A New Approach to Free-Piston Linear Electric Generators

A researcher in China is touting a new configuration for a piston-powered electrical generator that could overcome drawbacks of previous approaches to linear piston designs, Green Car Congress reports.

Linear generators use pistons on the opposite ends of a connecting rod to move a permanent magnet back and forth through a winding, thus producing electricity. Such systems are intended for use in series hybrid electric vehicles.

But it has been difficult to control combustion timing for the two cylinders that contain the pistons a critical requirement for efficient operation, notes researcher Ling Huang at the Nanjing University of Science & Technology.

Huang's gasoline-fueled design flips the traditional configuration. It uses a single cylinder with central combustion chamber and opposing pistons. Each piston has a rod attached to its own linear generator.

During combustion, the piston drives the generator against a mechanical spring. The spring then rebounds, pushing the piston back toward the center of the cylinder to compress the next air-fuel charge.

Huang notes that the proposed two-stroke design is inherently balanced, operates without intake and exhaust valves and permits higher compression ratios for a given stroke length. Simulations indicate the design is feasible and could produce 15 kW of electricity with a generating efficiency of 42.5%.

Huang describes modeling and simulation results for the generator in a technical paper (number 2012-01-1021) that was presented in April during the SAE World Congress in Detroit.