2-stroke engine animation

When MTBE (methyl tertiary butyl ether) was the replacement for tetraethyl lead in gasoline it solved some problems. In addition to increasing the octane, the oxygen molecules in the MTBE reduced the CO emissions in older engines (mostly carbureted). But then MTBE started showing up in ground and drinking water. Not only did the EPA want it replaced but the Midwest Corn Belt growers had the perfect replacement, ethanol. By adding up to 10% (now mandated by law in many states) ethanol to gasoline, we could replace the MTBE and reduce our dependence on foreign oil by 10%.

The automotive industry started putting fuel injection in their engines in the ‘80s and today almost all cars, trucks, and even some motorcycles are fuel injected. These systems are computer controlled and do a much better job of delivering the correct fuel/air mixture to the engine reducing the need for oxygenated fuels to reduce CO emissions.

The ethanol will dissolve uniformly in the gasoline. Water will not mix with gasoline to any great extent. (You can dissolve a slight amount of water in gasoline). On the other hand, water is miscible in ethanol. You can take some water (up to about .5%) into the gasoline via the ethanol. However, the gasoline will get fed up and say “OK, out with the both of you, ethanol, and water. It’s called “phase separation” and the ethanol and water go right to the bottom of the fuel tank, completely separated from the gasoline. If this mixture gets to the engine, it quits.

Many older engines designed to run on pure gasoline have metals and parts that will corrode or melt in the presence of ethanol. Some of the deposits like petroleum varnish that were in the fuel system but stable, will now be dissolved by the ethanol and move down stream clogging orifices that were previously open. Plastics are ever increasing in engine parts and many gasoline tolerant plastics will degrade over time with ethanol present even in small percentages.

Many of small lawn care engines are having problems with gasohol. Two stroke engines will run hotter and get less lubrication on gasohol. Dump some two stroke oil and some ethanol oil in a small container, shake it up and you will end up with glop.

The need to use fresh gas is more important than ever because gasohol does not store well even with stabilizers. If an engine is not going to be used for several months, drain the gas and run the engine until it quits. This will eliminate water condensation and incompatibility problems. –Les Lowman Jan12

Engineering ideas

  • gasoline, tetraethyl lead, MTBE, octane, ethanol, CO2 emissions, phase separation, miscible, fuel system injection, corrosion, deposits, orifice, gasoline tolerant plastic, two stroke engine, lubrication, stabilizer, condensation