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Someone who lives with me but shall remain nameless put a whole load of unleaded in a diesel van we were using to move house; luckily I spotted what she was up to before she'd put more than a third of a tank in. We filled it up the rest of the way with diesel and it ran fine... lucky escape I think...
High Octane fuel actually evaporates much faster then lower octane fuel, if something is evaporating, creating heavy dense cool vapor, you can get more fuel into a cylinder. And more air and more oxygen. Cold air contains more oxygen.
William,once again some of your post (expressed in a very matter-of-fact style) is complete and utter nonsense.I will pick particularly onQuoteHigh Octane fuel actually evaporates much faster then lower octane fuel, if something is evaporating, creating heavy dense cool vapor, you can get more fuel into a cylinder. And more air and more oxygen. Cold air contains more oxygen.High Octane fuel does not necessarily evaporate much faster. Both rates of evaporation are very similar. Both types of fuel are mixtures that contain some components that evaporate faster and some that evaporate slower, and rates of evaporation, provided they exceed a certain minimum, are quite irrelevant to the performance of a petrol engine.There is some cooling associated with evaporation of fuel, but the total amount of cooling is proportional to the amount of fuel that evaporates, not to its rate of evaporation. The most important difference between a low octane and a high octane fuel is that the latter can more effectively limit the chain branching steps in the detailed mechanism of the combustion reaction that lead to explosions Cold air does not contain more oxygen than hot air. Obviously 2 gram of cold air contains more oxygen than 1 gram of hot air. You can use that argument to say that a lemon is sweeter than a grape, because it contains more sugar! In terms of mixing ratio (= proportions by number of molecules) or proportions by mass, cold air and hot air are identical in composition.About the other parts of your post, some is OK, but boiling in the carburettor is equally undesirable for motors whether they run on high octane or low octane fuel, and no less likely to happen for high octane than low octane. In fact there is even a contradiction between your ideas that faster evaporation and less chance of boiling in the carburettor can go together -- boiling is simply a fast evaporation that occurs when the temperature of a liquid generates a vapour pressure that is equal to atmospheric pressure (or, more precisely, the pressure in the local environment).
Quote from: William McCormick on 25/08/2012 01:08:50The ping is caused by not enough fuel or to much advancement of the timing. The ping is the diesel effect. It is very bad for gasoline cars, there connecting rods, the rods that connect the pistons to the crank shaft are not built for that kind of firing, so many degrees before top dead center. So most car manufacturers do not tweak the amount of timing advancement very much. It is easier to just use a safe setting. Spark plugs can actually melt, if the engine pings to much. "Dieseling" is when you shut off the key of a gasoline engine, and the engine keeps running due to compression ignition like a Diesel engine. It is caused by a hot engine and high compression. I suppose it would only happen with the key off with a carbureted engine, and not an injected engine, and I haven't heard it happen for years. The Dieseling could also occur while the engine is running in certain situations causing a "ping". It is independent of the engine timing as the fuel is ignited without the spark. The higher octane rating of the fuel would tend to prevent this compression related pre-ignition, or dieseling which is why it is used in high performance cars.Ethanol (CH3-CH2-OH) behaves much like high octane fuel, and is often used in race cars. However, it is in fact much less volatile (evaporates less readily) than most of the gasoline.Diesel in a gasoline engine would be much less likely to cause compression ignition as the in cylinder pressures aren't high enough.Intercoolers are sometimes used with turbos because the turbo compresses the air making it hotter (like a heat pump or refrigerator). The intercooler then cools the air which would effectively increase the air density and increase the amount of air being pushed into the cylinder. I don't know if fuel atomization/vaporization would also affect the air capacity per stroke. Certainly it would only make a difference if the fuel entered the system prior to, or during the intake stroke, but not if it was injected during the compression stroke.
The ping is caused by not enough fuel or to much advancement of the timing. The ping is the diesel effect. It is very bad for gasoline cars, there connecting rods, the rods that connect the pistons to the crank shaft are not built for that kind of firing, so many degrees before top dead center. So most car manufacturers do not tweak the amount of timing advancement very much. It is easier to just use a safe setting. Spark plugs can actually melt, if the engine pings to much.
