Article Photos: Fracking for natural gas being powered by it, too 6/7

In this photo made on Thursday, Jan. 17, 2013, exhaust comes from the emissions converter as the 50 litre,16 cylinder Cummins diesel engine, with four turbo-chargers, fires up for the first time after it was converted to run on a blend of diesel and natural gas at the Cummins Bridgeway facility in Gibsonia, Pa. Since there was no natural gas available at the facility, the engine was running on diesel fuel alone. 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)