Performance Under the Heat
High-speed surface temperature measurements on the crown of the piston can be especially significant for understanding the combustion event and for evaluating material property limits in the piston. For instance, highly sensitive and high-speed surface thermocouples can distinguish between flame and liquid fuel impinging on the surface. Having high-speed temperature measurements allows recording surface temperature fluctuations at Helmholtz frequencies (4-5 kHz) caused by engine knocking conditions.
These measurements increase the understanding of the physical combustion event and help improve the performance and efficiency of the engine. A surface temperature measurement combined with a sub-surface temperature measurement built in the same transducer can provide a heat flux measurement and aid in material selection and cooling design within the piston.
IR Telemetrics Has Been Designing and Building Custom Thermocouples for Over 30 Years
Accurate surface temperature measurements are not easily obtained. First, it is necessary to place the junction of the thermocouple precisely at the surface to be measured. Second, for high-speed, dynamic surface temperature measurements, the thermocouple junction itself must be very small and low mass and the thermocouple wires themselves should be as small as possible.
IR Telemetrics accomplishes this by laser welding a very small piece of metal, like platinum, across the thermocouple leads, flush to the surface. When performed under a microscope, this is a very low mass junction.
A platinum welded surface thermocouple is made utilizing stainless steel sheathed, mineral insulated, J-type probe stock along with a pure, thermocouple grade platinum ribbon used as the junction material. The creation of the physical junction is done using a 50W Nd:YAG pulsed laser welder
Currently 0.060” thermocouple stock and a 0.001” x 0.003” platinum ribbon makes the thermocouples. These platinum welded surface thermocouples have proven to be robust in extremely harsh environments with response times in the 10-100us range.
