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Discussion Starter #1
After 2 years of ownership I'm still not sure of the answer to this.

My petrol / electric hybrid has a choice of several driving modes. The default mode is to use electricity only until the batteries are almost exhausted, then to switch to petrol. This is the mode I normally use because I want to minimise the use of petrol, and most of my journeys are less than the 30 mile electric range. There is also a hybrid mode where the car automatically selects the appropriate fuel and switches between them as necessary. I'll ignore the other modes for now (battery saving, GTE etc).

My question is this:- with a full petrol tank and a fully charged battery, which mode gives me the maximum range under normal conditions? Or in other words, is the hybrid mode more fuel efficient than the hybrid mode? In theory the hybrid mode should be slightly more efficient because the car can select the ideal fuel for the speed and conditions, but is it more fuel efficient in practice?

My car is a Golf GTE but the question applies to any hybrid vehicle.
 

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That's a how long is a piece of string questions, there are too many variables. Unless you specify the journey neither we nor the car can optimise it. The default of using the stored energy in the battery first is best on electric only journeys. Otherwise it is best to only use the ICE when high power levels are required as that's the most efficient use of it, but still to exhaust the available battery by the end of the journey. But that assumes that you can recharge before the next journey. There are also the special cases of moving emissions out of certain areas, hence reserving the battery capacity for those times.
So practical examples. Imagine a journey beyond battery only range, mainly in town with a high speed motorway section in the middle. The only use of the ICE would ideally be on the high speed section. But if it were a return journey with no recharging possible and insufficient battery for all of the low speed parts, the ICE may be advantageous on the restart to warm up the vehicle without using the battery and reserve the last bit of charge for the final slow part. But how can the car optimise that without you first giving it the full route between charges and allowing it to guess driving styles? Further integration with your lifestyle (e.g. knowledge of your appointments both on a calendar and from messages and phonecalls perhaps) would help help the planning, but at the price of privacy.
 

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Discussion Starter #3
I think you have misunderstood my question dk6780. Let me re-phrase it slightly.
Imagine two identical cars, side by side, each with a full charge and a full petrol tank.
One is set in default mode (using the battery first then the petrol), and the other is set
in hybrid mode (using both fuels as determined by the car).
The simple question is which can travel further before both fuels have run out?
 

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The simple question is which can travel further before both fuels have run out?
The simple answer is you will go the furthest at constant speed using battery only then petrol only. Converting from petrol to battery to kinetic results in a loss of efficiency compared to petrol to kinetic.

You have a certain amount of usable petrol energy and a certain amount of usable battery energy and a certain energy requirement per mile at a given constant speed. The fewest # of energy conversion steps results in the greatest efficiency.

You will get the greatest miles per kilowatt hour while using the battery only because the electrical to mechanical/kinetic conversion efficiency % is far higher than petrol energy to mechanical/kinetic energy.
 

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The simple answer is you will go the furthest at constant speed using battery only then petrol only. Converting from petrol to battery to kinetic results in a loss of efficiency compared to petrol to kinetic.
Agreed, although it could be done either way around. But you have assumed the constant speed part, and not the possible need to heat the car or potentially operate outside of the peak efficiency of the electric motor on occasion.
 

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Discussion Starter #6
Metastable. Have you confused this with a range extender vehicle such as a BMW i3? I'm talking about a conventional hybrid vehicle with an electric motor and a petrol engine, either of which can drive the vehicle directly., not a vehicle where a petrol engine is used just to charge the battery. With the Golf GTE the petrol engine isn't charging the battery in hybrid mode, so there's no resultant loss of efficiency.

The question I'm asking is simply whether it is better to exhaust the electricity supply first then use the petrol engine, as in the default mode, or to allow the car to choose the optimum fuel to suit the conditions, as in the hybrid mode. Logic suggests that the car in hybrid mode will travel further on the same combined fuel load because the car will choose the more efficient drive method for any given condition. For example it could decide that the petrol engine is more efficient at its optimum torque output, and use the electric motor at times when the petrol engine is not running at that speed. I'm not suggesting that it uses those actual parameters to decide when to use petrol and when to use electricity, but the point is that a sophisticated system should be able consider a range of parameters in order to make the choice. This suggests that the hybrid mode should be more fuel efficient than the default mode where the electricity is exhausted before switching to petrol. In other words, the car in hybrid mode should travel further than the car in default mode with the same combined fuel load.
 

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With the Golf GTE the petrol engine isn't charging the battery in hybrid mode, so there's no resultant loss of efficiency.
^I can't find evidence this statement is true.

Assuming it is true, at constant speed, using electric only mode 1st, you get the highest miles per kilowatt hour while using that mode. As soon as it switches over to petrol, the miles per kilowatt hour averaged over the trip will begin decreasing, and the lowest avg miles per kilowatt hour will occur at the very end of your trip when the petrol tank becomes exhausted.
 

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There have been many threads on here debating this.

I don't believe that there's a significant difference either way but, if the arguers get onto this thread, it could become very long.

