Recent findings indicate that the energy-conversion process must take place faster and more uniformly in order to achieve a further reduction of fuel consumption and exhaust emissions from present-day engines. A swirl-chamber spark plug developed by Bosch can contribute toward reaching these goals.The spark plug has a small chamber with 5 orifices (1 central, 4 tangential). On the compression stroke the 4 tangential orifices generate a marked swirl in the chamber. The ignition spark jumps from a small lateral pin on the customary center electrode across to the cylindrical wall of the swirl chamber. As a result of the swirl, a very rapid combustion takes place in the chamber and generates 5 torch jets which insure rapid and uniform energy conversion in the main combustion chamber.Tests on engines indicate considerably smoother engine running than with customary spark plugs. At the lower end of the part-load range and during warm up, thermal efficiency is improved.