Car things (Why does lead increase the octane rating)?

[FiggelHorn]

Hey guys and girls

The first thing I should probably ask is why do fuels (Hydrocarbons) spontaneously ignite when they are compressed, this seems rather strange to my brain in fact it makes my brain feel like it's having a meltdown (if you have ever had that feeling). The whole idea confuses me, what I understand of heat is that it is the average kinetic energy of the substance so how does compressing the substance increase its heat energy that much?

My main question is actually how lead relates to this, how it stops this process from happening?

Since I already started a thread I might as well ask if you happen to know, premium unleaded assuming it has an octane rating of 95 does that mean it has 95% octane and 5% heptane?

FIY - this is for a chemistry assignment; we are currently doing the gas laws etc. so we have to relate all the chemistry (stoichiometry) and the gas law things back to a car engine.

So I choose to compare the carbon emissions of a diesel CX-7 with a premium unleaded one. Rather complex chemistry for year 11 in my opinion, not that I'm complaining I have always like chemistry thinking about going to uni and studying something to do with chemistry when I finish school . . . that is if I live to see that day

 

[Borek]

1. When you compress the gas, you do work on this gas - no wonder it heats up.

2. It is not lead. Check wikipedia entry on leaded gas.

3. No, octane rating of 95 doesn't meant it has 95% octane and 5% heptane. Check wikipedia entry on octane rating.

In general - remember: library first, wiki/google second, ask on forums third! Answers to your questions are easily available from many sites.