Petrol; agaín

Started by Petrus, August 15, 2022, 10:43

0 Members and 1 Guest are viewing this topic.

Petrus

Some of you may be aware that Spain has had a heat wave since late June and as it now is August, the hottest month of the year, basically still is in it.

The compression end temp is thé critical factor for detonation.
Putting the two together means that ambient temp. has an effect on potential detonation.

We have already amply covered the petrol vs ´performance´ of the engine and one conclusion was that the octane number does affect the way the engine delivers because the knock sensor will adjust the ignition timing. Meaning that it will adjust, dial up or down, power to the petrol.

Now add high ambient temps and ... indeed. Unless air density is down as much as the temp. is up, the knock sensor will dial the power down.
My car has the MAF mod. making this more prominent: I already noticed that the higher octane fuel allows the engine to run with more ingnition advance and pull stronger.

Although I am rather skeptical about fuel additives, I also know from experience with vintage engines that some octane boosters do boost the octane number.
With the stupidly high ambient temperatures here and normal barometric pressures, I wondered... and added octane booster to the Premium 98 RON (this only 89-90 MON).  WOW :o   

Ok, so it is not backed up by dyno readings.
Also fuel economy is affected by so many variables that the current improvement is not scientific fact.
Still, the perceíved difference is such that I think it worth the money  :'(  for my fun hobby car.










shnazzle

Remember that the car doesn't have an EGT sensor or cylinder pressure sensors.

Long before it gets to the point of knock control, it is using the intake air temp from the MAF to adjust the fueling. 
Next in line is o2. It will adjust it based on IAT and the effect of any change in barometric pressure, and then if it's still running lean, it will add some fuel to compensate and change timing accordingly.

It takes a LOT of advance to get the knock sensor to kick in. Ask me how I know.... ;)  It involved a piggyback ECU, bad quality fuel and a fair bit of stupidity on my part.

All in all, I would bet that if you did back/back dyno runs with intake temps between 25-40 degrees, you'd see a very minimal difference in power output.

The Toyota ECU is very good at making environment changes as invisible as possible.

...neutiquam erro.

Petrus

All well and good Patrick, but the issue is not the mixture in this case because of the emission parameters.
If mixture is used to reduce the compression end temp. then it will result in running rich.
 
The temperature in the combustion chamber is a key factor in detonating it.
This pressure is primarily a function of the compression of air sucked in. The compression being obviously a constant, the ambient temp. directly affects this.
Ignition is not ´explosive´ but a flame front moving through the combustion chamber. raising the pressure, possibly causing detonation elsewhere in the chamber.
Where the piston is in the cycle is crucial. Moving down will mean the chamber volume increasing and thus detonation risk deminishing. Thís makes the ignition timing crucial and related to ambient temp.

I do agree with your observation that the ECU will adjust the timing to the ambient temp. well before the knock sensor will need to step in.
I should have written this better. My appologies.
The point remains that the EU will adjust the advance of the ignition timing.

I do possibly disagree with your observation that this does not affect output.
In my decades of competition RAD has been just about a linear factor just as the mechanical compression ratio is.
Maybe we are talking on different tracks again.

Then we get to the crux.
You basically explain, imo correctly, that the octane rating of the engine is a parameter in the ECU tables and as such the ignition never maladjusted in a way needing a higher than specced rating. That a higher temp is well within the tables. No bone of contention there.
Enter the MAF mod designed to fool the ECU in thinking there is less flow than there is, thus advancing the timing outside of factory spec.
Cap Weir observed that this would need a higher octane rating ánd added that it would be more so with higher ambient temps.
I thínk my recently revised engine running here under the sun is a point in case.

Getting back to the knock sensor. When do you think (have seen) it doés step in?




shnazzle

Yup all makes sense. 
But wrt timing, it most definitely impacts pressure. Hence timing is adjusted with fueling. Exactly as you say, to account for difference in flame propagation as you add fuel.
But in this way the stock ECU can keep the burn efficient. Unfortunately it can only tell whether it is efficient or not by way of the narrowband o2 sensors. Which is a bit kak but hey ho.

It's been a hell of a long time since I messed about with the piggyback but I believe on the faithful day when I was knocking like an angry neighbour I was adding 8 deg advance over and above whatever stock was doing varying across the load range. No idea what the final number was, as I wasn't logging basically I got greedy. I advanced by a bit (3-4deg) and added about 7-8% fuel (essentially MAF mod) and the car felt great. Super responsive on the throttle, until the stock ECU overrode the fueling changes and I lost power due to the timing now being too advanced for the fueling.
Hence the piggyback ultimately got taken out.

But I pushed it too far and just shoved like +8deg advance in. Also, I messed with the MAF signal in a attempt to compensate for the off readings due to my aftermarket intake. That also messes with timing. Stupid piggyback. 

Anyway, all in all, lots of unpleasant noises and kangarooing but luckily managed to nurse the car to a petrol station whilst being told off by Helen the entire way and shoved 3 bottles of octane booster in. That helped and got me home, where I reset the map back to what it was. 



...neutiquam erro.

Alex Knight


I think you are experiencing a placebo.

Petrus

Quote from: Alex Knight on August 15, 2022, 16:13I think you are experiencing a placebo.

I could.

Still.
As Patrick confirms;  ´I advanced by a bit (3-4deg) and added about 7-8% fuel (essentially MAF mod) and the car felt great. Super responsive on the throttle, until the stock ECU overrode the fueling changes and I lost power due to the timing now being too advanced for the fueling.´ when you start messing with the parameters of the ECU tables...
Without the MAF mod, without the recent revision and without the messing with pump fuel, all compounded by the silly ambient temps, I would not even have gone there.

@shnazzle  ´Anyway, all in all, lots of unpleasant noises and kangarooing but luckily managed to nurse the car to a petrol station whilst being told off by Helen the entire way and shoved 3 bottles of octane booster in. That helped and got me home, where I reset the map back to what it was. ´
Good thing it placeboed the crap out of the issue  :))

Petrus

Went to the coast today.
The weather conditions almost chilly, some 28 degrees (I did write relatively), and humidity double: More air, more moisture, cooler combustion; só notable accelerating up the pass.
Complicated traffic of HGVs, overloaded MPVs from Morocco, faster cars and race driven delivery vans navigating the triple and double lanes merging halfway up the incline.
Ok, not quite driving in 3rd vs 4th gear but líke that; a shorter overall gearing:  More lively, responsive everything. Came in handy  ;)

No, the proper heat wave conditions here did the already not overpowered 1ZZ no favours.
Yes, am définitely staying with the 98 and possibly booster for hot conditions. With the mileage I do the cost is less than the extra fun.

Ardent

@Petrus

"With the mileage I do the cost is less than the extra fun."

Beautifully put. That simple.

Petrus

Quote from: Ardent on August 29, 2022, 19:57Beautifully put. That simple.

Thanks for the compliment.

It may appear differently  O:-)  , but I do like things to be simple  ;D

Ardent

From what you have shared here in  general about your life.

If that's your simple version.  :o

Petrus

Quote from: Ardent on August 29, 2022, 20:45From what you have shared here in  general about your life.

If that's your simple version.  :o

Well... looking around me seeing people with so called simple lives, mine is rather uncomplicated.