?url_ver=Z39.88-2004&rft_id=10.3390%2Fen11112934&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.aufirst=G.T.&rft.au=Chala%2C+G.T.&rft.aulast=Chala&rft.issue=11&rft.volume=11&rft.issn=19961073&rft.atitle=Natural+Gas+Engine+Technologies%3A+Challenges+and+Energy+Sustainability+Issue&rft.title=Energies&rft.date=2018&rft.genre=article