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Post by petrochemist on Aug 14, 2024 16:54:12 GMT
102 octane, remember when you could get "5-star" 101 octane at the pumps? Now it's not much better than the old 3-star unless you buy one of the "super" variants which are still only 4-star. Most of the rest are only fit for lawn mowers. I use the E10 and get an average of around 40mpg from an Audi A5, which is neither small nor short of performance. Over an extended period I have never found the “super” fuels to give better mileage or performance. Your Audi would have been tuned to run on normal unleaded. Racing cars are often tuned specifically to run on higher octane fuels, making use of higher compression ratios, which allow more power. If they were run on normal 95 octane fuel pre detonation would destroy the engines fairly rapidly. The main championships we supply have engines tuned very carefully to get the absolute maximum from the fuel being used so consistency throughout the year is also very important. I gather we also have a fuel made for the american racing market that comes in at 114 RON (research octane number - the octane under full power conditions) Often high octane fuels have lower calorific values, so while more power can be produced the fuel consumption is worse. My own cars at one point included a 1977 Celica 2000GT, designed to run on leaded 4 star (97 octane minimum IIRC). Unlike many cars of it's era it's valve seats allowed it cope without lead additives. It would not run well on normal unleaded (95 octane) but was quite happy on super unleaded for most of the 10 years I used it. |
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Post by zx9 on Aug 16, 2024 10:03:27 GMT
Modern petrol engines do benefit from all the electronics, pre and post cat O2, anti knock sensors and variable valve timing and injection pulse width to accommodate a wide range of fuels.
I do use E5 in the bike and 2T garden equipment as it has potentially less methanol giving a lower moisture absorption from the atmosphere if left unused for extended periods, I also run the carbs dry before parking the bike in the garage or putting away the garden kit which helps a lot.
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Post by peterob on Aug 16, 2024 14:14:13 GMT
Modern petrol engines do benefit from all the electronics, pre and post cat O2, anti knock sensors and variable valve timing and injection pulse width to accommodate a wide range of fuels. I do use E5 in the bike and 2T garden equipment as it has potentially less methanol giving a lower moisture absorption from the atmosphere if left unused for extended periods, I also run the carbs dry before parking the bike in the garage or putting away the garden kit which helps a lot. Yes indeed. I'm convinced that E10 denatures in storage. Two-stroke mix seems to go off very badly. It was always advised to drain and strip clean garden machinery for winter storage but it seems more necessary now. Not only is ethanol hydroscopic but I seem to remember that the vapour pressure of ethanol/hydrocarbon mixtures is complicated and not easily calculated. We had endless cold start problems with our car on [aged] E10 and these problems went away when I filled it with E5. The car is just used to go to the allotment and back, less than 2x 2 miles, and a tank of fuel lasts for ages. The car stands outside and is barely used in the winter months so a half-tank of fuel could be six months old come April. |
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Post by andy on Aug 16, 2024 15:00:32 GMT
Perhaps premium unleaded typically has more fuel stabilisers in it than regular unleaded? If premium has more knock inhibitors, detergents and whatever else in it maybe they have to include more stuff to stop it separating and going off faster.
FWIW just double checked the results a guy on YouTube got with E10 and it was between 2% and 6% ethanol so results with E5 could potentially be very similar.
