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A story in the Tulsa World two weeks ago caught my eye. Tulsa Public Schools (TPS) found an innovative way to convert half its school bus fleet from diesel to compressed natural gas.

The story, 140 TPS buses to run on CNG, explains the great plan the district has for its transportation sector. The plan offers cost-savings for the schools and environmental benefit for us all. But, what truly struck me in reading the article was that the CNG conversion process would add another 15 to 20 years to the “life expectancy” of a brand new bus. Think of the money that could save a school district.

Here are a few facts on why CNG is said to extend the engine-life of vehicles. CNG has almost no carbon in it. Carbon is what turns engine oil black. With less carbon, a vehicle’s engine oil will stay cleaner. In addition to cleaner oil running through the engine, you get the added benefit of less frequent oil changes – saving you time, money and, well, oil.

Here’s another benefit that shows why those TPS buses will last longer. reports that CNG is injected into the engine as a vapor, so no "raw" fuel enters the cylinders washing the lubricating oil off the cylinder walls. This means the piston rings stay better lubricated and CNG engines last up to three times longer than the same engine on traditional fuels.

I’m sure the TPS administrators weighed many of those factors in making this decision to covert half its bus fleet. In the Tulsa World article, a TPS spokesperson says the school may consider converting the other half of its fleet in another five years or so. And the school also expects that many other districts are watching this deal unfold as an example of how they too may be able to convert their own fleets.

So, the big question – how to pay for it. For starters, school officials say the money the district will save on fuel costs will pay for the conversion of the buses. Then, there’s innovative way the school found to make this all work. You see, schools and other tax exempt institutions can’t receive certain federal tax credits that can help pay for the conversion, so TPS figured out a way around it. It’s a rather complex plan of selling the buses to a local dealer who can get the funds and take care of the engine conversion, then buying the buses back. Andrea Eger’s explains it all in the March 15th story. Click here to read more.

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..the money the district will save on fuel costs will pay for the conversion of the buses.