As engine efficiency targets continue to rise, additional improvements must consider reduction of heat transfer losses. The development of advanced heat transfer models and realistic boundary conditions for simulation based engine design both require accurate in-cylinder wall temperature measurements. A novel dual wavelength infrared diagnostic has been developed to measure in-cylinder surface temperatures with high temporal resolution. The diagnostic has the capability to measure low amplitude, high frequency temperature variations, such as those occurring during the gas exchange process. The dual wavelength ratio method has the benefit of correcting for background scattering reflections and the emission from the optical window itself. The assumption that background effects are relatively constant during an engine cycle is shown to be valid over a range of intake conditions during motoring.
The diagnostic was validated by simultaneous in-cylinder surface temperature measurements during motored engine conditions, with three independent measurement techniques: thermocouple, laser-induced phosphorescence, and the dual wavelength infrared diagnostic. All of the techniques were applied at different intake conditions. However, characteristic differences are observed between the measurements of each technique.
Heat flux is obtained from both the thermocouple and infrared measurements by application of Fourier's law. The infrared measurements show that time-average and transient terms increase as intake pressure increases at constant intake gas temperature, and only that time-average term increases as intake gas temperature increases while charge density is constant. Average cycle thermocouple, laser induced phosphorescence and IR diagnostic temperature measurements agree within 12 °C for all conditions tested. The temperature range determined by the IR diagnostic is greater than that obtained from the thermocouple, but less than that from the phosphorescence technique. Peak dynamic heat flux determined from the IR diagnostic is nearly twice as high as the flux determined from the thermocouple. An examination of the measured temperatures in the frequency domain shows that the IR diagnostic has greater contribution by higher frequency terms, illustrating the fast response advantage of the technique.