Researchers Tout Hybrid-Natural Gas Diesel

Swiss scientists say their hybridized natural gas-fueled diesel system can reach efficiencies of nearly 40% and cut carbon dioxide emissions as low as 43 g/km.

The researchers, who are part of ETH Zurich's Institute for Dynamic Systems and Control, report their results in the online technical journal Energies.

The dual-fuel system mixes air and natural gas in the intake manifold and ignites it with a small amount of diesel fuel injected directly into the combustion chamber.

The researchers say their system requires no oxides of nitrogen aftertreatment at light engine loads and can be operated stoichiometrically at higher loads with a conventional three-way catalytic converter.

The team's test engine is a Volkswagen 4-cylinder, 2.0-liter industrial diesel, modified with port fuel injection for the natural gas, a low-pressure exhaust gas recirculation system and pressure sensors in all four cylinders.

In-vehicle performance was calculated by linking the engine to a dynamometer and emulating the rest of the powertrain and vehicle. The team evaluated two versions of their system, one with an automatic stop-start system and a hybrid variant that added an electric motor between the clutch and gearbox. They also simulated the engine in small, medium and large vehicles driven on the European and harmonized worldwide test procedures.

Results showed nitrogen oxide emissions below 75 ppm in all situations where the engine operates lean. Soot concentrations were less than 3 mg per cubic meter under all conditions. CO₂ emissions varied between 43 g/km and 78 g/km, depending upon vehicle size and test cycle.

The researchers note that hybridization drastically reduces CO₂ emissions by eliminating engine operation during inefficient low-load conditions.