About Pulse and Glide deltas

[Appletank]

I see a lot of advice regarding PnG to have at least a 10 mph difference in speeds, sometimes I see even 15 or 20 mph differences for even better efficiency. I'm a bit confused as to what car dynamics or physics causes this? Obviously a lower average speed helps, but I'm not talking about that.

Assuming the same average speed and roughly similar pulse mpg, shouldn't a 35 mph average 37-32 range produce similar results to 40-30?

[freebeard]

I thought I'd replied, but apparently I didn't hit Post. Apology if redundant.

shouldn't ]x\ produce similar results to [y]?

Perhaps it does. A 3MPH delta might signal lost in the noise.

The theory with pulse and glide is be either at the peak of BMEP or at idle/off. Wandering around the slopes is less efficient.


https://www.researchgate.net/profile...olute-fuel.png

The difference between 45-30 and 80-65 will be down to aerodynamics.

[Appletank]

Originally Posted by freebeard

I thought I'd replied, but apparently I didn't hit Post. Apology if redundant.



Perhaps it does. A 3MPH delta might signal lost in the noise.

The theory with pulse and glide is be either at the peak of BMEP or at idle/off. Wandering around the slopes is less efficient.
The difference between 45-30 and 80-65 will be down to aerodynamics.

Yeah, I know that PnG exploits how the engine is more efficient when under load, then coasting to take advantage of the excess energy.

It's easy to tell 80-65 would use a bit more gas since the higher average speed will require fighting through more air, but my question is about the same average speed, but smaller deltas. So, 45-30 vs 40-35.

[Joggernot]

I Texas the minimum speed is 20 mph below the speed limit. That sets boundaries on your PnG values.

[Appletank]

That's seems probably about the same for most places, but is completely unrelated to my question.

[freebeard]

Has your question not been answered? The smaller the delta the more similar the result.

[Appletank]

Originally Posted by freebeard

Has your question not been answered? The smaller the delta the more similar the result.

Yes I understand that it's generally recommended to have a speed range of at least 10 mph (when traffic conditions are appropriate), but I'm curious to know if anyone knows why. Whether some aspect of aero drag or engine inefficiencies.

[freebeard]

Signal-to-noise ratio
Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in decibels. A ratio higher than 1:1 indicates more signal than noise. SNR is an important parameter that affects the performance and quality of systems that process or transmit signals, such as communication systems, audio systems, radar systems, imaging systems, and data acquisition systems. Wikipedia

.

[Appletank]

... I don't get it. longer deltas reduce noise? But what the actual engine is doing shouldn't matter if the data system is inaccurate, you just have to measure it more directly?

[freebeard]

Maybe I'm wrong, I have no idea.

Perhaps someone who actually employs the P&G technique will respond.