Hypermiling and emissions.

[2000neon]

I remember a little while back there was a thread about how some hypermiling (specifically engine off coasting) was potentially bad for emissions. I can't seem to find the thread but I think it had something to do with the catalytic converter not being kept hot enough during engine off coasts..?

I wanted to give my experience today as a data point for the discussion about whether or not hypermiling may lead to increased emissions. I just bought a 94 Civic VX, which has a little under 113000 miles on it. I have started doing EOC's during my commute to and from school since having the car, and the previous owner did some as well.

To register the car, I needed to do an emissions test and it passed no problem, despite having done engine off coasts.

Here are the raw numbers:
At 2217 rpm.

HC: Limit= 82/ Reading=29
CO%: Limit= 0.45 / Reading= 0.03
NO ppm: Limit= 636 / Reading = 13

At 644 rpm.

HC: Limit = 200 / Reading = 115
CO%: Limit= 1.00 / Reading= 0.56
NO ppm: Limit: N/A / Reading = N/A

For anyone wondering about EOC and it's potential effect on emissions, here is one data point to consider. Although it is not applicable to every car/ situation, but is something else to consider.

[GRU]

I think the issue was since the engine was off for a long period of time (while coasting) the engine, when re-started would pollute more (catalitic cold) than it would if the engine was previously running because the catalitic converter would have been hot

[RobertISaar]

an emissions test won't show the real effects of EOC unless it were hooked up to a dyno that could simulate road friction and inertia of the vehicle, so that you could shut it down while at speed, let the vehicle "slow", then fire it back up to get back to your target speed. then the emissions readings immediately after firing would be useful to look at.

it SHOULD NOT effect cat life(or effectiveness, when it is in it's designed operational scenario) much, if at all.

[Duffman]

I am not wild on the warm air intakes, higher combustion temperatures create more NOx.

[some_other_dave]

Notice that the readings are in percentages or PPM (parts per million). And that an engine spinning at 2000 RPM is pushing out 3 times as much exhaust as one spinning at 667 RPM. So the total amount of pollutants emitted is not as lopsided as it looks at first.

And if you consider the pollution caused by drilling, pumping, refining, transporting, etc. the fuel that you burn, it might actually be that the idle RPM has less total emissions than the high RPM condition due to burning less fuel. Depending on a lot of factors, of course!

-soD

[Piwoslaw]

Originally Posted by 2000neon

I remember a little while back there was a thread about how some hypermiling (specifically engine off coasting) was potentially bad for emissions. I can't seem to find the thread but I think it had something to do with the catalytic converter not being kept hot enough during engine off coasts..?

Here it is:
The dirty cost of one man's hypermiling?

[euromodder]

Originally Posted by 2000neon

I remember a little while back there was a thread about how some hypermiling (specifically engine off coasting) was potentially bad for emissions.

That was mostly about the emissions while pulsing & gliding , i.e. with multiple restarts, engine staying cold(er), and fairly hard accelerations during pulses.

[cRiPpLe_rOoStEr]

Nowadays with more efficient engine management systems, the multiple start-stops are not so problematic anymore. The major problem is still related to the catalysts temperature, then it's not hard to justify some newer setups with the cats mounted closer to the exhaust manifold...

[RobertISaar]

some cats are integrated into the manifold..... along with "precats" as well.

[cRiPpLe_rOoStEr]

Originally Posted by RobertISaar

some cats are integrated into the manifold.....

Just like my grandma's Chevrolet Prisma