Diesel engine without injection pump

[Christophe]

In general, the octane number increases when:
- the length of the carbon chains decreases
- the number of secondary chains increases (for the same number of atoms of C)
- the number of cyclic structures (cycloalkanes and aromatics) increases

so if the reactor is cracking as many people think, it's normal for it to ignite less.

Completely agree I will simply say that for your third dash (increase in aromatics) this poses a problem: they resist the detonation so much that they are sources of unburnt enough. Oil tankers have a habit of adding aromatics which promotes the creation of unburnt ... (ppm HC)

Your remarks also mean that the simpler a compound, the better its octane number ... see the index of GNV octane 130 or methanol (which I don't know ... ethanol varies between 110 and 120 depending on the source ... I think methanol must exceed 140 ... advice to connoisseurs?) which allows incredible compression rates on a petrol engine (up to 17 - 18) and therefore better yields and lighter engines. These simple compounds have not only this advantage but also that of burning very easily (hence the danger of methanol) unlike aromatics.

So why the builders so reluctant to use on-board reformers that would ONLY have advantages (make a simpler fuel with a heavier fuel directly: better octane and better combustion) .... The answer must be found on the side of their friends the tankers ...

[Philippe Schutt]

the octane number is in the 150 (160 RON).
"Methanol is a very toxic substance. Its consumption can lead to blindness and even death." (Wikipedia)
Four milliliters can cause blindness and 80 to 150 milliliters of methanol can be fatal. About half a milliliter of methanol per kilogram of weight is fatal.
The problem is that the smell and taste are not repulsive enough. So do not put pure on the market. as long as to do, we prefer to use ethanol, which is not so harmful, and which is less volatile. hips!

[Vroom143]

From a safety point of view, methanol poses a big problem during combustion ... it burns making a barely visible flame and yet relatively hot, which makes it very dangerous in the event of an accident for example ...

It is not surprising that the octane rate is so high ... in model making, you have to add nitromethane so that the "glow plug" engines auto-ignite, and you have to see the volumetric ratios of these engines !!! (30/1 quite frequently ...)

[petitclamart]

Hello everybody

Your discussion on the octane number is very interesting for our reflections, but I am surprised that nobody has spoken of the flash point of a fuel. For the phenomenon of uncontrolled ignition (the very principle of diesel) to be triggered, the heat must be sufficient to ignite the fuel. It is for this reason that the compression ratios on a diesel are increased compared to a conventional gasoline engine (ie with spark ignition).
To be more precise, it is the rapid reduction in volume for the same amount of air that increases the heat, and when a fuel is injected into it, it ignites if the T ° is higher than its flash point.

In my own way, which is worth what it is worth, I will try to explain this phenomenon of temperature increase by compressing a volume.
Let us take two volumes which we will call A for one and B for the other.
Volume A is 1 m3 at 20 ° C. Inside, there is a certain amount of calories (therefore heat). This quantity is greater than the volume B making 1 cm3 at 20 ° C.
If we compressed A until it was only 1cm3 without losing heat, there would be more heat in A than in B while having the same volume. So it would be warmer ...

I don't know if I made myself clear.
It is true that it is not much to advance our pantonizations, but I believe that to remember bases of this kind can only help us to progress, and believe me, I am sure I will need it ...

Greetings to all

Petitclamart

[Philippe Schutt]

In fact, in a diesel one is higher than the flash point, see definition of the flash point

Flash point:
Lowest temperature at which the concentration of vapors emitted is sufficient to produce a deflagration on contact with a flame, spark or hot spot but insufficient to produce the propagation of combustion in the absence of " pilot flame "

rather it would be a classic gasoline engine setting.
does this flash point vary with the concentration of vapors?