Fuel combustion under compression alone VS combustion under heat

In summary: They use a fuel-air mixture that ignites through compression alone, rather than a spark. This allows for a more efficient combustion process and lower emissions. However, controlling the timing of the combustion can be challenging. In summary, the conversation discusses the possibility of using a fuel that would always explode at a certain compression ratio, regardless of air-fuel ratio, and the potential benefits and challenges of this concept. The mention of homogeneous charge compression ignition engines suggests a potential solution.
  • #1
timjustindodd
1
0
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
 
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  • #2
You might want to look into homogeneous charge compression ignition engines (HCCI).
 

1. What is the main difference between fuel combustion under compression alone and combustion under heat?

The main difference between these two types of combustion is the source of energy used to ignite the fuel. In fuel combustion under compression alone, the heat generated by compressing the fuel-air mixture is enough to ignite it. On the other hand, in combustion under heat, an external source of heat, such as a spark plug, is used to ignite the fuel.

2. Which type of combustion is more efficient?

In general, combustion under heat is more efficient than fuel combustion under compression alone. This is because an external source of heat can provide a more controlled and consistent level of heat, resulting in a more complete combustion process. However, the efficiency also depends on other factors such as the type of fuel and engine design.

3. What are the advantages and disadvantages of fuel combustion under compression alone?

One advantage of fuel combustion under compression alone is that it does not require an external source of heat, making it simpler and more cost-effective. However, this type of combustion also has its disadvantages. It can lead to incomplete combustion, which can result in higher emissions and reduced engine performance. It also requires a higher compression ratio, which can put more strain on the engine.

4. How does the compression ratio affect fuel combustion under compression alone?

The compression ratio plays a crucial role in fuel combustion under compression alone. A higher compression ratio means a higher pressure and temperature inside the engine, which can result in a more efficient combustion process. However, if the compression ratio is too high, it can also lead to engine knocking, which can damage the engine.

5. Which type of combustion is commonly used in modern engines?

In modern engines, combustion under heat is the most commonly used method. This is because it allows for better control and optimization of the combustion process, resulting in improved efficiency and lower emissions. However, some engines, such as diesel engines, still use fuel combustion under compression alone due to their high compression ratios.

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