zero emissions?

[jamarimutt]

I have seen several posts, in this and other forums, which suggest that some Prius owners believe that our cars are zero emission vehicles. Could someone more knowledgeable explain what the ultra-low emission or no emission classifications actually mean? Also, what comes out of the Prius' tailpipe? I am sure that it's not water and oxygen; some pretty noxious stuff likely comes out of that pipe, although in smaller quantities than in other cars.

[newts]

I am sure the scientists will explain in more detail but the Prius is a "Partial Zero" emissions vehicle. This means that certain times, like "stealth mode" and stopped for a light or in traffic it is running on electric only and thus has no emissions during those periods.

At other times it is emitting the same combustion products as any other gas car. Hopefully not as much as others and also with the ranges of the ICE better controlled the harmful byproducts are minimized as compared with other cars.

[jchu]

When the ICE is running the emissions are 10% of a standard ICE engine. This is due in part to using a 5 cycle (Atkinson) setup instead of a 4 cycle (Otto) setup. Atkinson provides less torque but this is more than made up for with the Electric portion. (i.e. why you always see the Electric Motor arrows when doing any decent acceleration)

[DonDNH]

For a visual of the Atkinson Cycle, see:

http://www.keveney.com/Atkinson.html

[boa8]

Originally posted by jchu
When the ICE is running the emissions are 10% of a standard ICE engine.  

Not when ICE is running, but combined cycle produces 10% emissions of an AVERAGE (incl. models produced 5-10 years ago).

[htmlspinnr]

The AT-PZEV rating also comes from the additional steps taken to prevent evaporative emissions. This includes prewarming the intake ports/head before starting the engine with stored warm coolant, carbon/charcoal filters in the air cleaner to prevent vapors from escaping through the intake hoses, tight seals on the filler neck, bladder in the fuel tank and the purge methods used to reduce vapors within the tank, etc.

The clean burning engine is a large portion of course, but not the whole picture. Some of the other various technologies which help the ICE to burn cleaner is the variable valve timing on the intake cam, the Atkinson cycle (controlled by the variable valve timing), and the fact that the air/fuel mixture is always stoichiometric (14.7:1 or thereabouts depending on the fuel and additives) and the multiple various air/fuel and O2 sensors that help achieve that, the "oblique squish" area of the cylinder, and other technologies. While some of these may exist on other cars, the combination of all of this technology in this engine, and how it is implemented makes a big difference.

[Brian]

I like driving on EV mode because you KNOW you won't be letting off emissions.

[Frank Hudon]

I've got to hand the crown to Rick and his piece on the emission target and reduction methods of the Prius. He pretty well nailed the whole thing down to the floor. Good work Rick!

[htmlspinnr]

I like driving on EV mode because you KNOW you won't be letting off emissions.

It's probably more accurate to state that using EV mode delays the creation of emissions. Unless you're using solar (or some other renewable, non-polluting method) to recharge your HV battery, those emissions will be created eventually. You're simply choosing when to do so :-)