# Fuel combustion under compression alone VS combustion under heat

1. Jul 29, 2012

### timjustindodd

I'm just trying to figure out a theory. Forget what you know about a reciprocating piston engine, and just dream with me for a second. Say a piston could just turn around and come back down the cylinder at ANYTIME in the stroke, would the fuel always burn most efficiently?

It's hard to explain, but I'm looking to find out if there's a fuel in which you can add it to air (pre-chamber) and it will explode once it (and the air) reach a certain compression? I know diesel ignites when injected due to high heat (caused by compression), but say diesel was mixed pre-chamber, would it explode due to the heat or due to the compression?

For example, say you sent a piston up 100 times with diesel/fuel mix and kept the same A/F ratio, would it explode at the exact same point in the stroke every time? Or would it vary deeply depending on intake charge, engine operating temp etc etc? Would detonation always occur at an exact time or would it sometimes go off under only 30% stroke and the next stroke go off at 80% stroke or something like that?

Would that also change if the A/F changed? Say you had a 1:1 A/F ratio (I know ridiculously rich) would it EVER go off under even 50:1 CR? 100:1? What would it take? If it did go off, would it be VERY powerful, or would it be so rich it would be slow burning and weak?

Sorry I know this is weird and very hypothetical, but I'm trying to prove a theory here and I don't know enough about how diesel (or other fuels) work. If not diesel, is there another fuel that will explode every time, at an exact compression ratio (or near abouts) regardless of A/F?

So again, to recap, pretend I took 3 different chambers.

1. a 50:1 A/F around what CR would it eventually detonate at room temp? (in a perfect world with perfect seals, etc etc)

2. a 15:1 A/F around what CR would it detonate?

3. a 1:1 A/F, would it EVER detonate regardless of the CR?

Thanks guys! First post here, lots of good replies out there, I'm looking forward to hearing what you have to say!

Thanks :)

- Tim

2. Jul 30, 2012

### Aero51

You might want to look into homogeneous charge compression ignition engines (HCCI).