On Coasting (Two interesting papers)
 

I have found two interesting papers that seem to provide some answers to frequent questions on Ecomodder about some specific hypermiling techniques, and how those integrate with BSFC (brake specific fuel consumption).

1. "Coasting on Highways – Potentials and Realization" (
https://www.hs-heilbronn.de/5023311/...n-highways.pdf) by Prof. Hermann Koch-Groeber, Heilbronn University, Faculty of Mechanics and Electronics, Automotive Systems Engineering. June 2013.

2. "Criteria for Coasting on Highways for Passenger Cars", by Hermann Koch-Groeber and Jue Wang of Heilbronn University (ASE, as above). Published April 2014 by SAE.

Fantastic find!

Here is another paper on a related topic:

Li & Peng (2011). Strategies to Minimize Fuel Consumption of Passenger Cars during
Car-Following Scenarios. It also discusses pulse & glide in relation to BSFC.

http://www.dae.tsinghua.edu.cn/publi...0Scenarios.pdf

Anybody care to pull out the percentage of energy savings from coasting?

I started looking through one study, but I am here at work, and I can't take more time right now.

That said, the figures are for a particular road, terrain and driving speeds. The potential will be different for other circumstances. I think the value of these papers is not so much in the percentages that were concluded, but in (1) the confirmation that fuel savings can be substantial, and (2) the discussions of the operational and mechanical factors that are involved.

Main conclusions:
-Their testing showed EOC got 5% to 10% less fuel consumption than constant speed on cruise.
-Any coasting (even with the engine on) helps.
-In testing and simulations, coasting consistently helped.
-Maximizing the time spent coasting maximizes its benefis.
-Smaller glide downs get smaller results.
-This was an engineering study. The real benefits of coasting depend on the driver's willingness to gain them.
-YMMV. This study only tested one car on one route, but the general tendencies shown in the work will prevail.

Fun highlights:

The fourth paragraph of the report opens (cleaned up a bit):
It is basic knowledge, that an integration of coasting phases can reduce the fuel consumption of a motor vehicle over driven distance... In the US the general public knows such activities as "pulse&glide" or "hypermiling".

Accelerating under high load is good for FE.
For low engine loads, the increased time to regain speed entails a significant reduction in coasting duration and less fuel savings due to higher integral ‘friction’ losses for higher mean engine rpm.

DWB FTW!
Additionally all drives with significant use of the brake were omitted since the dissipated energy cannot be quantified and the vehicle is not hybridized. Braking can be completely avoided in surprisingly many drives by decent anticipation, even in German workday’s daytime situations.

In the summer, I typically see 20% to 30% increase in efficiency by EOC driving, but apparently I am willing to drive over a larger speed variation on those old country roads.

Thanks for the nice summary!

Jim.

BTW, I found these papers through a search for "specific fuel consumption" instead of "brake specific fuel consumption." That gives a lot of interesting hits, most of them aviation related and not of interest here. To reduce the clutter I used additional search terms such as "Ford Focus" or Duratec (a Ford engine type). Similar kinds of searches by others reading this thread may stumble upon other interesting sources that we haven't tapped yet on Ecomodder.