A Mid-Infrared Laser Absorption Sensor for Gas Temperature and Carbon Monoxide Mole Fraction Measurements at 15 kHz in Engine-Out Gasoline Vehicle Exhaust

Abstract

<div>Quantifying exhaust gas composition and temperature in vehicles with internal combustion engines (ICEs) is crucial to understanding and reducing emissions during transient engine operation. This is particularly important before the catalytic converter system lights off (i.e., during cold start). Most commercially available gas analyzers and temperature sensors are far too slow to measure these quantities on the timescale of individual cylinder-firing events, thus faster sensors are needed. A two-color mid-infrared (MIR) laser absorption spectroscopy (LAS) sensor for gas temperature and carbon monoxide (CO) mole fraction was developed and applied to address this technology gap. Two quantum cascade lasers (QCLs) were fiber coupled into one single-mode fiber to facilitate optical access in the test vehicle exhaust. The QCLs were time-multiplexed in order to scan across two CO absorption transitions near 2013 and 2060 cm<sup>–1</sup> at 15 kHz. This enabled in situ measurements of temperature and CO mole fraction to be acquired at 15 kHz in the engine-out exhaust of a research vehicle (modified production vehicle) with an 8-cylinder gasoline ICE. Three different vehicle tests were characterized with the LAS sensor as follows: (1) cold start with engine idle, (2) warm start with a drive cycle on a chassis dynamometer, and (3) hot start with a drive cycle on a chassis dynamometer. The measurements obtained from the LAS sensor had a time resolution that was three orders of magnitude faster than that of thermocouple and gas analyzer data acquired at the Ford vehicle emissions research laboratory (VERL) in Dearborn, Michigan. This enabled the LAS sensor to resolve high-speed engine dynamics and exhaust gas transients, which the conventional instrumentation could not, thereby providing valuable insight into the evolution of ICE emissions during transient engine operation.</div>