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Steve Whelan, Technology Director,
Clean Air Power urges the transport industry to standardise measurement
of emissions by using the ‘Well To Wheels’ (WTW)
evaluation formula. This gives a true and realistic figure for all
fuels from source to powering the engine, rather than simply taking the
emission reading from the exhaust. It covers all stages of the fuel
cycle, from energy and feedstock recovery in the case of biofuels, to
energy delivered to the vehicle’s wheels.
As early as 1995, with funding from the
US Department Of Energy’s (DOE) Office of Transportation Technologies,
the GREET model was developed by the Argonne National Laboratory, one of
the US DOE’s largest research centres, as an analytical tool to estimate
WTW energy use and emissions associated with transportation fuels and
advanced vehicle technologies. This model separately calculated:
- Fuel-cycle energy consumption for
total energy (all energy sources), fossil fuels (petroleum, Natural
Gas and coal), and petroleum
- Fuel-cycle emissions of GHGs – CO2,
Methane and N2O
- Fuel-cycle emissions of five
criteria pollutants, separated into urban and total emissions –
Volatile Organic Compounds, CO, NOx, particulate matter and SOx
Since then, WTW has formed the basis of
numerous high level studies into viable alternative fuel around the
world. This includes the study of WTW Energy Use commissioned by the US
DOE, and the more recent evaluation of bio-methane in the research
paper ‘Fuelling the Future’, produced by
Biogas West and Business Region Göteborg, Sweden.
Steve says: “We believe that WTW gives
the true reading of emissions from source to powering the vehicle and
should be adopted by the heavy goods transport industry in the UK, and
in fact globally. Our technical team has used the WTW formula to
calculate the efficiency of Dual-Fuel™, using Natural Gas substitution
of diesel. The results are extremely positive, and provide further
evidence that our technology delivers an immediate solution to
substantially reduce CO2 emissions and generate cost
savings.”
As shown in the table above, using the
WTW emissions model, fuelling a standard diesel engine with Natural Gas
(NG), facilitated by Dual-Fuel™ technology equals the best current WTW-efficient
fuel. As NG contains less carbon and more energy than diesel, the
Dual-Fuel™ WTW efficiency translates into a c.20% reduction in WTW
carbon footprint over diesel.
In the drive to cut pollutant – air
quality related – exhaust emissions, especially particulates (soot), NG
is a clear winner. Whether delivered in compressed (CNG) or liquefied
(LNG) form, it scores highly in any WTW evaluation. NG drawn from the
earth’s plentiful underground reserves has high methane and energy
content and requires minimal energy-intensive processing, other than
compression or liquefaction and transportation.
When engines are fuelled with NG in the
form of renewable bio-methane, the WTW balance is even more favourable,
the gas being produced typically close to the point of use, minimising
tanker or pipeline costs. Furthermore, the fuel is wholly renewable.
When Bio-methane is considered, the WTW carbon footprint can approach
zero as Bio-methane production gives the best energy yield per hectare
of any bio-fuel. Dual-Fuel™ operates with bio-diesel and bio-methane.
As Dual-Fuel™ uses the liquid fuel as an ignition source only; it
requires only a fraction of the liquid fuel of a conventional diesel
engine. Therefore, it makes best use of the scarce bio-diesel resources
and the plentiful bio-methane sources. With the shortage of available
land for low-yield bio-diesel production, Dual-Fuel™ has the potential
to optimise the use of bio-fuels; taking what is available and using it
efficiently.
A Dual-Fuel™ engine running on
bio-methane with bio-diesel in its ‘pilot’ fuel tank – brings together
the fuel’s WTW attributes and the universally acknowledged fuel
efficiency of the Diesel combustion cycle. As a fuel-engine combination
it offers the highest possible WTW energy efficiency, which translates
also into low greenhouse gas (CO2) and air-quality emissions.
When whole-life costings for the truck or bus operator are also taken
into account, Dual-Fuel™ technology based on bio-fuel usage offers a
unique blend of environment-friendliness and attractive economics.
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