Unfortunately, Gary, what you posted is incorrect. An ICE is always more efficient when loaded, up to the trorque peak, that is. The increase in efficiency for an Otto cycle engine is much more pronounced than for an Atkinson/Miller cycle engine, which is why the FE hit for your Explorer is less than for the FEH. As an example, get your hands on Miller's book "Propulsion Systems for Hybrid Vehicles" and look at the graph on page 43. It shows the BSFC for a Ford Focus ICE. For 2000 RPM, the BSFC for 5HP is 710 g/kWh, for 10HP it is 500, for 15HP it is 320. So, going from 5HP to 15HP @ 2000RPM your power increases by 200%, but your fuel consumption only increases by 35%! In an Atkinson/Miller hybrid this is less dramatic, but still good enough to allow better FE by storing energy and pushing EV as much as possible.

This is one of the many reasons the FEH highway FE is more affected by winter than an over powered Otto cycle vehicle. The increased load of the cold, dense air has the above affect. Also, the large expansion ratio of the Atkinson/Miller results in cooler combustion temps, exascerbating the effects of the cooler atmosphere. Winter blend gas also effects the low DCR Atkinson/Miller more than the Otto.

 

Thanks Carl. We got our answer. Mystery solved.

 

I think the disagreement here is in the way the word "load" is being used.

 

 

Yes, reducing the load will improve MPG despite reducing the thermodynamic efficiency of the ICE. Towing a boat may require 100% more power, but only 85% more gasoline due to the efficiency improvement in the ICE when loaded. But this thread is about why the highway MPG drops more in an FEH in cold weather than in Otto cycle vehicles. Your explanation for this phenomenom was incorrect. Dry air is denser than humid air, cold air is denser than warm air, so the power required to move at 70mph in winter is more than in summer. This is a fixed load you can't do anything about. An Atkinson/Miller engine has a flatter BSFC curve than an Otto, so incremental increases in load result in comparatively less efficiency improvement, therefore larger MPG hit. QED.

Why the temperature of the combustion gasses decreases with a larger expansion ratio is basic thermodynamics. It has been nearly 30 years since I took thermodynamics, fluid mechanics and flight dynamics, but I still have my books and I still can run through the numbers, and I doubt the laws of physics have changed much since then....

The graph I referred to was measured data of a real Ford Otto cycle engine. It wasn't an academic exercise, and it does reflect what happens in the real world. Lugging an engine is always better for FE, but Ford won't let us do that in the FEH due to the eCVT and throttle-by-wire. Lugging gives better FE but is harder on the engine. Ford has always been very conservative with respect to engine performance, and the FEH is certainly no exception. I have had IC's I designed put into both Ford and GM vehicles, and Ford was definitely the more **** of the two during qual.

If loading an ICE didn't give better efficiency, then pushing EV would give you substantially worse FE. It doesn't.

 

Carl (Desert Dog) thanks for the free education. We learn a lot in this forum. Maybe we should feature "on-line classes" to further our knowledge.

Wwest--thanks for detailing basic differences between the Prius and Ford Escape Hybrid. Both are parallel design hybrids. Does the Prius normally allow the operator to discharge the hybrid battery down to 30%? What is the normal upper charge limit for the hybrid battery in the Prius? There was a recent thread in consumer report website on the Prius's deficiencies on the highway in regards to a degenerating hybrid battery state of charge. Most posters were then thrashing hybrid vehicles (all makes) in environments where regenerative braking would not occur.

 

That's what I said because it was 100% correct. You were wrong, so just own up to it, and move on, please.

Actually, it is. I ALWAYS, 100% of the time get better fuel economy ( for Gary, I'm literally saying 40 MPG vs. 35 MPG) when I make complete round trips to the mountains and return. This is substantially better. And the results are so obvious, I don't even have to worry about trying anything fancy to get the results. Other persons notice the same. Carl has done a great job explaining to you why. You just choose to follow your gut ( which is wrong in this case ) vs. science.

Put another way, gaining elevation under heavy load gets you up that hill with the least amount of gasoline.
Taking the gentle route up the hill would take more gas total, even if your Instant MPG looked better.

Yes you would have. Disagreeing is your hobby.