A laser-absorption sensor for in situ detection of biofuel blend vapor in engine intakes

A novel, mid-infrared laser-absorption sensor was developed for measurements of biofuel blend (E85) vapor in the intake runner of a single-cylinder internal combustion engine. The sensor used two mid-infrared interband cascade lasers to target a region of strong E85 absorbance near 3.35 & mu;m. The lasers were co-aligned and fiber-coupled into the engine, and a two-color, online-offline differential absorption strategy was used to provide sensitive measurements of E85 vapor mole fraction and reject interference due to beam-steering and fuel droplet spray. An intensity-modulation spectroscopy (IMS) sensing scheme was employed to reject lowfrequency additive noise and allow for frequency-domain multiplexing of the two lasers. High-resolution E85 absorption cross-section measurements were conducted in a static cell at a range of intake-relevant conditions. Validation experiments were performed in a laboratory setting to demonstrate sensor accuracy and noise rejection capability. The sensor was deployed on a single-cylinder development engine during dynamometer testing to provide time-resolved E85 vapor mole fraction measurements at a measurement rate of 40 kS/s, which corresponds to one measurement per crank angle degree at 6700 rpm. Time-resolved and average sensor measurements provide key performance insights for the development of intake systems in(C)2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

A novel mid-infrared laser-absorption sensor was developed for measuring E85 vapor in the intake runner of an internal combustion engine. The sensor used two interband cascade lasers and a differential absorption strategy to achieve sensitive and accurate measurements. High-resolution measurements and validation experiments were conducted to demonstrate the sensor's performance. The sensor was deployed on a single-cylinder engine during dynamometer testing to provide time-resolved measurements.