43

The purpose of this nozzle is to achieve maximum acceleration of the flow to obtain the highest possible exit velocity. The shape of convergent / divergent (de Laval) nozzles is dictated by the thermodynamic properties of gases. For a subsonic gas flow, a converging passage accelerates the flow. The physics are opposite for supersonic flows: they are ...


29

The short answer is no -- an internal combustion engine needs to pull oxygen from the air to operate, and no solid bodies in the solar system have that kind of atmosphere. Venus' atmosphere is mostly carbon dioxide with a small amount of nitrogen; neither of those is combustible. Mars, similarly, has a mostly inert atmosphere; there's a trace of oxygen ...


22

The gas at the narrowest part (the throat) of a convergent-divergent nozzle used in a rocket engine is ideally moving at the Mach 1, the speed of sound. This creates a choked flow condition. After the throat, the gas expands, the temperature drops, and because of the Venturi effect, it speeds to beyond Mach 1. A convergent-divergent nozzle thusly converts ...


19

Short answer: no, it won't increase the performance of the rocket. Platinum (or other catalysts) can be used in fuel cells, where the purpose is to get a chemical reaction at (relatively) lower temperatures. That means without having to burn the gases, in other words. (It achieves this by reducing the "activation energy" of the reaction as the question ...


18

You've got it slightly incorrect. Staged combustion engines pre-burn the propellants at a higher, not lower pressure than the main chamber. The exhaust from the preburner isn't pumped into the main chamber but flows through the turbine, dropping in pressure there and in the ducting before it enters the main chamber. The preburners generally run at a lower ...


18

The pressure sensors do need to be shielded somehow from the full fury of the combustion chamber. Here's a schematic showing the connection of the Space Shuttle Main Engine chamber pressure (Pc) sensors to the combustion chamber. You can see that the Pc sensor is not connected directly to the chamber, but interfaces with it via a hole drilled up to one of ...


17

For the Space Shuttle Main Engine, four checks were done to set the "Ignition Confirmed" condition. The High Pressure Fuel Turbopump shaft speed was checked against a minimum limit. The Main Combustion Chamber pressure was checked twice, once against a minimum limit, and once to ensure it was between an upper and lower bound. The Antiflood Valve was checked ...


14

The main reason for this is the temperature. Depending on the actual fuel the temperature in the main combustion chamber can be above 3000K. However, in the gas generator the temperature is kept below 1400-1600K. These lower gas temperatures allow uncooled chamber construction and prevent melting or limit the erosion of turbine blades. Source: Sutton - ...


10

I'm going to start off with a warning: if you want to get started with model rocketry, it is about a thousand times safer and easier to start with off-the-shelf solid rockets. Don't even consider trying to build your own liquid fueled engine until you've learned a lot more. That said, reaching the RP-1 specification from commercial kerosene is probably ...


10

In early versions of the Space Shuttle Main Engine (SSME), the main injector was baffled. The baffles were formed by extra-long liquid oxygen posts protruding from the injector face. Block IA engines and later removed the baffles. (See "Taxonomy of the SSME" in this answer.) The injectors on the preburners were also baffled in a similar manner. As far as ...


9

There are three types of aerospace detonation engines I heard of, one of which being an air-breather. The first one is a variant of the Shock-Induced Combustion Ramjet, or Shcramjet (and yes, I also read Schramjet the first three times) named the Oblique Detonation Wave Engine (ODWE). A shcramjet is a variant of the hypersonic scramjet, where H2 fuel is ...


8

There is one flight-tested engine that uses the design you're suggesting: the Blue Origin BE-3. It is a liguid hydrogen/liguid oxygen fueled engine that produces 110,000 lbf of thrust (throttleable to 20,000 lbf). It powers the New Shepard suborbital launch vehicle, which was first flown on April 29, 2015, and then contributed in the first ever soft ...


8

The combustion of propellants is an exothermic process, it mainly provides heat. Initial velocity (think of the turbo pumps) and the changed specific gas constant of the combustion product are negligible. Heat also translates into pressure via the gas law. Heat and pressure are somewhat useless once the exhaust gas does not interact with our rocket any more....


8

$v_{\rm injection}$ of liquids, as a rule of thumb, doesn't get higher than 10 m/s (dictated by a general limitation of pressure losses). Given that exhaust velocity could be 2500 - 4500 m/s, you can calculate the ratio. For gaseous fuel/oxidizer it's of course different. Now, where to get that original estimation...


7

According to the super-detailed and very informative NASA-CR 165404 Fuel/Oxidizer-Rich High-Pressure Preburners, the primary advantages of hydrocarbon-fueled oxidizer-rich staged-combustion engines is that "carbon formation, coking, and the attainment of ignition are no longer issues." (page 133) This useful rocket engine cycle overview presentation from ...


