Higher Pressure and Octane Fuel: A Relationship Explained Through Testing
In order to understand the relationship between higher pressure and octane fuel, it's essential to first grasp how these two elements interact with each other. When you want to create that peak pressure necessary for optimal ignition, you need to have a certain amount of power in your engine. However, if you're using a low-octane fuel, you could run into knock, which is undesirable and can cause damage to your engine. So, here's basically a curve that I've drawn out to explain this: our pressure peak is going to be around here, and that's kind of what you want when you want to have optimal ignition. In order to have the timing to do that, you can't use a low-octane fuel because you'll prevent knock from occurring in this example we're going to say that knock will occur some point around if you have your peak pressure occurring here based on your ignition timing.
So, what does higher octane fuel do? It allows you to advance the timing a little bit earlier preventing knock and allowing you to have that peak pressure a bit higher. This ultimately results in more power being created by your engine. If you haven't yet watched my videos on octane rating and knock, as well as ignition timing, you may want to check those out because I'll include links in the video description.
A really cool test has been done, where they've got this four-cylinder engine with two of the cylinders running on one fuel and the other two cylinders running on a different fuel. These fuels are going to have different octane ratings - one's going to be low, and one's going to be high. The engine is going to run with these two different fuels in the two different cylinders, so each of these cylinders is going to have a pressure gauge. The pressure gauge will measure the peak pressure, and we can actually look at the average of these two cylinders versus the average of these two cylinders. One will have a higher octane fuel, and we'll see if one can actually get higher pressures and thus create more power.
We have here two separate high-pressure pumps and each pump is feeding two cylinders. We have special fuel pipes here so that we can have an external fuel supply as you see on the right and on the left. At the moment, two cylinders are running from the red can which is in that case shelby power, and on the left side, two cylinders are running on regular shell unleaded fuel - 95 front fuel during the demonstration. We will run this engine on the same time with those two fuels. We measure the difference in cylinder pressure. Each cylinder has a pressure sensor where we directly can see the pressure from the cylinders.
We have each cylinder's pressure measured, and then we will swap the fuels from the right if you like right bank to the left bank, and vice versa. So, we just change fuels from right to left, and you will see that the difference we will then as well see in the cylinder pressure will just belong to the fuel and not somewhere to the engine.
We will start now the car so here we have the data readout and we're going to go ahead and switch over to the average pressures for each of the cylinder banks. If you look on the left, here is cylinders one and two, with an average pressure of 20.31 cylinders three and four, with an average pressure of 21.18. That gives us a cylinder delta of 4.12 percent.
So, what we're looking at is cylinders three and four have 4.12 percent higher pressure than cylinders one and two, and this is because the ignition timing is advanced because it can take advantage of that higher octane fuel and not have knock. The knock sensors in cylinders one and two are preventing it from advancing that timing anymore now, so that you can trust the test.
Shell went ahead and switched the two fuel cylinders, so that one and two were now running the higher octane fuel, and three and four were running the lower octane fuel. As you can see, it creates a higher pressure in cylinders one and two which are running the higher octane fuel.
So, you know it's purely based on the ignition timing. Now, let's take a look at the ignition timing now, it's a bit hard to see but as you look on the left, you've got a peak in green and yellow, and green and yellow represents cylinders one and two, and then red and blue which you see on the right peaking that cylinders three and four.
As you can see, cylinders three and four are firing later. So, cylinders one and two using the higher octane fuel are able to ignite earlier and have advanced ignition timing.
