2012 Bio-fuel trials

In the spring and summer, of 2012 ASTT undertook trials using compressed wood chips, wood briquettes, torrefied wood and bio-coal, aimed at gaining an understanding of what might be achieved using these alternative fuels.

The plan was to start the trials on miniature locomotives and then provided trials were successful, scale up to narrow gauge, then standard gauge. This strategy also meant that for the early trials we did not need large quantities of the bio-fuels, which in 2012 were in short supply.

Trials were started in April 2012 on the Stapleford Miniature Railway – a 10¼” gauge line with a two-mile track run. Here we had sole use of the railway, so we could run as required, without affecting service trains. These trials experimented with compressed wood chips, wood briquettes and torrified wood. Bio-coal was first tried in June 2012.

Wood chips, wood briquettes and torrified wood were soon discounted because of smoke, spark throwing and inability to maintain steam.

Wood Briquettes

Torrefied Wood

Bio-coal showed the most promise, though the product available in 2012, while it came closer to the energy content of coal, was less dense, dusty and could break up when handled.

June 2012 Sample of bio-coal

On the left biocoal, in the middle ovoid’s, on the right Welsh steam coal


Stapleford Test Locomotive – Curwen Atlantic

Checking Firebed Temperature

In July 2012, the trials moved to the Wells and Walsingham Railway – another 101/4” gauge railway but with substantially larger engines and an 8-mile round trip on a line with heavy gradients.

The bio-coal used for this trial was an improved version of the previous grade with less dust and fines.

Wells & Walsingham Railway’s test loco – 2-6-0+0-6-2 Garratt “Norfolk Heroine”

Three runs on service trains were carried out. The trial provided useful information about the product, some confirmed earlier findings and some were new.

The earlier trials of bio-coal at Stapleford gave concerns about fast burning, and spark and smoke emissions, but hinted that heat output might be satisfactory. The trial with a larger engine and firebox and a far more rigorous duty cycle confirmed that the heat output was satisfactory.

The major concern was the excessively fast burn rate under high draught conditions, which combined with the lower bulk density of the product made it virtually impossible to build a workable firebed, without constant firing. As a rough estimate, the consumption of bio-coal was around 4 to 5 times the volume of Welsh Steam coal normally used on this engine.

A steam locomotive can work very effectively with a thin fire provided the fuel is sufficiently dense so that it is not sucked off the firebars. Under light draught, bio-coal was observed to perform reasonably well and it could be intermittently fired and maintain steam pressure, but immediately a higher draught was required then holes appeared immediately in the firebed. Trying the alternative thick bed required constant firing and, even then, the bottom of the fire was burning away so quickly that it was not possible to build to a suitable depth.

The view at the time was that if the bio-coal could be produced during manufacture with greater compression and hence with greater bulk density and in larger sizes, it would decrease the burn rate and reduce smoke and spark emissions.

Our trials came to end in 2012 because we could not get supplies of an improved product.

In 2017 we carried out a further trial at the Wells and Walsingham Railway using a biocoal produced in the UK and the results were the same as in 2012.

CSR Biocoal Trials, USA

During 2016 to 2018, the Coalition for Sustainable Rail (CSR) in the USA has carried out trials with bio-coal in a similar manner to ourselves but using a denser product. They also started their trials on a narrow-gauge railway. Wolf Fengler of the CSR came over to the UK in October 2017 and gave a presentation on the results at ASTT’s 2017 Conference.

In October 2019 Wolf flew over again to attend ASTT’s 2019 Conference where he gave an update on CSR’s later trials. These were conducted at the Everett Railroad in Pennsylvania on a standard gauge locomotive, using a denser product closer to the characteristics of coal.


Our current conclusion is that bio-coal and its use in locomotives is still in the development phase. It may be a viable successor to coal, provided it can come close to the characteristics of coal and can be produced in bulk and made commercially available at an economical price.

ASTT is in discussion with CSR and the UK’s Heritage Railway Association about conducting trials in the UK, using the USA bio-coal being developed by CSR and their partners, the Natural Resources Research Institute of The University of Minnesota.