Understanding the EPA's upcoming regulation of ATVs and the fate of 2-cycle engines

Aug. 01, 2005 By George Szappanos
You may have heard the rumor that the Environmental Protection Agency is forcing ATV manufacturers to install exhaust catalysts on your favorite sport quad. Or that in 2006 two-stroke ATV's will be out-lawed. Well, it's not exactly true, but not too far off. Back in 1990 the Clean Air Act was passed which essentially called for the clamping down of the exhaust emissions from cars and light trucks. Since that time, the stuff emitted from the tailpipes of cars and trucks has been cleaned up so well, that in some cases the air coming OUT of the tailpipe is actually cleaner than what's going in the intake. The ultimate effect has been steadily decreasing air pollution levels even though the number of vehicles on the road has increased by over double since the time study was begun.
Air pollution over the last 35 years has steadily improved since the Clean Air Act was instated, especially surprising considering the dramatic increase in how much we Americans drive.

Not ones to be satisfied with good enough, the EPA has shifted their attention to motorcycles - on-road bikes, as well as off-highway motorcycles (OHMCs), snowmobiles, and ATVs. Nationwide, these vehicles account for nearly 10% of national hydrocarbon emissions (HC), and almost 5% of carbon monoxide (CO). Put into perspective, a typical two-stroke ATV produces as much pollutant as a dozen modern cars. 

Although these machines represent a considerably small percentage of emission producing vehicles, they do nonetheless produce many nasties that left unchecked long enough, can have a very negative impact on the environment and our sport. Take the case of Yellowstone National Park which although for many years enjoyed a reputation of being a fantastically beautiful place to go snowmobiling, had to completely shutdown motorized winter recreation due to the seemingly omni-present blue cloud of two-stroke smoke that would blanket the area in the wintertime. 

But what are these "pollutants" and why do we care? Having spent many years sniffing the exhaust of motorcycles, many of us can probably, with little sarcasm, admit to actually enjoying the sweet smell of burnt racing fuel. The darker side to fuel combustion is that it's not perfect. If it was perfect, the complex hydrocarbon compounds of the fuel (Hydrogen and Carbon molecules) would react with air (Oxygen and Nitrogen molecules) and produce very benign molecules of CO2 (carbon dioxide), H20 (water), and N2 (nitrogen). Theoretically that's how it works. But unfortunately, it doesn't work out so nicely in the intense heat of an engine, and we get CO (carbon monoxide), unburnt hydrocarbons (HCs), some water, and various oxides of nitrogen (NOx) as the products of combustion. All but the water are very bad for you. 

As for those bad actors, we all know that CO is a colorless, odorless gas that can kill you if you spend too much time behind closed doors listening to the drone of your beloved bike. But with over a million pounds of CO per year pouring out of ATVs alone, the cumulative effect of all motor vehicles is significant and detrimental on those with weak cardio-vascular systems.

The infamous LA smog pictured above is primarily ground-level ozone (O3), which is formed by chemical reactions of volatile organic compounds (primarily HC) and NOx in the presence of heat and sunlight. Not only is the effect unsightly, but can cause real problems with the respiratory system (lung damage). If left uncontrolled, the EPA expects that off-road vehicles will constitute a fourth of the total HC emissions from mobile sources by 2020. 

Engine category ATV emission rates (grams / mile)
current 2-stroke 53.9 54.1 0.2 2.1
current 4-stroke 2.4 48.5 0.4 0.1
EPA std. 1.6 42.9 0.3 0.1

To head this off at the pass, the EPA has instituted regulation of nonroad engines nationwide starting in 2006. At that time, half of a manufacturer's new motorcycle models must meet the regulation. By 2007, every new machine (with the exception of "competition-only" machines) must meet the standard, or it cannot be sold or operated in the United States. They have not specifically declared how the OEMs are to meet the requirement, only that they must. And herein lies the fate the ubiquitous 2-stroke. 

Although the two cycle engine design can pack a lot of power in a small package, it does so with the compromise in efficiency. The beauty of the design is that it can accomplish all four required internal engine events (suck-squish-bang-blow) in a single revolution of the crankshaft. That means that it has twice as many power strokes per rev than the arguably more refined 4-stroke. That's where the superior power comes from, not from anything magical or inherently better about the engine design. In fact, it's quite crude in comparison to the 4-stroke which has valves to control the gas exchange process in a much more regimented manner. And there's the rub - as powerful as the 2-stroke is, it accomplishes it at the expense of wasted fuel that escapes the combustion process. Not only do the engines expel comparatively more HC (unburnt gasoline) due to imperfect scavenging, but there's also additional HCs in the exhaust in the form of burnt and unburnt 2-cycle oil. Even with the most advanced electronics and engine technologies, it will be nearly impossible for a 2-cycle powered ATV to become certified.

So what will this mean? The industry has been seeing the evolution to 4-stroke powerplants now for several years which is certain to continue. The good news is that the motorcycle manufacturers are building ultra high-tech 4-strokes that are rivaling the power of their ill-fated caustic cousins. Down the road, as in 2009 when an even tighter regulation is put in place, it wouldn't be unrealistic to start seeing exhaust catalysts and even fuel injection of your favorite quad. For the Japanese market, Honda plans by 2007 to have every single one of their motorcycles fuel injected - from their 180 mph superbikes, down to their 50cc scooters.  The upshot is that when the emission standards for recreational vehicles are fully implemented by all the OEMs, the EPA expects to cut in half the HC, NOx, and CO emissions from these engines by 2020. For those that ride, or don't ride, that'll mean fresher air, less trips to the doctor, and no more blood-shot eyes at supercross races.

For more info, see www.epa.gov/otaq/reqs/nonroad/recveh

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