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Post by peterob on Aug 16, 2024 15:25:27 GMT
Perhaps premium unleaded typically has more fuel stabilisers in it than regular unleaded? If premium has more knock inhibitors, detergents and whatever else in it maybe they have to include more stuff to stop it separating and going off faster. FWIW just double checked the results a guy on YouTube got with E10 and it was between 2% and 6% ethanol so results with E5 could potentially be very similar. Generally the higher petrol grade has a detergent package and higher octane, the lower oxygenate content means it has a higher calorific value. Knock is controlled [where possible] by the engine management system using the onboard knock sensors and variable ignition timing. Engines capable of it can run closer to their knock limit and this means a smaller ignition delay and more power - but this is only likely to be noticeable on [clean] high performance engines. Engine deposits can initiate knock. It is a good idea, especially if going on a long motorway journey, to take the opportunity to put a tank of premium fuel though an engine to benefit from the detergent package which can lift engine and fuel injection system deposits. |
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Post by petrochemist on Aug 16, 2024 18:17:36 GMT
Perhaps premium unleaded typically has more fuel stabilisers in it than regular unleaded? If premium has more knock inhibitors, detergents and whatever else in it maybe they have to include more stuff to stop it separating and going off faster. FWIW just double checked the results a guy on YouTube got with E10 and it was between 2% and 6% ethanol so results with E5 could potentially be very similar. It's not necessarily down to additives at all. Most people are totally ignorant on the complexity of petrol. I won't go into the full specification (which covers about 20 pages in the ASTM handbooks) It's very rare to come across a petrol that has less than 20 compounds present, & upwards of 100 is certainly not unheard of, indeed the use of higher renewably content materials is making them more common. In racing fuels there is normally a '5-30 rule' that specifies at least 30% of the fuel MUST be from components under 5% of the total. The rule differs slightly between FIM (motorbikes governing body) & FIA (cars governing body). The days of formula one cars running on practically neat toluene (back in the 70s) are long gone. AFAIF no such rule exists for road fuel, but economics, makes pure compounds much less desirable blending components here. I've heard the 5-30 rules were specifically introduced to make racing fuels more like road fuel. Making a gasoline cut directly from crude would typically result in an octane of around 55 - not much good for any engines in the last 100 years. Changing the composition of the fuel by means of reforming, isomerization, removal of n-paraffins etc can boost that very considerably. The strems produced by these processes will each consist of multiple compounds and it is usually blending several of these streams that produces the base fuel to which oxygen containing compounds like bio-ethanol are added. Cracking the crude produces shorter chain molecules many of which would be alkenes (with carbon carbon double bonds) These compounds are cheap, have quite high octanes, but are prone to polymerization (going off). Branched chain alkanes (enriched by isomerisation) on the other hand, are more expensive, high octane compounds that are stable for millions of years. The most common one in petrol is iso-octane (systematic name 2,2,4-trimethylpentane) has an octane of 100 (defined in the octane scale, n-heptane being the other defined anti knock point with an octane of zero) Aromatic compounds such as toluene & xylene have octanes above 100, but are limited by the specification to 30% max They are generally stable. A fuel blended using isomerate & aromatics can have octanes above 100, whilst being almost completely immune to going off (as long as evaporation is prevented). It would be relatively expensive to make. I have used 10 year old samples of racing fuels of this sort and they had no signs of going off at all. A cheap supermarket fuel will quite likely make more use of cracked gasoline cuts and will go off. It's composition is inherently less stable. Knock inhibitors such as tetraethyllead (leaded fuels) & methylcyclopentyl manganese tricarbonyl (MMT, a lead replacement) are now rarely used in bulk fuels, with high octane blending components being preferable. |
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Post by petrochemist on Aug 16, 2024 18:39:53 GMT