"WEBVTTKind: captionsLanguage: enhello everyone and welcome in this video i'm going to be explaining how an octane rating can affect an engine's performance the octane rating of the fuel now the cool thing about this video is at the end we're actually going to have an experiment uh conducted by shell which actually shows on a volkswagen golf tsi how the octane rating will actually affect that car's performance so very cool test but before we go into the test we need to understand the theory so a higher octane fuel allows for you to advance your ignition timing now why would you want to advance your ignition timing well ignition timing is all about a balance so let's look at the two different cases if you spark your ignition to light the air fuel mixture within your cylinder too early you're gonna have wasted energy so here we've got that example you've got your piston coming up you've ignited too early so you have this flame front you're burning the air fuel mixture and you're pressing down on that piston as it's still on its way up before it even reaches the power stroke and starts to move down to provide useful work so you don't want that to happen so you want to have the timing a little bit later but you don't want the work the timing too late because if you have the timing too late you'll waste work so here's that example so you've got your piston that comes up and then it starts to go down and then as it's going down you ignite the spark and so that flame front is now chasing the piston so that work isn't yet usable until you've expanded the pressure enough to actually start pushing that piston down so you've lost potential work because you didn't have that pressure when that piston was up closer to the top when you could force that piston down much earlier with a much greater pressure so there's a sweet spot in there and your problem is if you go too early to get that higher pressure to have the piston moving down uh with a higher pressure then you could run into knock if you're using a low octane fuel so here's basically a curve that i've drawn out to explain this so here we have our pressure and your peak pressure is going to be around here and that's kind of what you want when you want to have that ignition is to create that peak pressure but in order to have the timing to do that you can't use a low octane fuel because we'll for in this example we're going to say that knock is going to occur some point around if you have your peak pressure occurring here based on your ignition timing so what a higher octane fuel does is allows you to advance the timing a little bit earlier preventing knock and allowing you to have that peak pressure a bit higher and create more power ultimately so if you haven't yet watched my videos on octane rating on knock and on ignition timing you may want to check those out so i'll include links in the video description um now so what shell has done this is actually a really cool test is they've got this four cylinder engine two of the cylinders are gonna be running on one fuel and the other two cylinders are gonna be running on a different fuel and these fuels are gonna have uh different octane ratings one's gonna be low one's gonna be high and so the engine is gonna run this is a single uh cylinder bank this is a four cylinder engine the engine is going to run with these two different fuels in the two different cylinders so each of these cylinders is going to have a pressure gauge and the pressure gauge will measure the peak pressure and we can actually look at the average of these two cylinders versus average of these two cylinders and one will have a higher octane fuel and we'll see if one can actually get higher pressures and thus create more power so let's go ahead and check out the test so we have here two separate high pressure pumps and each pump is feeding two cylinders we have special fuel pipes here so that we can have an external fuel supply as you see on the right and on the left so at the moment two cylinders are running from the red can which is in that case uh shelby power and on the left side two cylinders are running on regular shell unleaded fuel so 95 front fuel during the demonstration we will run this engine on the same time with those two fuels that we measure the difference in cylinder pressure so we have each cylinder has a pressure sensor where we directly can see the pressure from the cylinders and then we will swap the fuels from the right if you like right bank to the left bank and vice versa so we just change fuels from right to left and you will see that the difference we will then as well see in the cylinder pressure will just belong to the fuel and not somewhere to the engine okay so we will start now the car so here we have the data readout and we're going to go ahead and switch over to the average pressures for each of the cylinder banks so if you look on the left here this is cylinders one and two and average pressure of those two cylinders in the center we've got the average pressures for cylinders three and four and then on the right we have the percent uh difference between uh the two cylinder banks so one and two versus three and four on the difference in pressure that you have so i'm going to go ahead and pause it here and explain what we're looking at so cylinders one and two the average pressure is 20.31 cylinders three and four the average pressure 21.18 and that gives us a cylinder delta of 4.12 percent so what we're looking at is cylinders three and four have four percent higher pressure than cylinders one and two and this is because the ignition timing is advanced because it can take advantage of that higher octane fuel and not have knock so the knock sensors in cylinders one and two are preventing it from advancing that timing anymore now so that you can trust the test shell went ahead and switched the two fuel cylinders so that one and two were now running the higher octane fuel and three and four were running the lower octane fuel and as you can see it creates the higher pressure in cylinders one and two which are running the higher octane fuel so you know it's purely based on the ignition timing so now let's take a look at the ignition timing now it's a bit hard to see but as you look on the left you've got a peak in green and yellow and green and yellow represents cylinders one and two and then red and blue which you see on the right peaking that cylinders three and four and as you can see cylinders three and four are firing later so cylinders one and two using the higher octane fuel are able to ignite earlier and have advanced ignition timing so thank you for watching and if you have any questions or comments feel free to