In this photo made on Thursday, Jan. 17, 2013, technician Sean Cline finishes up the conversion of a 50 litre, 16 cylinder, Cummins diesel engine with four turbo-chargers that has been

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In this photo made on Thursday, Jan. 17, 2013, technician Sean Cline finishes up the conversion of a 50 litre, 16 cylinder, Cummins diesel engine with four turbo-chargers that has been converted to run on a blend of diesel and natural gas at the Cummins Bridgeway facility in Gibsonia, Pa. Oil- and gas-field companies from Pennsylvania to Texas are experimenting with converting the huge diesel engines that operate pumps that propel millions of gallons of water, sand and chemicals down a well bore in the fracturing process to break apart rock or tight sands that trap natural gas. (AP Photo/Keith Srakocic) less