7

Mixing oxygen and hydrogen at ambient temperature doesn't do anything exciting -- it just yields a mix of the two gases. In the presence of sufficient heat, mixed oxygen and hydrogen will burn, combining into (mostly) water vapor and releasing still more heat, which maintains the reaction. This is technically called combustion and is much the same as what ...


6

Hydrogen-oxygen fuel cells, such as SOFC, have maximum specific energy density of ~ 17.9 MJ/kg (using 142 MJ/kg for compressed hydrogen and including oxygen at 1:7.93 2H-O mass fraction yielding water at a stoichiometrically perfect air to fuel ratio). Other chemical components yield lower specific energy density since they're using higher molar mass fuels. ...


6

It would work, but it would be far from optimal. Heat recovered from the nozzle would result in steam much colder than combustion chamber temperature (after all, we never allow the nozzle to reach these temperatures, that's what cooling is all about, so the steam wouldn't heat to temperatures higher than the nozzle). That would cool the combustion products, ...


6

It seems unlikely in principle Standard combustion engines rely on burning fuel in an oxidiser taken from the atmosphere. On earth we have an atmosphere which is about one fifth oxygen which does a good job in engines. We haven't yet observed any planets anywhere with a large supply of oxygen in their atmosphere. And there is a good reason for that. Oxygen ...


6

I assume you talk about average static pressure, not total pressure or high frequency acoustics. If this is untrue then please clarify the question. A boundary layer gets it's pressure from the main flow. Therefore it is not necessary to hold a pressure tap into the main flow. A thin tube (a capillary) is attached radially to the side wall. The longer the ...


6

You can referthis book Modern Engineering for Design of Liquid-Propellant Rocket Engines chapter 4. It depends the on the number of performance parameters such as $C_f, C^*$ and $I_{sp}$. From which the Throat area is calculated. Throat area is usually used as a starting point to have the thrust chamber dimensions. Characteristic length and Contraction ...


6

How do you confirm ignition in the combustion chamber of a rocket? Sometimes, you don't. Pressure sensors, flow sensors, and such are yet another device that can fail. Moreover, what if nothing can be done / needs to be done if ignition fails to occur? In the case of the Shuttle (Organic Marble's answer), all three main engines were needed for launch. ...


6

Wikipedia says of the composition of the lower atmosphere: Because methane condenses out of Titan's atmosphere at high altitudes, its abundance increases as one descends below the tropopause at an altitude of 32 km, leveling off at a value of 4.9% [the rest is mostly nitrogen] between 8 km and the surface. and in a separate article The average ...


5

In our solar system? No. None of the other planets would support a standard ICE from earth. In other systems? We think we've found some other earth like planets which are in the habitable zone which should support ICE's but no one has visited them yet and we lack the ability to directly measure the relevant characteristics. https://en.wikipedia.org/wiki/...


5

You're missing one thing: the combustion chamber (hidden behind the piping at the top of the photo). Here's a cross-section of a rocket engine: Thrust is defined as: F = qVe +(Pe-Pa)Ae F = thrust force q = the amount of mass going out Ve = exhaust velocity Pe = pressure at the nozzle end Pa = ambient pressure Ae = area of the nozzle end Edit to ...


5

Restartable hydrogen-oxygen engines like the RL10 (used on the Delta and Atlas upper stages) and J-2 (used on Saturn) use spark ignition. On the J-2, the spark igniter is positioned above the fuel injector face, in a small chamber above the main combustion chamber. It's apparently uncooled and actually operates continuously during engine firing. Presumably ...


4

I'm guessing, you are familiar with CEA, right? It's a nifty tool that you can use to calculate equilibrium chemistry and its effect on rocket combustion. By fiddling with the inputs, you should be able to answer all your questions.


4

The idea of using a high-power source of electricity to increase the thrust of an ion thruster is definitely sound, but inefficiency in transforming chemical energy to electrical energy is really the limiting factor. Add to that the complexity of the propulsion system, which translates into increased mass and hence lower overall Delta-V for the same amount ...


4

tl;dr: Gases can take up from hundreds to a thousand times the volume than their liquid counterparts, even at their boiling point. Pipes for these gasses would be too huge to even fit in the rocket. Because cryogenic propellants are challenging to keep cold in rockets where every bit of weight used for cryogenic storage would mean roughly 20 to 50 times ...


4

It is possible that the platinum would improve the performance, but not in the way you're thinking. Metal particles in rocket fuels have been used experimentally as a way of increasing the density impulse. This is discussed in chapter 12 of Ignition: an Informal History of Liquid Rocket Propellants by John D. Clark (available in PDF on the Internet if you ...


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