In terms of the efficient use of your time and effort, I suggest that you just drive in B-mode and let the car switch to hybrid when the electricity has gone. Very relaxing.

By the way, the GTEs are strictly plugin hybrids, not hybrids.
 

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it depends on how clever the hybrid mode is ! - i'm afraid your question isn't really valid unless it's aimed at a specific car with known "hybrid" efficiency. Basic idea is to avoid using the EV mode in its worst efficiency areas - hills, high speed.
 

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Discussion Starter #10
At last somebody who appears to at least understand a simple question!

My reason for asking was really that on the very rare occasions that I choose the GTE for longer journeys (ie. more than 50 miles), I'm not really sure whether to use the default "E Mode" or the "Hybrid" mode from the petrol saving point of view. My instinct tells me that the "Hybrid" mode should be slightly better for the reasons mentioned previously. Maybe one day I'll get around to reading the massive owner's handbook which came with the car
 

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With the Golf GTE the petrol engine isn't charging the battery in hybrid mode, so there's no resultant loss of efficiency.
"The high-voltage battery in the Passat GTE models can be charged via the external electricity grid or via the internal TSI engine and recuperation during the journey."


as I said before:

Converting from petrol to battery to kinetic results in a loss of efficiency compared to petrol to kinetic.

You have a certain amount of usable petrol energy and a certain amount of usable battery energy and a certain energy requirement per mile at a given constant speed. The fewest # of energy conversion steps results in the greatest efficiency.
 

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With my Prius Plug-in, which at the time had a 13 mile or so range, when I had a 20 mile each way commute (charging before returning) i tried various combinations, and it didn’t seem to make that much difference. Obviously if I needed the cabin warm I needed to start with the engine on, but otherwise I did what is suggested above - start in electric because on side streets, switch to petrol for the higher speed section, then back to electric. I used to cut the engine in a bit earlier than the car otherwise would still be running mostly on electric for a while until the engine warmed up, and that was inefficient (on the original PiP) as speed increased. But I was probably just kidding myself...
 

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If running hybrid mode first converts less total petrol energy into battery energy at constant speed till full petrol and battery depletion, then hybrid first is more efficient, because you're reducing the amount of energy you put through multiple conversion steps (petrol to battery to kinetic).

Petrol to kinetic then battery to kinetic is more efficient than battery to kinetic then petrol to kinetic and petrol to battery to kinetic.
 

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On the other hand if you aren't always running for max range to full battery and petrol depletion, then it makes sense to use the electric first... the more times you can use electricity exclusively & plugin recharge the battery per tank of petrol, the more miles per kilowatt hour and miles per gallon petrol you obtain.
 

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Discussion Starter #15
Thank you for a sensible contribution Astolat. The Golf's range is bit marginal at a claimed 30 miles, so I can sympathise - it must have been a real struggle for owners of the original Prius.

As for Metastable, yes the Golf version has the capability to recharge the battery from the petrol engine (Battery Hold Mode). But that has absolutely nothing to do with my original question.
No offence intended, but If you didn't understand the simple original question or can't make a constructive contribution, please refrain from comment.
 

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One is set in default mode (using the battery first then the petrol), and the other is set
in hybrid mode (using both fuels as determined by the car).
The simple question is which can travel further before both fuels have run out?
"as soon as battery level reaches 0 km, and the battery is empty, the car switches to "Battery Hold" mode automatically"

I do understand the question. I'm lead to believe hybrid first gives longer range, because otherwise you will use the battery up and the engine will automatically recharge the battery, which adds an extra energy conversion step, reducing efficiency.
 

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In my 30k miles in the GTE, for long journeys I've settled on: e-mode until down to ~50% (to allow full regen), GTE until close enough to finish the journey on e-mode, arrive as close to empty as possible. This returns a 'VW calculated' >55mpg without any effort..

131487


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In hybrid mode, my 2018 will top the HV battery up a little once the HV is depleted..I think :)
 

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Another thing to worry about is the "journey payment" - if you start on battery, unless your preconditioning is really good, you'll lose kwh just because the battery is cold. Plug In Hybrid "hybrid" modes are getting more intelligent - I believe the MB C350E used intelligent sat nav to enhance EV range, as does the new BMW X5, but I think all others basically rely on bringing in the ICE only when pushed by throttle position, or running out of electrons. You're suffering the well known EV disease known as range optimisation syndrome. Unless you can examine your journey profile, and be the intelligence the car lacks, you'll either drive yourself mad, or simply realise that your talking about pennies worth of financial savings !!
 

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The answer depends in part on the car. i3 REx, Amepera, Outlander are all PHEVs but have very different powertrains.

An informed answer is going to include details on the Golf GTE.

Moving the thread.
 

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This suggests that the hybrid mode should be more fuel efficient than the default mode where the electricity is exhausted before switching to petrol. In other words, the car in hybrid mode should travel further than the car in default mode with the same combined fuel load.
Yes. Agreed if you are talking of running it to empty with no refueling and no artificial issues such as low emission zones.
But that's not how PHEVs are designed to be used.
 
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