Differences Between Flex Fuel Engines & Gas Engines

by Ian Kenney
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In the 2008 US election season, politicians and the chattering class were all aflutter debating the merits of mandating that all US automakers produce only flexible fuel vehicles. FFVs, as they’re known, can run on gasoline or any blend of gasoline and up to 85 percent ethanol. The wisdom was that the industry could make the switch at very little cost as the necessary technology upgrades are minor. The presence of millions of new FFVs on the road would inspire station owners to install E85 pumps, creating the needed infrastructure for a more ethanol-dependent transportation sector. The underlying arguments are sound. The auto industry isn’t hurt with a heavy cost of compliance, therefore, consumers wouldn’t get dinged on the sticker price (much). Choosing E85 or gasoline would be up to the driver based on market movements of each fuel. As of 2009, there was no mandate, but manufacturers have increased production of FFVs anyway. If you don’t have an FFV (and wish you did), there are even conversion kits available, as the differences for most cars are that minor.

Fuel System Componants

Ethanol is more corrosive than gasoline, and it has a tendency to absorb moisture which creates additional problems. To combat this, FFVs cannot leave magnesium, rubber or aluminum parts exposed in the fuel system. Fuel lines are replaced with a plastic-lined stainless steel variety, and fuel tanks in FFVs are stainless steel instead of terne-plated steel.

Pulse Control

Ethanol is less energy dense than gasoline, meaning more ethanol is needed in the combustion chamber to produce the same energy output as a gasoline only engine. To account for this, FFVs have a wider range of pulse in the fuel injection sensors allowing up to 40 percent more liquid fuel into the fuel air mixture. The sensor can detect the presence of ethanol and analyze the concentration so that it injects the proper amount of fuel for conditions.

Additional Optional Changes

Since ethanol is conductive, meaning it can carry electrical current, some automakers include additional safety measures. For models with tank-mounted fuel pumps, safeguards against arcing are included in the design. Another possible issue is water contamination in the ethanol, which results in an abundance of formic acid in the combustion chamber. To protect against that unlikely eventuality, most makers recommend acid neutralizing motor oil.

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