When you buy a new snowmobile, you’ll find two items on the sled that refer to emission standards. There is an exhaust emissions engine label often on the tunnel or under the hood, and an exhaust emissions hang tag swaying from the handle bar to inform of the engine’s emission rating.

The hang tag identifies the engine type, it notes that the engine is certified compliant to U.S. Environmental Protection Agency (EPA) regulations and shows the engine’s Normalized Emission Rate (NER) on a scale of zero to 10. The tag must not be removed from the machine until after its retail sale.

The NER is calculated with the use of a formula set forth by the EPA. In the case of snowmobiles, that formula adds the hydrocarbons (HC) and carbon monoxide (CO) emission figures. A rating of zero is the cleanest and 10 is the least clean.

For Phase 1 of the EPA program, which started with model year 2006, engines must not rate more than 8. The EPA asks the manufacturers to round their calculations to the nearest whole number for use on the tags. Therefore, a calculation of 3.6 is noted as 4 and a rating of 5.4 is noted as 5. Nonetheless, some manufacturers have started posting fractional numbers on their tags.

Because of the rounding off intent of the EPA, some snowmobile engines could receive an NER of zero, but such a classification would not make much sense to a consumer because it would suggest the engine emits nothing. This isn’t possible unless you never started the engine. Another way to look at the rating is that it is an indication of how efficient an engine is at using fuel. A lower NER relates to better fuel mileage as well as reduced emissions.

After talking with several sales people at snowmobile dealerships near my hometown of Duluth, Minnesota, I’ve found no one who understands the hang tag’s meaning, other than its vague reference to an EPA mandate. When you look at that hang tag, simply remember that a lower number means fewer HC and CO emissions come from the exhaust and the better the sled’s fuel economy will be.


A 3-Step Phase-In

The emission standards are being phased-in in three steps with some changes being made during the multiple years of each phase. Phase 2 — which includes model years 2010 and 2011 — will require a further reduction of HC and CO. Standards have yet to be announced for Phase 3, which will include model years 2012 and beyond.

In addition to HC and CO, compounds measured by the EPA from automobiles and motorcycles, for instance, include nitrogen oxides (NOx) and particulate matter (PM). Many other compounds are in engine exhaust as well, such as carbon dioxide (CO2), water (H2O) and other compounds made up of elements found in the gasoline blends, air and oil blends.

In the case of snowmobiles, the agency measures and regulates only HC and CO levels in the exhaust. Levels of NOx are inherently low in two-stroke engines because of their lower combustion chamber temperatures. While four-stroke engines have higher NOx emissions than two-strokes, they are not of great concern in the winter when air isn’t warm enough to act as the energy to create smog.

PM is an issue with diesel engines, but the EPA does not anticipate the application of diesel engines in snowmobiles, so those levels aren’t evaluated. Emission levels of engines operated at summer temperatures require more stringent regulations than snowmobiles. Automobiles, for example, have NOx and PM level limits included in their regulations.

Most people know that CO2 is not a pollutant. If it were, we would all be dead because that’s what we release every time we exhale. The radical greenies who warn about global warming and climate change, however, say that good old CO2, which feeds all plant life, is the key compound that creates the so-called greenhouse effect.

The fact is that only 5 percent of the planet’s CO2 is man-made and only 0.5 percent of it is produced by the auto industry. That won’t stop the misguided environmentalists from screaming for more and more regulations, though. For now, CO2 is not a compound that the EPA is concerned with, but I’m certain there will be a push to include it as a pollutant in the future.

How Emissions Are Measured

Emissions are measured in grams per kilowatt-hour (g/kW-hr), and 1 horsepower equals 0.746 kW (1hp=0.746kW). To measure its output, an engine is run on a dynamometer and operated using a five-mode cycle that mimics the typical field use of a snowmobile. The fact that the sampling is measured against the kW-hr means that there is an advantage for manufacturers to clean up the larger, more powerful engines first so they can bank credits to lower the fleet average or extend the use of non-compliant engines.

For Phase 1 of the EPA regulations, the agency standard is 100 g/kW-hr HC and 275 g/kW-hr CO. This first step results in a 30 percent reduction of these pollutants — in complying engines — over the previous industry baseline.


Phase 2 of the standards will require hydrocarbon emission to be lowered to 75 g/kW-hr, but CO emissions will remain at 275 g/kW-hr. One hundred percent of the fleet must meet the requirement and fleet averaging will again be allowed. This means that credits banked from previous years can still be used to compute the average.

Fortunately, the EPA and the snowmobile manufacturers have a good working relationship that has not only spawned some interesting designs, but it has created better snowmobile engines. As we look ahead, however, model year 2012 is going to be very interesting.

Engine management systems become more complex every day and offer incredible control of the engine’s operation and efficiency. More direct injected two-stroke engine designs are near production and will have a profound effect on snowmobiles and other motorized industries.

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