The Glade 4.0

Regenerative braking (i.e. generation) and motoring are not thermodynamically reversible processes. The kinetic energy increase resulting from the increased m in 1/2mv^2 is not fully offset by generation of electricity when we need to accelerate the vehicle back to speed. The first reason, Corolinth alluded to: electric motor/generators and batteries have finite capacity and can charge at finite voltage and currents. Were this not a limiting factor, no electric car, plug in hybrid, PD hybrid or electric assist vehicle would need to the mechanical brakes except in the case of regen system failure.

It's also important to note that generation is limited and it limited so not by efficiency. "Efficiency" must be used carefully as there are as many ways to quantify the definition as there are prostitutes in Thailand. Even if a generator were completely reversible (ideal), this ideal generator would still not even come close to 100% 1st law efficiency. By analogy, consider aerodynamic drag and other similar forces acting on a vehicle. Even if a car goes up and down hills and converts the potential energy gains from ascension back to kinetic energy, aerodynamic losses still occur during both processes. This is analogous to adding mass to a vehicle which converts KE back to electro-mechanical PE as it accelerates. The detraction from overall performance resulting from increase mass is always greater the the gain in regeneration even assuming infinite regeneration/motoring, battery capacity and thermodynamically reversible processes.

Now, on the flip side, I've owned a number of different vehicles with different engine configurations: gasoline port injection, electric assist gas hybrid (Honda IMA) system, Toyota parallel drive hybrid (so called Synergy drive), VW diesel direct injection (TDi) and now a Subura BRZ (gasoline direct injection).

I can say that in real world diving scenarios, hybrids have very realized advantages. In smaller cars, Honda's IMA system is very lightweight because it's just a motor/generator bolted to the crankshaft/flywheel. It's also simple so it's easy to design, both in terms of parts (no special transmission which further reduced weight) and the regenration/braking and assist algorithims are also simplified. I wrangled a lifetime average of over 42mpg over 70,000 miles in under 2 years on my CR-Z driving to Maine, all throughout the East Coast, the Midwest (including Colorado and Wyoming) and up to Seattle. Even a simplified IMA system allows for electric only coast to stop and idling under certain conditions: <18mph, brakes applied, transmission out of gear in the case of the CR-Z.

Toyota synergy drive and similiar parallel drive systems are advantageous on larger vehicles that can afford the extra weight as the increase % is smaller. This affords greater battery capacity and battery temperature control systems (i.e. cooling and heating). However, the biggest advantage is the ability to drive on electric only. Combined with the better performing battery and these system excel at low speed town driving with most control systems only engaging the gasoline engine when the battery falls to a certain level, load demand increases beyond a specified threshold or at above a certain speed. I consider plug-ins essentially the same system but their battery capacity is pushed even further and their thresholds for electric only operation even greater. Putting only 14,000 miles in 9 months, I managed a lifetime average of 39.7. Granted, my driving habits weren't congruent with the CR-Z so this isn't scientific by any means. The downfalls are increased weight, but also, increased complication (parallel drivetrain).



Diesel, IMO, offers the greatest advantage where hybrids simply can't compete - long stints of highway cruising. The motor designs naturally offer more torque so cruising at 80mph, where hybrid fuel efficiency rapidly falls off as I've observed, does not appreciably degrade efficiency. I leased a VW Golf TDi and managed a lifetime average of 39.1 mpg over the lease term but it's worth noting, again, that many of those miles were at very high speeds (over 90mph) up in the Wyoming wind.




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It's also important to note that what is being referred to as "efficiency" is only fuel economy. An important efficiency hit hybrid designs don't necessarily pay for is a so-called wheel-to-wells analysis of the design and construction energy costs of such a vehicle.


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I enjoyed the Thailand hooker metaphor.

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Yes, i already have a basic understanding of all of this, which is why efficiency is low. We can't recover 100% of the momentum as energy -- we can't even recovery 50% of it.



