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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / May 2008air - fuel ratio
What are the thoughts on the air-fuel ratio values using todays fuels. How much does the (varied) alcohol content of todays fuels modify the 'de facto' standard of 14:1 as the target mixture? > What are the thoughts on the air-fuel ratio values using todays fuels. > How much does the (varied) alcohol content of todays fuels modify the > 'de facto' standard of 14:1 as the target mixture? Virtually all newer vehicles use three-way catalyst exhaust after-treatment systems. For maximum catalyst efficiency the A/F target average is stoichiometric (or the chemically correct mixture ratio). For 100% gasoline this is nominally 14.6:1. Most engine control systems purposefully dither on either side of stoich to maximize catalyst efficiency. As alcohol(ethanol)is added, the feedback ECU controls will adjust the fuel system to keep the mixture at the mixture's stoichiometric value. Here's a simple table to illustrate how stoich varies with %EtOH %EtOH Stoich A/F 0 14.6 5 14.16 10 13.74 15 13.35 20 12.98 85 9.55 100 9.00 >> What are the thoughts on the air-fuel ratio values using todays >> fuels. How much does the (varied) alcohol content of todays fuels [quoted text clipped - 18 lines] > 85 9.55 > 100 9.00 Excellent info, thanks... Dyno <dyno@null.torque.net> wrote in news:481dcd15$0$20205 $4c368faf@roadrunner.com: >> What are the thoughts on the air-fuel ratio values using todays fuels. >> How much does the (varied) alcohol content of todays fuels modify the [quoted text clipped - 18 lines] > 85 9.55 > 100 9.00 Interesting information. But no road-legal US/Canadian gasoline is 100% gasoline. How do the above numbers compare to fuels with other oxygenates, such as MTBE? And what if the fuel contains MMT or TEL, neither of which are oxygenates?  SignatureTegger > Dyno <dyno@null.torque.net> wrote in news:481dcd15$0$20205 > $4c368faf@roadrunner.com: [quoted text clipped - 28 lines] > MTBE? And what if the fuel contains MMT or TEL, neither of which are > oxygenates? Really? The certification fuel used by the automakers does not contain alcohol. And I believe, AMOCO still sells alcohol free fuel. FWIW, the 0% gasoline shown above IS for pump grade unleaded regular. So, I guess I'm not sure what you are driving at here. > Dyno <dyno@null.torque.net> wrote in news:481dcd15$0$20205 > $4c368faf@roadrunner.com: [quoted text clipped - 28 lines] > MTBE? And what if the fuel contains MMT or TEL, neither of which are > oxygenates? Not sure about MTBE, but MMT and TEL are added in such tiny percentages to do their jobs that they really don't affect the stoichiometric ratio in any measurable way. They're fractions of a percent by volume, not the 10% of ethanol in E10 fuel. >> How do the above numbers compare to fuels with other oxygenates, such >> as MTBE? And what if the fuel contains MMT or TEL, neither of which [quoted text clipped - 4 lines] > stoichiometric ratio in any measurable way. They're fractions of a > percent by volume, not the 10% of ethanol in E10 fuel. That's the answer I was looking for. If volume is the determining factor, I'd guess MTBE would have a similar effect on stoichiometric as ethanol, since it's added in concentrations up to 15%. SignatureTegger "Tegger" <tegger@tegger.c0m> wrote in message > That's the answer I was looking for. > > If volume is the determining factor, I'd guess MTBE would have a similar > effect on stoichiometric as ethanol, since it's added in concentrations up > to 15%. I dont think so, Tegger... Methyltertiarybutylether has a different ratio of hydrogen to carbon to oxygen.. It should not have the same stoichiometry as ethanol. Ethanol is almost 35% oxygen by weight. MTBE is only about 18% oxygen. > "Tegger" <tegger@tegger.c0m> wrote in message >> That's the answer I was looking for. [quoted text clipped - 9 lines] > > Ethanol is almost 35% oxygen by weight. MTBE is only about 18% oxygen. Then MTBE is about twice as efficient as ethanol, so the mixture can be leaner? SignatureTegger >> "Tegger" <tegger@tegger.c0m> wrote in message >>> That's the answer I was looking for. [quoted text clipped - 11 lines] > Then MTBE is about twice as efficient as ethanol, so the mixture can be > leaner? Some more fuel blend data. ****** MBTE ****** %MBTE Stoich A/F 0 14.6 5 14.42 10 14.25 15 14.07 20 13.91 100 11.69 ****** Methanol ****** %MeOH Stoich A/F 0 14.6 5 13.73 10 12.96 15 12.27 20 11.65 55 8.61 (most energy per unit mass of air) 100 6.45 "Tegger" <tegger@tegger.c0m> wrote in message > Then MTBE is about twice as efficient as ethanol, so the mixture can be > leaner? "Lean", to me, indicates a mixture which does not have an excess of fuel, or may even have an excess of the oxidant. It requires more oxygen to burn a unit amount of MTBE than it does to burn the same unit amount of ethanol, and the energy released is consequently greater. Most of the energy is derived from the oxidation of the hydrogen atoms in a hydrocarbon to form water. Less energy is derived from oxidation of the carbon to give CO2. The oxygen (in oxygenates such as alcohol and MTBE) just occupies space and doesnt contribute to the energy derived from combustion. So, since the ethanol has a higher percentage of oxygen in the molecule, it has a lower amount of energy that it can contribute upon combustion. The "octane rating" takes into account different properties of the fuel, not directly related to the stoichiometry. > "Tegger" <tegger@tegger.c0m> wrote in message > > [quoted text clipped - 11 lines] > the same unit amount of ethanol, and the energy released is consequently > greater. Not according to the EPA. They say it contains less energy than ethanol per gallon. Density might be different but doesn't matter - no one purchases liquid fuel by weight. > Most of the energy is derived from the oxidation of the hydrogen atoms in a > hydrocarbon [quoted text clipped - 7 lines] > energy that it can contribute > upon combustion. > The "octane rating" takes into account different properties of the fuel, not > directly related to > the stoichiometry. But octane is far more important to fuel economy and performance. That is more important to how much energy goes to the wheels. According to the EPA Ethanol and MTBE are almost the same for oxygen content, octane and energy content. According to the EPA it takes 10 percent ethanol to get the same oxygen as 11 percent MTBE. -Jim ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- >>"Tegger" <tegger@tegger.c0m> wrote in message >> [quoted text clipped - 44 