How does high octane fuel improve performance?

[finetuning]

Hi,

How does high octane improves performance?

Lets understand how octane rating affects engine performance.We all know as kilometers being added in new engine deposites stars accumulating on pistons,valves & combustion chamber.This is almost unavoidable.A dirty engine there after needs more octane fuel in order not to knock then the normal one.Put it simply octane rating of an older engine(higher deposites) is simply more then the cleaner engine.So say a clean engine with octane reating of 87 may function well till it gets accumulation of carbons & there after it starts demanding higher octane to perform well.

Now ths phenomenon gets into equilibrium at certain octane level.Means octane demand is saturated at certain level.This is different for different cars of same model & make.

So when we use higher octane fuel in our used car we feel slight increase in performance.

Apart from this aspect stock compression ratio do come into picture.Car is designed with certain specific CR which support certain octane rated fuel to give maximum benefits.Trend is upward now.So we see more higher CR cars demanding more octane rating.

RON of an engine totally depends upon CR when car is out from factory there after with carbon accumulation this rating goes up to maintain the performance.

[atul.singhal]

What is Fucon Fuel energizer device. Where can we get it? Can this be fixed for diesel cars also. How does it do its job......sounds interesting. In this age of Power and Speed fuel we still have a energizer in form of a device. can I have more information on this device

Cheers
Atul

Originally Posted by Roshun

Hi,
I have a 2002 model Wagon R Lxi. Till very recently I used to use only Speed 93 in the car... and managed to get 14.5 kmpl constant in the city (Delhi) with the AC on (all summer). But for the past 2 months, I've shifted to Speed 97 (It's a tad expensive, but worth it!). Now, that its getting cold around here I don't use the AC that much. The car gives about 16.3 (tankful to tankful calc) in the city. But the best part is the very smooth power delivery. It pulls away cleanly without knocking, and less downshifting needed.

I did a recent day trip to Jaipur (on a full tank of 97)... a round trip of 540 km. With intermittent use of the AC & some crowded city streets (around the Hawa Mahal)... as well as a constant 100 kph on the highway... the car averaged 18.6 kmpl (tankful to tankful). I kept a bottle of STP Octane booster handy (Speed 97 is not available in Jaipur), but didn't have to risk filling there... as the car got me there & back on a single tank.

Cheers,
Roshun

p.s: The car also has a fucon fuel energizer device fitted (apparently keeps carbon deposits down).

[rks]

After doing some research on the internet, one can conclude that this is a very controversial topic. Here is a website that suggests using higher octane fuels on older cars (whose engines have run at least 30000-50000 kms):

The Hindu : Metro Plus Vijayawada / Wheels : On a higher octane

The higher the compression of an engine, the higher its `octane requirement' and the more power it makes. But does it make any sense to put in higher-than-specified octane fuel into you car if your engine isn't knocking? Logically speaking, no. But real-world conditions are different. Factors like the deposits of carbon and drop in octane at petrol pumps play a role here. In fact, a number of studies have shown that cars that have done between 30,000 and 50,000 km could require additional octane, unless you decarbonize the engine regularly by using fuels like Speed and Power.

We tested fuels using a Honda City, a car with a comparatively high compression engine ratio of 10.5:1. The car was run on two types of fuels - 87 and 93 octane. As if to prove the point, the City performed much better with octane 93, 0.57 seconds quicker in a 0-100 kph run on the higher-octane fuel. Using higher-octane fuel, we also noticed that the engine fired the spark plug earlier for better power and performance.

Overall, the best way for you to ensure that your engine does not knock is to use petrol with detergents in them (like Speed and Power). This in turn lowers the engine's octane rating by clearing out a lot of carbon deposits that lead by knocking in the engine. Also a point to remember here is that the octane number requirement is reduced if you have an aluminium head, as it is a better conductor of heat and runs cooler. So the next time, remember to tank up with higher-octane fuel. It's certainly more expensive but will ensure the engine will enjoy a longer, happier innings.

Of course there are many other opinions on the internet which claim that one should not use higher-than-recommended octane fuel.

I have switched over to Speed 97 for my old Santro (65000 kms). There is a marginal improvement in performance and not much change in fuel economy as per my perception. Important point is that Speed 97 is almost guaranteed to be unadulterated as it is supplied mainly in company-operated bunks with not too many takers for it.

[vid6639]

Not really rks, I remember here in bangalore there was a racket with speed 97 being adulterated or it was speed 93 being sold as 97 and some expensive cars gave problems because of which.

For india manufacturers reduce the compression to compensate for the poor fuel quality. If you use the higher octane on a low compression engine your kind of running it rich in a way speaking.

Only top end cars like the merc's and bmw's need the 97 octane.

You may not do much harm but your not doing any good either.

[sgiitk]

Old logic was that there is no harm as long as the engine does not knock. Today most cars have knock sensors which retard timing as soon as knock is detected. Result - reduced power and higher consumption. For best performance and consumption you want the ignition as far advanced as possible.

A brand new engine has lower Octane requirements that an older engine (hot spots developing). When an engine is getting really worn the requirements again drop due to reduced compression.

To add to the confusion Octane rating also depends on whether you are buying fuel in a Euro III city or a Euro II city.

Euro III petrol has to be min 91ON. Euro II is 88ON but IOC XP is 93ON.

Thus forgetting 97 ON, in a Euro III city you get 91ON (93 is the same within errors), whatever you buy. In Euro II towns you get 88ON premium or regular exceptIOC Xtra Premium which is 93ON.

Add to this the confusion caused by the blending of 10% Ethanol in some states.

