I Does Pulse and Glide only work with manual transmissions and a kill switch?

[Lnewqban]

What surprised me greatly is I was able to achieve higher overall efficiency on the round trip up and down the mountain than I can at constant 61mph on flat ground behind a big rig… I ascribe that to the engine essentially being off half the time which is not the case on flat ground.

It seems that car’s manufacturers have discovered that anything that keeps the engine rotating and legally connected to the wheels without burning fuel is one of the ways to best fuel efficiency.

Keeping the engine idling is expensier than using gravity to make it spin, overcoming useless compression and valve train drag, via automatic transmission and torque converter (which works both ways, once certain amount of rpm’s is achieved).

Thank you for sharing that good test, @Devin-M

 

[jrmichler]

I was able to achieve higher overall efficiency on the round trip up and down the mountain than I can at constant 61mph on flat ground behind a big rig… I ascribe that to the engine essentially being off half the time which is not the case on flat ground.

The engine efficiency has a lot to do with this. Most cars use less than 10% power at a steady 61 MPH on a level road, which puts the engine at a low efficiency point on the performance map. See the example performance map in Post #20. Most gasoline car engines have peak efficiency at about 80% of peak torque at 1/3 to 1/2 of peak RPM. That's several times the power needed to run at steady speed on a level road.

Extreme gas mileage driving, AKA hypermiling, uses that knowledge by accelerating at a power and RPM near peak efficiency, then shutting the engine off and coasting. It's called pulse and glide (P&G), and works best in gentle rolling hills.

 

[Devin-M]

While climbing I was maintaining the engine rpms below 2700rpm which meant the car could only go about 41mph max in 3rd gear on certain sections of the climb.

 

[Devin-M]

The engine efficiency has a lot to do with this. Most cars use less than 10% power at a steady 61 MPH on a level road, which puts the engine at a low efficiency point on the performance map. See the example performance map in Post #20. Most gasoline car engines have peak efficiency at about 80% of peak torque at 1/3 to 1/2 of peak RPM. That's several times the power needed to run at steady speed on a level road.

Extreme gas mileage driving, AKA hypermiling, uses that knowledge by accelerating at a power and RPM near peak efficiency, then shutting the engine off and coasting. It's called pulse and glide (P&G), and works best in gentle rolling hills.

I did a Pulse and Glide test today over 339.8 miles of basically flat terrain... the "pulses" were me accelerating from 55mph to 65mph (about 10 seconds), and the "glides" were me coasting from 65mph back down to 55mph (also about 10 seconds). Speed limit was 70mph. Supposedly during the glides my fuel injectors were off because my foot was off the throttle in Drive gear, so essentially my engine was off half the time. Engine rpms were maintained at all times between 2200rpm and 2700rpm -- 55mph was 2200rpm and 65mph was 2700rpm. This took 9.42 gallons so I averaged 36.07 MPG. While this did result in better fuel economy than my 2008 Nissan Versa 4 speed automatic non-hybrid's advertised highway miles per gallon (33 MPG), it was worse than when I simply follow a big rig at constant 61mph, which results in 40.5 MPG.

(round trip)

 

[jrmichler]

P&G requires a manual transmission and a kill switch. The driver shifts to neutral and kills the engine at the start of a glide, then bump starts the engine for the next pulse. Pulse and Glide does not work with automatic transmissions. The engine is still spinning, so the engine friction combined with driveline losses is slowing the car down.

P&G is most useful at lower speeds. My Canyon showed little benefit from it at 55 MPH on level roads. The primary benefit was at lower speeds and/or rolling hills. The glides need to be longer than the pulses to see a benefit.

And not all cars shut off the fuel when the throttle is closed. My old Canyon would not shut off the fuel at 2000 RPM, although I have a hazy recollection that it would shut off fuel above 4000 RPM.

 

[russ_watters]

P&G requires a manual transmission and a kill switch. The driver shifts to neutral and kills the engine at the start of a glide, then bump starts the engine for the next pulse. Pulse and Glide does not work with automatic transmissions. The engine is still spinning, so the engine friction combined with driveline losses is slowing the car down.

That's real hypermiler shstuff though. Most - excuse me - normal people will not want to turn off their air conditioning and power steering and go through the effort of the P&G itself. Point being: are you sure P&G does not work if the car stays in gear? I mean, certainly you won't get maximum benefit, but you should still get some, right?