Friday, February 27, 2009

Smoke & Mirrors

So pretty much the accepted truth is that scooters and mopeds are cool, great on gas, but terrible for the environment.

'yeah, but your moped pollutes as much as like 40 SUV's'

If you own a moped or scooter, you've heard that one before. And, quite frankly, it always annoyed the shit out of me. It felt wrong to me but I couldn't say why. -Also because (car) people would rationalize their own pollution by believing that nowhere could there be a vehicle qualitatively better for the planet than any other. Sort of a 'we're all screwed', "pretty girls can't be smart" horsetrading ideology. Having said that, my digging around was motivated by spite for these people and also by the frustration of not being able to outfox those people with numbers. Awhile back, I got into a debate with my old roommate Dave Force who maintained this "40 SUV's" belief. It turns out he was right ...and wrong too. The truth is that environmental considerations get pretty murky when you examine classifications of vehicles, testing methods and ideologies.

Basically, there's 4 things coming out of the tailpipe of any internal combustion motor:
-Carbon Dioxide
-Water Vapor
-Unaltered Atmospheric Air

Obviously we don't care about Water Vapor and Unaltered Atmospheric Air, as they aren't bad for people or the planet in any appreciable way. Hydrocarbons and Carbon Dioxide are pollution, bad for the planet and people. Any emissions test will show you that 2-strokes are much 'dirtier' than 4-strokes, and with good reason. A 4-stroke engine (as the name indicates) divides the internal combustion process into four discreet phases, inside a closed cylinder wall with valves carefully metering incoming fuel and outgoing exhaust. Its easy to see how well contained the process is with a 4-stroke. 2-strokes however use ports (holes) in the cylinder wall for intake and exhaust, and the intake port is open at the same time as the exhaust, invariably allowing some unburnt fuel to escape. 2-strokes also burn a oil lubricant in the fuel mix, unlike 4-strokes which have closed oil channels and burn straight gas alone. So 2-strokes are dirtier:

-Because of the escaping unburnt fuel mixture
-Because of the oil in the fuel mix

It's useful now to point out that a well designed, well-maintained engine (2-stroke or 4-stroke) will approach the stoichiometric ratio (14.65 parts air per 1 part fuel) at which all fuel and all air are perfectly mixed and combusted together. The closeness to this figure indicates an engine's TRUE emissions quality, fuel efficiency, etc.. more than any other. In other words, gas combusts in a 2-stroke approximately the same as it does in a 4-stroke. If this were the only factor, emissions would closely mirror engine size on a pretty flat curve.

It's fair then to point out that by measuring the rate, and not the total amount of emissions gives larger vehicles a huge handicap. Measuring the amount of emissions a vehicle produces is probably the most common sense method. But creates problems because it announces the obvious: a bigger engine burns more fuel, and creates more emissions. This is a problem because many large polluters are popular vehicles and other vehicles that are necessary. To make things "fair" for these vehicles, emissions are measured by the rate, not the total amount.

So what happens when we measure emissions based on amounts and not rate?

First, my numbers are based on this article: Polluter Scooters, by Willamette Week in Portland, Orgeon.

The Vehicles:

2006 Subaru Tribeca 3.0L (3,000cc) 6-cylinder DOHC w' catalytic converter
1968 Vespa GTR 150cc (0.15L) single cylinder rotary valve 2% mix
2004 Genuine Stella 150cc (0.15L) single cylinder reed valve 2% mix w' catalytic converter

Polluter Scooters Test results:

Tribeca: 1% CO2, 10 particles per million (ppm) of hydrocarbons
Vespa: 8.6% CO2, 4,900 ppm of hydrocarbons
Stella: 7.1% CO2, 1,100 ppm of hydrocarbons

3.0L = 3,000cc's
150cc = 0.15L
1 Subaru Tribeca engine = 20 Vespa / Stella engines (3,000/150 = 20)
[1 Subaru engine = 60 moped engines]

So, if an 3,000cc engine runs for a minute at 1,000 rpm's and we capture all the exhaust out of the tail pipe, we should have 3,000, 000 cc's of exhaust total to measure from:

So where does that leave us? Using pretty remedial math, we can show that by measuring the amount and not the rate of emissions inverts the accepted idea that scooters produce more green house gas than cars, when by these numbers a '68 Vespa makes only 43% of what a modern car does, and the Stella does even better at around 35%. I'd be very interested to see the emissions figures on cars from 1968. -Even accounting for the multi-cylinder effect of the Tribeca creates a dead-heat, barely edging the Stella. So depending on how you slice it, these scooters are as good as, or significantly better than the Subaru on CO2/ Greenhouse gas.

As for the hydrocarbons, for every one particle the Subaru emitted, the '68 Vespa emitted 24.5 and the Stella emitted 5.5 (catalytic converters do make a big difference). The scooters' poor performance is due to the nature of 2-strokes:

-Because of the escaping unburnt fuel mixture
-Because of the oil in the fuel mix
(as mentioned above)

So, scooters are pretty good on CO2, and pretty bad on hydrocarbons. Whats the difference between hydrocarbons and CO2? Hydrocarbons mix with nitrogen at low atmosphere in sunlight to form the pollution that you can see and smell, and that will kill you if you’re in a closed garage with a motor running (smog). They are a urban health problem in dense asian cities, where mopeds and scooters fill the narrow streets. Hydrocarbons don't impact much more than their immediate local environment though, and thanks to advances in engine design, oil composition and ignition systems, continue to be reduced in 2-strokes. In the United States, 2-stroke motorbikes represent a tiny, almost negligible percentage of the total vehicles on the road. (within a rounding error) I personally have a hard time believing that mopeds & scooters are making a measurable impact on the air quality in our cities (outside of standing on the sidewalk at the start of a big rally ride!).

Let's review:
-Current Testing methodology gives large engines a significant handicap.
-Scooters (and mopeds, presumably) are actually significantly better than cars in CO2 emissions. or at worst, as good as modern cars.
-Scooters produce significantly more hydrocarbons than cars; but exist in vastly fewer numbers.

When you combine this knowledge with the known reduced fuel consumption of mopeds and scooters, the reduced carbon footprint in using a vintage machine vs. purchasing a brand new manufactured good, and the low impact on roadways and accident/safety concerns, I hope you’ll agree that while breathing Moped pollution isn’t good for people, owning a vintage scooter or moped is definitely better for the earth than many other machines.


Joel said...

AND... I've always maintained that while the pure traveling time of a car may be better for the environment, people that use mopeds, scooters, etc. as their sole mode of transportation, tend to modify their entire lifestyle and tend to spend LESS time actually traveling therefore creating less pollution merely because they aren't in the comfortable living room of a Hummer.

In simpler terms; people that ride two wheels tend to not commute as far.

genetuck said...

While scooters and small motorcycles produce a lot less Carbon Dioxide and Carbon Monoxide than cars, those harmful Hydrocarbon emissions are the reason two-strokes are being phased out. As for the small number here, there are 100-million two strokes in Southeast Asia, and those brown clouds of pollution regularly drift from over there to our West Coast. However, direct injection makes two-strokes slightly cleaner than four-strokes. Take a look at the YouTube video I prepared showing how Envirofit of Colorado State University is converting two-stroke taxis to direct injection to end that pollution.

Josh said...

Do you have any more information on the brown clouds drifting over? I'm intrigued.