Effect of fuel octane number on FE

[theunchosen]

Originally Posted by hummingbird

Answering a few open questions -
1. Yes Oil changed with the service. As synthetic was 2.5 times as costly as unbranded mineral, I chose mineral.
2. Yes they got the tyre pressure down to 32 (habit slaves!) I insisted and made them take it back to the compressor and filled it back up to 50. Lots of weird glances endured... I check and top up regularly at each weekend using a digital gauge and battery operated pump.
3. AC use was not significant. It was only two / three instances, each not lasting 5 minutes before I got nervous about the FE hit and switched to window cracks.
4. I P&G regularly since Dec 08, (when I got to know about it on joining ecomodder). The change I had with the octane change was switching from granny mode to jackrabbit mode for my acceleration, on reading about the ABA testing done by SVOboy.
5. My car is almost identical to FIT (same platform), has 1.5L 5MT IDSI engine (not the popular Vtec variety), and does not require premium fuel. the premium fuel was touted to make the vehicle run smoother, so was using it.

Unchosen: What is the diagnostic unit you are talking about?

aerohead: Is the knocking thing equivalent to lugging?

Diagnostic units are small calculator sized computers that read the signal the ECU receives from the various sensors in your car and then puts it in a code for you.

Basically its a box that you plug into a receptacle in your car(mine is on the passenger side behind/below the glove box) that tells you what a check engine light means. They usually come with a book that tells you what specific codes mean. Its what the dealer will do everytime you bring a car in because its easy.

Some vehicles have a memory. So it records important events. not like "I turned 12 weeks old today!" but "detonation in cylinder 4" and then also records all the temperature readings(intake, exhaust cylinder rpm all kidns of other stuff too).

It basically alerts you if something is wrong before it needs fixing. Typically I am going to say its not necessary. I have one because there are 3 Del Sols in my nuclear family along with 2 other cars that can use the same diagnostic and codes so its totally worth it for us.

Knock/detonation/ping occurs when the cylinder gets a little too warm or pressure gets a little too high.

The air gets compressed and the spark plug ignites the fuel air. As the spark front travels across the cylinder(from the crown/top) to the piston(bottom) the air at the bottom becomes extremely hot and suffers extremely high pressure. At this point that small pocket of air at the bottom detonates(normal engine cycle just involves the fuel burning not exploding) and causes abnormal pressure and stress against the cylinder walls and piston head/crown/top. Its not really dangerous in non-high performance cars(Ferraris Lamborghinis Honda NSX. . .) as long as its doesn't happen every stroke or every other stroke. If it happens every stroke the spark plugs, valve heads or the walls of the cylinder themselves can cause the fuel to ignite at the bottom of the compression cycle. At that point the engine is toast. Its going to have to compress super-heated high pressure air for 180 degrees of movement(opposed to just a few normally) during which time the heat and pressure are increasing rapidly. In effect you will know when that happens because the car stops immediately. it melts a hole in the piston, maybe the walls, maybe the crown and definitely cooks the valves.

That said your car is smart enough to avoid knocking becoming too intense as long as you don't short-circuit the knock wiring in hopes of higher FE. So don't worry about it unless you are really trying to push the envelope and get lean burn and high compression with the sensors unplugged.

[hummingbird]

I am very much interested in pushing the envelope on my FE achievements - my current short-to-medium term goal is 60 MPG and eventually, in long term, 70 MPG.

BUT I sincerely don't want to be stupid enough to allow all sorts of damage to happen to the engine in the name of FE. That's why this enquiry.

Can I get some links for the diagnostic unit you are talking about? Any brands/models you can point me to?

[theunchosen]

AMPERIT OBD-II Pocket Scanner : JC Whitney: Auto Parts & Accessories

I believe is the unit I have. I'm not sure if the fit has a memory unit attached to its ECU, but all you have to do is connect it before shutting it down and it will tell you what has been going on while you were driving.

