The team, led by Waseda University Professor Ken Naitoh, says its calculations show the engine would have a heat efficiency ratio as high as 60 percent, nearly double that of conventional engines.

Team members say by injecting air and fuel into the combustion chamber from multiple directions at sonic speed, they can concentrate the fuel for burning in one spot. That means heat is less likely to escape, which improves thermal efficiency.

The researchers say they conducted tests on a prototype 30-cubic-centimeter engine, and obtained results that matched their calculations.

Professor Naitoh says representatives from about 10 automakers have already visited their lab to see the new technology.

He says the engine could be used in small power generators in homes, as well as in aircraft and rockets.

But he says it will be 5 to 10 years before the technology is ready for practical use.