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Not much of a writer so apologies in advance.
There have been a few great/interesting posts on gasoline the last few weeks. Thought I would add my dime. Some of these threads mix apples, oranges, and bananas. This thread started as a discussion of fuel injector cleaners the cheaper of which are mostly kerosene (90%) with some fuel additive. The better fuel cleaner additives (e.g. techron concentrate and there are others) are usually formulated for engine/intake valve/combustion chamber cleaning as well as injectors. The better cleaners are more complex and cost a bit more. (Are they worth it? The better ones work as advertised. Techron gasolines regularly get praise from auto manufacturers, mechanics, and auto magazines for their cleaning properties.) These cleaners may increase octane but are not usually designed to do so (kerosene would actually decrease octane.) Similarly octane additives are designed to increase octane. They may have some cleaning ability but not much. So if you need/want to use a cleaner buy and use a cleaner (note: Chevron says if you consistently use their techron flavors you should not need to use an additional cleaner. FWIW their concentrate is about 10 times the amount of techron in a typical tank of their gas.) Different grades of gasoline are not always just the same old gasoline with different cleaning and octane additives. The larger more recognized companies may specifically formulate grades to get a “better gasoline” then add additives to get the octane rating and cleaning properties. However, since gasoline is a blend of long chain carbohydrates, as stated before the overall energy content is not going to vary significantly from one gallon to the next regular, mid-grade, or premium.
1. The problem with using other than premium fuel in our cars has been discussed in a few posts. All of the analysis is correct but a key point has been missed. When less than hi-test is used, the car runs with the tuning for the manufacturer’s recommended gasoline grade. It will maintain this tuning until it senses a problem – pinging or knocking – then the DME (computer) will retard timing to get the pinging to cease. Eventually the pinging will stop and the computer will advance timing to its normal set point. The problem is two fold: (1) You may never realize you car was starting to knock and will continue driving as if there is no issue since the DME corrected it and (2) You are relying on a protective function to keep your engine safe – a protective function that starts when the problem it attempts to stop is actually occurring. OBTW – this change in timing will show up in both power (if you could measure it) and gas mileage. Quite simply, engines perform best when using fuel with the octane rating they were designed and tuned for. If your non Boxster says regular is ok, using premium gets you nothing. However, if premium is recommended it will prevent knocking and protect you engine. (Historical note: Early internal combustion engines ran on gasoline with octane numbers between 60 and 70. Mechanical break down due to excessive knock was the leading cause of engine failure.) Finally, knocking can occur whenever the engine is under load -- accelerating, going up hill, starting from a standstill, etc. It is very difficult to control your driving to avoid knocking at all times.
2. Grades of gases will mix. Specific gravity is only a part of the equation that allows two liquids to mix or be miscible. For example, water does not mix with gas but will mix with rubbing (isopropyl) alcohol which will mix with gas. So we frequently use isopropyl alcohol (or ethanol) as the main ingredient in dry gas. They will not mix immediately but after a short time they are a blend. OBTW the octane of the mix is approximately equal to the volumetric octane average. (i.e. ˝ tank of 89 plus ˝ tank of 93 yields about 91 octane). Think about it, if the major difference in gasoline grades is their additives, how do we mix the additives with the gas. Moreover, how do you get the injector cleaners or octane boosters you add later to mix?
3. All gas is piped from the same refineries to the same tank farms and sold to different gasoline stations. In some cases, the same truck will serve several different gas chains in an area. However, the storage tanks at the station are all different, with different maintenance and cleanliness standards. Although these tanks are inspected, it is not as often or thorough an inspection as you might think. More often than not it is a safety/pollution inspection. There is a difference in gas companies, it is the stowage tanks at the station.
4. Techron is added to gasoline (Chevron/Texaco/and a few others – Citgo has their own blend as does Sunoco) primarily as a cleaning agent (and it is a pretty good one.) It helps to increase octane but it is not added as an octane booster. Techron Concentrate is designed as a cleaner not an octane booster. While it has 5 to 10% toluene/aromatics its primary ingredients are patented combinations of polyether amines about 85% or so for cleaning. Toluene is added to gasoline to increase octane – not act as a solvent/cleaner – because it is a solvent (think paint thinner) it does clean but it is less effective than commercial cleaners. There are two other problems with using toluene: (1) the purity/quality of paint thinner grade toluene is not always the greatest. (2) Toluene (and xylene) are two of the most common octane boosters (note: I did not say cleaners) added to gasoline. They lower the volatility of the gasoline and thus increase the octane. However, this causes a problem in the winter. Thus ethers are added to maintain volatility and in the winter … the ether content is increased and toluene content decreased. Some countries, Australia for example sell several blends of gasoline throughout the year -- think a monthly blend. In the US we have winter, summer and in some cases intermediate gas so adding toluene in the winter will change that mix. Adding toluene will increase your octane content; however, it is not a great cleaner and in the winter may not be what you want to do. But I must emphasize toluene is not the primary or active ingredient in techron as stated elsewhere. Final OBTW, many injector cleaner manufacturers (and mechanics) recommend addition the next to last fill up before an oil change. There is some sound engineering thought behind this. Although it may be unnecessary, it may be a good idea.
5. There was considerable discussion about the relation between octane and fuel energy that is about 3/4 right and misses another key point. First, if the only difference between grades was the octane additives. They would have about the same energy per gallon; maybe a bit less energy per gallon due to the volume of the octane additives but not much. However, octane simply makes the fuel burn less easily. The energy is released based on the breaking of chemical bonds in the fuel -- so energy content can be increased by increasing chemical bonds (carbon bonds are the primary ones of concern for gasoline) although it will still be less volatile. For some premium fuels (not all), the gasoline is formulated differently to maintain or in some cases increase the energy content. It is not just adding octane boosters and cleaners. Second, Higher compression gasoline engines are (in general) more efficient at extracting energy from gasoline. Higher compression gasoline engines require higher octane (less volatile) gasoline to run and avoid pre-ignition. The system, engine and gasoline, is designed to extract more power from the fuel. The gasoline is not more powerful but more energy can be converted due to the increased efficiency of the engine. In general this shows up as an increase in the engines power output.
Hope this helps.
ATB,
Tom
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