CVCC is a trademark by the Honda Motor Company for a device used to reduce automotive emissions called a Compound Vortex Combustion Chamber. This technology allowed Honda's cars to meet the 1970s US Emission requirements without a catalytic converter, and first appeared on the 1975 ED1 engine. It is a form of stratified charge engine.

Honda CVCC engines have normal inlet and exhaust valves, plus a small auxilary inlet valve which provides a relatively rich air / fuel mixture to a volume near the spark plug. The remaining air / fuel charge, drawn into the cylinder through the main inlet valve is leaner than normal. The volume near the spark plug is contained by a small perforated metal plate. Upon ignition flame fronts emerge from the perforations and ignite the remainder of the air / fuel charge. The remaining engine cycle is as per a standard four stroke engine.

This mix of rich mixture near the spark plug, and lean mixture in the cylinder allowed stable running yet complete combustion of fuel, thus reducing CO (carbon monoxide) and hydrocarbon emissions.

The initialism, "C V C C", is probably derived from the name of the Honda Civic car in which these names were used.

Advantages over previous stratified charge engines

Honda's big advancement with CVCC was that they were able to use carburetors and they did not rely on intake swirl. Previous versions of stratified charge engines needed costly fuel injection systems. Additionally, previous engines tried to increase the velocity and swirl of the intake charge in keeping the rich and lean mixtures separated. Honda was able to keep the charges adequately separated by combustion chamber shape.

References

Setright, L. J. K. (1975). Some Unusual Engines. London: Mechanical Engineering Publications Limited.