Associated Press: Advances in hydraulic fracturing technology have powered the American natural gas boom. And now hydraulic fracturing could be increasingly powered by the very fuel it has been so successful in coaxing up from the depths. Oil- and gas-field companies from Pennsylvania to Texas are experimenting with converting the huge diesel pump engines that propel millions of gallons of water, sand and chemicals thousands of feet down well bores to break apart rock or tight sands and release the natural gas trapped...