As I said its mostly to diagnose problems. I sincerely doubt you are causing enough knock to worry about and also if you are going to be exploring the lean burn regions you will need to re-map your Fuel-air ratios. If and when you do that you will probably have an on-board computer that runs a program to change the fuel maps, but then you can also get programs that read the diagnostic codes. If you straight-up hardwire the map(set it on a computer connect an ECU tuner to the computer and then unplug and connect the tuner to the engine) then you will want one of the above tools to make sure you aren't damaging something.

Honestly I would wait until you have decided you are going to go lean-burn settings and are getting the equipment to do that. Thats where that scary dangerous pre-ignition lair is. As long as you aren't tuning the ECU to inject alot less fuel than normal its not likely to pre-ignite.

[hummingbird]

Will a scangauge work as well? The JC Whitney device looks like a younger sibling of the scangauge, just giving out codes and not MPG feedback.

However, you are right about what I might be up to, I don't intend to go all that nerdy about messing with the engine.

Any pointers then to improve from where I am to where I want to be?

[theunchosen]

you could try some aero improvements although the fit/Jazz/city is pretty good initially. I know the US version did not come with a belly pan on the earlier models, you might take a look at covering the under side of the car with some inexpensive semi-heat resistant material. Wheel skirts for the back wheels using a similar material (like coroplast, linoleum something relatively light and easy to manipulate(and cheap)) improve aerodynamics.

If your version(I am less familiar with the overseas models) has roof racks or a wing/spoiler you could cinsider deleting those(although be wary because open bolt holes for either could cause rust so be sure and cover those). You could also delete interior components you don't use.

Another thing you could do, but depends on your driving hours, is to delete the alternator and replace it with maybe a good 70-80 pounds of batteries and a few "marine application" solar panels. The panels can go on the interior of your car on the dash(Honda likes to make very dark large dashes that generate heat mine is the same(del sol)). The panel would reduce the interior temperature somewhat heavily if sun is striking the panel instead of the dash. Also the panel would allow your batteries to charge when the car is sitting at work or school so you wouldn't have to pay legacy costs on energy.

[aerohead]

Originally Posted by hummingbird

Answering a few open questions -
1. Yes Oil changed with the service. As synthetic was 2.5 times as costly as unbranded mineral, I chose mineral.
2. Yes they got the tyre pressure down to 32 (habit slaves!) I insisted and made them take it back to the compressor and filled it back up to 50. Lots of weird glances endured... I check and top up regularly at each weekend using a digital gauge and battery operated pump.
3. AC use was not significant. It was only two / three instances, each not lasting 5 minutes before I got nervous about the FE hit and switched to window cracks.
4. I P&G regularly since Dec 08, (when I got to know about it on joining ecomodder). The change I had with the octane change was switching from granny mode to jackrabbit mode for my acceleration, on reading about the ABA testing done by SVOboy.
5. My car is almost identical to FIT (same platform), has 1.5L 5MT IDSI engine (not the popular Vtec variety), and does not require premium fuel. the premium fuel was touted to make the vehicle run smoother, so was using it.

Unchosen: What is the diagnostic unit you are talking about?

aerohead: Is the knocking thing equivalent to lugging?

hummingbird,knock is synonymous with detonation,a condition which occurs in the cylinder of the engine associated with piston slap caused by uncontrolled combustion which can lead to rapid engine damage.------------Lugging is described as a condition which exists when operating a vehicle in a gear too "high" for the rpm of the engine,which causes the vehicle to "buck" and shudder,immediately before the engine stalls.Lugging causes "jerk",which is an instantaneous acceleration in the power-train,and if maintained,can lead to bearing failure or gear failure under these instantaneous loads.

