Clatter, grumble, shudder, belch.

Sound familiar? Not if you drive one of the modern breed of diesel-engined cars, which have virtually banished all sign of their clattery, tractor-like forebears.

A modern Volkswagen TDI, for example, isn't just efficient and quiet--it even approaches fun, if you get your thrills from effortless low-down torque.

Not that it can't be made better, and a company called LiquidPiston (via GigaOM) is promising just that with its latest engine design.

It offers greater benefits even than current diesel engines--lighter weight, smaller size, greater efficiency and less noise. It's also simpler, and so the theory goes--cheaper.

The prototype X2 engine is based on a rotary design, which is immediately beneficial in terms of smoothness next to typical reciprocating designs.

It works on a patent-pending "High-Efficiency Hybrid Cycle" combustion method, which uses elements of Otto, Diesel, Atkinson and Rankine cycles. And impressively, it isn't restricted to diesel--gasoline, natural gas, biofuels and others can all be potentially used.

LiquidPiston claims the engine operates at more than 50 percent thermodynamic efficiency, next to figures of less than 20 percent in regular piston engines. And contrary to current rotary engines, which have a bit of a gas-guzzling reputation, the engine should also be fuel-efficient.

The first engines are unlikely to be seen as the main powerplants in passenger vehicles, but use as range-extending engines in plug-in vehicles is more likely. Defense, industry and other niche markets are other likely avenues.

The company has raised $12.3 million to develop its engine so far, and hopes to find another $20 million soon.


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