David McCormick

Progress towards non-intrusive optical measurement of gas turbine exhaust species distributions

We report on the development of three systems intended to provide fast, non-intrusive measurement of cross-sectional distributions of pollutant species within gas turbine exhaust flows, during ground-based testing. This research is motivated by the need for measurement systems to support the introduction of technologies for reducing the environmental impact of civil aviation. Tomographic techniques will allow estimation of the distributions of CO2, unburnt hydrocarbons (UHC), and soot, without obstruction of the exhaust, bypass or entrained flows, from measurements made in a plane immediately aft of the engine.

Implementation of non-intrusive jet exhaust species distribution measurements within a test facility

We report on the installation and commissioning of two systems for the measurement of cross-sectional distributions of pollutant species in jet exhaust, within the engine ground test facility at INTA, Madrid. These systems use optical tomography techniques to estimate the cross-sectional distributions of CO2 and soot immediately behind the engine. The systems are designed to accommodate the largest civil aviation engines currently in service, without obstruction of the exhaust or bypass flows and with negligible effect upon the entrained flow behavior. We describe the physical construction and installation status of each system. In the case of the CO2 system, we examine the challenges of achieving the structural rigidity necessary for adequate suppression of pointing error within 126 laser-based transmittance measurements, each utilizing a 7 m overall path length. We describe methods developed for efficient implementation of co-planarity and 4-degree-of-freedom alignment of individual paths within this beam array. We also present laboratory performance data for three alternative optical designs that differ in their approach to the management of pointing error and turbulence-induced beam wander and spread. The FLITES soot monitoring capability is based on laser induced incandescence (LII) and uses a short-pulse fiber laser and two CCD cameras, in an autoprojection arrangement. We describe the measurement geometry currently being implemented in the test cell and discuss optical design issues, including once again the effect of the plume itself.

In-situ soot particle sensing in an aero-engine exhaust plume

This paper reports the use of a fiber-laser to produce spatially resolved images of the distribution of absorbing particles in the exhaust plume of a modified helicopter gas turbine engine. In-situ sensing of soot particles by Laser-Induced Incandescence (LII) is demonstrated using fiber-lasers with higher power, longer pulse duration, and higher pulse repetition rates than conventional LII. The sensitivity of the method is illustrated by the detection of ambient absorbing particles prior to engine running. With a running engine images are obtained in 0.01s. The demonstration of LII using fiberlasers is a first step in the development of a new model for long-pulsed LII.

Conversion of EIT brain images for co-registration

Electrical Impedance Tomography (EIT) has previously been used to image brain function in evoked responses. The EIT images are based on a realistic 3D FEM model of the head. It would be advantageous to co-register the EIT images onto anatomical images generated through another modality, therefore allowing for an overlay of the measured functional brain activity with a true representation of the head. For realistic models, the problem is computationally intensive due to discrepancies between the tetrahedral mesh of the EIT images and the cubic meshes of other image modalities. This paper introduces Confeitir; a Matlab-based program, pioneering a novel approach to map the tetrahedral based EIT data onto a new structured cubic mesh, providing the capability of co-registration with other image modalities.

High-Sensitivity In Situ Soot Particle Sensing in an Aero-Engine Exhaust Plume Using Long-Pulsed Fiber-Laser-Induced Incandescence

A method to produce spatially resolved images of the distribution of absorbing particles in the exhaust plume of a modified helicopter gas turbine engine is presented. Over a small region of the plume, in situ sensing of soot particles by laser-induced incandescence (LII) is demonstrated using fiber lasers with higher power (~10 W), longer pulse duration (>100 ns), and higher pulse repetition rates (>10 kHz) than the conventional LII. The sensitivity of the method is illustrated by the detection of ambient absorbing particles in background conditions with engine at rest. With a running engine, single-beam images are obtained in 0.01 s. The feasibility of using long-pulsed fiber lasers for soot particle concentration measurement is investigated using a representative laboratory system. The time-resolved LII behavior and the measurement linearity are investigated, demonstrating the suitability of using fiber lasers for soot particle measurement for aero-engine emissions. Results for normalized soot concentration are compared with extractive measurements illustrating good correlation across a range of engine speeds. This paper is the first step toward the development of a non-intrusive system for the measurement of 2-D soot concentration in the cross section of an aero-engine exhaust plume.