[theunchosen]

Originally Posted by aerohead

hummingbird,knock is synonymous with detonation,a condition which occurs in the cylinder of the engine associated with piston slap caused by uncontrolled combustion which can lead to rapid engine damage.------------Lugging is described as a condition which exists when operating a vehicle in a gear too "high" for the rpm of the engine,which causes the vehicle to "buck" and shudder,immediately before the engine stalls.Lugging causes "jerk",which is an instantaneous acceleration in the power-train,and if maintained,can lead to bearing failure or gear failure under these instantaneous loads.

I would argue with that. Its not really uncontrolled any more than normal. It is suspected that it happens if/when the flame front strikes a pocket of stoich mix while the surrounding area is lean. the stoich burns faster and causes an uneven pressure spike on the bottom of the cylinder(against the piston) which ignites that fuel and creates very small pockets that detonate under the intense pressure and heat.

All said and done the combustion event is no less controlled(as there are no means for controlling the flame front).

[evolutionmovement]

Under ideal conditions, the flame front advances from the spark plug. What is important, though it that it IS less controlled in that the timing of the ignition is before the intended ignition. This causes a pressure wave that has to be absorbed by the piston, cylinder walls, head, valves, and plug. That affects power and durability. If unchecked, it can raise the heat level to a point where you can get pre-ignition and that's when you blow holes in pistons, bend rods, or throw them through blocks (which can be quite dramatic and entertaining if it's not your car).

When the knock sensor detects knock (basically, the knock sensor is a microphone that picks up the little pings through the metal block), it tells the ECU, which switches to a more conservative engine map. This would be retarded ignition timing (cools things down inside the cylinder, but is lousy for power or fuel efficiency) and possibly increased fuel, which cools the engine even further. I think some really paranoid ECUs might even lower the rpm limiter, but that's just what I heard and I don't know for sure. Not that I doubt it, but it could have just been the retarded timing and rich fueling naturally limiting the maximum rpms. Anyway, if the knock sensor stopped working in my old Subaru, it was supposed to go into a 'limp home' mode which did the ignition cut and the fuel enrichment (I heard of people getting 12 mpg from 2.2 liters like this!). Unfortunately for me, the early Legacys had knock sensors not up to the rest of the car's durability standards and my knock sensor went, but the ECU never noticed and I ended up yanking a real ringer of an engine (the N/A in that car was as quick as some stock turbo versions up to around 70) with a relatively young 250k miles because of it when I lost a cylinder (still maintained 85 mph). Even more unfortunate was that I had a turbo engine I was rebuilding in my kitchen and so I just swapped it out the next day (running the lower compression block normally aspirated. Went down to 23 mpg from about 26 and lost any breathing above 5k rpm) and all the ended up being wrong with the 'dead' motor was a melted $12 exhaust valve! I was pretty ticked at that point (especially when I saw how beautiful, even almost new, the rest of the internals looked), but committed to the other engine. So anyway, the point is, don't try to save a couple dollars by risking the engine. I'd play it safe and go with whatever the minimum octane is that works until you can monitor what's going on. Really, you shouldn't notice a difference, but if it feels slower or is getting worse mileage, then you're too low. If the recommended octane seems too low, you might have a problem. Could just be something other than knock is setting off the knock sensor (bad sensor, odd vibrations from something) or the plugs might be the wrong heat range or bad.

[theunchosen]

Originally Posted by evolutionmovement

Under ideal conditions, the flame front advances from the spark plug. What is important, though it that it IS less controlled in that the timing of the ignition is before the intended ignition. This causes a pressure wave that has to be absorbed by the piston, cylinder walls, head, valves, and plug. That affects power and durability. If unchecked, it can raise the heat level to a point where you can get pre-ignition and that's when you blow holes in pistons, bend rods, or throw them through blocks (which can be quite dramatic and entertaining if it's not your car).