lines] > http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups > ---= - Total Privacy via Encryption =--- the amount of oxygen required to stoiciometrically burn a unit of fuel is not directly related to the energy yielded by that process. those are two different properties of a fuel. nate Signaturereplace "roosters" with "cox" to reply. http://members.cox.net/njnagel >>> "Tegger" <tegger@tegger.c0m> wrote in message >>> [quoted text clipped - 38 lines] >> But octane is far more important to fuel economy and performance. That is >> more important to how much energy goes to the wheels. Jim, Octane rating has very little to do with fuel economy. Performance, yes. >> According to the EPA Ethanol and MTBE are almost the same for oxygen >> content, octane and energy content. According to the EPA it takes 10 [quoted text clipped - 13 lines] > > nate You probably meant the amount of energy "liberated" when burning; it's an exothermic reaction after all. LHV - Gasoline: 42 MJ/Kg LHV - Ethanol: 26.68 MJ/Kg LHV - Methanol: 19.95 MJ/Kg LHV - MBTE: 35.12 MJ/Kg For 1 kg of air here are some interesting data. Terms: LHV - lower heating value (liquid fuel into reaction, uncondensed water vapor in exhaust). The blend energy@stoic is the theoretical yield from a reaction using one kg of air and stoichiometric amount of fuel. Blend Blend Blend EtOH % Stoic LHV energy@stoich A/F MJ/Kg MJ/kg-air 0% 14.60 42.0 2.88 2% 14.42 41.7 2.89 5% 14.16 41.2 2.91 10% 13.74 40.5 2.94 15% 13.35 39.7 2.97 20% 12.98 38.9 3.00 40% 11.69 35.9 3.07 45% 11.41 35.1 3.08 50% 11.14 34.3 3.08 55% 10.88 33.6 3.09 60% 10.63 32.8 3.09 65% 10.40 32.0 3.08 85% 9.55 29.0 3.03 90% 9.36 28.2 3.01 95% 9.18 27.4 2.99 100% 9.00 26.7 2.96 Blend Blend Blend MeOH % Stoic LHV energy@stoich A/F MJ/Kg MJ/kg-air 0% 14.60 42.00 2.88 2% 14.24 41.56 2.92 5% 13.73 40.90 2.98 10% 12.96 39.80 3.07 15% 12.27 38.69 3.15 20% 11.65 37.59 3.23 40% 9.70 33.18 3.42 45% 9.31 32.08 3.45 50% 8.95 30.98 3.46 55% 8.61 29.87 3.47 60% 8.30 28.77 3.46 65% 8.02 27.67 3.45 85% 7.04 23.26 3.30 90% 6.83 22.16 3.24 95% 6.64 21.05 3.17 100% 6.45 19.95 3.09 Blend Blend Blend %MBTE Stoic LHV energy@stoich A/F MJ/Kg MJ/kg-air 0% 14.60 42.00 2.88 2% 14.53 41.86 2.88 5% 14.42 41.66 2.89 10% 14.25 41.31 2.90 15% 14.07 40.97 2.91 20% 13.91 40.62 2.92 40% 13.28 39.25 2.96 45% 13.13 38.91 2.96 50% 12.98 38.56 2.97 55% 12.84 38.22 2.98 60% 12.70 37.87 2.98 65% 12.57 37.53 2.99 85% 12.05 36.15 3.00 90% 11.93 35.81 3.00 95% 11.81 35.47 3.00 100% 11.69 35.12 3.00 While not shown above, in all cases if the amount of air is reduced to maintain constant energy@stoich, more fuel is still needed for all three oxygenates as the percentage increases. > Jim, > Octane rating has very little to do with fuel economy. Performance, yes. Having AF ratio designed to maximize efficiency in the catalytic converter doesn't have much to do with fuel economy. When fuel economy starts to really matter the catalytic converter is going to be replaced with systems that burn the fuel inside the engine and deliver it to the wheels. And octane will matter. -jim > >> According to the EPA Ethanol and MTBE are almost the same for oxygen > >> content, octane and energy content. According to the EPA it takes 10 [quoted text clipped - 90 lines] > maintain constant energy@stoich, more fuel is still needed for all three > oxygenates as the percentage increases. ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- >> Jim, >> Octane rating has very little to do with fuel economy. Performance, yes. [quoted text clipped - 6 lines] > > -jim Seeing as how 99%+ of the fuel already IS burned in the engine, I don't agree with your assertion. Octane rating is related to the susceptibility of the fuel to auto-ignition. This is generally most significant at high-load operating conditions. When I think of fuel economy, I think of light-load operation; cruising down the highway or driving around town. On a time-weighted basis, under these conditions engine loads (BMEP levels) are relatively low. It is also at these conditions that the octane requirement is also low. Increasing the octane rating of the fuel will not alter the energy inherent in the fuel nor will it boost fuel economy. > >> Jim, > >> Octane rating has very little to do with fuel economy. Performance, yes. [quoted text clipped - 9 lines] > Seeing as how 99%+ of the fuel already IS burned in the engine, I don't > agree with your assertion. Burning the fuel and using the energy as opposed to shooting it out the back at the guy behind you are 2 completely different things. The average car engine is using less than 30% of the energy in the fuel so talking about the total energy contained in the fuel as if all of it is being used is a complete absurdity. If you want to talk fuel economy in a serious way you need to look at the 70% that is trailing behind every automobile rather than focusing on whether a particular fuel has 1% more or less energy. The fact is that the catalytic converter is part of a design that is consuming additional fuel - not because of the small amount that is burned inside it but because of the constraints it places on the entire design that limits efficiency. > Octane rating is related to the susceptibility of the fuel to > auto-ignition. Well that is a very naive and simplistic view of a very complex subject. The fact is that almost any gasoline powered car on the road will get better fuel economy if you start fueling with aviation gas. Why is that? The issue of fuel economy and octane can't be reduced to a platitude and one simple number on a pump. Gasoline is not a single chemical with simplistic properties its a complicated mix and that mix is constantly changing. Motor fuel is not designed for the cars. It's designed for maximizing profits. And cars are designed for maximizing profits. Lead was used in gasoline not because it benefited you car but because it benefited the oil companies bottom line. MTBE was mandated not because it benefited your car or your pocket book or your environment - it was mandated because it benefited the oil industry. The EPA estimates it will cost 3 billion dollars to clean up and remediate the damage done to the environment by MTBE. And obviously when the work is actually done it will cost a lot more. And of course you will pay for it because the oil industry can't be held responsible because they were told by the government to use MTBE instead of lead. And this was all done for octane which you claim has nothing to do with fuel economy. But with fuel headed to $10 and $20 a gal. The driver might actually start having some say in the