Packet of three engines

Great news for model airplane enthusiasts and drivers of French cars! A California research institute has come up with a tiny engine powered by rubber bands and such - SRI International of California has developed an elastic internal combustion engine.

SRI has been working on portable engines for the US Army. Although designed for robots and spy-planes, they could also be used in hybrid cars, lawnmowers and gadgets, according to a patent filed by the company.

Conventional internal combustion engines rely on a piston moving inside a cylinder. Big ones are efficient because gas leakage round the piston wastes only a small percentage of the total power. But in smaller engines the leakage loss is proportionately high, so efficiency is poor.

SRI claim their design prevents leakage altogether. It burns fuel inside a sealed cylinder made from a tough elastic material. As the hot gases expand, the cylinder itself swells like a balloon then returns elastically to its original shape. A crank arm resting on the outside of the cylinder generates mechanical power.

Efficiency is high and heat is also dissipated effectively because the cylinder walls become temporarily thinner as the cylinder swells.

Read the rubbery combustion patent here