Biocoal research for use in heritage steam railways

The UK has over 200 heritage railway lines in operation. Traditionally these have run on coal, preferably Welsh steam coal, a form of bituminous coal known for its good calorific values, low sulphur content and semi smokeless properties. However, many of these mines in Wales are now either closed, or scheduled to close shortly. There is also competition for coal from other users (such as steel production). Similar coals sourced from Scottish mines were used up until 2020, when the last mines in Scotland closed.

Importing coal is one alternative, however this tends to be quite expensive and can yield varying results and is subject to geopolitical factors, e.g. a lot of coal was coming from Russia prior to the invasion of Ukraine.

One alternative that has been investigated is biocoal. These take various forms, but typically consisting of subjecting solid biomass (such as forest product residuals, wood chippings, bagesse, wood pulp, etc.) to pyrolysis to produce biochar. This is typically produced in the form of small pellets. However this produces a number of technical issues for steam engines.

Firstly, they have a much lower and more inconsistent calorific value compared to regular coal. Indeed there seems to be an absence of data on exactly how significant this is. Hence more fuel is needed to provide the same level of traction. Meaning the engines need to be refueled more regularly, increasing costs and reducing the range of engines between stops.

Secondly, incomplete combustion of the fuel. Coal, being of odd shapes and sizes, means air is able to easily circulate within the firebox, allowing the necessary air to circulate between the coal lumps. However, biocoal tends to sit together in a large pile, with only the fuel on the outside undergoing complete combustion. This also results in excessive amounts of ash.

It is worth noting that steam engines are largely naturally aspirated, relying on natural convection to drive air through the firebox and into the boiler. The boiler tubes are at a slight upward angle, ensuring the hot gases will pass through them at a suitable velocity to maximise heat transfer to the water in the boiler. The smoke box is designed to create a vacuum via a venturi effect in the smoke stack, to further draw air through the engine. Air is typically circulated from underneath the engine via the fire grate (primary air) but also via the coal chute doors (secondary air). In many cases operators have been forced to rely heavily on secondary air, which increases the draft level through the engine. While this increases the rate of fuel burn of the biocoal, much of the heat energy is subsequently lost up the smoke stack.

A third issue is the need to keep biocoal dry, as it is usual to store coal out in the open. Biofuels tend to be hydroscopic and will readily absorb moisture. This not only reduces their calorific value but also will increases the release of particulate matter, which produces much greater levels of pollution. Thus a means to keep the fuel dry must be found, e.g. supplying it in waterproof bags, or designing it to be less hydroscopic.

Proposed order of work:

• A more complete analysis of the problem, including investigation of the air flowrates through an engine, its energy consumption and fuel consumption.

• Investigation of the quality of biofuel and its calorific values, combustion temperatures and emissions via lab experiments. This will probably require the purchase of equipment, as we have very limited lab resources to support this kind of research.

• Development of new forms of biocoal, e.g. in different shapes to create air gaps, or with air vents cast inside of them, to improve combustion.

• Development of new storage and handling techniques to avoid moisture absorption.

• Consideration of design changes to the steam engines themselves, e.g. using forced convection of air (blowers/superchargers?) into the combustion process or use of a heat exchanger to pre-heat the input air. 

Academic qualifications

A first-class honours degree, or a distinction at master level, or equivalent achievements ideally in mechanical engineering and/or energy related topics.

English language requirement

If your first language is not English, comply with the University requirements for research degree programmes in terms of English language.

Application process

Prospective applicants are encouraged to contact the supervisor, Dr Dylan Ryan ([Email Address Removed]) to discuss the content of the project and the fit with their qualifications and skills before preparing an application. 

The application must include: 

Research project outline of 2 pages (list of references excluded). The outline may provide details about

• Background and motivation, explaining the importance of the project, should be supported also by relevant literature. You can also discuss the applications you expect for the project results.
• Research questions or
• Methodology: types of data to be used, approach to data collection, and data analysis methods.
• List of references

The outline must be created solely by the applicant. Supervisors can only offer general discussions about the project idea without providing any additional support.

• Statement no longer than 1 page describing your motivations and fit with the project.
• Recent and complete curriculum vitae. The curriculum must include a declaration regarding the English language qualifications of the candidate.
• Supporting documents will have to be submitted by successful candidates.
• Two academic references (but if you have been out of education for more than three years, you may submit one academic and one professional reference), on the form can be downloaded here.

Applications can be submitted here.

Download a copy of the project details here.