[Magnan]

What is Compression Ratio ? Can it be increased ? If yes, how ?.

[Rehaan]

Originally Posted by Magnan

What is Compression Ratio ? Can it be increased ? If yes, how ?.

Find your answers here :
http://www.team-bhp.com/forum/techni...ion-ratio.html (Is it possible to increase the compression ratio)

cya
R

[dadu]

For engine knock and related insight , read here (A Guide On Technical Jargons)

Originally Posted by sgiitk

Old logic was that there is no harm as long as the engine does not knock. Today most cars have knock sensors which retard timing as soon as knock is detected. Result - reduced power and higher consumption. For best performance and consumption you want the ignition as far advanced as possible.

For insight into Indian fuel specifications read here (TechSpec® : Diesel Fuel and the role of Cetane in Engine performance)

Originally Posted by sgiitk

A brand new engine has lower Octane requirements that an older engine (hot spots developing). When an engine is getting really worn the requirements again drop due to reduced compression.

To add to the confusion Octane rating also depends on whether you are buying fuel in a Euro III city or a Euro II city.

Euro III petrol has to be min 91ON. Euro II is 88ON but IOC XP is 93ON.

Thus forgetting 97 ON, in a Euro III city you get 91ON (93 is the same within errors), whatever you buy. In Euro II towns you get 88ON premium or regular exceptIOC Xtra Premium which is 93ON.

Add to this the confusion caused by the blending of 10% Ethanol in some states.

For Octane booster (not detergent cleaners !!), read here (Octane / Cetane booster - MP6Ty)

[bharatbs]

Any idea what is the octane rating for the Shell Premium fuel which costs a little more than Rs58 .... Bangy boys please reply?

[Sankar]

So does the compression ratio of you engine really warrant a high octane fuel?

Here's a table with recommended octane rating for the compression ratio. This is for a typical carb engine without engine management. The chart is just to give an idea regarding compression ratio and octane need.

Compression Ratio=======Octane Number=======Brake Thermal Efficiency(Full Throttle )

5:1 ======================= 72 ================ -
6:1 ======================= 81 ================ 25 %
7:1 ======================= 87 ================ 28 %
8:1 ======================= 92 ================ 30 %
9:1 ======================= 96 ================ 32 %
10:1 ====================== 100 =============== 33 %
11:1 ====================== 104 =============== 34 %
12:1 ====================== 108 =============== 35 %

This chart is for simple carb engines without knock sensors. So engines with ecu, fi & knock sensors can really drive around on lower octane fuels.

Here's the source with more information: http://www.faqs.org/faqs/autos/gasol...section-1.html

[rks]

Originally Posted by Sankar

So does the compression ratio of you engine really warrant a high octane fuel?


Compression Ratio=======Octane Number=======Brake Thermal Efficiency(Full Throttle )

5:1 ======================= 72 ================ -
6:1 ======================= 81 ================ 25 %
7:1 ======================= 87 ================ 28 %
8:1 ======================= 92 ================ 30 %
9:1 ======================= 96 ================ 32 %
10:1 ====================== 100 =============== 33 %
11:1 ====================== 104 =============== 34 %
12:1 ====================== 108 =============== 35 %

This chart is for simple carb engines without knock sensors. So engines with ecu, fi & knock sensors can really drive around on lower octane fuels.

Santro's compression ratio is 8.9:1. So this table confirms that Speed 97 is appropriate. I find a definite improvement in performance with Speed 97.

[Sankar]

But probably the manufacturer would've retarded the timing of the Santro so as to cope with our lower octane rated fuel. Santro should be happy if not with 87 then with 91 at the most.


Ignition timing also play a major part when it comes to choosing the right fuel for your engine. So don't just go by this chart. Manufacturer recommended fuel would be the best choice if you have a stock engine.

[rks]

Originally Posted by Sankar

But probably the manufacturer would've retarded the timing of the Santro so as to cope with our lower octane rated fuel. Santro should be happy if not with 87 then with 91 at the most.

Ignition timing also play a major part when it comes to choosing the right fuel for your engine. So don't just go by this chart. Manufacturer recommended fuel would be the best choice if you have a stock engine.

What I read was that almost any modern car wtih knock sensors and ECU will be able to adjust to the higher octane fuel. In addition, if the car has a high enough compression ratio, the performance ought to improve, as confirmed by the chart.

There is no doubt in my mind that the perfomance has improved noticeably with Speed 97 and the engine seems to run smoother at high speeds. Yesterday I hit 120 kmph (with something to spare) on the way to the IPL game in the stretch prior to Vashi bridge, with 5 people in the car and AC on. I think the problem with normal Speed is that the quality seems to be highly variable and there were days when the car really struggled. Now with Speed 97 the car's performance is much more consistent, and when I am driving alone, it is straining at the leash to hit 140+ speeds on the Expressway.

[Sankar]

As far as my understanding the ECU cannot detect the octane rating of the fuel. But it can detect the engine knocking, so if the engine knocks with a lower octane fuel the ECU would retard the ignition timing curve. And if the engine does not knock it will use the optimum ignition timing which is hardcoded into it's brain. So if you use a higher octane fuel ECU is not going to re adjust the ignition timing from the set factory optimum to utilise the higher octane fuel fed to the engine.

So imo if the engine runs without an knocks on 91 octane the ECU would use the optimum factory set timing curve. And if you use the 97octane and the engine does not detect any knocks and it will still use the optimum factory set timing curve which would be the same timing curve as the ecu used with 91 octane.

[ravikn]

does this mean LPG is more efficient fuel and should be used as it is 101 octane