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Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng #5425266 05/10/20 06:59 AM
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Always curious about this. Since the gasoline is not mixed with air and then compressed in a GDI engine but rather injected near the top of the compression cycle, is octane rating as important for these engines? I know they are still spark fired and that the rate of burn/ease of ignition may be affected. Any thoughts on this?


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Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Boomer] #5425284 05/10/20 07:26 AM
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To me on GDIs in particular, the most important thing in gas is How thoroughly does the fuel burn.
If it doesn't burn thoroughly you'll end up with deposits on the exhaust valve and piston head.

Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Boomer] #5425291 05/10/20 07:37 AM
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My opinion is that it's more important. However, most North Americans are addicted to 87 octane. What the auto makers supposedly do is make is program the ECU to keep the engine in safe operating limits. If your stuck in a Houston freeway traffic jam in a 1.4 GDI-T Chevy Cruze as an example and it's 95 degrees outside, the ECU gets feedback from the knock sensor and ambient air temp sensor and adjust the engine map to compensate. The ECU will richen the fuel to air ration in this scenario. Not to a point that would make running a higher octane gas more economical however.

BUT, 87 octane at the pump is holding gasoline engine design back. Many auto makers are wanting 87 octane go away of the Dodo bird and are calling for a new high octane standard.
You can be against it all you want, but this will insure future vehicles will be more efficient so we will be able to buy a gas vehicle instead of a hybrid or electric.
https://www.detroitnews.com/story/b...congress-higher-fuel-standards/33902227/


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Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Boomer] #5425320 05/10/20 08:31 AM
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But why is it more important? What operating parameters make this so? It is not in the cylinder during the compression cycle. Why wouldn't 50 octane fuel be sufficient? Diesel is selected on its ability to burn....high cetane rating which is OPPOSITE that of octane. Why wouldn't this be true for direct injection of gasoline? I really don't quite get it. I know my GDI VW Golf runs far better on higher octane fuel but want to know why.


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Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: skyactiv] #5425362 05/10/20 09:09 AM
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Originally Posted by skyactiv
My opinion is that it's more important. However, most North Americans are addicted to 87 octane. What the auto makers supposedly do is make is program the ECU to keep the engine in safe operating limits. If your stuck in a Houston freeway traffic jam in a 1.4 GDI-T Chevy Cruze as an example and it's 95 degrees outside, the ECU gets feedback from the knock sensor and ambient air temp sensor and adjust the engine map to compensate. The ECU will richen the fuel to air ration in this scenario. Not to a point that would make running a higher octane gas more economical however.

BUT, 87 octane at the pump is holding gasoline engine design back. Many auto makers are wanting 87 octane go away of the Dodo bird and are calling for a new high octane standard.
You can be against it all you want, but this will insure future vehicles will be more efficient so we will be able to buy a gas vehicle instead of a hybrid or electric.
https://www.detroitnews.com/story/b...congress-higher-fuel-standards/33902227/


Article claims a 3% increase in cost for 91 octane for a 3% efficiency increase.
I am highly doubtful we would only see a 3% increase in fuel cost when premium currently costs 15 - 25% more than 87 octane gasoline.
You can claim production efficiencies all day long. Still very doubtful.

Just remove ethanol from 87 octane and you will get your 3% efficiency back, which we lost when ethanol (with its lower BTU content) was mandated.


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Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Boomer] #5425363 05/10/20 09:09 AM
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Very important.


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Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Boomer] #5425402 05/10/20 09:52 AM
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I had what I think is a LSPI event in my Hyundai Kona AWD 1.6T when it was first new. I was running 87 octane. The felt like it jumped 5 ft off the ground when it hit as I hit full boost at 1,500 to 2,000 rpm and WHAM. After that event, I only run 93 octane 80% of the time and 89 octane here and there in winter. The car is speced for 87 octane even though it has a 9.5:1 compression ratio and 17 lbs boost at 1,400 rpm. So yes, a really crappy detuned OEM tune just hamstringing this engine and you can feel it too. 175 hp and 200ftlbs of torque. 0-60 for AWD in 6.6 seconds as per Car&Driver. It has been tested by many in the forums and people find no difference in increasing octane. It has been said by Hyundai that there are no adaptives that can change a map for higher octane. It is not a true performance car, so they found no need to spend the money into octane mapping, even though I have made my car into a performance car. I do some heavy sport driving so I will spend the extra money for premium because my car sees high combustion temps them the common Kona owner.


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Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Boomer] #5425428 05/10/20 10:19 AM
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Quote
Always curious about this. Since the gasoline is not mixed with air and then compressed in a GDI engine but rather injected near the top of the compression cycle, is octane rating as important for these engines? I know they are still spark fired and that the rate of burn/ease of ignition may be affected. Any thoughts on this?


