Tracer-free, non-intrusive, time- and space-resolved temperature and scalar measurements

The growth in air transport, and the need for base and balance thermal power in an electricity-powered future centres creates a pressing need for low emission, high efficiency gas turbines, particularly regarding NO, CO and soot. The key variables determining the production of these pollutants in the product gases are the local instantaneous product gas temperature and the local fuel fraction. The large fluctuations in gas temperature, and the exponential dependence of pollutant production on temperature means that predictions of NO, CO and soot in combustion are not possible without suitable accurate statistics of instantaneous local temperature measurements. Yet there are very few such measurements in practical devices to validate models. Local instantaneous temperature measurements in high pressure radiant devices require optical techniques which are rather complex for industrial laboratories. This proposal aims to extend a much simpler technique for the purpose to allow tracer free local measurements of temperature, pressure and water vapour.

Laser-induced grating spectroscopy (LIGS) has been shown to work even in highly radiant, soot-prone environments, and may also enable local measurements of additional target scalars (water vapour, pressure) using the easily accessible Nd:YAG laser wavelength of 1064 nm. The technique uses both the electrostrictive mode and weak absorption spectral lines in this wavelength range to enable measurements of both temperature and relative water concentrations in realistic devices. The signal to noise of the technique improves with pressure, a significant advantage for realistic devices, especially in environments such as gas turbines, which are prone to large amounts of radiant luminosity. The project will extend the current capabilities of the technique from point measurements to spatially resolved line measurements. Finally, it will extend the pump laser wavelength into near infrared, which will unlock the ability of the technique to use strong absorption lines for a range of widely available species (water, carbon dioxide and hydrocarbons), using industrial lasers at high repetition rates.

The final outcome of the project will be the development of an instrument and method for non-intrusive temperature and species measurements in high temperature, high pressure practical reacting flows, requiring only a fraction of the cost of previous techniques of comparable precision. Demonstration measurements will be produced in a high pressure, high temperature, realistic industrial facility. Data produced during these measurements will also allow researchers and developers to review and validate robust reacting flow models for industry and open up the possibilities for optimisation of clean energy conversion devices.

The plan for technology transfer is ensured by partnering with a company (Dantec) that has already packaged and commercialised similar instruments. An extension of the validation measurements to other industrial facilities at Rolls-Royce is planned once the instrument development and demonstration has been successfully concluded. Finally, the project will also offer opportunities to PhD students associated with the Energy CDT at Cardiff.

The UK continues to invest strategically in the aerodynamics and propulsion area, via the Aerospace Technology Institute, and the National Combustion Facility. The UK is one of the leading suppliers of gas turbine and automotive engines components and associated engineering services, both in manufacture as well as simulations, which rely on the continuing development of high-end capabilities. These will be challenged given the aggressive targets of reduction of aeroengine and industrial NOx, CO2 and and soot emissions.

The proposed project will further develop and demonstrate the non-intrusive laser-induced grating spectroscopy technique for temperature and water mass fraction measurements, which offers the best precision for practical high pressure systems, and which can be disseminated through the gas turbine, automotive and other propulsion systems.

The main impact of the project will be the development of an instrument and method for non-intrusive temperature measurements in high temperature, high pressure practical reacting flows, requiring only a fraction of the cost of previous techniques of comparable precision. The accurate and precise measurement of local and instantaneous temperatures in gas turbines and engines is key to understanding how to improve their energy conversion and emissions performance, leading to lower soot and nitric oxide emissions.

The use of the fundamental and easily accessible 1064 nm wavelength with laser induced grating spectroscopy opens up the application of the technique to a much wider range of researchers. The technique uses both the electrostrictive mode and weak absorption spectral lines in this wavelength range to enable measurements of both temperature and relative water concentrations in realistic devices, including those that may have significant amounts of luminous soot.

Data extracted by the technique will allow researchers and developers to review and validate robust reacting flow models for industry and open up the possibilities for optimization of clean energy conversion devices. Immediate benefits will accrue from the deployment of the technique to generate a database of temperature maps in a realistic gas turbine test facility; downstream benefits will arise from the eventual packaging and commercialisation of the instrument undertaken by one of the partners in the project. Finally, an exploratory extension into near infrared excitation may eventually yield a more powerful technique which would work with a larger number of species at lower energies.