Related by context. Frequent words. (Click for all words.) 71 cleaner burning 70 alternative fuels 62 renewable fuels 62 fossil fuels 60 biofuels 58 biofuel 57 fossil fuel 57 renewable energy 57 diesel engines 56 biodiesel 56 diesel 56 bio diesel 55 renewable energies 55 renewables 54 carbon capture 53 diesels 53 renewable 52 emission reduction 52 reduce carbon emissions 52 greener 52 ethanol 51 fuels 51 emissions 50 diesel powered 50 environmentally friendly 50 coal 50 biomass 50 flex fuel 50 emission 50 hydrogen fuel 50 cleaner 50 zero emission 49 carbon dioxide emissions 49 compressed natural 49 cellulosic ethanol 49 feedstocks 48 internal combustion engine 48 carbon emissions 47 greenhouse gases 47 greenhouse gas 47 coal fired 47 greenhouse gas emissions 46 hydrogen 46 greenhouse emissions 46 hybrid electric 46 diesel engine 46 fuel 45 reduce greenhouse gas 45 polluting 45 environmentally sustainable 45 carbon 44 liquefied natural gas 44 LNG 44 Hydrogen 44 diesel fuel 44 air pollution 43 gas guzzlers 43 sulfur 43 CNG 43 natural gas 43 CO2 emissions 43 GHG emissions 43 reducing greenhouse gas 43 feedstock 43 hybrids 43 pollution 42 EVs 42 environmentally sound 42 bioenergy 42 Renewable 42 Emissions 41 refiners 41 Biofuels 41 Biodiesel 41 retrofitting 41 energy 41 LPG 41 gasoline 41 Clean Energy 41 refineries 40 CO2 40 biogas 40 tar sands 40 gasification 40 boilers 39 palm oil 39 retrofits 39 hybrid 39 polluters 39 carbon dioxide 39 electric hybrid 39 burning fossil fuels 39 petroleum 39 Ethanol 39 E# [004] 39 environmental sustainability 38 desalination 38 sustainable 38 mercury emissions 38 pollutants 38 efficient