Siemens VDO Sensors Division general manager Bret Sauerwein said that achieving low combustion temperatures in the cylinder is key to lowering oxides of nitrogen (NOx) emissions because raw NOx is primarily emitted at the engine's peak combustion temperature and pressure.
The pressure-sensing GPPS, integrated into the glow plug, measures combustion inside the engine and provides feedback to the engine-management system, which can then control the timing and quantity of fuel injected into the cylinder to stabilize combustion temperatures, allowing the engine to adjust injection characteristics to avoid combustion conditions producing high NOx levels.
The GPPS contains a polycrystalline piezo ceramic disk that is mounted in the glow plug structure between two isolating washers. Increased pressure during the combustion process applies force to the glow plug. The degree of force is captured by the piezoelectric element and processed to deliver an accurate electronic measurement of cylinder pressure in the engine's combustion stroke.