Pittsburgh Electric Engines
is claiming to have developed a drop in replacement for diesel engines in CVs. Apparently, they have succeeded in compacting solid oxide fuel cell for use in vehicles. They call it as Turbo Fuel Cell Engine. Solid oxide fuel cells can take diesel, jp-8 fuel or natural gas as fuel and split it up chemically to produce current for electric motors. Don't know if it is more efficient compared to Wrighspeed's hybrid electric technology. But fuel cells are silent and cleaner compared to either internal combustion engines or gas turbines. While membrane fuel cells have been researched for vehicles, they are expensive and require hydrogen as fuel. Solid oxide fuel cells which use ceramic composites to catalyze and consume common hydrocarbon fuels are better. Issue till now has been their size and heat generation. If such issues are resolved, there's nothing stopping fuel cell as mainstream technology for vehicles.