process. When the purchasing habits change the motivation is also going to change significantly. >This is generally most significant at high-load operating > conditions. No. Octane and fuel economy are heavily intertwined. The government and the oil companies would prefer you do not look to closely at that fact - because it's money in their pocket and not yours. Octane ratings are based on both high load and light load testing and it is nowhere near an exact science nor are the constituent properties of the fuel constant - they vary a lot with time and place. But more important fuel economy is what you pay per mile and for starters that price on the pump has everything to do with octane. Did you know that the oil refineries call it "octane give away" if they ship a fuel that is 0.1% higher in octane than it is legally required to be. Giving the public .1% higher than it needs to be octane can cost a large refinery 20 million dollars a year. And you claim it has nothing to do with fuel economy. The oil companies, car manufactures and government are not interested in fuel economy. No one cares how much your personal transportation costs other than the driver and many of them apparently don't care either. Today the government is asking you to respond to higher gas prices by driving more - they might as well ask you to slit your own throat. Increased fuel consumption will only drive the price of fuel higher. The entire system from top to bottom is designed to use more fuel and for the most part people like you just go with the flow and don't question any of the platitudes handed down from above. It's only when consumers will stop buying it that things will change. > When I think of fuel economy, I think of light-load operation; cruising > down the highway or driving around town. On a time-weighted basis, under > these conditions engine loads (BMEP levels) are relatively low. It is > also at these conditions that the octane requirement is also low. No, incorrect, if you want to maximize fuel economy, the RON requirement is high under light loads. But your fuel supplier isn't telling you what the RON in the fuel you are using is. So you have no way of knowing how the octane in your fuel affects your fuel economy. > Increasing the octane rating of the fuel will not alter the energy > inherent in the fuel nor will it boost fuel economy. That belief is how fools are parted with their money. They would like you to focus on the inherent energy in the fuel. Octane has everything to do with how the oil companies make their money off you. Octane has everything to do with how an engine and its fuel can be designed to maximize fuel economy. The only hope is that as prices skyrocket that fuel economy will become a real issue, instead of a shell game, The realities of octane are going to have to be addressed head on rather than hidden as they are now. -jim ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- > > >> Jim, > > >> Octane rating has very little to do with fuel economy. Performance, yes. [quoted text clipped - 18 lines] > rather than focusing on whether a particular fuel has 1% more or less > energy. You *do* need to account for the energy content of the fuel, because even assuming that your engine is tuned to use the exact A/F ratio for every fuel that goes into it the overall efficiency of the engine itself does not change in any significant manner, so the fuel with the higher energy density will yield higher MPG. > The fact is that the catalytic converter is part of a design that is > consuming additional fuel - not because of the small amount that is burned > inside it but because of the constraints it places on the entire design > that limits efficiency. Huh? > > Octane rating is related to the susceptibility of the fuel to > > auto-ignition. > > Well that is a very naive and simplistic view of a very complex subject. > The fact is that almost any gasoline powered car on the road will get > better fuel economy if you start fueling with aviation gas. False. In fact, the opposite may be true, although to such a small degree that it's hard to say for sure one way or another. > Why is that? > The issue of fuel economy and octane can't be reduced to a platitude and > one simple number on a pump. Gasoline is not a single chemical with > simplistic properties its a complicated mix and that mix is constantly > changing. That much is true, but there is absolutely *no* advantage to using a higher octane fuel than the engine is optimized for. > Motor fuel is not designed for the cars. It's designed for maximizing > profits. And cars are designed for maximizing profits. Lead was used in > gasoline not because it benefited you car but because it benefited the oil > companies bottom line. No, TEL was used because it was a cheap and cheerful octane booster, allowing fuel companies to sell higher octane fuel without a significantly higher cost. It also offered other benefits like exhaust valve/seat protection. This allowed mfgrs. to offer more efficient engines with higher compression ratios once TEL-enhanced, higher octane fuels were available. > MTBE was mandated not because it benefited your car > or your pocket book or your environment - it was mandated because it [quoted text clipped - 4 lines] > held responsible because they were told by the government to use MTBE > instead of lead. Now that much is plausible, the MTBE thing does smack of policy set by politics. > And this was all done for octane which you claim has > nothing to do with fuel economy. Octane *does* have nothing to do with economy, once you are talking about octane ratings higher than that for which your car's engine was designed. > But with fuel headed to $10 and $20 a gal. The driver might actually > start having some say in the process. When the purchasing habits change [quoted text clipped - 4 lines] > > No. Octane and fuel economy are heavily intertwined. No, they're not. > The government and > the oil companies would prefer you do not look to closely at that fact - [quoted text clipped - 4 lines] > you pay per mile and for starters that price on the pump has everything to > do with octane. Of course higher octane fuels are more expensive, but that doesn't affect you if you don't need the higher octane. > Did you know that the oil refineries call it "octane give away" if they > ship a fuel that is 0.1% higher in octane than it is legally required to > be. Giving the public .1% higher than it needs to be octane can cost a > large refinery 20 million dollars a year. And you claim it has nothing to > do with fuel economy. That's right. It has nothing to do with