Design and development of a probe-based multiplexed multi-species absorption spectroscopy sensor for characterizing transient gas-parameter distributions in the intake systems of I.C. engines

Abstract

A 4-probe multiplexed multi-species absorption spectroscopy sensor system was designed and developed for gas property measurements on the intake side of commercial multi-cylinder internal-combustion (I.C.) engines; the resulting cycle- and cylinder-resolved concentration, temperature and pressure measurements are applicable for assessing spatial and temporal variations in the recirculated exhaust gas (EGR) distribution at various locations along the intake gas path, which in turn is relevant to assessing cylinder charge uniformity, control strategies, and computational fluid dynamics (CFD) models. The diagnostic is based on absorption spectroscopy and includes an H2O absorption system (utilizing a 1.39μm distributed feedback (DFB) diode laser) for measuring gas temperature, pressure, and H2O concentration, and a CO2 absorption system (utilizing a 2.7μm DFB diode laser) for measuring CO2 concentration. The various lasers, optical components and detectors were housed in an instrument box, and the 1.39-μm and 2.7-μm lasers were guided to and from the engine-mounted probes via optical fibers and hollow waveguides, respectively. The 5kHz measurement bandwidth allows for near-crank angle resolved measurements, with a resolution of 1.2 crank angle degrees at 1000 RPM. The use of compact stainless steel measurement probes enables simultaneous multi-point measurements at various locations on the engine with minimal changes to the base engine hardware; in addition to resolving large-scale spatial variations via simultaneous multi-probe measurements, local spatial gradients can be resolved by translating individual probes. Along with details of various sensor design features and performance, we also demonstrate validation of the spectral parameters of the associated CO2 absorption transitions using both a multi-pass heated cell and the sensor probes.