Dear All,
I have just read the article at http://www.metrication.us/content/demise-mpg
where I was struck by the first paragraph.
Even before the advent of partially- or fully-electric cars, it was
becoming increasingly apparent that the old fuel economy metric of
miles per gallon isn't as useful for measuring energy consumption in
vehicles as when it was first codified in the original Corporate
Average Fuel Economy standard in the 1970s. That is due in part to the
proliferation of new fuels--E85, LPG, LNG, CNG, methanol, and
hydrogen--but also because expressing the relationship between
distance and volume in this way obscured the diminishing returns to
higher levels of fuel economy. As a Wall St. Journal column earlier
this week put it, adding electricity into the mpg mix, "risks giving
consumers inaccurate information about the financial and environmental
costs of driving." But if we need a new metric, what should it measure?
I think that the time is rapidly approaching for energy to be measured
in the only SI energy unit – joule – and that old pre-metric measuring
words for fuel efficiency should be converted to the only SI unit
available for energy efficiency for road transport – joules per metre.
As a starting reference, here are some examples:
Average car
32 megajoules per litre (32 MJ/L) for lead free car fuel, and
10 litres per 100 kilometres (10 L/100 km) fuel consumption, then
an average car consumes 3 200 joules of energy for each metre it
travels (3 200 J/m).
Average truck
38.6 megajoules per litre (38.6 MJ/L) for diesel fuel, and
40 litres per 100 kilometres (40 L/100 km) fuel consumption, then
an average truck consumes 15 440 joules of energy for each metre it
travels (15 440 J/m).
Average (school) bus
38.6 megajoules per litre (38.6 MJ/L) for diesel fuel, and
35 litres per 100 kilometres (35 L/100 km) fuel consumption, then
an average truck consumes 13 510 joules of energy for each metre it
travels (13 510 J/m).
Average Boeing 747
34 megajoules per litre (34 MJ/L) for diesel fuel, and
16 litres per 100 kilometres (16 L/100 km) fuel consumption, then
an average truck consumes 5 440 joules of energy for each metre it
travels (5 440 J/m).
Summary
Car 3 200 J/m
Boeing 747 5 440 J/m
School bus 13 510 J/m
Truck 15 440 J/m
As usual, I commend to you the simplicity of SI units and the ease of
understanding using whole numbers (see http://www.metricationmatters.com/docs/WholeNumberRule.pdf
).
Sadly, I could not find comparative figures for electric cars – even
at http://www.optimalenergy.co.za/news/article.php?pk_news_id=112v
Cheers,
Pat Naughtin
Author of the ebook, Metrication Leaders Guide, that you can obtain
from http://metricationmatters.com/MetricationLeadersGuideInfo.html
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has
helped thousands of people and hundreds of companies upgrade to the
modern metric system smoothly, quickly, and so economically that they
now save thousands each year when buying, processing, or selling for
their businesses. Pat provides services and resources for many
different trades, crafts, and professions for commercial, industrial
and government metrication leaders in Asia, Europe, and in the USA.
Pat's clients include the Australian Government, Google, NASA, NIST,
and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com
for more metrication information, contact Pat at [email protected]
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