Modern petrol engines do benefit from all the electronics, pre and post cat O2, anti knock sensors and variable valve timing and injection pulse width to accommodate a wide range of fuels. I do use E5 in the bike and 2T garden equipment as it has potentially less methanol giving a lower moisture absorption from the atmosphere if left unused for extended periods, I also run the carbs dry before parking the bike in the garage or putting away the garden kit which helps a lot. Yes indeed. I'm convinced that E10 denatures in storage. Two-stroke mix seems to go off very badly. It was always advised to drain and strip clean garden machinery for winter storage but it seems more necessary now. Not only is ethanol hydroscopic but I seem to remember that the vapour pressure of ethanol/hydrocarbon mixtures is complicated and not easily calculated. We had endless cold start problems with our car on [aged] E10 and these problems went away when I filled it with E5. The car is just used to go to the allotment and back, less than 2x 2 miles, and a tank of fuel lasts for ages. The car stands outside and is barely used in the winter months so a half-tank of fuel could be six months old come April. If water gets into your fuel tank it will indeed extract ethanol from the fuel, and yes azeotropes make ethanol/hydrocarbon, ethanol/water & ethanol/hydrocarbon/water mixtures extremely complicated. The azeotrope data I've seen only covers a maximum of 3 pure components, but still includes dozens of different mixes. The volatility specification for petrol normally changes for winter & summer use (and also with altitude in the USA), this could cause issues if you only fill up on summer grade then want to use it on a cold winter's day. Evaporation is probably the main issue with 2-stroke mix going off, if it's just petrol evaporation probably won't change things too much, but with mixes the oil won't evaporate, so your 25:1 may become 15:1 or even 5:1... |
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Post by zx9 on Aug 16, 2024 18:47:32 GMT
Perhaps premium unleaded typically has more fuel stabilisers in it than regular unleaded? If premium has more knock inhibitors, detergents and whatever else in it maybe they have to include more stuff to stop it separating and going off faster. FWIW just double checked the results a guy on YouTube got with E10 and it was between 2% and 6% ethanol so results with E5 could potentially be very similar. It's not necessarily down to additives at all. Most people are totally ignorant on the complexity of petrol. I won't go into the full specification (which covers about 20 pages in the ASTM handbooks) It's very rare to come across a petrol that has less than 20 compounds present, & upwards of 100 is certainly not unheard of, indeed the use of higher renewably content materials is making them more common. In racing fuels there is normally a '5-30 rule' that specifies at least 30% of the fuel MUST be from components under 5% of the total. The rule differs slightly between FIM (motorbikes governing body) & FIA (cars governing body). The days of formula one cars running on practically neat toluene (back in the 70s) are long gone. AFAIF no such rule exists for road fuel, but economics, makes pure compounds much less desirable blending components here. I've heard the 5-30 rules were specifically introduced to make racing fuels more like road fuel. Making a gasoline cut directly from crude would typically result in an octane of around 55 - not much good for any engines in the last 100 years. Changing the composition of the fuel by means of reforming, isomerization, removal of n-paraffins etc can boost that very considerably. The strems produced by these processes will each consist of multiple compounds and it is usually blending several of these streams that produces the base fuel to which oxygen containing compounds like bio-ethanol are added. Cracking the crude produces shorter chain molecules many of which would be alkenes (with carbon carbon double bonds) These compounds are cheap, have quite high octanes, but are prone to polymerization (going off). Branched chain alkanes (enriched by isomerisation) on the other hand, are more expensive, high octane compounds that are stable for millions of years. The most common one in petrol is iso-octane (systematic name 2,2,4-trimethylpentane) has an octane of 100 (defined in the octane scale, n-heptane being the other defined anti knock point with an octane of zero) Aromatic compounds such as toluene & xylene have octanes above 100, but are limited by the specification to 30% max They are generally stable. A fuel blended using isomerate & aromatics can have octanes above 100, whilst being almost completely immune to going off (as long as evaporation is prevented). It would be relatively expensive to make. I have used 10 year old samples of racing fuels of this sort and they had no signs of going off at all. A cheap supermarket fuel will quite likely make more use of cracked gasoline cuts and will go off. It's composition is inherently less stable. Knock inhibitors such as tetraethyllead (leaded fuels) & methylcyclopentyl manganese tricarbonyl (MMT, a lead replacement) are now rarely used in bulk fuels, with high octane blending components being preferable. ^^^Thank you, that was a good read and brought back happy memories of A level chemistry. |
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Post by daves on Aug 16, 2024 19:01:45 GMT
Thanks petrochemist for the lucid explanation. Talk of azeotropes brings back memories of carrying out azeotropic esterifications in refluxing benzene 😱. We had a dry ice / acetone cooled trap on top of the condenser but even so... |
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Post by aitch on Aug 27, 2024 17:54:56 GMT
To return to the OP, I have been noticing these covers, or the lack thereof, more often. The other day I saw a large Audi, possibly an A6 but I wouldn't swear to it, with 3 of these types of cover on the front.  Three? Are they really heavy and difficult to tow? Or do the top two actually cover rocket launchers, for getting the plebs out of your way on the motorway?
