EPA Hydrocarbon Test Anomally

[swall]

I just read in a motorcycle publication about EPA hydrocarbon emission results for motorcycle vs truck and they seem counterintuitive to me. Specifically, a BMW motorcycle getting 45mpg emitted hydrocarbons at a level of 1.5/mile and a Ford F-150 getting 15mpg emitted only 0.1/mile. How can this be? Is it somehow do to the BMW having more combustion events per mile,or something like that? Both vehicles were fuel injected, with catalytic converters.

 

[GregLocock]

No, it is due to the extreme care and engineering that goes into the fuel system of a modern car, or truck.

The cat system may be a small part of it, but to achieve modern levels of HC emissions you need to address things like permeability of fuel tanks, and so on.



Cheers

Greg Locock

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[BrianPetersen]

Were those actual test results, or were they certification limits?

The standards for motorcycles are (for now) a lot less stringent than the standards for automobiles. The catalytic converters are designed to meet the standards in each case. There's no point using an expensive, really efficient catalytic converter when a cheaper but less efficient one will achieve compliance.

 

[swall]

Brian--from my read of the article (and the fact that they are nice even numbers) those would have to be emission limits, rather than actual test results. But your explanation makes sense--the EPA limit is driving the results, not something inherent with the two vehicles. Greg-- how can fuel tank permeability enter into this? As I understand the EPA exhaust emission test procedures, the exhaust is bagged and analyzed. No way for stray fuel vapors to enter into this.

 

[dgallup]

There are evaporative as well as tailpipe emissions requirements for both types of vehicles. My Triumph Speed Triple has a charcoal canister that feeds the intake to control evap emissions as well as air injection and exhaust catalyst for tail pipe emissions. It sounds like the article was only talking tailpipe since the units are in gm/mile.

 

[GregLocock]

Shrugs, I don't know how they measure it, but HC emissions consider all sources of HC in the vehicle (including, I vaguely remember the materials in the car itself).



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[franzh]

We did a shed test (the evaporative cycle) on a vehicle we were trying to get through EPA. Our raw HC numbers were through the roof. It turned out that the fuel hose we used was permeable (LPG, type 1 hose). The actual engine out emissions were on target.

The shed test measures all evaporative emissions, including tires, interior, all fabrics, gas tank, etc. I saw a Subaru that failed a shed test because the owner sent it through a detail shop first, where they sprayed the engine compartment and tires with a preservative. The real stinker was the tire shine compound.

Franz

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