Blessed by the Potato

Hybrids (like my Prius) contain many awesome innovations that give it that great efficiency, leading to lower fuel use (and lower expenses!). With plug-in hybrids starting to hit the market, the ways that technology provides efficiencies increase. Yet even though hybrids have been around for well over a decade, they are still very poorly understood (particularly by auto journalists).

Quick, which one innovation contributes the largest portion of the fuel savings in a hybrid like the Prius, is it:

a) regenerative braking
b) exhaust gas recirculation
c) atkinson-like cycle engine
d) electric motors and a battery to power acceleration
e) aerodynamics, including a tear-drop shape and a plastic cover for the underside to smooth airflow
f) lightweight aluminum construction
g) low rolling resistance tires
h) continuously variable transmission
i) an engine that turns off when not in use (coasting, at stops)

All of those innovations (and I’m sure a few I’ve forgotten) add to the efficiencies. Odds are good that you answered a, or d, or i, since those are the items that are the most distinctive about a hybrid, and which get the most press. And of course, none of those three are of much good when smoothly cruising on the highway, which is why auto writers keep saying stupid, easily disprovable things like “all that hybrid gear is useless on the highway.”

Yet a quick check of fuel consumption ratings shows that indeed, hybrids get fantastic highway mileage. The gap between them and a regular car isn’t as wide in the highway cycle as in city driving, but it’s still a really good improvement. So why is that?

It’s because the actual answer is (c): the atkinson-like cycle engine. Estimates vary, but something like half of the total improvement in overall mileage (and nearly all of the highway-rating boost) is because the engine is simply more efficient at turning hydrocarbons into motion (the “thermal efficiency”). All that business with the electric motors helps, and there certainly is some benefit from pairing the properties of an electric motor (which generates maximum torque at low RPM, and is great for helping to meet peak demand) with a gas engine (which needs to rev up to produce acceleration, and which has a high-density fuel source for steady-state power demands), but it’s there largely because with an Atkinson engine, you’re not going to get anything approaching an acceptable 0-60 time. That efficient engine needs help getting going.

If you wanted (e.g.: if you’re an automotive engineering student looking for a summer project), you could strip out all the electronic stuff from a hybrid and just drive around with the Atkinson engine, and you’d get a big part of the benefit. Of course, you couldn’t actually use that in traffic since it would take you forever to accelerate, but on a closed course to prove a point…

Anyway, once you’ve got the electric motor in there for the acceleration boost, you can do all the extra tricks with it to squeeze out even more efficiency, like shutting off the engine when coasting, regenerative braking, etc.

So now that you know about the importance of the Atkinson-cycle engine, you see why hybrids still rock on the highway. In fact, improved thermal efficiency is also the reason why diesels get decent fuel consumption numbers on the highway: the higher compression of a turbo diesel is also more efficient at turning hydrocarbons into motion. In terms of litres burned per hundred kilometers, diesel (like a Jetta or Golf TDI) is on par with a hybrid like the Prius; though once you factor in the higher energy density of diesel, well, you can see who the winner is (and I won’t get into the issue of city driving, too).

And of course, knowing that this is the single biggest source of efficiency is why I was so upset that GM didn’t include an Atkinson-like engine in the Volt, instead just slapping in an off-the-shelf engine, which is why its efficiency isn’t so great once the charge from the plug-in is used up.

Another idiodic piece about hybrids in the press. It never fails that they say such inflammatorily stupid things that I get all angry at them. It shouldn’t be all that surprising: you don’t become an automotive journalist because you’re smart or know science or can do basic math, you do it because you like G-forces and want to make engine noises all day. You crave the open road and have an expense account for gas. The typical automotive journalist is about as far from a hybrid buyer as one could possibly get.

But for people who are stuck in stop-and-go and pay for their own gas, a fuel-efficient hybrid is a great choice.

Asking “why carry around the battery on the highway” is like asking “why carry around gears 1-5+R if I’m only going to use 6th on the highway?” except even dumber. If you bother to look up the ratings, you’ll see that not only is the Prius efficient in the city, it is also head-and-shoulders above any gasser on the highway — even diesels. Holy crap, it even beats out the tiny Smart Fortwo by almost 20%. There might just be something to this hybrid thing. I could go into the why of it*, but the point is it’s an extremely easy fact to check, yet I’ve seen these assclowns get it wrong so. many. times.

And if you’re a travelling salesman? Then a hybrid should be the only thing on your shopping list. With a lot of miles to put on, you’ll find the payback to be phenomenal. Ditto taxi drivers, who have found it’s cheaper to get a brand new Prius than a surplus former police cruiser Crown Vic.

“So hybrids, apart from their benefit for city drivers, have failed to sweep the world. Will anything change this pattern?”

Perhaps if instead of panning them at nearly every opportunity, if auto journalists actually came out and started writing some articles more along the lines of “well, the ride’s ok, I guess, and by paying a few thousand more up-front, you’ll save thousands in fuel expenses over the life of the car. If you do a lot of city commuting, or a tonne of driving in general like a travelling salesman, you should take a look.” Then maybe people might buy.

And on the heels of that ill-informed article, this diesel-scented turd.

“Diesel fuel should be taxed at a lower rate than gasoline for one simple reason: the fuel carries more energy than a comparable amount of gasoline, thus it is more efficient.”

Actually, that’s a good argument for diesel to be taxed more on a per-litre basis, since it’s using more barrels of oil per litre to make. But, the fact is, diesel is taxed less than gasoline: the federal excise tax is 10 cents/L on gasoline, and 4 cents/L on diesel. In Ontario, the provincial excise tax on gasoline is 14.7 vs 14.3 cents/L on diesel fuel.

“The fuel-efficient turbodiesel delivers the highway fuel economy of a Toyota Camry sedan.”

…without accounting for the higher energy density of diesel, and allowing for a very large fudge factor (using the V6 Camry vs the more popular V4, and even then, he’s off by over 6%; off by over 21% when comparing to the 4-cylinder).

Now, I’m not totally against diesel: it is more efficient than gas in many driving conditions (though not more efficient than a hybrid, and with about the same cost premium). A select few models will end up being cheaper over their lifetime than a conventional gas car. But it is a dirtier fuel, and one of the benefits of hybrids is reduced emissions as well as efficiency: diesel presents a trade-off (better efficiency but higher emissions). I simply don’t get the auto-journalists’ thinking of “diesel good, saves money and fun; hybrid bad, costs more up front” when it could have just as easily been the opposite. I suppose it’s their pre-existing bias towards diesel (more torque, grunt grunt grunt). It seems so arbitrary since those positions could easily be reversed (“The diesel Touareg is $5000 more than the gas version, a premium that would take over twenty years to break-even on.” “There is hardly any difference in fuel economy in city cycle driving, and with diesel fuel a bit more expensive than regular unleaded, there’s no point if you do anything but cruise the open road.” “The new emissions systems for them are completely untested, and with so few VW diesels on the road, good luck finding a mechanic if you run into a problem down the road.” “The AdBlu emissions control additive will need to be replaced frequently, and VW is very secretive about the pricing. Unverified rumours we are too lazy to fact check indicate that this could cost you an additional $5000 down the road.” “Diesel: fine for early adopters, but not ready for primetime.”)

* – Because the engine is more efficient. Atkinson cycle, yadda yadda yadda. And that is because the battery and motors are there for peak demand. Even on the highway they are used (e.g., to pass, or go uphill). It’s a far cry from dead weight — and even if it is, well, the numbers speak for themselves.