Quote from: damocles on 25/08/2012 02:59:00William,once again some of your post (expressed in a very matter-of-fact style) is complete and utter nonsense.I will pick particularly onQuoteHigh Octane fuel actually evaporates much faster then lower octane fuel, if something is evaporating, creating heavy dense cool vapor, you can get more fuel into a cylinder. And more air and more oxygen. Cold air contains more oxygen.High Octane fuel does not necessarily evaporate much faster. Both rates of evaporation are very similar. Both types of fuel are mixtures that contain some components that evaporate faster and some that evaporate slower, and rates of evaporation, provided they exceed a certain minimum, are quite irrelevant to the performance of a petrol engine.There is some cooling associated with evaporation of fuel, but the total amount of cooling is proportional to the amount of fuel that evaporates, not to its rate of evaporation. The most important difference between a low octane and a high octane fuel is that the latter can more effectively limit the chain branching steps in the detailed mechanism of the combustion reaction that lead to explosions Cold air does not contain more oxygen than hot air. Obviously 2 gram of cold air contains more oxygen than 1 gram of hot air. You can use that argument to say that a lemon is sweeter than a grape, because it contains more sugar! In terms of mixing ratio (= proportions by number of molecules) or proportions by mass, cold air and hot air are identical in composition.About the other parts of your post, some is OK, but boiling in the carburettor is equally undesirable for motors whether they run on high octane or low octane fuel, and no less likely to happen for high octane than low octane. In fact there is even a contradiction between your ideas that faster evaporation and less chance of boiling in the carburettor can go together -- boiling is simply a fast evaporation that occurs when the temperature of a liquid generates a vapour pressure that is equal to atmospheric pressure (or, more precisely, the pressure in the local environment).You obviously have no experience with high octane fuels. High octane fuels have to be kept tightly capped or they will literally evaporate away on you, in a short period of time. I would put their ability to evaporate with the best lacquer thinners there are.
I would appreciate an apology because you are just on some kick to make light of what I am saying. If you ever worked with the stuff you would be laughing at yourself right now. And I am saying that as a friend. We would be laughing together if we had some of each fuel and tested them together.The only reason you can advance the timing, well beyond top dead center with high octane fuel over an equal amount of low octane fuel, and not get ping is because the low octane evaporates, and does not boil.
The problem with low octane fuel is that it boils in the carburetor in race cars. Causing a light vapor not a cool dense vapor to make it to the piston. The hot light vapor also heats air it is traveling with expanding it. Making it impossible to get all the fuel and air into a cylinder. This is very well known amongst race car experts.
Quote from: William McCormick on 26/08/2012 03:44:04Quote from: damocles on 25/08/2012 02:59:00William,once again some of your post (expressed in a very matter-of-fact style) is complete and utter nonsense.I will pick particularly onQuoteHigh Octane fuel actually evaporates much faster then lower octane fuel, if something is evaporating, creating heavy dense cool vapor, you can get more fuel into a cylinder. And more air and more oxygen. Cold air contains more oxygen.High Octane fuel does not necessarily evaporate much faster. Both rates of evaporation are very similar. Both types of fuel are mixtures that contain some components that evaporate faster and some that evaporate slower, and rates of evaporation, provided they exceed a certain minimum, are quite irrelevant to the performance of a petrol engine.There is some cooling associated with evaporation of fuel, but the total amount of cooling is proportional to the amount of fuel that evaporates, not to its rate of evaporation. The most important difference between a low octane and a high octane fuel is that the latter can more effectively limit the chain branching steps in the detailed mechanism of the combustion reaction that lead to explosions Cold air does not contain more oxygen than hot air. Obviously 2 gram of cold air contains more oxygen than 1 gram of hot air. You can use that argument to say that a lemon is sweeter than a grape, because it contains more sugar! In terms of mixing ratio (= proportions by number of molecules) or proportions by mass, cold air and hot air are identical in composition.About the other parts of your post, some is OK, but boiling in the carburettor is equally undesirable for motors whether they run on high octane or low octane fuel, and no less likely to happen for high octane than low octane. In fact there is even a contradiction between your ideas that