Real-world CNG vs. gasoline emissions

[echamberlain]

I've always been curious about the emission differences between CNG and gasoline. This year I had to get my bi-fuel 2000 Ford Contour smogged, so I thought I would find out.

When I first bought the car in 2005, I had it smogged on CNG. The guys working at the smog station had never smogged a CNG vehicle before and were actually fighting over who would get to smog my car.

This year, I smogged the car on gasoline. Same vehicle, same test, different fuels. There is a four year difference between the tests, but I'm too cheap to pay for two smog tests, so these numbers will have to do.

vBulletin doesn't have very good table capabilities, so I've scanned the smog reports and attached them to this post as jpg files.

CNG is clearly cleaner on CO2 and hydrocarbon emissions and NO emissions are virtually non-existent, the CO results favored gasoline.

[CH-4]

Re: Real-world CNG vs. gasoline emissions

Something doesn't make sense. CO distribution in NG is less than gasoline or else we'd be cooking with gasoline rather than NG. NGV and propane powered vehicles can run indoors, because they give off very little CO. I don't think your testers equipment is calibrated to read CNG emmissions correctly. A few years back before I had HOV stickers on my Contour, I was required to smog in California. At that time I did the same thing and the test was completely different than what you're showing, however I was told at that time they couldn't smog NGV's with their current equipment.

[Adrian]

Re: Real-world CNG vs. gasoline emissions

I've always been curious about the emission differences between CNG and gasoline. This year I had to get my bi-fuel 2000 Ford Contour smogged, so I thought I would find out.

When I first bought the car in 2005, I had it smogged on CNG. The guys working at the smog station had never smogged a CNG vehicle before and were actually fighting over who would get to smog my car.

This year, I smogged the car on gasoline. Same vehicle, same test, different fuels. There is a four year difference between the tests, but I'm too cheap to pay for two smog tests, so these numbers will have to do.

vBulletin doesn't have very good table capabilities, so I've scanned the smog reports and attached them to this post as jpg files.

CNG is clearly cleaner on CO2 and hydrocarbon emissions and NO emissions are virtually non-existent, the CO results favored gasoline.

When I smogged a Bifuel Ford F150, the smog guy told me he was required to run the smog test with the truck running on gasoline. I wander if he was full of it given you were able to do your smog on CNG the first time. Anyone here know what the actual smog rules for a Bifuel vehicle in CA are?

[CH-4]

Re: Real-world CNG vs. gasoline emissions

It's complicated in California and is not CNG indicated, but by county. In Los Angeles, Orange and Ventura Counties, CNG vehicles, need to be smogged unless the fuel type indicated on the registration is "N". All new vehicles including NGV's come with a gasoline rating and must be physically inspected at a DMV facility in order to get an "N" rating (different in each county). Our '09 GX had a gasoline rating even though dedicated and had to be inspected so as to get its fuel code changed in order to get HOV stickers as did all of our other vehicles, which are bi-fuel. I has them all inspected and now have "N" as a fuel code and all have HOV stickers and have not been required to smog test any of them since then. You can take your truck to your local DMV and have it inspected, but I normally apply for my HOV stickers first which generates the correct form that they send back to you.
http://www.dmv.ca.gov/pubs/reg_hdbk_pdf/ch21.pdf

[rtry9a]

Re: Real-world CNG vs. gasoline emissions

In at least some counties in Utah (Davis), bi fuel vehicles have to pass 3 tests to register: cng and gasoline emissions, and the on board computer.

cng is cleaner.

If CO is off, it indicates your engine is running too rich (needs more oxygen)- it is supposed to emit co2 and water vapor.

[larrycng]

Re: Real-world CNG vs. gasoline emissions

As far as California SMOG is concerned, and taking into consideration HOV, the SMOG Test station is required to "test as receive". Whatever fuel the vehicle is using when it comes into the station is the Fuel used to run the SMOG test. This includes all factory bi-fuel vehicles. The SMOG test Technicial is not and can not tell you what fuel to run. (I only exception, I know of, is Rousch LPG Ford, at last information, about 6 months ago, I was not going to be let into Calif; not Calif compliant.)

If the vehicle is an aftermarket conversion it and has a CARB E.O. number it is "test as received"; standard SMOG test. If the conversion is a non-CARB approved (and I haven't said anything about EPA), it should be refered to the referee and will probably be refused a certificate of compliance; will not be registered in Calif.

When the type of fuel is entered into the "SMOG machine" there is "correction factor" activated to modify the readings. This information is from one of the programers at the Bureau of Automotive Repair, the guys that run the SMOG program.

Larrycng

[CH-4]

Re: Real-world CNG vs. gasoline emissions

We haven't had to do a smog check on any vehicle for over 5 years, since the fuel rating was changed to "N". Perhaps a bureaucratic misunderstanding. However, DMV did tell me that when the vehicles were sold or transfered that they would be required to have a smog test and that the HOV designation would be revoked.
rtry9a, I agree as I had the same thing happen to my Contour untill it finally gave a fault code that was read even by the gas computer. It turned out to be the MAF sensor.

[larrycng]

Re: Real-world CNG vs. gasoline emissions

That is true, when a vehicle is sold it will require a smog test. I would have to check on the HOV lane designation. DMV and BAR often have differences of opinion. As a general rule, new vehicles do not have to be SMOGED for the first 5 years, after that every 2 years, with rare exception.

Also the SMOG test was run in 2 different gears when they could have been run in the same gear giving a different reading. The 15 mph was probably run in 1st gear and the 25 mph in second gear (the RPM is almost the same for both tests). The 25 mph test should have been run in 3rd gear, you would have had different emission readings since the engine would have been under higher load at a lower RPM during the 25 mph test. This is normally what is recommended for the SMOG test.

The test look very clean

Larrycng

[ajgiorgi]

Re: Real-world CNG vs. gasoline emissions

We haven't had to do a smog check on any vehicle for over 5 years, since the fuel rating was changed to "N". Perhaps a bureaucratic misunderstanding. However, DMV did tell me that when the vehicles were sold or transfered that they would be required to have a smog test and that the HOV designation would be revoked.

I had to smog my GX when the registration came the first year after buying it. I had to send in for a carpool sticker also, but it was from out of state and never had a sticker to begin with.

[Kevin Fern]

Re: Real-world CNG vs. gasoline emissions

The Gasoline NOx is pretty high buy todays Tier 2 standards, 100ppm NOx would equal about 1 to 1.5 grams per mile, which will or could account to a lower Carbon Monoxide level. Any issues with a dirty fuel filter or injectors on gasoline?