In reality, gasoline that is NOT mixed with air will not ignite. In fact the gasoline must be at a very specific mixture in order to ignite with a spark, and that mixture is very close to 12.2:1. Anything much on either side of that will either be too lean or too rich to burn. Also don't forget that higher octane fuel RESISTS fast ignition caused by hot spots or compression, not the other way around.

Even diesel engines require that the fuel be mixed with "some" air (atomized) to ignite.

There are plenty of videos online to explain all of this much better than I can.

Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: skyactiv] #5425437 05/10/20 10:26 AM
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Originally Posted by skyactiv
... BUT, 87 octane at the pump is holding gasoline engine design back. Many auto makers are wanting 87 octane go away of the Dodo bird and are calling for a new high octane standard.
You can be against it all you want, but this will insure future vehicles will be more efficient ...
"More efficient" in terms of energy out per unit volume in is pointless unless we also get more energy out relative to cost (both retail and at the refinery).


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Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Danno] #5425485 05/10/20 11:14 AM
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Originally Posted by Danno
Just remove ethanol from 87 octane and you will get your 3% efficiency back, which we lost when ethanol (with its lower BTU content) was mandated.

Ethanol or at least some oxygenate is not going away. There are very few effective octane boosters. MTBE is a nonstarter in the United States and other oxygenates are still under development (or at least research since candidates have been identified).

Maybe we could produce enough non-ethanol gasoline to just make 87 AKI octane. But that's not what we have. Gasoline production is about making as much fuel as possible without having to deal with too much fuel that has to be stored or disposed of. Right now ethanol gives us the cheapest, most effective way to boost the octane rating. Maybe gasoline prices are a little bit low right now, but typically ethanol costs less than gasoline.

Certainly around here almost all retail gasoline has 10% ethanol. Anything else would be impractical given the demand for 91 AKI octane. I guess in other parts of the country, 93 AKI E0 premium is common but then E10 87 octane is what most people buy. Or maybe limited supplies of E0 87 sold at a price premium. But in the end it's about tailoring the supply to meet the demand. You can make E0 available in some form or another if there's less demand for higher octane fuel. But if there's high demand it gets a lot tougher.

Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: y_p_w] #5425491 05/10/20 11:26 AM
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Originally Posted by y_p_w
Originally Posted by Danno
Just remove ethanol from 87 octane and you will get your 3% efficiency back, which we lost when ethanol (with its lower BTU content) was mandated.

Ethanol or at least some oxygenate is not going away. There are very few effective octane boosters. MTBE is a nonstarter in the United States and other oxygenates are still under development (or at least research since candidates have been identified).

Maybe we could produce enough non-ethanol gasoline to just make 87 AKI octane. But that's not what we have. Gasoline production is about making as much fuel as possible without having to deal with too much fuel that has to be stored or disposed of. Right now ethanol gives us the cheapest, most effective way to boost the octane rating. Maybe gasoline prices are a little bit low right now, but typically ethanol costs less than gasoline.

Certainly around here almost all retail gasoline has 10% ethanol. Anything else would be impractical given the demand for 91 AKI octane. I guess in other parts of the country, 93 AKI E0 premium is common but then E10 87 octane is what most people buy. Or maybe limited supplies of E0 87 sold at a price premium. But in the end it's about tailoring the supply to meet the demand. You can make E0 available in some form or another if there's less demand for higher octane fuel. But if there's high demand it gets a lot tougher.


Shell has no issues making 91 octane fuel for Ontario Canada consumption, and it is advertised as being ethanol free.
Don't really see the need for an oxygenate unless it is some state gov't ordinance as you might find in California.


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Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Danno] #5425506 05/10/20 11:51 AM
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Originally Posted by Danno
Shell has no issues making 91 octane fuel for Ontario Canada consumption, and it is advertised as being ethanol free.
Don't really see the need for an oxygenate unless it is some state gov't ordinance as you might find in California.

It's about meeting supply and demand. I mentioned it earlier. Where there's less overall demand for higher octane fuel, it might be possible to meet all the demand with some of the fuel sold without ethanol to bring up the octane rating.

This was an article about why 92 octane premium went away in California, but it does address the whole issue with how to deal with what you get out of refinery streams. It doesn't specifically mention ethanol, MTBE, or other octane boosters, but obviously an oxygenate like ethanol with a blending octane rating of about 105-110 AKI is going to be pretty useful to increase the overall octane rating of the fuel supply. It's also an older article and doesn't go into other things like hydrocracking which can be used to create a higher average octane rating for all gasoline produced. But the gist is about how to take all this stuff and manage to sell as much of it as possible. For the most part they don't want to sell it at a really cheap price for something other than vehicle fuel. By using ethanol they can produce more fuel that meets vehicle requirements.

