Renault doesn't sell any vehicles in the U.S.—unless you consider some Nissans that share a global platform—but there's a reason this tiny diesel from France is interesting: it gives us an idea of how internal combustion engines will evolve under pressure to increase relative output and efficiency at the same time. The humble two-stroke might be the engine of the future. What's old is new again, right?

Renault is a major small-diesel manufacturer, and it seems likely that with what the company calls the "POWERFUL" (POWERtrain for FUture Light-duty vehicles) concept, it might be first out the gate with a small two-stroke diesel for passenger cars.

READ MORE: Set the mood with a two-stroke-scented candle

By design, a two-stroke diesel is power-dense, with a power stroke every revolution, and inherently cleaner than a gasoline two-stroke. A major drawback is a narrow powerband. And "clean" is relative; emissions and economy standards in Europe and North America are extremely exacting for diesels. Several companies are trying to meet these challenges and produce a two-stroke engine suitable for a light automobile, but so far none have come to market.

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