Piezoelectric devices that would serve as spark plugs, power generators for spark plugs, and/or pressure sensors have been proposed for use in internal-combustion engines. Unlike conventional spark plugs, these devices would function without need for wire connections to external high-voltage sources. Also, unlike conventional spark plugs, these devices could function without need for external timing circuitry, and/or could function as parts of timing circuitry.

The most basic device of this type would be a self-timing, self-power-generating spark plug. The device would be mounted in a cylinder in an internal-combustion engine, in the manner of a conventional spark plug. The device would include a piezoelectric component with spark electrodes connected to its poles. The increase in pressure during the compression phase of the engine operating cycle would impose a strain on the piezoelectric component of the device and thereby give rise to a voltage between the electrodes. The voltage would increase with pressure until it was sufficient to cause a spark that would ignite the compressed fuel/air mixture in the cylinder. To increase the available voltage, the device could include a striker that would be driven by the increase in pressure to impinge on the piezoelectric component.

Immediately after ignition, the piezoelectric component would generate a voltage in response to the rapid increase in pressure associated with the combustion process. This voltage could be monitored to determine whether the engine is operating properly. The piezoelectrically generated voltage could also be monitored before as well as after sparking for more comprehensive monitoring of engine operation and, in particular, to detect such anomalies as pre-ignition, misfire, and knock.

The pressure-indicating piezovoltage could also be used, in conjunction with other indications of engine performance, to modify the spark timing. In a variation of the basic concept, the piezovoltage generated during the compression phase would initially be used to charge a capacitor; subsequently, under control by a timing circuit, the capacitor would be discharged through the spark electrodes. The spark timing could be in response to any combination of (1) the engine crank angle, (2) the pressure (as indicated by the piezovoltage), and (3) the rate of change of pressure.

This work was done by Jacob van Reenen Pretorius and Marthinus Cornelius van Schoor of Midé Technology Corp. for Glenn Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Electronics & Computers category.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center
Commercial Technology Office
Attn: Steve Fedor
Mail Stop 4 —8
21000 Brookpark Road
Ohio 44135.

Refer to LEW-16760.