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September 2009

Dennis takes to the road for dual fuel

Norman Thoday weighs up the options for low carbon refuse vehicle solutions before coming out in favour of dual fuel as the most practical technology

Driving down emissions is an increasingly important consideration for local authorities and waste management companies. But with cost also playing a major role, choosing a viable long-term solution is essential if returns on investment are to be delivered.

Customers want solutions that offer maximum reliability, efficiency and payback combined with minimum carbon emissions. Those who act now to reduce emissions will be in a strong position to meet the future challenges of a low carbon economy. However, with developments under way in the areas of dual fuel, gas and electric/hybrid, the question is, which type of technology will prevail?

All these systems present arguments for use in the RCV market, but as the practicalities of putting an infrastructure in place to support them become a reality, it is likely that one will emerge as a more viable option. At Dennis Eagle, we believe dual fuel is the strongest contender, which is why we are investing heavily in a development programme for this type of technology. Electric/hybrid is a popular concept and it is becoming widely accepted as a low carbon fuel alternative. But the inherent differences between RCVs and cars make it an impractical choice for the waste management sector.

Heavier technology will have a detrimental effect on payload, which is a major concern. Compared with a 26-tonne electrically powered vehicle, a dual fuel alternative will be 2,000 - 3,000kg lighter. There is also the fact that depots will need to put adequate charging facilities in place before the technology can be adopted on a wider scale, meaning additional sacrifices in terms of space, time and cost.

Power issues
Other considerations include the impact power requirements will have on the national grid and the true value the technology will deliver when weighing up fuel savings against electricity costs. Battery packs are another potentially problematic area. The technology is relatively immature and this presents some issues, particularly where 'pack on the move' is used. The power requirements to move the vehicle and to complete the packing cycle are considered detrimental to battery state and long-term battery life, both of which increase the environmental impact of an electric vehicle.

Gas also has limitations. Pure gas requires spark ignition, which gives power and torque characteristics well below those normally experienced with a diesel engine. Due to the stop-start work and low engine speed of RCVs, a rich mixture is required to maintain power at low revs, with higher fuel consumption meaning vehicle range is severely limited. Clearly this is not an option for customers who want to collect the same waste volume for the same cost and efficiency.

Consider capital costs
Dual fuel systems overcome the problems associated with pure gas by using a standard diesel engine, combining the fuel efficiency, torque and power benefits of diesel with the lower emissions levels and cost benefits of gas power. In addition, capital costs for the equipment are lower than those for a dedicated compressed natural gas (CNG) fuel system and operators have the flexibility of reverting to 100% diesel in the event of problems with CNG fuel supply or technical issues.

CNG fuel costs are around 40% lower than for diesel, but if liquefied bio-methane is used, further benefits can be gained by the carbon offset that is produced. Our parent company, Ros Roca, is investing heavily in anaerobic digestion technology, which is potentially one of the most important renewable energy sources of the future. The micro-organisms used in anaerobic digestion create methane-rich biogas that can be used to produce bio-methane to fuel vehicles. Ros Roca is working currently with Biffa to develop technology for a number of large scale UK plants.

Norman Thoday is managing director of Dennis Eagle

This article first appeared in LAWR September 2009 page 13

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