Abstract
1-methylnaphthalene (1-MN) is a widely used laser-induced fluorescence (LIF) tracer for planar imaging of mixture formation and temperature distributions in internal combustion (IC) engines. As the LIF measurement results can be biased by partial tracer oxidation, the conversion of 1-MN and the base fuel isooctane is analyzed in a calibration cell. First, measurements using supercontinuum laser absorption spectroscopy (SCLAS) are presented in order to quantify the conversion by detection of the produced H2O mole fraction. A single mode fiber (SMF) coupled setup is presented, with the fiber core acting as entrance slit of a Czerny-Turner spectrometer. Dependencies on residence time and global air-fuel ratio are presented at pressures up to 1.5 MPa and temperatures up to 900 K, at which distinct tracer and fuel consumption is observed. Signal loss due to intense beam steering was partially compensated using a self-stabilizing double-pass setup with a retroreflector.
Highlights
Laser-induced fluorescence (LIF) based on tracers is a well-established diagnostic technique for measurements in the gas, liquid, and solid phase
The tracer is usually added to a fuel, so that the thermo-physical and chemical properties of the tracer and the fuel should closely match to avoid a bias in the mixture formation, ignition, and combustion processes
We investigate the fuel/tracer reaction in a continuously scavenged calibration flow cell (HTC2 ) at various conditions and residence times via the detection of water formation while using near infrared (NIR) supercontinuum laser absorption spectroscopy (SCLAS)
Summary
Laser-induced fluorescence (LIF) based on tracers is a well-established diagnostic technique for measurements in the gas, liquid, and solid phase. The tracer is usually added to a fuel, so that the thermo-physical and chemical properties of the tracer and the fuel should closely match to avoid a bias in the mixture formation, ignition, and combustion processes. The auto-ignition temperature gives a rough indication of the chemical stability of fuel and tracer. The residence time of the fuel and tracer in the hot ambience are relatively short during compression (few milliseconds), but relatively long for calibration measurements in a static chamber or flow cell (e.g., several seconds) [8]. The LIF-calibration data may be biased in the case of pyrolysis and oxidation of the tracer at long residence times. Kinetic studies in a shock tube exist for some tracers, but the conditions studied usually deviate from those present in IC engines and calibration cells [7]. In situ measurements during calibration are favorable to identify tracer consumption
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