So you think a slow burn is the most Fuel Efficient way to drive?

[Jus-A-CMax]

We heard it here and and many other place where people tout: "Drive slowly, don't gun it! Accelerate S L O W L Y. You save gas and increase your MPGs"

 

Based on my experience, I don't believe that statement to be true so I decided to do a couple of runs to do some testing.

 

So here are my test conditions and criterias:

 

Measurement Tool: I used my Trip2 computer to record the data. I do not have Scangauge. Trip2 has 2 decimal for the gas used vs 1 in the Trip Summary.

Where: Found a "quiet" stretch of level road and used the same side of the road on all the runs. This eliminated any chance of slope bias that would have influenced the result.

How it was tested: Reset the Trip2. Accelerate from zero immediately in ICE to 35 mph with the 1 bar or 2 bar (dependent on run). As soon as 35mph is hit, foot off the gas, brake and pull over. Turn on camer and snap the pic. 2 runs were done for 1 bar, 2 runs done for 2 bars, results averaged.

 

So which one was the most Fuel Efficient?

 

 

MPG: they are both pretty close, with the 2 bar burn pipping the 1 bar burn.

Distance: it took 3 to 4 times the distance to reach the same speed.

Time: whilst there is some whim at how long it would take me to reset the Trip2 and kick in the gas, and the time to turn on the S4 camera and focus, it still show at least double the time for a 1 bar burn vs 2 bar burn to reach the 35mph cut off speed.

Gas: To me, this is the most telling and if you want to hypermile and get the most out of the LIMITED gas and break the 600, 700, 800 or dare I saw, 900...then 0.00 is always far better than 0.02.

 

Now I am going to throw a monkey wrench into the works.....what the readings does not show is the LEVEL of battery regen. I have no way to measure the state of charge (SOC) and there is no practical way for me to drain the battery to the same level either - so this is based on my observation. The 1 bar does generate more battery than 2 bar because you are using the ICE to do this. I am not going to do into the glide phase for batt regen, thats another topic for discussion.

 

This is Run 1, 2 bar burn:

 

This is Run 1, 1 bar burn:

 

Not shown is Run 2 pictures, yeah, too lazy but I think you guys get the picture by now.

 

 

What does this mean to YOU?

Heres what you have to understand with driving FE. You have limited gas. Gas is needed for ICE. ICE is needed for the power pulse phase. Pulse is what you need to get up to traffic speed (unless you like ENJOY getting RPGed :finger:  by the rear driver  :rant:  along with the sound horn effects and the 1 finger salute :runaway: )....so burn the acceleration at a 2 bar and not 1 bar rate. Both burns still have regen - unless your SOC is already > 80% in which case the threshold for regen has dropped below the 2 bar (time to swtich strategy).

 

 

Now...having said that I will still use 1 bar burn and keep it as a tool in the box. Huh? :headscratch:

 

WTF are you talking about now Jus, after telling us all the crap above?

 

 

A 1 bar burn is good for one thing: regen the battery and sometimes you need a higher SOC for a part of a road such as a mild upslope to get home, use it - BUT make sure there is no one behind one to PO. But do realize that you are sacrificing some gas for the higher battery - but as long as what you sacrifice in the 1 bar burn IS LESS than what it will cost you to kick in the ICE (say 3 bar burn) going upslope...then you are on a winner.

 

You can't fight physics but you can make it slightly more palateable in your FE world.

 

Happy 4th and enjoy, :shift:  safely out there.

:)

Edited July 4, 2013 by Jus-A-CMax

[plus 3 golfer]

In a non-hybrid, it has been shown many times that one wants to get ICE into the most efficient area of the Brake Specific Fuel Consumption area as quickly as possible.  Long slow acceleration up to speed uses more fuel than getting to a more efficient part of the BSFC sooner for the same given distance. Also, this is the fundamental principle as to why P&G works (hybrid or non-hybrid cars).  Accelerate above the desired speed to a more efficient point of the BSFC, coast down to a lower speed than desired and then briskly accelerate back up to the more efficient point.  The overall efficiency of ICE is higher than running at the constant desired speed.   Wish we had the BSFC curve for the C-Max.  Read Chapter 3 here.

 

Jus, maybe you should spring for a Scanguage. :)  You could then see the difference in SOC of the HV battery when running the tests.  Also, you should run the tests for the same distance and your final speed should be the same under 1 and 2 bar acceleration.  This is because you have traveled 0.25 miles further on the 2 bar vs 1 bar tests. So, there is fuel that would be burned to travel the extra 0.25 miles in the 1 bar test to be equivalent.

 

Having said the above, we have to remember that the PCM controls where ICE runs in the hybrid.  So, I would assume that the PCM always tries to run ICE in the most efficient areas of the BSFC.  

