Wednesday, November 27, 2013

Pulse and Glide in Honda Accord Automatic

After achieving 39 mpg in our 2007 Honda Accord automatic without doing anything special, aside from using Marvel Mystery Oil in gas, watching the speed and doing a couple of things from my post on maximizing fuel efficiency, I decided to try "Pulse and Glide", a.k.a. "Burn and Coast".

The idea behind P&G is simple: the engine is more efficient at moderate throttle openings at moderate RPMs. There are so-called brake-specific efficiency maps for every engine, and the ones I saw show that the maximum efficiency was reached at RPMs close to the torque peak at throttle openings of 40-80%.

Pulse and Glide involves accelerating at moderate-to-high throttle in highest gear possible (to keep the engine in the most efficient range, close to its torque peak) and then, ideally, shifting into neutral. Then coasting for a while and repeating the process. So instead of driving, say 50 mph, accelerate to 55, coast to 45, repeat.

Some people even switch off the engine during coasting, but this is unsafe as the power assist in steering and brakes is lost.

The easiest application of the P&G is in a car equipped with manual transmission. Since the driver has a full control over the gear selection, you can push on the gas pedal almost all the way to get maximum efficiency at a high gear without the transmission downshifting. In the automatic transmission equipped cars, one has to be careful to just enough pressure on the gas pedal so that the transmission does not downshift.

Also, I have reservations about shifting into neutral in an auto-equipped Honda Accord. While some cars are purportedly safe to do so, the others aren't. Furthermore, I am not willing to conduct experiments that might result in a failure of a part that costs thousands to fix and would result in hassle and time lost.

As a result, here is my experiment: apply P&G for one tank of gas as follows:

  1. Accelerate moderately
  2. Coast with the transmisision in "Drive"
  3. After the speed decreases 5-10 mph, repeat.
While not the most efficient P&G method there is, I suspect I might be able to finally get over 40 mpg. Stay tuned.

Update #1: I was unable to mostly drive in the manner described above for the first tank of gas and as a result got 34.7 mpg. I will try again with the next tank.

Update #2: Not really getting good results with this approach. Switched to mild drafting behind trucks instead :)

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