OK, here's an approach that, by sacrificing about 5% Carnot efficiency,
minimizes risk of thermalization by maximizing the water to gas mass ratio.
Converting the methane to H2 and doing air separation the rocket is
non-cryogenic water-injected 2H2+O2:
Results
Propellant composition
Code Name mol Mass (g) Composition
976 WATER 7.0000 126.1070 2H 1O
458 HYDROGEN (GASEOUS) 2.0000 4.0318 2H
685 OXYGEN (GAS) 1.0000 31.9988 2O
Density : 1.285 g/cm^3
2 different elements
H O
Total mass: 162.137522 g
Enthalpy : -12348.27 kJ/kg
9 possible gazeous species
2 possible condensed species
CHAMBER THROAT EXIT
Pressure (atm) : 100.000 54.897 1.000
Temperature (K) : 835.059 733.670 284.038
H (kJ/kg) : -12348.266 -12565.137 -13449.670
U (kJ/kg) : -12733.668 -12903.745 -13580.760
G (kJ/kg) : -21020.564 -20184.487 -16399.475
S (kJ/(kg)(K) : 10.385 10.385 10.385
M (g/mol) : 18.015 18.015 18.015
(dLnV/dLnP)t : -1.00000 -1.00000 -1.00000
(dLnV/dLnT)p : 1.00000 1.00000 1.00000
Cp (kJ/(kg)(K)) : 2.17422 2.10419 1.86125
Cv (kJ/(kg)(K)) : 1.71270 1.64267 1.39973
Cp/Cv : 1.26947 1.28096 1.32973
Gamma : 1.26947 1.28096 1.32973
Vson (m/s) : 699.46859 658.59170 407.94142
Ae/At : 1.00000 9.43090
A/dotm (m/s/atm) : 9.36549 88.32507
C* (m/s) : 936.54934 936.54934
Cf : 0.70321 1.58474
Ivac (m/s) : 1172.73046 1572.51039
Isp (m/s) : 658.59170 1484.18532
Isp/g (s) : 67.15766 151.34478
Molar fractions
H2O 1.0000e+00 1.0000e+00 1.0000e+00
O2 2.1736e-06 2.1736e-06 2.1736e-06
On Tue, Apr 9, 2013 at 1:00 PM, James Bowery <[email protected]> wrote:
>
>
>
> On Tue, Apr 9, 2013 at 12:36 PM, Henry Spencer <[email protected]>wrote:
>
>> ...
>>
>> In a Kelvin generator (yet another name for the same thing), the droplets
>> are decelerated electrostatically. (Doing this will of course require
>> that the exhaust not be electrically conductive at that point.) That will
>> produce aerodynamic drag on the gas, but whether that will be enough to
>> decelerate the gas well is a good question. In a practical system the
>> droplet deceleration will probably have to be fairly abrupt, given the
>> high exhaust velocity and the short range of electrostatic forces in a
>> practical system, which doesn't augur well for gas deceleration. This
>> will mean high relative velocities between droplets and gas, which will
>> tend to cause friction heating of both, and atomization of the droplets.
>>
>
> The mass ratio of water to the gas it must drag down with it is 1:2 and it
> starts out at very low (near 0) vapor pressure.
>
> This mass ratio has to enter into the thermalization calculation (hence
> the efficiency).
>
> Its unclear how far one could take this mass ratio. For instance, by
> using an air separation prestage one could not only lower the gas in the
> plume to near 0, but one could increase the amount of water injected.
>
