Operators participating in the DfT sponsored Low Carbon Truck Trial have said the fall in the price of diesel, a lack of availability of Euro-6 dual-fuel models and methane slip has ‘killed the business case’ for dual fuel HGVs.

Last month it was revealed that independent academic analysis on 217 dual fuel gas trucks in the trial saw greenhouse gas emissions rise between 50% and 127% as a result of methane slip – leading to the RHA to accuse the trial of wasting £25m of taxpayers' money.

Methane slip is an increase in greenhouse gas emissions due to the incomplete combustion of methane as the engine switches from one fuel to the other.

The final report to the DfT Low Carbon Truck and Refuelling Infrastructure Demonstration Trial Evaluation acknowledged concerns over methane slip – but said that the independent testing was not comparable with its own testing data findings.

Operators were quoted in the report as saying: “We have [Euro-6 dual fuel] orders pending, awaiting confirmation that our new catalyst is removing methane from the exhaust stream.”

Another said that methane slip was a major barrier to adoption, while a third said that methane slip reduced the credibility of dual fuel vehicles.

A fourth argued that: “Diesel price is the main barrier; this has killed it [the business case] over the last 12 months.”

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The report, compiled by consultants Cenex and Atkins, urged the DfT that more understanding of different dual fuel technologies was required before any government policy was set in favour of certain technologies.

The trial, which began in 2012 saw the DfT, Office for Low Emission Vehicles and Innovate UK provide £11.3m to support the procurement of low emission HGVs. This resulted in 12 consortia, comprising of 35 different businesses, running 371 trucks across nine different technologies – who in turn invested an additional £12.1m in the trial. Fuels included natural gas, biomethane and UCO – a cooking oil derivative.

Over its duration the trial the low carbon truck trial fleet covered some 65 million kms, at an average distance of 3,300kms (2,050.5 miles) a week.

However trail trucks saw increases of unplanned maintenance activity per truck by two events a year and a 19% increase in downtime duration - which was primarily cited as bedding in issues caused by faulty fuel gauges and emission warning lights.