In situ sensor for cycle-resolved measurement of temperature and mole fractions in IC engine exhaust gases

Abstract

We present a multi-species mole fraction and temperature sensor for in situ exhaust gas diagnostic of internal combustion (IC) engines. The sensor is based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) and incorporates four optical channels - two miniature White cells and two double-traversal cells - with base lengths of 6 cm. It has been demonstrated at a hot air test stand and in the exhaust manifold of a single-cylinder research engine, with measured temperatures of up to 1000 K. Stable operation was achieved with absorption lengths of up to 192 cm (test stand) and 97 cm (engine). Employing time-division multiplexed detection, six species were measured simultaneously in the engine exhaust, at wavelengths ranging from 1.4 µm to 5.2 µm: water vapor (H2O), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), nitrogen dioxide (NO2) and nitric oxide (NO). The effective measurement rate was as high as 1 kHz, and cycle-to-cycle variations were clearly detected. We show the correlation of the air-fuel equivalence ratio with the spectroscopically measured mole fraction of each species. At a cycle-resolved rate, detection limits for the legally regulated species NO and NO2 were 1 ppm and 4 ppm, respectively. The sensor is intended to help improve the understanding of IC engine emission behavior during fast transients.