I wish my Pri would pollute more, so it could...

Really? What makes you say this? My understanding is that this is not true; if the emissions system were not properly warmed up, the pollution would be A LOT more then what you put out by burning 10% more gas (with a properly operating emissions system), I believe.

This is something that I'm sure was considered when designing this car; otherwise, why bother designing the car to minimize emissions?

I'll also point out that it's not ONLY the warming up of the emissions system that leads to worse mileage in the winter. Winter gas and cabin heating are two other things that significantly contribute. . .

 

It all comes down to what you call pollution. If C02 is your main concern, then you have a valid point. But if you count all the other pollution created by a dirty burn, you're being kinder to the environment by burning a bit more gasoline to keep the exhaust "cleaner"

Jeez. I don't even know if THAT made sense either. Anyway... burning less gas isn't always the answer. There have been several vehilces in recent history that have gotten better mileage than the Prius... but they polluted WAY the hell more.

 

I agree with Betelgeuse. I'm sure it was considered and a CAT when warm does a great job of cleaning emmision so it's probably worth keeping the CAT (and engine) warm and loose 10% MPG. That said I have no hard facts to back this up.

 

Bah! What do you know about gas-powered cars, anyway?

More seriously, is CO2 not "dealt with" by the emissions system? Is the CO2 output just proportional to gas burned? Is it only the "hard stuff" that is captured by the emissions sytem?

 

part of the mpg loss is also because batteries hate cold. your battery is unhappy in winter, puts out less energy, makes you rely more on the ice.

and of course, cabin heat makes the ice run more too.

 

CO2 is proportional to gas burned, and there's nothing to be done about that, except driving less or striving to get better mpg. CO2 is pretty inert to most things except plants, so not something the emission system can get rid of. Sulfur oxides (SOx) and nitrogen oxides (NOx) and any incomplete combustion byproducts, CO and carbon solids are what the emission system helps to get rid of.

CO is a poison to humans, and SOx and NOx are what help cause smog and acid rain, so it's a good thing to get rid of them. Carbon solids are bad too, because they're particulates which can contribute to problems like asthma. Someone else may know more about the emissions control than this, but this is the general idea.

The metal catalyst systems used to convert these products need heat to get the reaction going, so that's why your car has to warm up to have low emissions, but has to give off a little extra CO2 in the process.

 

Actually, the NiMH chemistry isn't nearly as cold-phobic as lead-acid, for example. NiMH is exothermic, and in many applications, power is reaquired to COOL the pack. NiMH does very well in the cold actually (and since the battery is inside the passenger compartment of the Prius, it never gets all THAT cold when in use). Yes, the output is reduced in extreme cold, but that's not nearly as significant as the engine having to run longer just to keep the catalyst hot and the water warm for cabin cooling. In the cold, the battery is STILL the most efficient part of the system.

 

now this thread has to go back to why we get worse mileage in the winter time and most of the reasons have nothing to do with how efficiently the Prius runs while warming up.

anyone here in cold country will verify that the mileage does not suddenly spring into summer time numbers after the car is warmed up and it wont. it cant.

 

OK. I'm going to ask for some more information, because I don't see how the 22 pounds can come from 1 gallon of gasoline. I just went and stood on my bathroom scale with a gallon of milk. It weighed ~5 pounds (well, 4.5 pounds, but I had just had a glass). OK. So, imagining that 100% of that mass is Carbon (not totally true, but maybe close to correct), and we convert all of it into CO2 (also not correct; some of it's going to go into CO, some into soot and other nasties), we'll still end up with a mass of only ~18 pounds.

So, where did I go wrong? Is gasoline significantly denser than milk? Is there something else that I'm not considering?

 

Boy I don't know. Milk has a lot of pain old water in it. I don't know what percent but I would bet it is a fair amount. Gas is less dense but it is all hydrocarbons not much water. Milk water, fat, some protein, a lot less carbon overall. I don't think it is a good analogy even with one glass short! :lol:

 

If gas is less dense, then a gallon of gas would weigh less than a gallon of milk. That would mean that the maximum mass of CO2 it could produce would be even less.

EDIT: OK. Sorry. Didn't see kirbinster's post. OK. I believe that my bathroom scale's precision may not be good enough to distinguish between 5 and 8 pounds.

 

OK. So I found a couple of places on the web that say that a gallon of gas weighs 5.85 lbs. Assuming that's correct, and with 100% of the gas being C, and 100% of that C being transformed into CO2, I get a mass of 21.45 lbs. Now, I'd be OK with that being rounded to 22 lbs, but it seems like the two assumptions I made (100% of the gas being C and 100% of that C being transformed into CO2) can't be right. So, does anyone know how "wrong" they are?

 

Gas is a mixture of 5-12 hydrocarbon chains, so it's hard to get an exact #, but since H is so light relative to C, you get about 0.85 lb C/lb gas. Then, I calculate gasoline's density to be a little higher, about 6 lb / gal of gas. Then if you take 1 mol CO2 (44 g/mol) produced for every 1 mol C (12 g/mol). That leaves you with about 18.7 lb CO2 per gallon of gasoline. I had found a value of around 19 when I did my web search (I can't remember the website), so the mass ratio I calculated is probably a little low. Basically, you get a lot.

 

Ha. Generous of you! I believe I said "about" 22 pounds... and I Think we can all agree that 21.45 is "about" 22 pounds. This number will vary a bit, and is not precise. How about if we say "over 21 pounds" ??

Regardless, it is not insignificant, and it is "constant" (as constant as a variable number can be!) regardless of how the gas is burned.

I do agree with DaveinOly. This isn't the reason we get worse mileage in the winter! Different gas blends and COLD are!

 

Almost not at all wrong: any C that doesn't get burned completely comes out of the engine either as CO (a poison), or as soot, or as icky (HC)n compounds. The catalytic converter is designed to burn essentially all of this to CO2 (if it doesn't it's not working right and the poisonous cr@p comes out the tailpipe). So yes, one gallon of gasoline turns into about 21 pounds mass of CO2. This is about 1300 gallons of gaseous CO2 once it expands and cools to room temperature. It's the force of a little bit of liquid turning into a whole lot of gas that drives the pistons in the engine.

Just to bend your mind further, that same gallon of burned gasoline also creates about 8 lbs mass of water vapor, or about 1 gallon of liquid water if condensed.

 

On the web you can find values as low as 19 pounds CO2 per gallon of gaoline, up to (at least) 21.45, so take your pick. For priusblue, CO2 is actually quite reactive. Water and silicate rocks come immediately to mind. But back to the topic of the thread, I don't wish my Prius would pollute more.

 

The catalytic coverter is a small part of the drop in MPG you see in the winter. In no particular order, the main reasons that I know of are:

1. Decreased Engine Efficiency until it warms up
2. Leaching of engine compartment heat to warm up the passenger cabin, back to (1.)
3. Increased air density
4. Increased road friction on wet roads
5. Dehumidifier use
6. Cool grease/oil that increases friction at mechanical linkages

While it is true that the engine runs initially to heat up the cat, 90% or so of that mechanical energy is sent to the battery for later use, so at most 20% loss for the minute or two until the cat is toasty.

I understand and agree with your worries about CO2, but you are picking on a friend here.