ENN Group Co Ltd, one of China's largest private companies, is quietly rolling out plans to establish a network of natural gas fueling stations for trucks along U.S. highways. With plans to build 50 stations this year alone, ENN joins a small but formidable group of players -- including Clean Energy Fuels Corp and Royal Dutch Shell Plc -- in an aggressive push to develop an infrastructure for heavy-duty trucks fueled by cheap and abundant natural gas. Clean Energy is backed by T. Boone Pickens and Chesapeake Energy Corp. The move is yet another example of China's ambition to grab...