Development of a local continuous sampling probe for the equivalence air–fuel ratio measurement. Application to spark ignition engine |
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Authors: | P Guibert E Dicocco |
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Institution: | (1) LMP, Laboratoire de Mécanique Physique. UPRES-A 7068 Université Pierre et Marie Curie Paris 6 2, Place de la Gare de Ceinture 78210 Saint Cyr l'Ecole, Francee-mail: guibert@ccr.jussieu.fr , FR |
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Abstract: | This paper is a contribution to the development of an original technique for measuring the in-cylinder equivalence air–fuel
ratio. The main objective was to construct an instrument able to furnish instantaneous values of hydrocarbon concentration
for many consecutive cycles at a definite location, especially at the spark plug location. The probe is based on a hot-wire-like
apparatus, but involves catalytic oxidation on the wire surface in order to be sensitive to the hydrocarbon concentration.
In this paper, we present the different steps needed to develop and validate the probe. The first step focuses on the geometric
configuration to simplify as much as possible the mass transfer phenomena on the wire. The second step is a parametric study
to evaluate the sensitivity, confidence and lifetime of the wire. By physical analysis, we propose a relationship between
the electrical signal and the air–fuel equivalence ratio of the sampled gases. The third step is the application of the probe
to in-cylinder motored engine measurements, which confirms the ability of the technique to characterise, quantitatively, the
homogeneity of the air–fuel mixture, especially during the compression stroke. This work points out that the global sensitivity
is estimated at 4 V per unit of equivalence air–fuel ratio and the response time is estimated at about 400 μs. The equivalence
air–fuel ratio range is from pure air to 1.2. Experiments show that it is necessary to calibrate the system before use because
of the existence of multiple catalysis states. The probe presents advantages associated with its simplicity, its low cost
and its direct engine application without any modifications.
Received: 1 November 2000 / Accepted: 30 May 2001 |
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