leave them belowhello everyone and welcome in this video i'm going to be explaining how an octane rating can affect an engine's performance the octane rating of the fuel now the cool thing about this video is at the end we're actually going to have an experiment uh conducted by shell which actually shows on a volkswagen golf tsi how the octane rating will actually affect that car's performance so very cool test but before we go into the test we need to understand the theory so a higher octane fuel allows for you to advance your ignition timing now why would you want to advance your ignition timing well ignition timing is all about a balance so let's look at the two different cases if you spark your ignition to light the air fuel mixture within your cylinder too early you're gonna have wasted energy so here we've got that example you've got your piston coming up you've ignited too early so you have this flame front you're burning the air fuel mixture and you're pressing down on that piston as it's still on its way up before it even reaches the power stroke and starts to move down to provide useful work so you don't want that to happen so you want to have the timing a little bit later but you don't want the work the timing too late because if you have the timing too late you'll waste work so here's that example so you've got your piston that comes up and then it starts to go down and then as it's going down you ignite the spark and so that flame front is now chasing the piston so that work isn't yet usable until you've expanded the pressure enough to actually start pushing that piston down so you've lost potential work because you didn't have that pressure when that piston was up closer to the top when you could force that piston down much earlier with a much greater pressure so there's a sweet spot in there and your problem is if you go too early to get that higher pressure to have the piston moving down uh with a higher pressure then you could run into knock if you're using a low octane fuel so here's basically a curve that i've drawn out to explain this so here we have our pressure and your peak pressure is going to be around here and that's kind of what you want when you want to have that ignition is to create that peak pressure but in order to have the timing to do that you can't use a low octane fuel because we'll for in this example we're going to say that knock is going to occur some point around if you have your peak pressure occurring here based on your ignition timing so what a higher octane fuel does is allows you to advance the timing a little bit earlier preventing knock and allowing you to have that peak pressure a bit higher and create more power ultimately so if you haven't yet watched my videos on octane rating on knock and on ignition timing you may want to check those out so i'll include links in the video description um now so what shell has done this is actually a really cool test is they've got this four cylinder engine two of the cylinders are gonna be running on one fuel and the other two cylinders are gonna be running on a different fuel and these fuels are gonna have uh different octane ratings one's gonna be low one's gonna be high and so the engine is gonna run this is a single uh cylinder bank this is a four cylinder engine the engine is going to run with these two different fuels in the two different cylinders so each of these cylinders is going to have a pressure gauge and the pressure gauge will measure the peak pressure and we can actually look at the average of these two cylinders versus average of these two cylinders and one will have a higher octane fuel and we'll see if one can actually get higher pressures and thus create more power so let's go ahead and check out the test so we have here two separate high pressure pumps and each pump is feeding two cylinders we have special fuel pipes here so that we can have an external fuel supply as you see on the right and on the left so at the moment two cylinders are running from the red can which is in that case uh shelby power and on the left side two cylinders are running on regular shell unleaded fuel so 95 front fuel during the demonstration we will run this engine on the same time with those two fuels that we measure the difference in cylinder pressure so we have each cylinder has a pressure sensor where we directly can see the pressure from the cylinders and then we will swap the fuels from the right if you like right bank to the left bank and vice versa so we just change fuels from right to left and you will see that the difference we will then as well see in the cylinder pressure will just belong to the fuel and not somewhere to the engine okay so we will start now the car so here we have the data readout and we're going to go ahead and switch over to the average pressures for each of the cylinder banks so if you look on the left here this is cylinders one and two and average pressure of those two cylinders in the center we've got the average pressures for cylinders three and four and then on the right we have the percent uh difference between uh the two cylinder banks so one and two versus three and four on the difference in pressure that you have so i'm going to go ahead and pause it here and explain what we're looking at so cylinders one and two the average pressure is 20.31 cylinders three and four the average pressure 21.18 and that gives us a cylinder delta of 4.12 percent so what we're looking at is cylinders three and four have four percent higher pressure than cylinders one and two and this is because the ignition timing is advanced because it can take advantage of that higher octane fuel and not have knock so the knock sensors in cylinders one and two are preventing it from advancing that timing anymore now so that you can trust the test shell went ahead and switched the two fuel cylinders so that one and two were now running the higher octane fuel and three and four were running the lower octane fuel and as you can see it creates the higher pressure in cylinders one and two which are running the higher octane fuel so you know it's purely based on the ignition timing so now let's take a look at the ignition timing now it's a bit hard to see but as you look on the left you've got a peak in green and yellow and green and yellow represents cylinders one and two and then red and blue which you see on the right peaking that cylinders three and four and as you can see cylinders three and four are firing later so cylinders one and two using the higher octane fuel are able to ignite earlier and have advanced ignition timing so thank you for watching and if you have any questions or comments feel free to leave them below\n"