Most efficient speed (mph)

[ffe]

What is the most efficient speed for the 2018 Fusion chassis?

 

Assuming tires properly inflated, and let's say 70F, 50% humidity, sealevel, what is the optimal miles per hour to get the most miles per kwh.

 

I believe this is an attribute of the aerodynamic drag of the car and that all cars have a sweet spot.  At 100mph the wind resistance kills you.  At 1mph, the idling kills you.  somewhere inbetween, you get the best mph.  If I had to guess, I'd say take the ICE' most efficient RPM, and work out how may kw it produces at that RPM.  Then figure out how fast the car can go using that many kw of energy, and there you go your most efficient MPH.

 

What is that sweet spot for the Fusion?

 

If nobody knows, then maybe next road trip, I'll see if I can't plan for a long stretch of straight level road on which to go 10-20 miles at each of several different speeds and measure consumption.

[MeeLee]

35MPG for full electric,
~50MPH for gasoline.
It's like that on most cars.

The 2.0 atkinson engine idles at around 2k RPM, at which the CVT can propel the car to about 50MPH.

[ffe]

That sounds right to me!  Thanks MeeLee!

 

I didn't realise the 'sweet spot' was idle rpm.  Is it like that for most gas engines? I've got Torque Pro hooked up now via obd2, so I'll play around seeing what speed I can attain at idle rpm and share what I find.

 

Do you remember where you found 35/~50?  I'd like to learn how it's calculated.

[Waldo]

I don't understand what you mean by "idles at around 2k RPM".  Idle RPM is when the engine is operating but not under any load.  That is somewhere around 700rpm and it won't propel the vehicle at all.  In fact it is very rare for the hybrid system to ever run the engine at true idle speed.  Idle by definition is never the most efficient condition for any gas engine.

 

If you really want to understand the "sweet spot", research the concept of BSFC (Brake Specific Fuel Consumption).  Generally this is how much fuel an engine takes to make a given amount of power.  Most engines operate most efficiently when under load, ie full throttle, but not necessarily at high rpm.  For example if you need 50hp to move your vehicle at 60mph, the most efficient engine would be one that can run at full throttle making that 50hp.  That might mean a very small engine running at high rpm or a larger engine running at a lower rpm.  The problem though is if at some other time you want 100hp for acceleration, that engine that makes 50hp efficiently can't make 100hp.  That's where turbos and/or hybrids come in.  They let the engine run efficiently at low power demands while having a reserve for when more power is needed.  In the case of the hybrid it gets even more complicated, because the hybrid system can use the extra energy and store it for later.  So say you have an engine that makes 50hp efficiently, but you only need 40hp.  The Hybrid can allow the engine to run at it's efficient 50hp condition, but convert that extra 10hp into electricity stored in the battery.  That electricity can then be used the next time you need 60hp.  The engine can be run at it's efficient 50hp condition and the extra 10hp is provided by the battery.

 

So what I'm trying to say is it is very, very difficult to determine the "sweet spot" of a hybrid vehicle because it changes all the time, based on battery charge.  When you're running in pure electric mode, you generally would drive as slow as possible, since electric motors don't have a BSFC curve, they run equally efficiently at all rpms and power outputs.  But then you have to balance the negative aero and rolling resistance of going faster against the power draw of keeping the vehicle running for a longer time when going slower.  When the gas engine is running, you have to balance the aero and rolling resistance of going faster against the BSFC curve of the ICE engine, the conversion efficiency of the battery system and the variable drive ratio provided by the CVT.

 

Basically the whole point of a hybrid is to eliminate the "sweet spot" completely.

[ffe]

Thanks Waldo, that is a good explanation.

 

So if 50hp is the sweetspot and I only need 40 to drive, the battery can store up that extra 10 until it's full then shut off the ice and run off battery until the battery is low, then repeat the cycle?

