Development of an instantaneous local fuel-concentration measurement probe: an engineapplication

Abstract

This work presents a new tool which can deliver instantaneous local measurements of fuelconcentration in an engine cylinder with a high temporal resolution, particularly duringcompression strokes. Fuel concentration is represented by means of equivalence fuel–airratio, i.e. the real engine mass ratio of fuel to air divided by the same ratio in idealstoichiometry conditions.Controlling the mixture configuration for any strategy in a spark ignition engine and forauto-ignition combustion has a dominant effect on the subsequent processes of ignition,flame propagation and auto-ignition combustion progression, pollutant formationunder lean or even stoichiometric operating conditions. It is extremely difficult,under a transient operation, to control the equivalence air/fuel ratio preciselyat a required value and at the right time. This requires the development of ahighly accurate equivalence air/fuel ratio control system and a tool to measureusing crank angle (CA) resolution. Although non-intrusive laser techniques haveconsiderable advantages, they are most of the time inappropriate due to theiroptical inaccessibility or the complex experimental set-up involved. Therefore, as aresponse to the demand for a relatively simple fuel-concentration measurementsystem a probe is presented that replaces a spark plug and allows the engine to runcompletely normally. The probe is based on hot-wire like apparatus, but involvescatalytic oxidation at the wire surface. The development, characteristics andcalibration of the probe are presented followed by applications to in-cylinder enginemeasurements.