As car engines continue to shrink in size and adopt technologies such as direct injection and turbocharging, fuels with high octane will be necessary to prevent engine knock. This is because smaller engines are more prone to engine knock, said Jim Szybist, senior research staff at Oak Ridge National Lab. 

"A high octane rating is more necessary than before," he said. 

Jim Anderson, technical expert fuel science for research and advanced engineering at Ford Motor Company, said high octane fuels improve engine efficiency by 6 percent which presents significant advantages in fuel efficiency and reducing CO2 emissions. 

"Ethanol is a good source of octane and reduces CO2 emissions," he said. 

In addition, Anderson said it is more economical for carmakers to reduce emissions via mid-blends of ethanol than electric vehicles or hybrids as a carmaker would only have to make a few changes to existing internal combustion engine powertrains.

David McShane, executive vice president of business development and strategy at Ricardo, said internal combustion engines can be continously improved with new technologies to improve fuel efficiency and reduce emissions. 

"There's plenty of life left in internal combustion engines," he said. 

McShane said 45 percent of new cars feature direct injection and more would feature the technology if high octane fuels were available. 

Ford's Anderson agreed. He said carmakers cannot meet their emissions goals without the right fuel and ethanol meets that requirement.