fuel economy. Of course the oil co's don't want to make fuel a higher octane than it needs to be, because higher octane fuels are more expensive to produce. That's why they charge more for them. > The oil companies, car manufactures and government are not interested in > fuel economy. No one cares how much your personal transportation costs [quoted text clipped - 6 lines] > platitudes handed down from above. It's only when consumers will stop > buying it that things will change. OK... so what does this have to do with octane? > > When I think of fuel economy, I think of light-load operation; cruising > > down the highway or driving around town. On a time-weighted basis, under [quoted text clipped - 10 lines] > > That belief is how fools are parted with their money. No, it's fact. > They would like you > to focus on the inherent energy in the fuel. Octane has everything to do [quoted text clipped - 3 lines] > become a real issue, instead of a shell game, The realities of octane are > going to have to be addressed head on rather than hidden as they are now. I'd suggest you do a little more research before posting incorrect wild conjecture as fact. Or, if you're going to make claims that contradict what most educated people believe to be the case, at least provide some supporting documentation for your assertions. nate >>>>> Jim, >>>>> Octane rating has very little to do with fuel economy. Performance, yes. [quoted text clipped - 152 lines] > > nate Thanks, Nate! I was all set to fire off a followup, but you beat me to it, almost point by point. A lot of the nonsense that gets posted could easily be avoided is some posters would simple go buy an engine text book and simply browse through it. > I was all set to fire off a followup, but you beat me to it, almost > point by point. A lot of the nonsense that gets posted could easily be > avoided is some posters would simple go buy an engine text book and > simply browse through it. Here is what you said on how octane affects fuel economy. > When I think of fuel economy, I think of light-load operation; cruising > down the highway or driving around town. On a time-weighted basis, under > these conditions engine loads (BMEP levels) are relatively low. It is > also at these conditions that the octane requirement is also low. If you read your engine textbook you will find that the RON rating is made under light load conditions just as you describe. You are correct to say driving consistently under light load is how the best fuel efficiency is achieved and because of higher fuel prices more people are driving like that. Driving at 45 mph instead of 70 mph significantly reduces engine load and may as much as double some vehicles mileage if given the right fuel. The fuels properties to knock under light loads is exactly what the RON test determines. Engines do knock under light loads even if you think they don't ( and even if you can't hear it) and that does impact on gas mileage. The problem is you don't have any idea what the RON rating is for the fuel in your gas tank and it can vary quite a lot for any given posted pump octane rating. But in spite of the fact that you have no idea what the octane is in your gas tank under those conditions that could potentially be giving you better mileage, you are positive it has no affect on mileage cause you read something in a book. -jim ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- >> I was all set to fire off a followup, but you beat me to it, almost >> point by point. A lot of the nonsense that gets posted could easily be [quoted text clipped - 10 lines] > If you read your engine textbook you will find that the RON rating is > made under light load conditions just as you describe. You are correct to No it is not. Apparently you do not know under what conditions the octane ratings are obtained. Contrary to what you said both the Motor method and Research method are obtained at WOT. Do I really need to list the specifics of methods used? > The fuels properties to knock under light loads is exactly what the > RON test determines. Engines do knock under light loads even if you think > they don't ( and even if you can't hear it) and that does impact on gas > mileage. Interesting assertion here. Please provide a source for this. In my 30 years of engine testing this is a new "fact" for me. And in much of my testing, I have acquired and viewed the in-cylinder pressure data and have not seen this. > The problem is you don't have any idea what the RON rating is for the > fuel in your gas tank and it can vary quite a lot for any given posted [quoted text clipped - 4 lines] > > -jim This is absurd. You dismiss textbook information that has been verified over and over just because it doesn't fit your pet theory; a theory that you have yet to provide any refereed literature on. Have even read any of the books? Here's a good one: Heywood's "Internal Combustion Engine Fundamentals". This book not only explains the major phenomena but also provides literally thousands of technical journal articles as references. Can you do the same? > > If you read your engine textbook you will find that the RON rating is > > made under light load conditions just as you describe. You are correct to > No it is not. Apparently you do not know under what conditions the > octane ratings are obtained. Contrary to what you said both the Motor > method and Research method are obtained at WOT. Do I really need to list > the specifics of methods used? WOT? It's a test engine there is no throttle adjustment per se. The engine runs at 600 RPM. Does that sound like WOT? The engine load conditions are described as light (according to ASTM) as a result it yields a different (higher) octane number than the MON test which is not a light load test (again according to ASTM). And by the way the test engines that are still used today were designed something like 80 years ago - so exactly how much does an 80 year old push rod and carb engine tell you about how a modern engine will perform with respect to fuel economy. Oh that's right your textbook says it doesn't have anything to do with fuel economy . Well DUH! The point is motorists don't know what the RON octane number is for the fuel in their gas tanks. Or more to the point they don't what the octane number is that could be useful when driving for fuel economy, Thus if you change pumps in the interest of getting better fuel economy you have no idea if you are really increasing or decreasing the knock characteristics of the fuel at light load conditions. > > The fuels properties to knock under light loads is exactly what