David Jones wrote: ↑
Tue Nov 23, 2021 2:46 pm
Because I was heavily involved in quantifying the quality of gasoline in the refinery in which I worked before retirement I still retain an interest in the goings on as regards gasoline evolvement so forgive me for posting the following. Don't think I am a lover of ethanol, on the contrary I do not believe that in the long run it is really beneficial to use except perhaps in Brazil where it is economically feasible because it is derived from sugar cane. Following screed is I believe factual in content so decide for yourself what is best to use.
Ethanol adds two to three points of octane to ordinary unleaded gasoline, so it boosts the performance of your engine. Because of its high oxygen content, ethanol burns more completely than ordinary unleaded gasoline and reduces harmful tailpipe emissions. Ethanol prevents gas line freeze-up.
Ethanol which is an oxygenate can cause damage to fuel system hardware and has a low energy content which can reduce range.
Many people think high-octane gasoline is more powerful than low octane gasoline. This is not true. The energy produced from a gallon of high and low octane gasoline is almost the same. Any minor variation depends on what additives are used by refiners and blenders. The key features of high-octane gasoline are a higher ignition temperature and a slower burning rate.
The higher ignition temperature of high octane gasoline reduces the chance of detonation from "hot spots" within the engine's cylinders and minimizes pre-ignition. A slower burn rate allows for more efficient use of the ignited fuel's pressure buildup to be converted to mechanical energy instead of heat. That is why a high performance engine will run smoother and will feel more powerful when high-octane gasoline is used.
Using a low-octane gasoline whose ignition temperature is too low causes pre-ignition. Low-octane automotive gasoline (87-octane) has a typical ignition temperature of 300 degrees Celsius; high-octane (93-octane) automotive gasoline has a typical ignition temperature of 400 degrees Celsius. Aviation gasoline is blended to ignite at 500 degrees Celsius. High compression and high cylinder temperature will cause the fuel to ignite before the sparkplug fires.
Detonation occurs after the spark plug fires. Ideally, when the spark plug fires and ignites the fuel, a progressive flame path develops producing a smooth increase in temperature and pressure within the engine cylinder to drive the piston. Detonation occurs when other ignition sources ignite the fuel charge. Red-hot bits of carbon and hot spots in the cylinder also ignite the fuel causing a second or third flame path to develop. This phenomenon causes the gasoline charge to burn instantaneously, producing a violent increase in cylinder pressure and temperature.
If you use a fuel with lower-octane than is recommended by the engine's manufacturer, this can cause serious damage to the pistons, valves, cylinders, heads, and bearings in a short period of time. Low-octane gasoline ignites quickly and produces a pressure-temperature peak that can exceed the design limit of the engine. This condition is exacerbated the more you run the engine. The heat buildup can not be dissipated fast enough from within the cylinder, causing more pre-ignition and uncontrolled detonation.
If your engine is designed to use low-octane fuel, the use of a higher-octane gasoline will not improve performance. Engine dynamics, timing and compression ratio are what determine which gasoline octane the engine manufacturer recommends. It is possible to burn the exhaust valves if you use a high-octane gasoline in an engine that is designed to use 82-octane gasoline. Retarded ignition timing and a slower fuel burn rate can increase exhaust temperature because the fuel charge is still burning at high pressure when the exhaust valve opens. Excessive heat and pressure will quickly erode the valves and seats.
Ethanol is going to be with us for a very long time so we all have to get used to it and act accordingly. Using leaded gasoline is not a realistic option unless you have a local gas station that carries it and you are happy paying more for it. The higher price is probably not going to be offset by the improved gas mileage and the reality is that the 10% corn derived ethanol added to gas though it has downsides is probably not quite as bad as it appears but I would personally prefer to see it not used when it has a negative cost impact to the consumer overall.