We normally think of individual CNG stations as serving a local community or city. However, with the 500-mile range of the Baker dedicated CNG van, these individual CNG stations were linked into a cross-country CNG corridor, as we drove 9,256 miles, round trip, through the sunbelt states and back up through the northern states (see the Round Trip Map tab on the Home Page).
Normal CNG vehicle driving range is 20-percent less than the maximum driving range.
Vehicle CNG tank capacity is stated in gasoline gallons equivalent (GGE), at the maximum rated tank pressure of 3,600 PSI. The maximum driving range is calculated by multiplying the total GGE capacity of the vehicle tanks by the rated MPG of the vehicle. For example, if a CNG vehicle has a 42-GGE tank capacity and gets 15-MPG, it should have a maximum 630-mile range. As we traveled across the USA, we found that this maximum range calculation should be reduced by around 20-percent, for normal operation. Our CNG van's ideal range would be 630-miles, yet the longest distance driven between fills was 540-miles (Denver->Topeka), arriving on Empty. Based on our experience, we deduct 20-percent of the maximum CNG range calculation, when estimating our 500-mile normal highway driving range.
Here's why...
- The average pressure of our cross country CNG fill ups was 3,284 PSI.
- Public CNG stations provide a "fast fill." The rapid filling of the tanks creates heat and some additional pressure. The tank pressure normally decreases by 200 PSI, within 30-minutes of fast filling, as the tanks and CNG cool down to ambient temperature.
- Tank pressures begin to negatively affect engine performance at approximately 300 psi and continue to degrade engine performance in direct correlation with further decreases in system pressure, until engine shutdown occurs. Operation at system pressure of lower than 300psi is not recommended.