When the knock sensor detects knock (basically, the knock sensor is a microphone that picks up the little pings through the metal block), it tells the ECU, which switches to a more conservative engine map. This would be retarded ignition timing (cools things down inside the cylinder, but is lousy for power or fuel efficiency) and possibly increased fuel, which cools the engine even further. I think some really paranoid ECUs might even lower the rpm limiter, but that's just what I heard and I don't know for sure. Not that I doubt it, but it could have just been the retarded timing and rich fueling naturally limiting the maximum rpms. Anyway, if the knock sensor stopped working in my old Subaru, it was supposed to go into a 'limp home' mode which did the ignition cut and the fuel enrichment (I heard of people getting 12 mpg from 2.2 liters like this!). Unfortunately for me, the early Legacys had knock sensors not up to the rest of the car's durability standards and my knock sensor went, but the ECU never noticed and I ended up yanking a real ringer of an engine (the N/A in that car was as quick as some stock turbo versions up to around 70) with a relatively young 250k miles because of it when I lost a cylinder (still maintained 85 mph). Even more unfortunate was that I had a turbo engine I was rebuilding in my kitchen and so I just swapped it out the next day (running the lower compression block normally aspirated. Went down to 23 mpg from about 26 and lost any breathing above 5k rpm) and all the ended up being wrong with the 'dead' motor was a melted $12 exhaust valve! I was pretty ticked at that point (especially when I saw how beautiful, even almost new, the rest of the internals looked), but committed to the other engine. So anyway, the point is, don't try to save a couple dollars by risking the engine. I'd play it safe and go with whatever the minimum octane is that works until you can monitor what's going on. Really, you shouldn't notice a difference, but if it feels slower or is getting worse mileage, then you're too low. If the recommended octane seems too low, you might have a problem. Could just be something other than knock is setting off the knock sensor (bad sensor, odd vibrations from something) or the plugs might be the wrong heat range or bad.

Not correct. The spark timing and ignition event take place as normal. literally the only detectable difference between a knock combustion event and a normal one is the pressure wave is non-homogenous and in no way whatsoever could be considered quasi-equilibrium(properties are different for different parts of the volume by substantial measures).

As I originally said what happens is the fuel and air for some reason don't mix properly. Theorized reasons are the intake air may have pockets that are warmer and disperse the fuel more rapidly increasing the air's saturation for that pocket. Valve opens it all gets sucked in. Now you have a pocket of rich fuel particles undispersed and a bubble of ignition ready 14.7 AFR. Go spark. Flame front travels normally across the sliver or dz. The flame front then encounters several things at the same time. It encounters the pocket of 14.7 that is hot and almost to ignition due to pressure, it encounters a pocket with too little fuel and is not quite ready to ignite(it needs a touch more pressure and heat) and a pocket that has fuel droplets(not in the vapor state). Flame front ignites the stoich mix, pressure increases on the lean section causing it to ignite and the flame front expands rapidly through both. Meanwhile the pressure climbs dramatically along with the temperature, but the increased pressure "holds" the droplets(or at least some small part of the droplets) from becoming a vapor. At that point the pressure is akin to that of diesels and the droplets literally explode, not ignition, but a pulse of pressure that rattles the block. This is how Isobaric bombs work. Fuel-air bombs are more dangerous against open air unarmored targets but in a closed system(caves or engine cylinders) causing the same fuel to detonate causes a much more devastating effect.

Any time ignition happens before your engine normally wants it to is pre-ignition. period. Even if it happens 1-2 degrees in advance of normal your engine will not survive more than a few strokes of it. If it occurs any more than about halfway through compression its toast and is likely to put your other cylinders in jeopardy from the heat soak of the molten slag.

[evolutionmovement]

I was only incorrect in my horribly unclear wording. While the ignition event during detonation may take place at the correct time of the piston cycle, the direction of the flame front(s) is still uncontrolled in that it does not ignite in the intended order. The ignition event is supposed to be a controlled burn from the spark plug out. Any part of the mix that ignites prior to the intended flame front reaching it would be sooner than anticipated, but not the same thing as pre-ignition, where an ignition source other than the spark plug initiates the event before intended ignition is to take place. I didn't mean to imply that they were the same. Hopefully, that's a little more clear.