 

That's pretty slick and a great reason to have a hybrid.  But I recognize there are conversion losses in charging and discharging, so I'd prefer to drive at a speed that consumes 50hp if that's legal.  Or at least I'd sure like to know what that speed is and/or how to calculate it.

 

In my last hybrid there was a lot of talk of "Pulse and Glide driving", and I think I used it to good effect a few times on long drives.  accelerating to make full use of the ICE, then idling the hybrid throttle until it was as close to neutral on the accelerating side of the line as I could get it.  So basically only using the ICE 1/4 to 1/5 of the time, at the cost of widely varying speeds.  It could piss off whoever's behind me, BAD.  So I would only do it when I was alone on the highway.  Come to think of it that's using the kinetic energy of the vehicle the same way as the battery scheme above.

 

I heard of Brake Thermal Efficiency.  Is that the same as BSFC?  This diagram isn't for our car, but I'd LOVE to find one for Ford's 2L I-4 Atkinson.

NOTICE:  THE ABOVE GRAPH IS FOR SOME TOYOTA, NOT A FUSION.  SHOWN FOR EXAMPLE OF WHAT I'M SEARCHING FOR ONLY

 

What's the proper part number or model name for the ICE in a 2018 Energi?

Edited March 18, 2021 by ffe

[Waldo]

Yes that's exactly what I'm talking about.  With a conventional car and transmission, you'd match the gear ratios so that this engine runs in that 2500-3000rpm range when you're cruising along in situations that require 120kW.  But with a hybrid there are a lot more options because you can vary the gear ratio and battery charge/discharge to keep it at the peak more often.

[MeeLee]

Testing out this car more, I want to correct my statement above.

The electric range seems to diminish with speed. So the most efficient speed on electric (also taking time into consideration, since no one wants to drive at 5mph; as well as taking into consideration things like ac and lights further draining the battery the slower you go, as you'llneed to run them longer), would be 35-40mph.

I find I have only a few seconds of electric range at 60 mph, but nearly a minute of coasting at 30-40mph.

This curve diminishes at lower speeds, as the lights, charging system, and ac use up roughly 1kW of power. Half your travel time means roughly half your ac and power use, but also could mean more than double your rolling and wind resistance. 

For that purpose, ~35mph to 40mph may be close to the optimal electric performance sweetspot.

 

For gasoline, it appears the electric motor interferes with the readings. You'd have to be driving at 70mph or greater, for the electric motor not to come on while coasting.

At that speed (and level ground, no wind), the engine does about 1400rpm.

With some backwind, and tailgating I truck, you could reach an insane 50-55mpg, by finding the optimum throttle position (allowing the engine to rev at an astonishing 1.1-1.2k rpm while coasting at 75mph). This throttle position is right before the engine cuts off and switches over to electric. I've been able to hold my car at these speeds and mpgs for longer periods on the highway, and duplicated the results a few times.The conditions are to:

1- have LRR tires (the stock tires or better)

2- have 40psi or more of air in the tires.

3- reduced wind drag (driving behind a truck/have a tail wind),

 Or, can also be achieved on a mild downhill

4- Engine must be warmed up, and batteries fully charged. The first few miles the mpg slowly creeps up from 20mpg to 36 as the car charges up the battery. It takes a good 10 min before it actually surpasses the 40mpg mark, staying at ~42mpg without a tailwind.

When the conditions are just right, gently hold back a little on the throttle, until rps are 1.1-1.2k rpm. Surprisingly, the car keeps speed just as it did at 1400rpm.

 

Concerning my previous post,

I'm not sure what I meant by 2k idle rpm. I probably meant to say that while driving the car seems to naturally prefer 2k rpm to accelerate in eco mode; or, when the engine does come on, I find it revving most around 2k rpm. It takes me to press the pedal quite deep for it to aim for 3k rpm, but that could be entirely the eco mode throttle programming.

 

I drive eco mode all the time, since this mode allows for easier gentle acceleration, which is what my passengers seem to favor.

Edited March 27, 2021 by MeeLee