They very well might, much of the time. However, the 2012 Mazda CX-5 with it's 2.0L SkyActiv engine got 5.7L/100KM (49.6 MPG) on the highway, 7.8L/100KM in town (36.2 MPG), while putting out 150HP and 155 lb-ft of torque. It's an SUV. It wasn't the fastest, but it wasn't sluggish either. You're hard pressed to find any hybrid or diesel that could compare. (I haven't seen the figures on the 2014, but they switched to a 2.5L SkyActiv engine, so it's likely more power, less mileage.) Point being, fuel efficiency is not ruled by hybrid engines, or even diesel (your Golf TDi is half the size of the CX-5 and consumed more fuel.)

Edit: Perhaps I should ammend the diesel bit. Mazda makes a SkyActiv-D (Diesel) engine in Japan, and apparently it compares with SkyActiv-G in much the same fashion as standard diesel compares to standard gasoline engines. Mazda's doing some pretty amazingly innovative things... when the SkyActiv-D gets to North America, it'll be fun.

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You'd be surprised what a basic understanding might mislead you to believe, though. A great deal of people insist that electric vehicles would naturally be less wheels to wheel fuel efficient than a gasoline car because there are even more steps which have losses between the combustion process and locomotion of the vehicle, i.e. transportation of the electricity through conductive networks. However, the reason why gasoline engines are so thermally inefficient has to do with the dynamics of driving in relation to their second law behavior. Power on demand means that the gases do not get to expand isentropically which would approximate a reversible process. Large, mobile power generation beat these efficiencies because the process parameters are designed to run a known, steady state.

We could recover over 50% of the kinetic energy; there's no practical or physical limitation stopping us from doing so, but it would require rethinking the way transportation and traffic works.



5.7L/100km and 7.8L/100km are not 49.6 mpg and 36.2 mpg respectively, US or Imperal liquid gallons - you're looking at 41.26 and 30.15 respectively. What range and load cycle did you average this fuel economy over? I average over 90 mpg driving from Summit County to Denver, CO. There are people in the hypermiling community that can regularly get over 100mpg out of a plain jane 3rd generation Honda Accord with an F20 and F22 series engine. The point is, citing one number is not a comparison between two vehicles. I averaged my mileage driving over 30,000 miles a year on average through a bevy of different load conditions, in all seasons, in traffic, weather and a host of different tires using fuel mass measurement to get STP fuel volume and GPS data logging to record my automobile lifetime mileage. How did you measure your fuel amount? More importantly, what sort of load cycle was the car put through? I could probably wring over 150 mpg out of most cars but without telling you I had a partner in a Ford Excursion I could draft within 15 inches coordinated through cb radio, that doesn't mean much.

The CX-5 (and Mazda/Fords in general) is(are) a great car and engine technology in general is very satisfying in its current state. We have HCCI engines on the horizon, GDi type engines are available and improving on commonly available fuels and all of these plants make more power than anything in the past 30 years even without the octane boosting advantage of tetra-ethyl lead in fuels. However, to say you got 49 mpg in your car and that metric is a good indicator that gasoline engines are the apogee of fuel economy is misleading. I've seen Glocks jam. I've seen it happen twice in my life where it was absolutely not attributable to operator error but if I had to carry any handgun (and I wasn't going to be thrown into water), it'd be a Glock or another striker fire design. Remember that I have about 100,000 miles in the past 3.5 years. If I were to drive a CX-5 and put up lifetime numbers on the car in the range you're talking about, I'd be prone to hailing the engine as a revolutionary piece of engineering. I don't know anyone who has, though, in any of the hypermiling message boards I've been a member of since 2010.

Again, not a dig at the car. I'm going to have to buy an SUV soon, too, as I have my first child on the way, and I'll definitely keep the Fords in mind. It's not an apple to apples comparison, though.

Best Regards - Ryan

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"It's real, grew up in trife life, the times of white lines
The hype vice, murderous nighttimes and knife fights invite crimes" - Nasir Jones