Regular gas for Volvo?

It would depend on the terrain and the cost of gas.

I'm talking about driving in mountainous country, or on a route with many smaller hills. I'mm jot "conflicting with myself".

(...)

You're mistaken. Octane is a measure of how volatile the gasoline is, and higher octane gas is less volatile - less explosive. That's why it lets the engine run with more advanced timing without knocking.

Octane is a flammable gas. Octane rating is an inverse measure of the rate of autoignition or more precisely:

"The octane rating is a measure of the autoignition resistance of gasoline (petrol) and other fuels used in spark-ignition internal combustion engines.

Octane is measured relative to a mixture of isooctane (2,2,4-trimethylpentane, an isomer of octane) and n-heptane. An

87-octane gasoline, for example, has the same knock resistance as a mixture of 87 vol-% isooctane and 13 vol-% n-heptane. This does not mean, however, that the gasoline actually should contain these chemicals in these proportions. It simply means that it has the same autoignition resistance as the described mixture.

The octane ratings of n-heptane and iso-octane are exactly 0 and 100, by definition.

A high tendency to autoignite, or low octane rating, is undesirable in a gasoline engine but desirable in a diesel engine. The standard for the combustion quality of diesel fuel is the cetane number. A diesel fuel with a high cetane number has a high tendency to autoignite, as is preferred. [Diesel fuel is not very volatile and very low octane.]

Typical "octane booster" additives include tetra-ethyl lead and toluene. Tetra-ethyl lead is easily decomposed to its component radicals, which react with the radicals from the fuel and oxygen that would start the combustion, thereby delaying ignition.

It might seem odd that fuels with higher octane ratings burn less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation (pre-ignition = engine knock) as opposed to the ability of the fuel to burn (combustion). However, premium grades of petrol often contain more energy per litre due to the composition of the fuel as well as increased octane.

Using a fuel with a higher octane lets an engine run at a higher compression without having problems with knock. Actual compression in the combustion chamber is determined by the compression ratio as well as the amount of air restriction in the intake manifold (manifold vacuum) as well as the barometric pressure which is a function of elevation and weather conditions.

Compression is directly related to power (see engine tuning), so engines that require higher octane usually deliver more power. Engine power is a function of the fuel as well as the engine design and is related to Octane ratings of the fuel... power is limited by the maximum amount of fuel-air mixture that can be stuffed into the combustion chamber. Furthermore, most gasoline vehicles today are variable compression. At partial load, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than what is available. It is only when the throttle is opened fully and the manifold pressure increases to atmospheric (or higher in the case of supercharged or turbocharged engines) that the full octane requirement is achieved.

Many high-performance engines are designed to operate with a high maximum compression and thus need a high quality (high energy) fuel usually associated with high octane numbers, and thus demand high-octane premium gasoline.

The power output of an engine depends on the energy content of its fuel, and this bears no simple relationship to the octane rating. A common myth amongst petrol consumers is that adding a higher octane fuel to a vehicle's engine will increase its performance and/or lessen its fuel consumption; this is mostly falseengines perform best when using fuel with the octane rating they were designed for and any increase in performance by using a fuel with a different octane rating is minimal."

See:

Octane is a flammable gas. Octane rating is an inverse measure of the rate of autoignition or more precisely:

"The octane rating is a measure of the autoignition resistance of gasoline (petrol) and other fuels used in spark-ignition internal combustion engines.

I'm not sure why you are so vociferous in agreeing with me, but, um, thanks.

Michael Cerkowski wrote:

You obviously don't understand the meaning of volatile. Volitility is:

"n 1: the property of changing readily from a solid or liquid to a vapor"

Some gasses have zero octane. They are nonflammable but they are always a vapor. Other gasses such as octane are 100 octane. No correlation. Zero. Kleine. Nichts. Geen. Rien. Nadie. Ingen. Nenhum. Gjinien. Nikdo. Neniom. Nullus.

Only on usenet....

I am talking about G.A.S.O.L.I.N.E. "Gas" is a commonly used term for "gasoline", and in this context that was quite clear. If you meant to waste my time, congrats. If you still think that what I write isn't what you read, that's your problem. Carry on.

And adding antiknock additives to GASOLINE doesn't change the volatility, just the octane. They are active chemical additives that work by slowing down the reaction, not physical chemical additives that change the vapor pressure. I quoted literature that shows this.

Find just one credible reference that shows there is a relationship between volatility and octane. There isn't one. Waving hands and cute chatter doesn't create one.

I am being persistent because many urban legends start by such misconceptions being posted as fact on USENET.

It won't knock because the computer will retard the timing. I use regular in non-turbos and mid or premium in turbos depending on how high the boost is turned up, works fine. A slightly overboosted 240 Turbo (no knock control) does ping on regular.