the > > RON test determines. Engines do knock under light loads even if you think [quoted text clipped - 4 lines] > testing, I have acquired and viewed the in-cylinder pressure data and > have not seen this. The RON test is done under light load. It does indeed detect knock under those conditions. How can you claim an engine can't knock under light load? The test protocol is all well documented. What isn't documented is the results of that part of the test that would actually be useful for increasing fuel economy. > > The problem is you don't have any idea what the RON rating is for the > > fuel in your gas tank and it can vary quite a lot for any given posted > > pump octane rating. But in spite of the fact that you have no idea what > > the octane is in your gas tank under those conditions that could > > potentially be giving you better mileage, you are positive it has no > > affect on mileage cause you read something in a book. > This is absurd. What specifically is absurd? Are you saying it's absurd that I said you read a book? It's not absurd to say that you don't know how octane interacts with fuel mileage in your own car. You have made it clear that for the specific types of driving conditions that would lead to fuel economy you don't know what the specific octane characteristics are of the fuel in your car's tank. Sure, you may know what the octane characteristics of the fuel are when you punch it to pass some guy who is going 65, but that has nothing to do with good fuel economy. You dismiss textbook information that has been verified over and over just because it doesn't fit your pet theory. What have I dismissed in textbooks? As far as I know they are pretty silent on the issue. The octane ratings are designed to benefit auto manufacturers so they can build cars that don't get harmed by the fuel. The octane rating system as it is now in North America makes it close to impossible for motorists to use the displayed octane numbers as a guide to purchasing for fuel economy. But that doesn't mean it has to be that way or that it always will be that way. -jim ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- >>> If you read your engine textbook you will find that the RON rating is >>> made under light load conditions just as you describe. You are correct to [quoted text clipped - 13 lines] > engine will perform with respect to fuel economy. Oh that's right your > textbook says it doesn't have anything to do with fuel economy . Well DUH! WOT means wide open throttle which means intake pressure is at atmospheric. That determines engine load, not the speed of the engine. Operating conditions for research and motor methods Research Motor ASTM D-2699 ASTM D-2700 Inlet T 52 deg C 149 deg C Inlet Pr Atmospheric <-----WOT! Humidity 0.0036 -0.0072 kg/kg-dry-air Coolant T 100 deg C Speed 600 rpm 900 rpm Spark 13 deg BTDC 19-26 BTDC Const varies with CR A/F Adjust for Max Knock > The point is motorists don't know what the RON octane number > is for the fuel in their gas tanks. Or more to the point they don't what [quoted text clipped - 7 lines] >>> they don't ( and even if you can't hear it) and that does impact on gas >>> mileage. Again you confuse speed with load. They are not the same. >> Interesting assertion here. Please provide a source for this. In my 30 >> years of engine testing this is a new "fact" for me. And in much of my [quoted text clipped - 8 lines] > What isn't documented is the results of that part of the test that would > actually be useful for increasing fuel economy. The purpose of the test is to determine the fuels susceptibility to detonation. For this purpose the test is perfectly valid. Sure the speed is less than that of today's vehicles. Researchers have worked on developing a "road octane rating" and what they found was that the more realistic road test method provided results the fell somewhere in between the RON and MON ratings. This is one of the reasons that things were simplified to using the pump rating of (RON+MON)/2. >>> The problem is you don't have any idea what the RON rating is for the >>> fuel in your gas tank and it can vary quite a lot for any given posted [quoted text clipped - 7 lines] > What specifically is absurd? Are you saying it's absurd that I said you > read a book? What is absurd is your willingness to disregard the body of published information on this subject (and there is plenty). The octane rating of any fuel is only used to rate the propensity of the fuel to detonate. It does not indicate the heating value of the fuel itself. This is easy to see. Commercial fuels are sold with octane ratings of 87 and 93 (pump ratings). Yet both fuels have heating values within a couple percent of one another. Another example, methanol has (R+M)/2 = 109, yet has half the heating value per kg as gasoline. The octane rating does not correlate with the energy in the fuel. > It's not absurd to say that you don't know how octane interacts with fuel > mileage in your own car. You have made it clear that for the specific [quoted text clipped - 3 lines] > when you punch it to pass some guy who is going 65, but that has nothing > to do with good fuel economy. If the engine does not detonate at a particular operating condition, it does not matter what the fuel's octane rating is. It was sufficient to preclude abnormal combustion. > Inlet Pr Atmospheric <-----WOT! You are talking about a naturally aspirated one cylinder engine with a carburetor attached to a very narrow intake manifold. The pressure, temperature and humidity of air entering the engine is carefully controlled so that daily variations in atmospheric conditions don't skew the results. This has nothing to with WOT. The ASTM literature claim the test is designed to simulate mild operating conditions. They characterize the load on the engine as light. > Again you confuse speed with load. They are not the same. You are the one that is confused. The engine operates with below atmospheric pressure in the intake manifold and that limits engine speed. The load on the engine is light. > What is absurd is your willingness to disregard the body of published > information on this subject (and there is plenty). I'm ignoring your misinterpretations > The octane rating of any fuel is only used to rate the propensity of the > fuel to detonate. It does not indicate the heating value of the fuel > itself. There actually is a fairly consistent negative correlation between octane and heating value in most motor fuel components so actually your wrong aboutr that. But your assumption that heating value alone determines fuel economy is also