The CA smog test is composed of tests for 6 different, specific pollutants. Each test is calibrated in terms of a low to high range of particulate matter. So ranges for the tests would be: 4 to 180, 10 to 125, etc. They are stated low to high.
Since the Ford Contour I bought had spent its entire life running only on CNG, the engine was remarkably clean. So clean that the results surprised the technician. He showed me the results and in 5 out of 6 of the tests, my car registered ZERO. In the remaining test, my car registered a ONE when the minimum was a FOUR.
An astounding result but evidence of how cleanly CNG burns that it leaves no residue in the engine. Another important point to add: CA requires the smog test for a bi-fuel car to be conducted while the car is running on gasoline. This means that short term emissions from gasoline use in a bi-fuel car primarily run on CNG are reduced.
Actually using CNG as a fuel is almost a culture shock. The ’98 Contour runs on 3,000psi CNG. Fast fill CNG refueling stations like that at Long Beach Energy Dept. take mere seconds to fill its 4.8 GGE (Gasoline Gallon Equivalents) tank. All you do is attach the proper pressure nozzle to you refueling receptacle and throw the lever. You hear a loud WHOOOSH as the tank fills. It stops when the tank is full. That’s it. No odor; no spillage, see details.
There are 2 CNG standard pressures which are in use: 3000psi, as mentioned, and 3600psi. What’s the difference? You pay the same price for either pressure because you are charged by the GGE. Yet you can drive 20% further on the higher pressure since the pressure is 20% higher – given the same volume – yet different pressure rated – tanks.
Driving a CNG car is no different than a gasoline car except the engine runs and accelerates smoother and faster. Here’s why it accelerates faster: gasoline comes in 3 octanes at the pump: 87, 89 and 93. The octane rating of natural gas is 130. This results in a dedicated CNG engine being designed for the fuel. Specifically, gasoline engines have compression ratios of 8.9 to 9.0 to 1. Dedicated CNG engines have a compression ratio of 13 to 1.
Another part of the driving experience is the lack of odor. Natural gas has mercaptan added to it so you can smell a leak. Well, because natural gas burns a lot hotter than gasoline, it incinerates mercapton as well as any pollutants in the air that enters the engine as well.
The EPA set up a dedicated CNG Ford Crown Vic next to an air quality sampling station in downtown L.A. and measured the pollution coming out of its tailpipe and compared it with ambient downtown L.A. air. The results showed that the CNG car took in polluted air and emitted cleaner air. They attributed this to the higher burning temperature of natural gas and its incinerator effect. The car literally vacuumed pollution out of the air.
I have to mention another aspect of running on CNG. No lines at the pumps. No matter where I’ve refueled across the country, there’s never a line. I’ve passed many gasoline stations over the years – when supplies got tight and prices peaked – which had miles long multiple lines. And again I have to mention speed of refueling. My factory CNG only Crown Vics (which have 6 tanks totally 16 gallons – GGE) only take 45 to 60 seconds to fill.
Next time I’ll discuss my dedicated CNG 1999 Crown Vics. They are a fat ride and stretched 6″ at the factory.
- Tom Drury was born in Iowa in 1956. The recipient of a Guggenheim Fellowship, Drury has published short fiction and essays in The New Yorker, A Public Space, Ploughshares, Granta, The Mississippi Review, The New York Times Magazine, and Tricycle: The Buddhist Review. His novels have been translated into German, Spanish, and French. “Path Lights,” a story Drury published in The New Yorker, was made into a short film starring John Hawkes and Robin Weigert and directed by Zachary Sluser. The film debuted on David Lynch Foundation Television and played in film festivals around the world. In addition to Iowa, Drury has lived in Massachusetts, Connecticut, Florida, and California. He currently lives in Brooklyn and is published by Grove Press.