View Full Version : Gas
I was wondering if someone would be willing to explain to me, in depth, the differences in diesel fuel and unleaded. I'm not sure of the differences. Let me know!
Diesel is a petroleum-based fuel, ignited by compression rather than spark; commonly used for heavy duty engines including buses and trucks.
Unleaded is unsurprisingly not treated with lead, so does'nt polute the atmosphere with lead compounds. Vehicles with a catalytic converter must use unleaded.
That's about as much detail as I could get into.
deus-redux
2007-04-24, 22:26
Different parts of oil.
Anyway, this isn't even GP material.
-deus-
fuel is made up opf carbon chains. you have short ones, like propane (four carbons) which is a gas. methane is just one carbon. unleaded is a mixture of chains 5-12 carbons long, deisel is 10-15.
they are pretty similar. diesel ignites itself under high pressure (temperature) and does not need a spark. this is because it has a lower autoignition temperature than petrol.
diesel burns far cleaner than petrol, producing less damaging emmisions even though it appears dirtier. it is also safer as it cannot be made to ignite below about 60C, whereas petrol is -42.
Prometheus
2007-04-26, 10:51
It's called unleaded because until the 70s it contained tetra ethyl lead to boost the octane rating. Now ethanol and other chemicals serve that purpose.
The main difference between gasoline and diesel is octane.
Gasoline has octane ratings from the mid 80s to over 100. Look at the pump some time.
Diesel has an octane rating between 10 and 15.
Octane is a measure of the ability to withstand pressure without detonating.
The scale is derived from heptane and octane. Of the straight chain hydrocarbons found in gasoline, heptane detonates at the lowest pressure, and octane the highest. The octane rating of gasoline measures detonation pressure as equal to the percentage of octane in an octane heptane mixture. An octane rating of 85 is equal to 85% octane, and 15% heptane.
The operational difference in gasoline and desiel engines is simple. Because desiel detonates at such low pressures, compression alone will detonate it. Thus, no spark plug needed. This is also why sports cars need high octane fuel. The compression is high enough to detonate low octane fuels.