Modern Diesel Fueling Strategies

[cRiPpLe_rOoStEr]

Originally Posted by freebeard

It's an invasive species in Oregon

It's also found in Rio Grande do Sul, where it ruined natural pastures. At least it seems to have some medical application on Bach flower remedies.

[Isaac Zachary]

Originally Posted by mpgmike

It is Avogadro's Law which states:



Therefore at any given temperature and pressure, whether the cylinder is filled with nitrogen, water vapor, carbon dioxide, or other, there will be a calculated number of molecules. Furthermore, 1 degree rise in temperature provides for the exact expansion rate regardless of the gas. It then boils down to how much thermal energy is required to raise the temperature of any given gas by 1 degree. This is Thermal Density.

While Avogadro's Law seems to be generally correct, it seems to me that there may be another factor we're overlooking here, or the small inconsistencies in this imprecise Law end up causing more pronounced effects in the extreme environment of an internal combustion engine.

I say this because the equation I quoted before is used in many places including many text books. It normally is used to identify the thermodynamic efficiency of a certain compression ratio. But it needs the heat capacity ratio of the working fluid (also known as the adiabatic index, the ratio of specific heats, or Laplace's coefficient) in order to work. Most people just set this to 1.4, the heat capacity ratio of Air or Nitrogen, but when you set it to a lower HCR, such as that of water vapor or CO2, the efficiency decreases in the calculation.

Another thing is that I've read in several places that Noble Gasses make the best working fluids for Stirling Engines. This places Neon, Argon and even Krypton at an advantage over other gasses such as water vapor and Nitrogen. Of course noble gasses have only one atom per molecule, but even though N2 should be better for a Stirling engine than Argon or Krypton, it apparently isn't.

The fact that different gasses can have different heat capacity ratios, that is, ratios of the heat capacity at constant pressure (CP) to heat capacity at constant volume (CV), suggests to me that Avogadro's Law may be overly simplified for use in every situation, especially calculating the efficiency of a working fluid in a combustion engine.

[Isaac Zachary]

https://www.youtube.com/watch?v=kZO-XQdBwqk

What did we do back when we didn't have YouTube?

[cRiPpLe_rOoStEr]

Originally Posted by Isaac Zachary

What did we do back when we didn't have YouTube?

Either consulting an encyclopaedia or attending supplemental classes after school.

[Piotrsko]

I have a shelf of aerodynamic books for newcommers, a shelf of automotive repair books, a shelf of cookbooks..........

The county library has shelves of books that make my head hurt trying to wrap around what they contain most of which aren't politically correct.

[mpgmike]

I've been rolling these thoughts through my mind for some time now. I keep coming back to the steam engine. Why did Watts choose steam over ambient air if the expansion properties of air exceed those of water vapor (steam)? Furthermore, why have many manufacturers continued to use water vapor in external combustion engines for hundreds of years since? If air has a greater expansion rate, why hasn't anybody figured that out??

[freebeard]

I've been rolling these thoughts through my mind for some time now.

For me it's that pure steam has aerostatic lift approximate to Helium: en.wikipedia.org/wiki/Thermal_airship

A lenticulat toroidal airframe: lynceans.org/wp-content/uploads/2021/09/Thermo-Skyships_hybrid-thermal-airships.pdf

How light can you make an insulative solar-thermal envelope?

[Isaac Zachary]

Originally Posted by mpgmike

I've been rolling these thoughts through my mind for some time now. I keep coming back to the steam engine. Why did Watts choose steam over ambient air if the expansion properties of air exceed those of water vapor (steam)? Furthermore, why have many manufacturers continued to use water vapor in external combustion engines for hundreds of years since? If air has a greater expansion rate, why hasn't anybody figured that out??

Gasoline and diesel engines do use air as the expansion medium. When gasoline powered cars became available the efficiency doubled over that of the current steam engines.

But it's not that steam is less efficient than air. Same for CO2 and other mediums. You can make up for the lost efficiency by means of a greater compression ratio and other methods. Even gasoline engines should be able to get better fuel efficiency with water injection, but only if the engine is designed for it. Just simply injecting water spray into the intake will usually lower engine efficiency. Increase the compression ratio and advance the ignition timing and water injection can make the engine more efficient beyond a level possible with just air.

I do believe that water is used in external combustion engines due to it's ability to keep temperatures down. If you add x amount of BTU's to water in a steam engine the steam may hit a few hundred degrees, whereas if it were air it would hit tens of thousands of degrees. This works in an internal combustion engine where the flame is right there and the heat wave is only temporary, but transferring tens of thousands of degrees to air through a heat exchanger would be extremely difficult.

Noble gasses are also touted as great working fluids that could substitute water, but are also expensive. Water is very abundant.

Hot air can explode when it reaches oiled parts, unlike steam.

[cRiPpLe_rOoStEr]

Originally Posted by mpgmike

Why did Watts choose steam over ambient air if the expansion properties of air exceed those of water vapor (steam)?

Most likely because water has a greater thermal conductibility than air, so the conversion of thermal energy into mechanical power would be more efficient.

[mpgmike]

Isn't that what we want inside a combustion chamber? Doesn't that explanation cover what an Expansion Medium is supposed to do?? Thank you!