Combustion Engineering

The development and implementation of alternative fuels is currently of significant interest to the aviation industry. As the concern over the environmental impact of the emissions of traditional fuel increases, so does the demand for newer, innovative, cleaner fuels to be used. The uncertainty as to the availability and cost of traditional fuel based on oil resources is also a factor driving the development of new fuels. Synthetically produced fuels can be obtained via various methods and sources. These fuels are similar in composition and properties to those of traditional jet fuel. This allows the composition of jet fuel to be augmented by integrating synthetic fuel and using the blended fuel for aviation.

While the emissions of many of these fuels have been considered previously, there is a significant knowledge gap when it comes to considering the other significant factors that affect an engines performance and lifespan. This project would seek to fill that gap by generating a holistic model that would seek to categorise the entire engine response to a range of alternative fuels.

This project would seek to investigate the performance of a variety of combustion systems using different variations of alternative fuel blends. This would include analysing the effect on:

i) Combustor and Engine Noise
ii) Combustor and Engine Vibration
iii) Combustion Instability
iv) Engine Life
v) Size and Density of Particulate Emissions
vi) Heat Signature

This project would be comprised of four stages:

i) Fuel Selection

A range of alternative fuels, blends and surrogates will be selected. This will involve a systematic review of all currently available alternative fuels, surrogates and blends. The combustion characteristics being studied are predominantly determined by the boiling point, viscosity, vapour pressure, density, energy density per volume, energy density per unit mass, flame speed and cetane rating of the fuel in question. For this reason, the range of fuels selected will need a variety of performance characteristics to fit these criteria. Gas chromatography analysis would be used on each fuel selected to determine its chemical composition.

ii) Experimental Phase 1

The fuels selected will be burned at a range of equivalence ratios to investigate the effect of each fuel on the criteria listed previously. A majority of low emission technologies burn fuel where there is a lower proportion of fuel compared to air, also known as a lean burn. For this reason, particular emphasis will be placed on experimenting with fuels at lean ratios in order to effectively evaluate each alternative fuel as these results will have the most relevance. Two different sizes of combustor will be used at this stage in order investigate and analyse the instabilities in different combustor sizes, both of which are available at the LCCC.

iii) Experimental Phase 2

A small gas turbine engine, or APU, will be used with the fuels selected with a similar methodology to Phase 1. During this phase however, baseline fuels will also be burnt in order to provide a comparison in terms of performance. As a gas turbine introduces higher pressure ratios not found in stand-alone combustors, testing on this platform will provide performance instability data using a configuration more relevant to actual engines.

iv) Data Analysis and Modelling

The experimental data will be analysed in order to generate a holistic model of the effect of alternative fuels on a variety of factors, such as vibrations, noise, emissions, heat signature, combustion instability, the size and density of particulates and would allow predictions of the engine life and any potential maintenance. The model will be tested by making predictions on currently available fuels not included in the experimental phase, testing them and then comparing the models predictions to the experimental data.