ETA: I'm not good enough with Google to find out what they are really for.
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Post by spinno on Aug 27, 2024 17:56:55 GMT
To return to the OP, I have been noticing these covers, or the lack thereof, more often. The other day I saw a large Audi, possibly an A6 but I wouldn't swear to it, with 3 of these types of cover on the front. View AttachmentThree? Are they really heavy and difficult to tow? Or do the top two actually cover rocket launchers, for getting the plebs out of your way on the motorway?
ETA: I'm not good enough with Google to find out what they are really for.
It's where the indicator fairies are imprisoned, doomed never to flash... |
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Post by davem399 on Aug 27, 2024 18:34:46 GMT
To return to the OP, I have been noticing these covers, or the lack thereof, more often. The other day I saw a large Audi, possibly an A6 but I wouldn't swear to it, with 3 of these types of cover on the front. View AttachmentThree? Are they really heavy and difficult to tow? Or do the top two actually cover rocket launchers, for getting the plebs out of your way on the motorway?
ETA: I'm not good enough with Google to find out what they are really for.
Steve, I think they might be the headlamp washers. |
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Post by geoffr on Aug 27, 2024 18:38:24 GMT
To return to the OP, I have been noticing these covers, or the lack thereof, more often. The other day I saw a large Audi, possibly an A6 but I wouldn't swear to it, with 3 of these types of cover on the front. View AttachmentThree? Are they really heavy and difficult to tow? Or do the top two actually cover rocket launchers, for getting the plebs out of your way on the motorway?
ETA: I'm not good enough with Google to find out what they are really for.
The two under the headlights are pressure washers, a requirement where HID headphones are installed. Unfortunately, in my extensive experience, they are a complete waste of time, I’ve never known them to shift anything but water. The headlights seem just as dirty after a pressure wash as before. I suppose they might shift wet mud. |
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Post by aitch on Aug 27, 2024 19:15:46 GMT
To return to the OP, I have been noticing these covers, or the lack thereof, more often. The other day I saw a large Audi, possibly an A6 but I wouldn't swear to it, with 3 of these types of cover on the front. View AttachmentThree? Are they really heavy and difficult to tow? Or do the top two actually cover rocket launchers, for getting the plebs out of your way on the motorway?
ETA: I'm not good enough with Google to find out what they are really for.
The two under the headlights are pressure washers, a requirement where HID headphones are installed. Unfortunately, in my extensive experience, they are a complete waste of time, I’ve never known them to shift anything but water. The headlights seem just as dirty after a pressure wash as before. I suppose they might shift wet mud. Ah, another little complication to go wrong. Assuming it works in the first place. Which it sounds like it doesn't. Keeps the main dealers is little, but expensive, jobs, I suppose.
Thanks for the info.
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Post by peterob on Aug 27, 2024 19:21:39 GMT
To return to the OP, I have been noticing these covers, or the lack thereof, more often. The other day I saw a large Audi, possibly an A6 but I wouldn't swear to it, with 3 of these types of cover on the front. View AttachmentThree? Are they really heavy and difficult to tow? Or do the top two actually cover rocket launchers, for getting the plebs out of your way on the motorway?
ETA: I'm not good enough with Google to find out what they are really for.
The two under the headlights are pressure washers, a requirement where HID headphones are installed. Unfortunately, in my extensive experience, they are a complete waste of time, I’ve never known them to shift anything but water. The headlights seem just as dirty after a pressure wash as before. I suppose they might shift wet mud. My headlights have pressure jet washers, just one per headlamp. They seem to work. |
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