Patent Application
20230323838
A typical rocket thruster employs a de Laval nozzle, which is a convergent-divergent nozzle. At the smallest point of convergence, where the velocity of the exhaust gas is greatest, the flow of exhaust gas is limited and becomes choked. Attempts to increase a mass flow rate may result in exceeding the limits of the pressure chamber.
Embodiments disclosed herein use monopropellants and not requiring a pressure chamber to produce thrust in a rocket engine. In a first aspect, a monopropellant rocket thruster includes a thruster, a pump, a decomposition catalyst, and an igniter. The thruster housing includes a reaction chamber and a divergent nozzle. The pump, coupled to the thruster housing, is operable to pump a monopropellant liquid into an inlet of the reaction chamber. The decomposition catalyst, located near the inlet between the pump and the reaction chamber, is configured to decompose at least one component of the monopropellant liquid into a mixture of liquid and gas in an exothermic reaction. The igniter is disposed at an outlet of the reaction chamber, such that the igniter ignites the mixture of liquid and gas for producing expanding gas into the divergent nozzle.
In a second aspect, a method for producing thrust in a rocket thruster includes (i) pumping a monopropellant liquid into an inlet of a reaction chamber of the rocket thruster; (ii) decomposing at least one component of the monopropellant liquid into a mixture of liquid and gas in an exothermic reaction using a catalyst near an inlet of the reaction chamber; and (iii) igniting the mixture of liquid and gas near an outlet of the reaction chamber for producing expanding gas into a divergent nozzle of the rocket thruster.
Reference throughout this specification to “one example” or “one embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present invention. Thus, the appearances of the phrases “in one example” or “in one embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more examples.
where ṁ is mass flow rate, and νe is exit velocity at nozzle exit. Current rocket technology attempts to maximize the exhaust temperature, which increases the speed of sound in the exhaust gas, which may then increase the maximum velocity of the rocket.
Embodiments disclosed hereinbelow describe a monopropellant thruster, which improves upon thruster 100 and remedies the limit imposed by the choked flow by, in part, removing the need for a convergent nozzle.
Without a convergent nozzle, the monopropellant is not intended to be in gas form as it traverses reaction chamber 202 before being ignited by ignition system 250. Consequently, the choked flow limit on the amount of mass per second that can leave the thruster no longer applies but instead relates to the temperature and vapor pressure in the liquid mixture. As monopropellant liquid-gas mixture 215 exits reaction chamber 202 into divergent nozzle 226, it undergoes a phase transition and becomes a gas. The back pressure of the exhaust gas at this transition point does not choke the flow of the liquid, and any pressure can be overcome with pump 212. Advantageously, the phase change from liquid to gas causes the volume to expand and results in increase in pressure and velocity, resulting in the thruster to produce force as the combination of this velocity and an unchoked mass per second.
In an example of operation, pump 212 pumps monopropellant liquid 213 into reaction chamber 202. In embodiments, and in the following description, monopropellant liquid 213 is a mixture of liquid that includes hydrogen peroxide, water, and ethanol that are well-mixed. Ethanol may also be any miscible fuel, such as methanol and propanol. As monopropellant liquid 213 passes in liquid form from inlet 232 through decomposition catalyst 220, hydrogen peroxide decomposes into water and oxygen in an exothermic reaction. The temperature increase from the reaction raises the temperature of the monopropellant mixtures to at least 80° C., which in turn phase-changes ethanol in the mixture into gas. The resulting liquid-gas mixture 215 passes through ignition system 250, which ignites oxygen and ethanol that are diffused throughout liquid-gas mixture 215, and results in an ignited mixture 216. The additional increase in temperature from the ignition phase-changes water into steam, which in the form of expanding gas 217 provides thrust.
In embodiments, the composition of liquid-gas mixture 215 is optimized to reach a sufficient concentration of phase-changed ethanol gas for thrust after the decomposition of hydrogen peroxide. For example, to reach the boiling point of ethanol, hydrogen peroxide concentration needs to be above 27% weight per weight (w/w). Additionally, to generate sufficient energy to phase-change water, ethanol may be added to reach 10% w/w to a mixture of 45% w/w of hydrogen peroxide. Other optimization points or alternate choices of fuel components may require different ratios of components.
At the point of ignition, liquid-gas mixture 215 may be mostly liquid water with bubbles of oxygen and ethanol. Because the ethanol and reaction oxygen start in solution, they become gases while still diffused in the propellant. The gases have a much higher dielectric constant than the liquid water, which means that the path of least resistance will be through the bubbles, such that the spark may jump around as a result. Accordingly, the electrodes may experience electrical stress from this process.
In an example use of the thruster disclosed herein, monopropellant rocket thruster 200 may be scaled up by pumping propellant through the system. For example, with optimized pump size and monopropellant mixture, the thruster may generate up to 15,550 Newtons of thrust with a specific impulse of 1,342 seconds. Current rockets have a specific impulse of approximately 360 seconds.
Step 420 includes decomposing at least one component of the monopropellant liquid into a mixture of liquid and gas in an exothermic reaction using a catalyst near the inlet of the reaction chamber. In an example of step 420, as pumped monopropellant liquid 213 of step 410 passes decomposition catalyst 220, hydrogen peroxide in monopropellant liquid 213 decomposes into water and oxygen gas producing heat in an exothermic reaction. The heat produced from the reaction phase-changes ethanol in monopropellant liquid 213 into gas resulting in liquid-gas mixture 215 that may include water, oxygen gas, and ethanol gas. Liquid-gas mixture 215 then continues to flow from decomposition catalyst 220 toward ignition system 250 in reaction chamber 202.
Step 430 includes igniting the mixture of liquid and gas near an outlet of the reaction chamber for producing an expanding gas into a divergent nozzle of the rocket thruster. In an example of step 430, ignition system 350 in
Changes may be made in the above methods and systems without departing from the scope of the present embodiments. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. Herein, and unless otherwise indicated the phrase “in embodiments” is equivalent to the phrase “in certain embodiments,” and does not refer to all embodiments. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.
This application claims priority to U.S. Provisional Application No. 63/269,494, filed on Mar. 17, 2022. The application is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63269494 | Mar 2022 | US |