faster evaporation and less chance of boiling in the carburettor can go together -- boiling is simply a fast evaporation that occurs when the temperature of a liquid generates a vapour pressure that is equal to atmospheric pressure (or, more precisely, the pressure in the local environment).You obviously have no experience with high octane fuels. High octane fuels have to be kept tightly capped or they will literally evaporate away on you, in a short period of time. I would put their ability to evaporate with the best lacquer thinners there are. If you are talking about high octane fuels in terms of specialized racing blends, then you are quite right -- i do not have much experience. If you are talking about what you would buy as a premium blend at a petrol station then I have plenty of experience. If you are talking about methanol, I also have plenty of experience of its general properties, though not of its use as an automotive fuel.When I am talking, on the other hand, about radical chain reactions and radical explosions, which are the scientific explanation of combustion processes, then I would venture to say that you probably have absolutely no experience nor even second hand knowledge."Pinging" and the inefficiency or low octane fuels in vehicles not tuned to run on such materials is quite definitely associated with straight chain rather than branched molecular structures, and relates to the much greater tendency of the former to burn explosively. Boiling in the carburettor would certainly cause performance problems, but they do not bear any great connection with pinging, other than reducing fuel supply so that the engine runs lean, which does increase the balance of a very complicated combustion reaction more towards explosion.There are two main internal factors that control rate of evaporation: boiling point, and heat of vaporisation.Some important components of automotive fuels: methanol -- used only in blends for motor sportsethanol -- a cheap way of raising the octane ratingn-heptane -- the standard 0 point for octane numbers2,2,4-trimethylpentane or iso-octane -- the standard 100 point for octane numberstoluene -- a relatively expensive way of raising the octane numberIf you check out the boiling points, heats of vaporisation, and octane numbers, and the blend of these and similar materials in standard and premium petrol bowser fuel, you will find (remembering that fast evaporation goes with low boiling point and low heat of vaporisation) that apart from the extremely fast evaporation of methanol, there is no particular pattern. Incidentally, in terms of what this thread is about, there is absolutely no prospect of diesel fuel boiling in the carburettor, though blocking it may well be an issue. QuoteI would appreciate an apology because you are just on some kick to make light of what I am saying. If you ever worked with the stuff you would be laughing at yourself right now. And I am saying that as a friend. We would be laughing together if we had some of each fuel and tested them together.The only reason you can advance the timing, well beyond top dead center with high octane fuel over an equal amount of low octane fuel, and not get ping is because the low octane evaporates, and does not boil. You are not going to get that apology, William. Among other reasons that is because the last sentence makes little sense, unless you are in the business of trying to mis-tune motors. As far as scientific considerations are involved here evaporation and boiling are the same thing. I suppose the real problem here has to do with a gas bubble blockage in the liquid feed line, because the only real difference between evaporation and boiling is that the latter term is used when gas bubbles are formed within the bulk of the liquid. In any case, this is far from the only reason or even the major reason -- it has more to do with the relationship between explosive limits, pressure, composition, and temperature in a very complicated combustion reaction. Also I am not on a kick to make light of what you say. I am interested in seeing that answers on the science parts of these forums make reasonable sense in the light of current scientific knowledge, and that discussions are carried out in a tone where we all recognize our limitations. QuoteThe problem with low octane fuel is that it boils in the carburetor in race cars. Causing a light vapor not a cool dense vapor to make it to the piston. The hot light vapor also heats air it is traveling with expanding it. Making it impossible to get all the fuel and air into a cylinder. This is very well known amongst race car experts. You are probably quite right here. I have no experience with race cars. A failure of evaporative cooling would certainly lead to less fuel and oxygen intake, and a lower amount of vapour if there was a reduced intake of fuel would lead to less evaporative cooling. BUT if we are talking only about ordinary petrol in the absence of "boiling in the carburettor" there is almost no difference between low octane and high octane fuels in this regard.