incorrect. >This is easy to see. Commercial fuels are sold with octane > ratings of 87 and 93 (pump ratings). Yet both fuels have heating values > within a couple percent of one another. Another example, methanol has > (R+M)/2 = 109, yet has half the heating value per kg as gasoline. The > octane rating does not correlate with the energy in the fuel. No, with almost all constituent components of motor fuels it negatively correlates, but that is also beside the point as it doesn't really say anything about octane and fuel economy. > If the engine does not detonate at a particular operating condition, it > does not matter what the fuel's octane rating is. It was sufficient to > preclude abnormal combustion. Sure just keep repeating your mantra over and over and maybe you someday you will achieve enlightenment. Your point isn't incorrect - it just doesn't shed any light on the relationship between fuel economy and the tendency for a particular fuel in a particular engine to detonate. If a load of fuel and air exhibits no detonation at all then that is a good indication that some of the energy that could have been converted to mechanical power failed to convert (it's wasted). How much power goes to the wheels is a function of how much pressure can be applied to the pistons over the proper period of time. The most significant limit to this pressure integral is detonation. Detonation and the measure of fuel to resist detonation is far more important than the energy content of any particular fuel because most of that energy content ends up being wasted. In other words, Octane has everything to do with fuel economy. -jim ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- >> Inlet Pr Atmospheric <-----WOT! > [quoted text clipped - 4 lines] > with WOT. The ASTM literature claim the test is designed to simulate mild > operating conditions. They characterize the load on the engine as light. One last time. WOT means the throttle is fully open with the intake manifold at atmospheric. This is exactly what the test specifies. >> Again you confuse speed with load. They are not the same. > > You are the one that is confused. The engine operates with below atmospheric > pressure in the intake manifold and that limits engine speed. The load on the > engine is light. Say what? The speed is limited by the dynamometer. >> What is absurd is your willingness to disregard the body of published >> information on this subject (and there is plenty). [quoted text clipped - 45 lines] > http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups > ---= - Total Privacy via Encryption =--- Once you start using insults rather that verifiable data, there's no point in continuing this discussion. > >> Inlet Pr Atmospheric <-----WOT! > > [quoted text clipped - 7 lines] > One last time. WOT means the throttle is fully open with the intake > manifold at atmospheric. This is exactly what the test specifies. You are misinterpreting the specs. Variations in ambient atmospheric pressure are known to cause variation in fuel octane characteristics, therefore the test specifies that atmospheric pressure be controlled. It does not mean there is a heavy load on the engine. The standard atmosphere pressure that the test protocol requires to be maintained at air inlet is not the same thing as manifold pressure. They also control for humidity and temperature. Read the ASTM literature. > >> Again you confuse speed with load. They are not the same. > > [quoted text clipped - 3 lines] > > > Say what? The speed is limited by the dynamometer. Like any other gas/carb/spark engine the engine speed is limited by the intake air flow. And the air flow restriction on the test engine is designed to simulate an engine under light load conditions. That's how the ASTM describes their test set up. And yes the test is designed to run at a constant RPM for all tests so the engine is connected to a synchronous electric motor which can keeps the RPM's constant even when fuel/air supply can't - like when the engine is knocking heavily or converting from one test fuel to another. But the test methodology is a distraction from the point. The point was the test results (the RON octane number) aren't revealed to the public. So you don't know what the RON octane is for the fuel in your tank. -jim > >> What is absurd is your willingness to disregard the body of published > >> information on this subject (and there is plenty). [quoted text clipped - 47 lines] > Once you start using insults rather that verifiable data, there's no > point in continuing this discussion. ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- > >> I was all set to fire off a followup, but you beat me to it, almost > >> point by point. A lot of the nonsense that gets posted could easily be [quoted text clipped - 42 lines] > provides literally thousands of technical journal articles as > references. Can you do the same? Heh. that was actually a textbook for one of my college courses. Thanks for the flashback. I think I still have it, as it was a third or fourth year class so I wasn't able to sell it to buy the next year's books... nate > But octane is far more important to fuel economy and performance. That is > more important to how much energy goes to the wheels. Not true. Thermal efficiency aids BOTH performance and fuel economy. A higher CR without detonation will provide more power without any increase in fuel flow rate. If we had higher octane fuels without serious environmental consequences, we could have better fuel milage. The higher CR that modern fuels allow is one reason fuel milage is better on a ton-mile per gallon basis than it was pre-WW2. > > But octane is far more important to fuel economy and performance. That is > > more important to how much energy goes to the wheels. > > Not true. Thermal efficiency aids BOTH performance and fuel economy. > A higher CR without detonation will provide more power without any > increase in fuel flow rate. Not sure exactly why you are disagreeing with my statement. I agree that thermal efficiency is the issue. HOWEVER, I think CR is only one element of many in the equation. But you do seem to at least grasp that octane does play a role. That role is going to be much more apparent as price of fuel continues to climb. If you look at the big picture refining higher octane base blend motor gasoline requires more barrels of crude to produce. In addition, as it happens each of those gallons of that higher octane fuel contains slightly less energy. So high octane base blend gasoline by its very nature is energy inefficient even before you get it to the engine. But the