02-25-2006, 07:43 PM
Current practice is to utilize higher expansion ratios with conventional fuels. What if we looked at that from a different perspective? How about using conventional expansion ratios and lowering octane requirements. When you look at most of the emission problems we have are they from the gasoline or the additives we put in the fuel to increase the octane rating?
Almost every one agrees the high quality fuels will be the first to deplete. So maybe we have to get used to adapting to lower octane fuels. Doesn't change the fact that slowing down the burn rate at high load and increasing the burn rate at light load is the way to go. ( Patent 4,961,406 which was 15 years before Toyota somehow got a patent on the same thing 6,848,422)
03-07-2006, 12:41 PM
hey in a normal otto cycle, when you accelerate and there are "pumping" losses how do you know if these losses are irrvelerant? (ok maybe they are but can you reconize it when your driving, and how can it be prevented?)
03-07-2006, 02:30 PM
I don't think I completely understand your question.
High vacuum readings used to mean high efficiency but thats not true in an Atkinson cycle.
Does this help at all? http://modifiedatkinsoncycleengine.blogspot.com/
05-17-2006, 04:28 AM
I might be misunderstanding but I don't think expansion ratios are the problem. Compression ratios are the reason we can't use cheaper gas. In a "normal" engine expansion and compression ratios are the same but in an Atkinson they are different.
05-17-2006, 07:10 AM
The octane rating of a fuel simply refers to its resistance to ignition. The higher the octane, the harder it is to ignite it. In many ways a higher octane fuel is truly better than a lower octane fuel, but only if engine design takes advantage of it. Many manufacturers of high-performance cars take advantage of this by designing engines with a higher compression ratio. This squeezes the air/fuel mixture more than, say, my Honda, essentially adding heat to this mixture on the way. If you squeeze a mixture too much it can "detonate," which is the early bulk ignition of the mixture. In its ligher form, "pinging," detonation is just a sign that the engine is out of its operating parameters. At its worst, this can completely destroy an engine. But I digress...
The advantage of burning high octane fuel in a high compression engine is increased thermodynamic efficiency. This is the case for both the atkinson cycle and the otto cycle, though it matters less in the atkinson cycle since its efficiency is inherently very high. You can use this efficiency to make more power or you can use it to make an engine that uses less fuel; manufacturer's choice. So the take home message is that lower octane fuels won't really buy you anything.
05-17-2006, 02:25 PM
its a shame most 91 octane cars are designed with performance in mind and not efficency. I had dreams of my civic being optimized for 91 octane fuel and power ratings are the same but the effiency was well worth it even if it costed overall 5 bucks more to fill up the tank.