Auto Service World
Feature   November 1, 2000   by David Booth

Saab Combustion Control System

Air-assisted direct injection cuts emissions and boosts efficiency

Saab recently unveiled its new Combustion Control System (SCC) which it claims reduces fuel consumption and exhaust emissions by up to 75 percent.

The Swedish company’s SCC system incorporates some existing technology, like variable valve timing, and some very advanced systems such as Saab’s variable spark gap and direct injection that sees the spark plug doubling as a fuel injector.

The variable spark gap is achieved by using two ground electrodes. The first is the common one used on every spark plug, though the SCC’s version is set at a huge 3.5mm gap for burning ultra-lean mixtures.

The second is truly innovative, being mounted on the top of the piston. This ground electrode’s gap is only 1.0mm. Depending on the load, SCC chooses the electrode that best serves combustion.

The other triple-cool technology is having the injector and spark plug integrated into one unit known as the spark plug injector (SPI). The fuel is injected directly into the cylinder by means of compressed air. Immediately before the fuel is ignited (in low torque conditions) a second brief blast of pure air creates turbulence in the cylinder, improving combustion efficiency.

The SCC system also uses variable cam timing that allows a measure of exhaust gas recirculation. Exhaust gases can be mixed into the combustion chamber that lets Saab lean fuel/air ratios at all times. In low demand conditions, the exhaust gases can compose up to 70 percent of the cylinder contents during combustion.

All these measures allow the direct injection engine to use a common three-way catalytic converter while still reducing carbon dioxide (CO2), water (H2O) and nitrogen (N2) gases. Saab claims the SCC engine is unique in this regard.

The SCC control system was developed at Saab’s Engine Development Department, which is also GM’s worldwide center of expertise for the development of turbocharged gasoline engines.

The variable spark gap in the SCC system is a further development of the spark-to-piston concept that Saab unveiled at the Frankfurt Motor Show in 1995. In the air-assisted direct injection system, Saab engineers are cooperating with the Australian company Orbital. The SCC system will be launched in the next generation of Saab cars. SSGM