calculus is complicated. Gaining 5% energy efficiency inside the engine at a loss of 10% of the energy from the source crude is not really a winning thermal efficiency equation and it is going to inevitably cost you more. The point is these cost benefit calculations are already being made, but they are not being made with thermal efficiency in mind. That is, the tradeoffs are being calculated but the goal is to maximize the oil industry and government's interests. Unfortunately, that often works directly against thermal efficiency. > If we had higher octane fuels without serious environmental > consequences, we could have better fuel milage. The higher CR that > modern fuels allow is one reason fuel milage is better on a ton-mile > per gallon basis than it was pre-WW2. Where did you come up with that? It is my observation that 1940 cars were pretty heavy and quite fuel efficient compared to cars in the 50's of the same weight. Not that anyone cared in the 50's about fuel efficiency, but fuel efficiency was an issue before WW2 so cars were designed to be more fuel efficient. It wasn't until the early 70"s that anyone much cared about fuel efficiency. Increased Fuel efficiency in the late 70's and eighties was mostly achieved by shedding weight. -jim ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- > > If we had higher octane fuels without serious environmental > > consequences, we could have better fuel milage. The higher CR that [quoted text clipped - 10 lines] > > -jim No, higher CRs and higher operating temperatures (sealed cooling systems) also contributed to higher fuel efficiency these days. Better combustion chamber design allows higher CR today without higher octane. Not many hemi head designs these days. > Not according to the EPA. They say it contains less energy than ethanol > per gallon. Density might be different but doesn't matter - no one > purchases liquid fuel by weight. You do not purchases liquid fuel by weight. BUT A/F ratio is by weight. So if the specific gravity of the gas at the pump changes so does your A/F ratio unless something else changes. > > Not according to the EPA. They say it contains less energy than ethanol > > per gallon. Density might be different but doesn't matter - no one [quoted text clipped - 3 lines] > So if the specific gravity of the gas at the pump changes so does your > A/F ratio unless something else changes. I wasn't responding to any claim about AF ratio. Here is what I was responding to that you snipped: >It requires more oxygen to burn a unit amount of MTBE than it does to burn >the same unit amount of ethanol, and the energy released is consequently >greater. That statement doesn't specify what "unit amount" means. Ethanol is a lot denser than MTBE so the same volume has about the same energy. According to the EPA you will get better mileage with ethanol based reformulated gas than MTBE based reformulated gas - not that I would endorese any of the EPA's claims. The point is any claims about what fuel releases what energy should be regarded with suspicion. Simply releasing energy is not supposed to be the object of burning transportation fuel. -jim ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- > Simply releasing energy is not > supposed to be the object of burning transportation fuel. OK, then, what *is* the object? Getting high from huffing it? nate >> Simply releasing energy is not >> supposed to be the object of burning transportation fuel. > >OK, then, what *is* the object? Getting high from huffing it? Making a profit, of course. That's what ALL consumer products are about. --scott Signature"C'est un Nagra. C'est suisse, et tres, tres precis." > > Simply releasing energy is not > > supposed to be the object of burning transportation fuel. > > OK, then, what *is* the object? Getting high from huffing it? All you have to do is dump it on the ground and toss a match if you want to release some energy. Out the tail pipe or radiator is where most of the energy is going. Making precise calculations of the total energy contained in a fuel is absurd - those calculations it has no direct bearing on how much is being used to move the vehicle. If you believe in those calculations, then why not put diesel in your car? That would give you the best mileage. Right? ----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups ---= - Total Privacy via Encryption =--- >>>Simply releasing energy is not >>>supposed to be the object of burning transportation fuel. [quoted text clipped - 9 lines] > used to move the vehicle. If you believe in those calculations, then why > not put diesel in your car? That would give you the best mileage. Right? Oddly enough, it does. nate Signaturereplace "roosters" with "cox" to reply. http://members.cox.net/njnagel >> If you believe in those calculations, then why >> not put diesel in your car? That would give you the best mileage. Right? > > Oddly enough, it does. I've always wondered: is it the higher compression ratio or the different fuel which gives diesels their greater fuel economy and their greater low-end torque. Or a combination of the two? >>> If you believe in those calculations, then why >>> not put diesel in your car? That would give you the best mileage. Right? [quoted text clipped - 3 lines] > fuel which gives diesels their greater fuel economy and their greater > low-end torque. Or a combination of the two? Diesels benefits from three main factors: 1: Higher mechanical compression ratio. Cycle efficiency is a function of expansion ratio. This is one of the biggest reasons Diesel have higher torque. 2: Unthrottled operation. In the Diesel cycle load is controlled by fuel alone. This reduces gas pumping losses incurred during the intake/exhaust strokes. In future Diesels this may fade somewhat as throttling is being used to facilitate achieving the EGR levels needed to meet oxides of nitrogen regulations. 