Why charge the battery while driving?

[ian4x4]

I did find this: http://ratherlightvehiclecompany.com/figefficiencycurveswdots455by326.gif

I was not aware the efficiency has a big impact based on the "load"

I have been looking at graphs like this:

They specify Brake Specific Fuel Consumption, more or less how much mechanical energy you get out of every liter of fuel burned, and IMHO show better why you want to stay in an area of load / RPM.

So ... in theory the best efficiency for the engine .. is going full power at 170km/h .. this should also avoid to "age" the battery with recharging it :mrgreen:

I don't see how you come to that conclusion. As RPMs go up beyond the sweet spot, efficiency goes down again ....

The graph shown is very reminiscent of the graphs for BMEF (Brake Mean Effective Pressure)
which used (and still is) to be a good guide of the power and efficiency of an Internal Combustion Engine.
Below is a typical graph, but saying that, I can't find a graph for an Atkinson Cycle ICE, so am unsure as to the most efficient rpm/load.
In a normal car you change to a higher gear to bring the RPM down and increase the engine load to give a better efficiency.
https://www.bing.com/images/search?q=brake+mean+effective+pressure&view=detailv2&&id=821E29664EB44E090F4F66D003DD7866FC016139&selectedIndex=25&ccid=oUV0sD%2b2&simid=608032401105290773&thid=OIP.Ma14574b03fb6632c3ceb1260954feb0bo0&ajaxhist=0

 

[pasquinade]

Hi all,

Just a small experience of mine regarding this efficiency topic.

I recently went up a mountain (approx 2000m above sea level at highest point) and then down (lets say around 30 kms each way.... not sure exactly how many). I started with battery depleted as the hotel had no charging facilities.

On the way up the petrol engine was revved up most of the way (very noisy) and I got to the top with an (expectedly) high average consumption (not sure about the exact number, but something like 12 l/100km). Then my kids played a bit in the snow and a couple of hours later we came down (not enough to reset the fuel consumption counters).

Going down was very good, no engine use and by keeping it in B5 was able to reach the bottom with 30kms of electric autonomy. Once it was depleted I checked average fuel consumption of around 7 l/100km. This is a very good value for me (with full family in the car) and was the only use case where I could achieve it (and repeated it the next day). Usually in flat roads (well some small hills) I can get around 8 l/100km when battery depleted.

So the question is if perhaps the Petrol engine is more efficient at high revs / high torque situations like the one described above.

I remember once checking "hyper-milling" pages (no, I'm not one of those) claiming that for Petrol engines, the more efficient use on a highway is to floor the pedal up to a maximum speed (lets say 120km/h) and then let it coast to a minimum speed you select (lets say 80km/h). Perhaps something similar is happening here with the steep incline forcing me to "floor it".

Note that energetically the incline is not per-se fuel inefficient (it is a potential field and all energy "spent" going up can theoretically be recovered when going down) except for the engine and mechanical inefficiencies).

Perhaps it was mostly due to the average speed at which it was run than the up and down load case, but it has made me think a bit...