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GrandZ45 · 11-25-2012, 06:28 PM

Not an expert on gasoline nor a mechanic or even a Z owner yet (ordered), but what I learned about gasoline as an amateur recreational pilot agrees with Southark's post earlier. The alcohol increases the anti-knock index and therefore the octane rating of the gasoline but decreases the energy and increases problems with water.

The main problems in aviation are the lower energy content, the effect of alcohol on gaskets, seals and fuel lines not designed for it, and the attraction that alcohol and water have for each other. Many airplane engines are high compression engines that require higher octane ratings to avoid detonation and pre-ignition in high power operations (as in take off when the trees at the end of the runway can get close really fast). Takeoffs in small airplanes are full throttle maximal performance operations. Every bit of rated power is demanded so the lower power production of ethanol is a safety issue. Detonation can destroy the engine. It is also more likely when the engine is hot and the recommended action is to cool the engine by increasing speed (they are air-cooled) and reducing throttle. Avgas still contains lead as the anti-knock agent. Small airplanes sometimes sit for weeks unused. The air in the unfilled space in the tank contains moisture that may condense into the fuel on cool nights. Over time this can put enough water in the gas that it can cause problems--like engine failure and crash on takeoff. If the gas contains alcohol, the water can combine with the alcohol causing it to separate from the gasoline and create a large layer of water-alcohol sitting at the bottom of the tank.

Having said all that it just makes sense to me to prefer alcohol free fuel if it is available at the octane rating that the manufacturer recommends for any engine, especially if the fuel will sit there for a long time. More so in winter. The condensation problem can be countered by keeping the tank full instead of nearly empty. The less air space in the tank, the less water vapor will be available to condense each night. I gather that some Z owners use their cars only recreationally rather than daily drivers. It also makes sense to, if one must run fuel of a lower than recommended octane rating, to keep rpms and engine temps down and, if you value your engine, to not forge ahead if you think you hear knocking.

I have one vehicle that can sit for weeks unused. After some fuel problems, I began toping it off with ethanol free fuel before leaving it to sit. But the fuel is of the recommended octane rating so I am not compromising in that regard.

Not the place to rant about the ethanol racket but if one adds the information about reduced gas milage to the available data about fossil fuel requirements to produce ethanol, it is sort of obvious to any who care to look. Nuf said.

11-25-2012, 06:28 PM	#20 (permalink)
GrandZ45 Base Member Join Date: Nov 2012 Location: Baton Rouge Posts: 33 Drives: 2013 370z Base AT Rep Power: 13	ditto SouthArk Not an expert on gasoline nor a mechanic or even a Z owner yet (ordered), but what I learned about gasoline as an amateur recreational pilot agrees with Southark's post earlier. The alcohol increases the anti-knock index and therefore the octane rating of the gasoline but decreases the energy and increases problems with water. The main problems in aviation are the lower energy content, the effect of alcohol on gaskets, seals and fuel lines not designed for it, and the attraction that alcohol and water have for each other. Many airplane engines are high compression engines that require higher octane ratings to avoid detonation and pre-ignition in high power operations (as in take off when the trees at the end of the runway can get close really fast). Takeoffs in small airplanes are full throttle maximal performance operations. Every bit of rated power is demanded so the lower power production of ethanol is a safety issue. Detonation can destroy the engine. It is also more likely when the engine is hot and the recommended action is to cool the engine by increasing speed (they are air-cooled) and reducing throttle. Avgas still contains lead as the anti-knock agent. Small airplanes sometimes sit for weeks unused. The air in the unfilled space in the tank contains moisture that may condense into the fuel on cool nights. Over time this can put enough water in the gas that it can cause problems--like engine failure and crash on takeoff. If the gas contains alcohol, the water can combine with the alcohol causing it to separate from the gasoline and create a large layer of water-alcohol sitting at the bottom of the tank. Having said all that it just makes sense to me to prefer alcohol free fuel if it is available at the octane rating that the manufacturer recommends for any engine, especially if the fuel will sit there for a long time. More so in winter. The condensation problem can be countered by keeping the tank full instead of nearly empty. The less air space in the tank, the less water vapor will be available to condense each night. I gather that some Z owners use their cars only recreationally rather than daily drivers. It also makes sense to, if one must run fuel of a lower than recommended octane rating, to keep rpms and engine temps down and, if you value your engine, to not forge ahead if you think you hear knocking. I have one vehicle that can sit for weeks unused. After some fuel problems, I began toping it off with ethanol free fuel before leaving it to sit. But the fuel is of the recommended octane rating so I am not compromising in that regard. Not the place to rant about the ethanol racket but if one adds the information about reduced gas milage to the available data about fossil fuel requirements to produce ethanol, it is sort of obvious to any who care to look. Nuf said.