“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

Monday, October 12, 2009

More on efficiency

The spreadsheet I created for my recent post on acceleration has enough data to enable me to make another estimate of the overall efficiency of my transportation system (the Land Rover LR3 HSE) during the acceleration phase. This is because I have a tenth of a second by tenth of a second tabulation of energy used to accelerate and to overcome external forces as well as a tabulation of the fuel used.

Summing the fuel and knowing the heat energy available in the amount burned and summing the energy expended to do useful work and dividing yields the answer: 21.0% using the 45 seconds to 55 m.p.h. regime and 22.7% using the 10 seconds regime. This is actually a little better than I would have imagined. I typically calculate cruise figures estimating 25%, but I'd have thought that accelerating from a dead stop would have a larger negative impact on efficiency. Admittedly, it's a long chain from the data I actually have obtained to the figures I've calculated and the weakest link is my use of a composite engine map adjusted with only a very few points from my specific car but as I've said repeatedly, I love it when multiple lines of data and/or reasoning converge.

If my car required half as much energy through weight and drag reductions and was twice as efficient, I'd use one fourth my current fuel. If we all did.....

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