable of transferring heat away from a portion of the piston engine such as a combustion section. The heat pipe may be included as part of a piston assembly, a cylinder, or both. The heat pipe may be filled with a suitable heat pipe fluid that may undergo a phase change such as, for example, water, ethanol, ammonia, sodium, other fluids or combinations thereof. Boiling and condensing of the fluid within the heat pipe may utilize the latent heat of the fluid during heat transfer. Multiple heat pipes may be used in some instances.

Abstract: A piston engine may include a piston assembly, which may include a piston having a self-centering feature. The piston assembly may be configured to translate in a bore of the cylinder, and contact a combustion section and/or gas driver section. The self-centering feature may use a flow of blow-by gas in a clearance gap to provide a self-centering force on the piston assembly. The self-centering feature may include one or more slotted pockets, a step, a tapered portion, any other suitable feature, or a combination thereof. Optionally, a piston assembly may include a feature that aids in self-centering such as, for example, a labyrinth seal.

Abstract: Various embodiments of the present invention are directed toward a two-piston linear combustion engine, comprising: a cylinder having a cylinder wall and a pair of ends, the cylinder including a combustion section disposed in a center portion of the cylinder; a pair of opposed piston assemblies adapted to move linearly within the cylinder, each piston assembly disposed on one side of the combustion section opposite the other piston assembly; a pair of driver sections, each driver section comprising a compression mechanism that directly provides at least some compression work during a compression stroke of the engine; and a pair of linear electromagnetic machines adapted to directly convert kinetic energy of the piston assembly into electrical energy, and adapted to directly convert electrical energy into kinetic energy of the piston assembly for providing compression work during the compression stroke, wherein each linear electromagnetic machine is located distal to an end of the cylinder; wherein the engine

Abstract: Various embodiments of the present invention are directed toward a linear combustion engine, comprising: a cylinder having a cylinder wall and a pair of ends, the cylinder including a combustion section disposed in a center portion of the cylinder; a pair of opposed piston assemblies adapted to move linearly within the cylinder, each piston assembly disposed on one side of the combustion section opposite the other piston assembly, each piston assembly including a spring rod and a piston comprising a solid front section adjacent the combustion section and a gas section; and a pair of linear electromagnetic machines adapted to directly convert kinetic energy of the piston assembly into electrical energy, and adapted to directly convert electrical energy into kinetic energy of the piston assembly for providing compression work during the compression stroke.

Abstract: Various embodiments of the present invention are directed toward a linear combustion engine, comprising: a cylinder having a cylinder wall and a pair of ends, the cylinder including a combustion section disposed in a center portion of the cylinder; a pair of opposed piston assemblies adapted to move linearly within the cylinder, each piston assembly disposed on one side of the combustion section opposite the other piston assembly, each piston assembly including a spring rod and a piston comprising a solid front section adjacent the combustion section and a gas section; and a pair of linear electromagnetic machines adapted to directly convert kinetic energy of the piston assembly into electrical energy, and adapted to directly convert electrical energy into kinetic energy of the piston assembly for providing compression work during the compression stroke.

Abstract: Various embodiments of the present invention are directed toward a linear combustion engine, comprising: a cylinder having a cylinder wall, the cylinder including a combustion section disposed in a lower portion of the cylinder; a piston assemblies adapted to move linearly within the cylinder, the piston assembly located above the combustion section; a driver section disposed in an upper portion of the cylinder, the driver section comprising a compression mechanism that directly provides at least some compression work during a compression stroke of the engine; and a linear electromagnetic machine adapted to directly convert kinetic energy of the piston assembly into electrical energy, and adapted to directly convert electrical energy into kinetic energy of the piston assembly for providing compression work during the compression stroke, wherein the linear electromagnetic machine is above the upper end of the cylinder; wherein the engine includes a variable expansion ratio greater than 50:1.

Abstract: Various embodiments of the present invention are directed toward a two-piston linear combustion engine, comprising: a cylinder having a cylinder wall and a pair of ends, the cylinder including a combustion section disposed in a center portion of the cylinder; a pair of opposed piston assemblies adapted to move linearly within the cylinder, each piston assembly disposed on one side of the combustion section opposite the other piston assembly; a pair of driver sections, each driver section comprising a compression mechanism that directly provides at least some compression work during a compression stroke of the engine; and a pair of linear electromagnetic machines adapted to directly convert kinetic energy of the piston assembly into electrical energy, and adapted to directly convert electrical energy into kinetic energy of the piston assembly for providing compression work during the compression stroke, wherein each linear electromagnetic machine is located distal to an end of the cylinder; wherein the engine