 

I also saw this on TDIClub recently as it also demonstrates the point.  There's really no reason why Ford couldn't put this screen on the MFT (instead of that "worthless" :) energy flow diagram.  We would know exactly where ICE was operating.

 

[ScubaDadMiami]

I know that I still know nothing, but . . .

 

I have been trying to learn my C-MAX.  I have been repeating the same routes, and I have tried different techniques to see what works.  I rarely have my SOC on the higher end of the spectrum.  Most of where I go is 30 to 45 mph type driving.  (Next tank will have more highway with ICE High learning.)

 

For my driving, I have noticed that my FE drops when using two bars for acceleration, when compared to speeding up using one bar.  By going up to only one bar, I seem to get the most charge per burn of fuel. 

 

Just to account for other factors, here is what I typically do.   If I can, I start in EV to get rolling to about 10-15 mph, more if nobody is behind.  I go with ICE with one bar to around 25 to 30 mph.  By then, I can get a decent quick charge to 25-35 percent SOC.  I'll glide back down to about 15-20 percent SOC before pulsing with ICE.  Doing this over the course of 12 miles is yielding an average that is probably around 51 mpg.

 

When I was experimenting with two bars on my last tank, and I still wound up with 46 MPG or so.  Not bad, but I seem to be doing better by using one bar.  After getting 46.9 on my first tank, my Lifetime has gone up to about 47.7 on just over half of the second tank.

Edited July 4, 2013 by ScubaDadMiami

[MikeB]

The car's computer already knows the BSFC graph, it should be easy to display it.

 

But more importantly, the car should be able to keep your engine in the optimal BSFC range without driver intervention. If you are accelerating slowly, the car should just use the electric motor and leave the ICE off. And if you are accelerating hard, it should push the load up just a bit to get into the optimum BSFC range, and then use the extra load to recharge the battery. Oh wait, I think that's exactly what the computer is doing already!

 

Maybe the computer isn't being aggressive enough about keeping the engine in the optimal BSFC range? Or maybe the computer would be more aggressive if it had a larger battery, so it had more opportunity to alternate between EV drive and high-load BSFC optimal running of the ICE?

[plus 3 golfer]

Yes, agree the computer should be adjusting load (charging) so ICE is in an efficient BSFC range.
 
In fact, the referenced study above for the 2004 Prius concluded that the HV battery was an effective "kinetic energy" storage device compared to pulse and glide.

 

In conclusion, engine load leveling with the battery by the HEV control strategy in steady speed driving is as efficient as storing KE in vehicle inertia by the PnG driving strategy but the fuel economy improvement (1 – 11 %) is achieved in 20 – 30 mph and 30 – 40 mph speed ranges by the PnG driving strategy even if it is much smaller than the simulation results.

[plus 3 golfer]

The more I read, test, and analyze Hybrids. I see speed (related to aerodynamic drag) as the biggest driving factor to improving FE all else being equal.  I believe the next most significant factor is allowing the kinetic energy of the car be used in slowing down the car.  Even though one achieves a 100% brake score, there are still losses associated with the storage and use of the energy that likely is at least 20%.  This means coast, coast, and coast more.  The goal would be to drive without using the brakes. Lastly, I believe accelerating evenly and slow / moderate will enable the PCM to keep ICE in the most efficient part of the BSFC curve. 

 

Is it coincidental that the 3 coaches are: cruising, acceleration, and braking???  ;)  :)

[ScubaDadMiami]

I agree.  'Tis better to glide to a stop than to apply thy brakes.

[11StiLimited]

Will post my results after testing.  I will also do 2 runs at each to average them out.

[11StiLimited]

Your test SUCKS to execute, lmao! Managing the camera, switching displays, proper throttle, that is a lot at once with 2 hands.  Of course, I was attempting to video the test, not camera the test, so admittedly, I made it harder.  Going to look into mounting the camera in a fixed position which won't block use of the wheel or view of the cluster.  My hope, is that using video, we can remove the seconds of lag involved with switching displays and executing the test.

[11StiLimited]

Until I get a better mount, or different camera, I am not going to try this.  It seems like a waste of gas, if you are not recording quality results.  I think I will stick with your initial assessment, for now.

[salsaguy]

Check out this video to see how a photographer I admire and follow uses his tripod and gets a very stable secure position to do his time lapse photography

there are 3 parts

this is part 1

http://youtu.be/7zQW0BWzfIY

if u are into photog watch all 3 parts

the mounting of the tripod to be stable starts around 2 min mark

of course youd have to change this a bit to take the video over your shoulder instead of in the middle of the back seat as he does but maybe you can come up with something

 

Until I get a better mount, or different camera, I am not going to try this.  It seems like a waste of gas, if you are not recording quality results.  I think I will stick with your initial assessment, for now.

Edited May 25, 2014 by salsaguy