Quote
https://forum.e46fanatics.com/showp...c63a91e80&p=9046264&postcount=23
You see, when crude oil is refined into gasoline, the refinery doesn't have all that much control over what comes out. Crude oil is full of all kinds of stuff, and a refinery simply separates it, sorting all the iso-this and hepta-that in order of density. The really heavy stuff, like tar, is near the bottom, while the really light stuff, like butane, is near the top.

Somewhere in the upper ranges of the stack are the components of gasoline. There are between 10 and 15 different blend stocks, each with a different octane rating, which are mixed together to make gasoline.

The crude oil being used and little else determine the amount of each blend stock available for mixing. Generally, if you just dump all the blend stocks into a bucket, you end up with something around 88 or 89 octane. If you're selective and only mix the good stuff, you can make 92, 93 or even 95 octane. But once you take out the good stuff, you're left with crap--something like 85 octane. Then you have to leave enough good stuff in the bucket to bring this pee-water up to at least 87 octane. This limits the amount of 95-octane gas you can make. If you make 93-octane premium instead, you use up less of the high-octane stocks, allowing you to make a higher proportion of premium fuel.

In the Midwest, where an extensive customer base of good old boys in pickup trucks consume vast quantities of 87 octane, demand for premium fuel is low enough to make genuine high-octane premium.

In California, however, Lexus-driving executives suck down premium fuel like it's Evian, so 92 was the rule.

Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Danno] #5425746 05/10/20 06:24 PM
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Originally Posted by Danno
Shell has no issues making 91 octane fuel for Ontario Canada consumption, and it is advertised as being ethanol free.
Don't really see the need for an oxygenate unless it is some state gov't ordinance as you might find in California.

Let me restate it. Yes it is possible to make 91 AKI fuel without ethanol. The question is what does the refiner do with the remainder of the fuel that might average about 84 AKI? There are several ways to boost the octane rating - by adding whatever high octane gasoline is still available and/or adding an oxygenate.

This is really more of a math/economic exercise. The higher the demand for higher octane fuel, the harder it would be to sell all the fuel produced without an oxygenate. The advantage is that it's also typically cheaper than gasoline and you're only using up to 10% so it has a small effect on fuel economy. And the effect on fuel economy may even be less than the typical deviation in gasoline energy content. Ethanol's energy content is fixed, but gasoline can have a somewhat random mixture of hydrocarbons that varies in energy content.

Maybe in Ontario there isn't enough demand for 91 that Shell thinks they can sell ethanol free. Certainly it's something they can market. However, the regular they sell is E10. In some markets with lower demand for premium they sell 93 octane E0. In others they sell some 87 octane E0, but at a higher price. But that ain't happening in California where people pump a lot of premium into various performance cars. But the weird thing is that there are a lot of cars where 93 AKI is recommended but we really can't find any unless it's blended with specialty 100 octane street legal racing fuel.

I mean - there's a fairly easy to obtain liquid that when blended at 10% with common gasoline boosts the AKI octane more than two points and usually costs less than gasoline. Is it really that hard to understand why this would be desirable even without any government mandate?

Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Boomer] #5425994 05/11/20 03:30 AM
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Want ethanol free 91 grade in Montana? Here is a shot from last July. It was 14% more than 91 Octane with ethanol.

DBE99E14-3E54-4733-BB8E-745208A732B3.jpeg
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Re: Is the Importance of Octane Rating Less in GDI Engines than in Port Injected Eng [Re: Boomer] #5427026 05/12/20 06:50 AM
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Originally Posted by Boomer
Always curious about this. Since the gasoline is not mixed with air and then compressed in a GDI engine but rather injected near the top of the compression cycle, is octane rating as important for these engines? I know they are still spark fired and that the rate of burn/ease of ignition may be affected. Any thoughts on this?



Yes. The same rules apply. DI just allows for better management of the combustion cycle (Better control of fuel metering into each cylinder). Same way port fuel injection was an improvement over carbs. A lot of engines today have some sort of VVT to make power so they required better fuel in order to advance timing.

Originally Posted by Boomer
But why is it more important? What operating parameters make this so? It is not in the cylinder during the compression cycle. Why wouldn't 50 octane fuel be sufficient? Diesel is selected on its ability to burn....high cetane rating which is OPPOSITE that of octane. Why wouldn't this be true for direct injection of gasoline? I really don't quite get it. I know my GDI VW Golf runs far better on higher octane fuel but want to know why.


Remember diesel fuel must be able to auto-ignite off the heat created by the comparatively high compression ratio (14:1 to 25:1). Cetane is important for cold starts and low load conditions, not so much when operating at full power.

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