The combination aluminum and water was theoretically analyzed to assess its performance potential for space propulsion, in particular for microrocket applications.Heat of reaction, impulse density, and handling safety are features making this combination interesting for chemical thrusters, especially since thrust is higher than typical of satellite electric thrusters and whenever a compact package is desirable.Ideal specific impulse (Isp), thrust coefficient, adiabatic flame temperature and combustion products were calculated for chamber pressures 1 to 10 atm, nozzle area ratios 25 to 100 and mixture ratios (O/F) 0.4 to 8.0. Isp reaches up to 3500 m/s. Also the effect of hydrogen peroxide addition to aluminum and water on performance was explored. This combination improves performance slightly at the expense of simplicity, making it less attractive for microrocket engines. Ignition delay times were conservatively estimated assuming aluminum coated with its oxide, and ignition occurring after melting of the aluminum oxide.To this purpose heating and kinetics times were evaluated, the first by a 1-D physical model, the second by a reduced scheme. Results indicate the heating time of a 0.1 µm diameter 2 aluminum particle may be of order 0.4 µs, while overall kinetics takes 10 µs: thus, the Al/water combination looks in principle practical for micro-rocket chambers, characterized by short residence times. burns in the vapor phase if its boiling temperature (2792.15 K for Al at 1 atm) is lower than the volatilization temperature of its oxide. In fact, for a liquid or solid fuel to burn as vapor, its flame temperature must be higher than its f uel saturation temperature, so that it can vaporize, diffuse towards the oxidizing atmosphere and react [Ref. 6]. Thus, were pure Al vapor to burn with O 2 , the adiabatic flame temperature would be much higher than the Al 2 O 3 boiling point and corresponding to the volatilization temperature (of order 3500 K at P = 1 atm). Actually, the flame temperature of an oxide-coated Al particle has instead an upper limit, that is, the boiling temperature of the oxide, since the boiling enthalpy of Al 2 O 3 is greater than that available, that is, the reaction enthalpy of Al (∆H R ° (298 K) = -404 kcal/mol for Al/O 2 ) minus the enthalpy required to heat Al 2 O 3 above its boiling point (see Table 1). Aluminum Alumina Melting temperature 933.52 K 2327 K Boiling temperature 2792.15 K 3273 K Volatilization temperature ______ 3450-4000 K Melting heat 2.57 kcal/mol Al 28.29 kcal/ mol Al2O3 Boiling heat 70 kcal/ mol Al 444 kcal/ mol Al2O3 Volatilization heat ______ 444 kcal/ mol Al2O3
