Related by context. Frequent words. (Click for all words.) 75 internal combustion engine 72 internal combustion 66 combustion engines 65 combustion engine 59 diesel engines 56 diesels 55 diesel engine 54 fossil fuels 54 electric motors 54 combustion 54 turbocharging 54 alternative fuels 53 electric propulsion 52 hydrogen 52 diesel powered 52 hydrogen fuel 51 PHEVs 51 hybrid electric 51 powerplants 51 cleaner fuels 50 diesel 50 hydrogen powered 50 exhaust emissions 50 electric motor 49 hybrid powertrain 49 cleaner burning 49 powertrains 49 ultracapacitors 48 electrically powered 48 carburetors 48 fossil fuel 48 hybrids 47 Lithium ion batteries 47 propulsion 47 Hybrids 47 motors 47 automobiles 47 lithium ion 46 fuel injectors 46 liquid fuels 46 engines 46 fuels 46 electric hybrid 46 acid batteries 46 biogas 46 nickel metal hydride 46 catalytic converters 46 V8 engines 46 syngas 46 tailpipe emissions 45 turbocharger 45 turbochargers 45 powertrain 45 PHEV 45 alternative energies 45 compressed natural 45 bio fuels 45 thermoelectric 45 bio ethanol 45 particulate emissions 45 biodiesel 44 renewable fuels 44 propulsion systems 44 zero emission 44 Hydrogen 44 synthetic fuels 44 turbos 44 battery powered 44 lithium ion batteries 44 EVs 44 methanol 44 NOx 43 electrics 43 electric hybrids 43 drivetrain 43 turbine engines 43 E# ethanol 43 NOx emissions 43 biofuel 43 electric 43 gas guzzlers 43 electrochemical 43 HEV 42 automatic transmissions 42 cylinder engines 42 naturally aspirated 42 biofuels 42 bio diesel 42 flex fuel 42 V8 engine 42 powerplant 42 coal gasification 42 catalytic converter 42 ethanol blends 42 manual gearbox 41 carbon emitting 41 pistons 41 gas guzzling SUVs 41 lithium batteries 41 fuel 41 GHGs