Four-color fiber-coupled mid-infrared laser-absorption sensor for temperature, CO, CO₂, and NO at 5 kHz in internal combustion engine vehicle exhaust

A mid-infrared (MIR) laser absorption spectroscopy (LAS) sensor was developed for temperature, CO, NO, and CO₂ measurements at 5 kHz in engine-out exhaust. It used fiber-coupled quantum cascade lasers (QCLs) for measuring CO and NO, and an interband cascade laser (ICL) for measuring CO₂. Validation tests in a heated gas cell confirmed that the LAS measurements of CO, CO₂, NO, and temperature are accurate to within 4.8%, 5.1%, 4.6%, and 3.1%, respectively, at 1–2 atm and 300–1000 K. The LAS sensor was applied to characterize the engine-out exhaust gas of an 8-cylinder gasoline engine in a light-duty truck at operating conditions where commercial instruments lack sufficient time response to quantify important emission dynamics.