I spent the day digging up lab reports on the subject of "The coefficient of expansion for gasses", "Thermal density for gasses", and several other search phrases. Whereas I would like to say I got an education, It's more like I'm rather confused now.
There is Boyle's and Charles' Laws, molecular density considerations, thermal conductivity, specific heat index at a given temperature, and some constants tossed in for good measure. Some perspectives seem to support some of your conclusions, but then others don't. However, none of them fully support my postulation either. I never did find your "k" factor you listed for the various gasses.
From what I can gather, there are 2 factors at play:
1) Thermal density of the molecule; how much BTU heat does it require to raise 1 mol of the gas 1 degree
2) Expansion factor for 1 degree rise in temperature. This overwhelmingly seems to be constant for all gasses.
The one consistency is that the larger the mass of the molecule, the more heat energy is required to raise the temperature of 1 mol by 1 degree. So, here is what I'm putting forth: First, let's establish the atomic mass for each of the players (rounded to the nearest whole number).
H = 1
C = 12
N = 14
O = 16
From this we can calculate the atomic mass for the molecules being discussed:
H2O = 18
N2 = 28
Air ~ 29 (79% N, 20% O, 1% He)
O2 = 32
CO2 = 38
Using the universal constant expansion rate for BTU input, we can therefore expect H2O to rise in measured temperature with the least thermal energy input. It then should be the most powerful expansion medium of the list. On the other end of the spectrum, CO2 will absorb the most thermal energy without raising in temperature. Thus, CO2 has the lowest coefficient of expansion per unit of energy input.
Avagadro's Law states that there will be the same number of molecules in any given volume at a given temperature and pressure, so that also supports the constant coefficient of expansion rate per temperature rise theory.
So the Report from my day's research can be summed up as:
1) Water vapor injection will enhance the Expansion Medium, delivering more power to the piston crown per unit of thermal energy released from the fuel.
2) Carbon Dioxide has the highest ability to reduce peak combustion temperatures, and thus reduce the formation of NOx
Am I getting closer?? Just so you guys know, once this discussion is concluded, I intend to go back to the
Ecoceptor site and update the
Combustion Efficiency page to reflect the results.