Does anyone here know what the standards used in federal emissions programs are for converting emissions data, given in gas percentages, to the grams-per-mile that is most often used as the measure in federal/state programs?
Put another way, the gas analyzers I’m using output the relative percentage of the different gases. What needs to be done to convert these numbers to GPM? It seems that some basic assumptions need to be made (about vehicle speed, etc), thus I suspect there is a standard out there somewhere for doing this, I just haven’t found any info on it yet. If anyone here knows about this, or if anything I’ve said above is wrong, I’d be grateful for the input! Until then, I’ll keep searching on my own
I don’t think the Feds use standards to covert tail pipe numbers to the grams per mile. IIRC the federal test is based on what is called the LA loop a 26 mile drive through LA. In the old days, they actually drove the car being tested through LA with test equipment attached. Needless to say, this introduced some uncontrollable variables like traffic and weather.
So now they do the same drive on a dyno. The exhaust is collected into a REALLY large bag, and then analyzed. They can determine the total weight of HC, CO, NOX in the bag. . Divide the total of each by 26 and you have your grams per mile.
FWIW, The LA loop includes a cold start. One of the engineers in my company told me last year that our new cars run so clean that between 90-95% of the total pollution in a 20 minute drive from cold comes in the first 30 seconds.
I don’t know what kind of number you are seeing, but I can recall doing smogs in a shop next to the San Diego Freeway. Several times I had tailpipe reading of negative HC. In other words with a hot cat, the exhaust out of the tailpipe had less hydrocarbons in it than the air in the shop.
I don’t think the Feds use standards to covert tail pipe numbers to the grams per mile. IIRC the federal test is based on what is called the LA loop a 26 mile drive through LA. In the old days, they actually drove the car being tested through LA with test equipment attached. Needless to say, this introduced some uncontrollable variables like traffic and weather.
So now they do the same drive on a dyno. The exhaust is collected into a REALLY large bag, and then analyzed. They can determine the total weight of HC, CO, NOX in the bag. . Divide the total of each by 26 and you have your grams per mile.
FWIW, The LA loop includes a cold start. One of the engineers in my company told me last year that our new cars run so clean that between 90-95% of the total pollution in a 20 minute drive from cold comes in the first 30 seconds.
I don’t know what kind of number you are seeing, but I can recall doing smogs in a shop next to the San Diego Freeway. Several times I had tailpipe reading of negative HC. In other words with a hot cat, the exhaust out of the tailpipe had less hydrocarbons in it than the air in the shop.
