Thursday, October 13, 2005

The Peak Oil Crisis: Pulse & Glide

Falls Church News-Press

September 1, 2005

Two weeks ago, five guys took a stock Toyota Prius and drove it for 1398 miles on one tank (12.78 gallons) of gas –- about 110 miles per gallon. Considering that a stock Prius going with the Interstate flow gets about 53 mpg and that a even a careful eco-driver going 55 mph can only get eke out something over 60 mpg, there might just be a lesson here. How did they do it?

“Pulse and Glide” is a technique worked out by Prius enthusiasts in which the car is first gently accelerated to 40 mph then permitted to coast back down to 30 mph while keeping the Prius’s electricity generator disengaged.

For those of you without Hybrid experience, it is helpful to know that on a Prius and similar vehicles a battery recharging generator is activated during deceleration. While this recharges the battery, it also cuts down on the distance one can coast by converting momentum into electricity. In the case of pulse and glide, the gentle acceleration does not require any electricity so allowing the generator to cut on during coasting simply wastes gasoline.

The record was achieved by pulsing and coasting, back and forth, over an 18 mile section of 30-40 mile per hour four-lane highway outside Pittsburgh , chosen because it was flat, unimpeded by traffic lights or heavy traffic, and had a suitable speed limit.

After the test, another enthusiast tried out the technique on a Toyota Highlander Hybrid SUV that has a similar engine. In a shorter test, the Highlander came up with a pulse and glide fuel consumption of 47 mpg— very impressive by SUV standards.

All this suggests there may be more fuel economy buried in our current fleet of cars and light trucks than we realize. It just takes a strong motivation and some changes in our driving technique to bring it into the open. While I have no idea if our fleet of some 210 million non-hybrids could double their mileage by careful, ultra-economic, perhaps computer-assisted driving, it just might be worth finding out.

A good place to start would be on a flat, empty road in the middle of the night, so there is nobody around to think you are crazy. Trying pulse and glide on the beltway would have a very short half-life, for you would soon be run over from behind, forced off the road, shot by someone with an acute case of road rage, or arrested for causing a monumental traffic jam.

If we ever get to hyper-economical driving and the millions of barrels a day it might save, there will have to be some strong incentives and help from the government and the manufacturers.

The incentives to drive economically will come as soon as the price of gasoline gets high enough. What is enough? Well, gasoline is currently pushing $7 a gallon in Europe , so $10 per gallon clearly is not enough to induce people to drive 30-40 miles per hour. Let’s arbitrarily take $20 per gallon as the “take pulse and glide seriously” point. At those prices, it would cost $200 to fill up a small tank, $400 to fill up the standard car and $880 to fill up a large SUV or pickup truck. At these prices, it is obvious that nearly every thing related to driving, except the miles per gallon, disappears.

Long before we get to $20 per gallon, let’s hope our various levels of government establish “economy lanes” on our highways where people would be free to drive as slowly as they wish in order to extract the last speck of mileage from their vehicles.

Of course, the manufacturers could help by testing their products to determine maximum fuel economy profiles and adding aftermarket pulse and glide buttons to their cars and trucks. These devices would be programmed to automatically extract every smidgeon of mileage from a vehicle, no matter how it was run.

The concept of a car alternately accelerating and coasting across country at 30 to 40 miles per hour may seem bizarre today, but very high priced gasoline is a virtual certainty before we can transition to alternate forms of transportation. Given the lack of alternatives, “economy lanes” may indeed appear on our highways.


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