3: Fuel heating value. Diesel fuel contains around 10% more energy per gallon than gasoline. Diesel fuel is formulated to promote autoignition, the Diesel cycle ignition method. The metric for this is called the cetane rating. The higher the cetane rating the lower the octane rating. For Diesel engines high cetane fuel is desirable. This is obviously undesirable in a spark ignition engine. > >>> If you believe in those calculations, then why > >>> not put diesel in your car? That would give you the best mileage. Right? [quoted text clipped - 22 lines] > For Diesel engines high cetane fuel is desirable. This is obviously > undesirable in a spark ignition engine. What he said. I'm not sure how much 2) contributes, but sort of as an aside, this is the reason why you see sewer-pipe sized exhaust pipes on Diesel vehicles - they are essentially pumping the full displacement of the engine (or more, if supercharged) of air through the engine every two revolutions, unlike a gasoline engine where this only happens at WOT. nate > > 2: Unthrottled operation. In the Diesel cycle load is controlled by fuel > > alone. This reduces gas pumping losses incurred during the > > intake/exhaust strokes. In future Diesels this may fade somewhat as > > throttling is being used to facilitate achieving the EGR levels needed > > to meet oxides of nitrogen regulations. > What he said. I'm not sure how much 2) contributes, but sort of as an > aside, this is the reason why you see sewer-pipe sized exhaust pipes > on Diesel vehicles - they are essentially pumping the full > displacement of the engine (or more, if supercharged) of air through > the engine every two revolutions, unlike a gasoline engine where this > only happens at WOT. and why they can sit and idle all day on a teaspoon of fuel. On May 8, 1:50 pm, N8N <njna...@hotmail.com> wrote: > > > 2: Unthrottled operation. In the Diesel cycle load is controlled by > > > fuel > > > alone. This reduces gas pumping losses incurred during the > > > intake/exhaust strokes. In future Diesels this may fade somewhat as > > > throttling is being used to facilitate achieving the EGR levels needed > > > to meet oxides of nitrogen regulations. So having an excess of air, compared with the minimum needed to fully burn the fuel, is actually a bad thing for a diesel, is it, as regards the production of NOx? > > What he said. I'm not sure how much 2) contributes, but sort of as an > > aside, this is the reason why you see sewer-pipe sized exhaust pipes > > on Diesel vehicles - they are essentially pumping the full > > displacement of the engine (or more, if supercharged) of air through > > the engine every two revolutions, unlike a gasoline engine where this > > only happens at WOT. I'd not thought about it like that, till now, but you're right. At a typical cruising speed of maybe 70 mph, that's about 2500 rpm so for a 2-litre engine that's 2500/2 * 2 = 2500 litres of air per minute or 2500/60 = 42 litres of air per second. That's quite a flow rate through a pipe that's maybe 8 cm in diameter. Even at idling speed, there's a real draught from the exhaust pipe on my car! How much does the effect of the turbo vary with engine speed and therefore exhaust gas flow? Presumably the faster the engine is going, the higher the inlet pressure of air that the turbo delivers to the inlet-stroke cylinder(s) and so the greater the amount of air and therefore the greater the amount of fuel that can be burned efficiently before you get partial combustion. > and why they can sit and idle all day on a teaspoon of fuel. Yes, which is why at fairgrounds etc you often see little generators on sideshows and stands with the engine just ticking over and a tiny fuel tank on top. Interesting to hear how little the engine note changes as extra electrical load is applied, unlike petrol generators which are running much faster (to get the required torque) but which slow down as more current is drawn. > On May 8, 1:50 pm, N8N <njna...@hotmail.com> wrote: >>>> 2: Unthrottled operation. In the Diesel cycle load is controlled by [quoted text clipped - 7 lines] > the fuel, is actually a bad thing for a diesel, is it, as regards the > production of NOx? Yes. Even though the overall A/F is lean, the nature of the Diesel combustion process is that of a stratified charge process. This, to simplify, means that overall while there is just air in the cylinder, as the fuel is injected, the charge is locally closer to stoichiometry (which burns pretty hot). So, when you have high temperatures and plenty of excess O2, you get high NOx production. > How much does the effect of the turbo vary with engine speed and therefore > exhaust gas flow? Presumably the faster the engine is going, the higher the > inlet pressure of air that the turbo delivers to the inlet-stroke > cylinder(s) and so the greater the amount of air and therefore the greater > the amount of fuel that can be burned efficiently before you get partial > combustion. the effect of the turbo varies essentially with the amount of *fuel* being burned, because the fuel comes into the engine as a liquid (atomized, but still) and the combustion products are all gases. So the volume of gas going through the turbo is dependent not only on engine speed, displacement, and VE (with no fuel at all being injected, this would determine the amount of gas passing over the exhaust turbine) but also the amount of fuel burned and the resultant temperature (remember, pv=nrt) so basically, unless you did well in thermodynamics, trying to figure it out exactly will make your head hurt :) (I think I got a B or C in all of the thermo classes that I took, and now I need another cup of coffee...) nate > "Tegger" <tegger@tegger.c0m> wrote in message >> [quoted text clipped - 3 lines] > "Lean", to me, indicates a mixture which does not have an excess of > fuel, or may even have an excess of the oxidant. Then maybe I am using "lean" incorrectly. My intent in the use of that word was to describe a mixture that contained closer to the traditional emissions-desired stoich of 14.7:1 air/fuel, versus a "rich" mixture that was lower than 14.7:1 (more fuel, less air). > It requires more oxygen to burn a unit amount of MTBE than it does to > burn the same unit amount of ethanol, and the energy released is > consequently greater. Because MTBE does not contain as much oxygen as ethanol...? I think you can tell I'm no chemist. > Most of the energy is derived from the oxidation of the hydrogen atoms > in a hydrocarbon > to form water. Less energy is derived from oxidation of the carbon to > give CO2. My faulty long-term memory coughs up something here... As I recall, the original purpose of oxygenates was to reduce CO by increasing C02, this to be achieved by making more oxygen available to the engine by packing it directly into the fuel. > The oxygen (in oxygenates such as alcohol and MTBE) just occupies > space and doesnt > contribute to the energy derived from combustion. So, since the > ethanol has a higher percentage of oxygen in the molecule, it has a > lower amount of energy that it can contribute > upon combustion. Hmmm. Then it appears to make a difference in combustion whether the oxygen is contained within the intake air or contained within the fuel. Why? SignatureTegger |
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