The precombustion chamber is connected to the main combustion space of the cylinder by a multiple orifice called a burner. During the compression event, a relatively small volume of compression-heated air is forced through the burner into the precombustion chamber. Heat stored by the burner increases the temperature of the compressed air and facilitates initial ignition. Only a small part of the fuel is burned in the precombustion chamber because of the limited amount of oxygen. Engines that have precombustion chambers do not require fuel injection pressures as great as engines that have open-type chambers.
Some engines have auxiliary combustion chambers.
They differ from precombustion chambers in that nearly all of the air supplied to the cylinder during the intake event is forced into the auxiliary chamber during the compres-sion event. For this reason, a high percentage of the air in the cylinder is forced into the turbulence chamber during the compression event. The opening to the turbulence chamber becomes smaller as the piston reaches TDC, thereby increasing the velocity of the air. Velocity plus deflection of the air as it enters the auxiliary chamber creates considerable turbulence. This ensures a thorough mixing of the air and fuel.