WOLFSBURG -- To cut CO2 emissions, Volkswagen sees a future in engines that combine the best qualities of gasoline and diesel units.

"With the issues of pollution mostly solved, CO2 now dominates the environmental debate," said Jürgen Leohold, VW's executive director for group research. "A critical question is where does the energy come from in the future."

As part of a future-technology briefing, VW showed two low-emissions engine projects it sees as energy savers.

1. A diesel engine that uses the homogenous air-fuel mixing style of a gasoline engine. The result is a fuel-sipping powertrain with low CO2 and virtually no soot, which is a key problem with conventional diesels. VW calls this the Combined Combustion System, and says it could be road ready within a decade.

2. A gasoline engine that can switch to diesel-like compression ignition mode. This strategy is to combine the cleaner exhaust properties of gasoline engines and the better fuel economy of diesels. VW calls it Gasoline Compression Ignition. VW did not reveal its launch goal for the technology.

Cutting CO2 at lower cost

Both VW engine concepts offer the promise of higher fuel economy and lower emissions. They would also work with the existing refueling infrastructure. Critics cite a lack of refueling stations as a key barrier for hydrogen-fed fuel cells.

Other automakers are also working with several engine strategies, such as homogeneous combustion, variable valve timing and lift, or adjusting compression ratios. But VW thinks still more gains are possible from mature technology.

"Diesel and petrol engines have had long evolutions, but there is more to be gained," Leohold said.

The goal of all these efforts is to improve fuel economy and cut emissions – while avoiding the cost and weight penalties of hybrid powertrains and fuel cells.

Despite the advanced concepts, VW has developed a hybrid powertrain. Leohold confirmed that VW will put a hybrid into production, without offering specifics. And he confirmed that VW is working on its own fuel cell powertrain.

European lawmakers want CO2 emissions cut to 120 grams per kilometer by 2012. Average emissions for Europe's car fleet currently are about 160g/km.

There are drawbacks to VW's concepts.

The Combined Combustion System works best with synthetic and biomass fuels, but the production and availability of those fuels is extremely limited, and they are expensive.

The Gasoline Compression Ignition engine requires sophisticated controls to closely manage the air-fuel mixture and cylinder temperature. Also, the diesel mode is available only in low speed and cruising conditions. When the engine reverts to conventional spark-ignition mode for starting and at higher speeds, fuel economy falls.

You may e-mail Dale Jewett at djewett@crain.com