An In Situ Laser-Absorption Sensor for Crank Angle-Resolved Temperature, Pressure, and Humidity in Intake-Runner Flows

Intake-runner fluid dynamics represent a vital component in the global performance of internal combustion engines, but limited diagnostics exist to characterize these gas flows. In this work, a laser absorption-based sensor was developed to measure intake-runner gas temperature, pressure, and water (H₂O) mole fraction with crank-angle resolution. The sensor was designed to target two temperature-sensitive 1.8 μm absorption transitions in ambient H₂O vapor. A high-resolution study of both lines was conducted, and a novel, multi-harmonic wavelength-modulation-spectroscopy (WMS) detection technique was developed to achieve sensitive measurements at 31 kS/s (once per crank angle degree at 6000 RPM). The sensor was validated in the laboratory across a range of intake-relevant conditions and subsequently demonstrated during dynamometer (dyno) testing of a single-cylinder development engine under motored and fired conditions. Beyond this demonstration, the sensor can readily be adapted for integration with a broad range of engine-intake architectures.