Smart Sensors for Advanced Combustion Systems


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Introduction

This research is directed at the development and application of a new class of optical
sensors, based on absorption of light from tunable diode lasers, which enable in situ
measurements of temperature and gaseous composition, in real time and in a variety of
research-oriented and practical energy-conversion systems. These sensors have
significant potential to enable exploratory research on new energy conversion concepts,
to expedite the pace of development of new combustion technologies with reduced
pollutant and greenhouse emissions, and to facilitate gains in performance (reduced
greenhouse emissions and reduced maintenance) in existing combustion systems. In
addition, the real-time capability of these sensors will enable explorations of new,
unsteady energy-conversion schemes with the potential for reduced emissions through
real-time control.

Background

The Stanford University research on smart optical sensors investigates a unique
sensor strategy that exploits the use of wavelength-multiplexing to combine the beams
from multiple diode lasers onto a single path as shown in Fig. 2. The optical absorption
signal expected in a practical combustion application is modeled using laboratoryvalidated
quantitative spectroscopic constants. These models enable selection of the
optimum molecular transitions from the tens of thousands of potential candidates. The
combination of process and spectroscopic modeling enables the design of smart
absorption-based sensors tailored to the specific combustion application. This sensor
design strategy is quite different from that used by past researchers.

Future Plans

Quantitative measurements of fuel are crucial to combustor development and
combustion control applications. Earlier in the project we investigated the potential of
fuel sensing in the mid-infrared and concluded that a wavelength tunable light source
near 3.3μm was needed. We have contracted to have such a specialty light source
fabricated and anticipate delivery in the next few weeks. This diode laser-based light
source uses difference frequency mixing to provide tunable light for hydrocarbon fuel
sensing. Our first measurements are anticipated to be on gasoline for internal combustion
engine applications.