Affiliation:
1. Purdue University, School of Mechanical Engineering, USA
2. Ford Motor Company, Research and Advanced Engineering, USA
3. Purdue University, School of Aeronautics and Astronautics, USA
Abstract
<div>Measurements of air–fuel ratio (AFR) and <i>λ</i>
(AFR<sub>actual</sub>/AFR<sub>stoich</sub>) are crucial for understanding
internal combustion engine (ICE) performance. However, current
<i>λ</i> sensors suffer from long light-off times (on the order of
seconds following a cold start) and limited time resolution. In this study, a
four-color mid-infrared laser absorption spectroscopy (LAS) sensor was developed
to provide 5 kHz measurements of temperature, CO, CO<sub>2</sub>, and NO in
engine-out exhaust. This LAS sensor was then combined with 1 kHz hydrocarbon
(HC) measurements from a flame ionization detector (FID), and the Spindt exhaust
gas analysis method to provide 1 kHz measurements of <i>λ</i>. To the
authors’ knowledge, this is the first time-resolved measurement of
<i>λ</i> during engine cold starts using the full Spindt method.
Three tests with various engine AFR calibrations were conducted and analyzed:
(1) 10% lean, (2) stoichiometric, and (3) 10% rich. The measurements were
acquired in the exhaust of a light-duty truck with an 8-cylinder gasoline
engine. The LAS-FID-based <i>λ</i> sensor results were compared with
those obtained from a universal exhaust gas oxygen (UEGO) sensor. The LAS-FID
method provided robust <i>λ</i> measurements from the first combustion
exhaust event (avoiding the light-off time associated with traditional
<i>λ</i> sensors) in addition to enhanced temporal resolution (on
the order of 100× increase compared to traditional diffusion-based
<i>λ</i> sensors). The insight gained from this novel method could
be used to benefit crank, cold start, and open- or closed-loop air–fuel ratio
control strategies in gasoline engines for reduced emissions.</div>