RP-1

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RP-1 (alternately, Rocket Propellant-1 or Refined Petroleum-1 ) is a very fine form of kerosene similar to the material jet fuel, used as a rocket fuel. RP-1 has a specific impulse lower than liquid hydrogen (LH ₂), but is cheaper, stable at room temperature, much less than the dangers of explosion, and much denser. RP-1 is significantly stronger than LH ₂ by volume. RP-1 also has a toxicity fraction and a carcinogenic hazard of hydrazine, another room temperature fuel.

Video RP-1

Uses and history

RP-1 is most often burned with LOX (liquid oxygen) as an oxidizer, although other oxidations have also been used. RP-1 is fuel on the first stage riders of Soyuz-FG, Zenit, Delta I-III, Atlas, Falcon 9, Antares and Tronador II rockets. It also supported the first stages of Energia, Titan I, Saturn I and IB, and Saturn V. ISRO also developed RP-1 fueled engines for future rockets.

During and immediately after World War II, alcohol (mainly ethanol, sometimes methanol) was the most common fuel for large liquid-fueled rockets. Their high evaporative heat makes the regenerated refrigerant engine from melting, especially considering that alcohol typically contains a few percent water. However, it is recognized that hydrocarbon fuel will increase engine efficiency, due to slightly higher density, lack of oxygen atoms in fuel molecules, and negligible water content. Whatever hydrocarbon is selected, it must replicate the cooling ability of the alcohol.

Many early rockets burned kerosene but as time burns, combustion efficiency, and combustion chamber pressure increases, engine mass decreases causing uncontrolled engine temperatures. Raw kerosene used as a coolant tends to separate and polymerize. Light products in the form of gas bubbles cause cavitation, and heavy in the form of a wax deposit block the narrow cooling conduit in the machine. The resulting cooling hunger increases the temperature even further, and causes more polymerization that accelerates the damage. This cycle is rapidly increasing (ie, thermal runaway) until the breakage of the machine wall or other mechanical failure occurs, and it continues even when the entire cooling stream comprises kerosene. In the mid-1950s, rocket designers turned to chemical engineers to formulate heat-resistant hydrocarbons, which resulted in RP-1.

Maps RP-1

Fraction and formulation

First, sulfur compounds are very limited. A small amount of sulfur is naturally present in fossil fuels. It is known that sulfur and sulfur compounds attack metals at high temperatures. In addition, even small amounts of sulfur help polymerization.

Alken and aromatics are dropped to very low levels. These unsaturated hydrocarbons tend to polymerize not only at temperatures, but over long storage periods. At the time, it was thought that oil-fuel missiles would probably remain for years waiting for activation. This function is then transferred to solid fuel rockets, although the high temperature benefits of saturated hydrocarbons persist. Because alkene and aromatics are low, RP-1 is less toxic than jet and diesel fuel, and much more toxic than gasoline.

More preferred isomers are selected or synthesized. Linear alkanes are removed for branched and cyclic molecules. This increases the resistance to thermal disturbance, as this type of isomer increases the octane rating in the piston engine. Jet engines and heating and lighting applications, previous users of kerosene, are not too concerned with heat damage and isomers. The most desirable isomers are polycyclic, loosely resembling ladderanes.

In production, this value is strictly processed to remove impurities and side fractions. Ash is feared to block fuel lines and engine conduits, as well as worn valves and turbopump pads lubricated by fuel. Fractions that are too heavy or too light affect lubrication ability and tend to be separated during storage and under load. The remaining hydrocarbons are at or near the mass C ₁₂. Due to the lack of light hydrocarbons, the RP-1 has a high flash point and fewer fire hazards than gasoline/petrol or even some jets and diesel fuel.

All told, the end product is more expensive than kerosene. On paper, any oil can produce multiple RP-1 with sufficient processing. In practice, fuel is sourced from a small number of oil fields with high quality base stock. This, coupled with a small demand in a niche market compared to other oil users, pushed up prices. The military specifications of RP-1 are covered in MIL-R-25576, and the chemical and physical properties of RP-1 are described in NISTIR 6646.

Soviet and Russian rocket kerosenes are very similar to RP-1 and are named T-1 and RG-1. Higher density, 0.82-0.85 g/ml, compared with RP-1 at 0.81 g/ml. For a short time, the Soviets achieved a higher density with kerosene super-chilling in rocket fuel tanks, but this partially defeated the purpose of using kerosene on top of other super-cold fuels. In the case of Soyuz and other R7-based rockets, the temperature penalty is small. The facility is readily available to manage liquid oxygen cryogenic vehicles and liquid nitrogen, both of which are much cooler than kerosene temperatures. The main kerosene kerosene tanks are surrounded on four sides and the top by an oxygen-liquid tank; liquid-nitrogen tank near the bottom. The kerosene tanks of the four amplifiers are relatively small and compact, and also between the liquid-oxygen and liquid-nitrogen tanks. So, once kerosene is cooled at first, it can stay that way for the short time it takes to complete the launch preparation. The latest version of Falcon 9, Falcon 9 Full Thrust, also has a sub-cooling capability of RP-1 to -7 Ã‚ Â° C fuel, providing 2.5-4% density increase.

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Comparison with other fuels

Chemically, hydrocarbon propellants are less efficient than hydrogen fuel because hydrogen releases more energy per unit of mass during combustion, allowing higher exhaust speeds. This, in part, results from the high mass of carbon atoms relative to the hydrogen atom. Hydrocarbon engines are also usually run rich in fuels, which produce some CO instead of CO ₂ as a consequence of incomplete combustion, though this is not unique to hydrocarbon engines, since hydrogen engines also typically run fuel-rich for performance overall best. Some Russian engines run their oxygen-rich turbopump praburners, but the main combustion chamber is still fuel-rich. All told, the kerosene engine produces I _sp in the range 270 to 360Ãƒ, seconds, while the hydrogen engine reaches 370 to 465 seconds.

During the engine shutdown, the fuel flow to zero quickly, while the engine is still quite hot. Trapped and trapped fuels can polymerize or even carbonize at hot spots or in hot components. Even without hot spots, heavy fuel can create petroleum residues, as can be seen in gasoline, diesel, or jet fuel tanks that have been operating for years. The rocket engine has a power cycle measured in minutes or even seconds, preventing really heavy deposits. However, rockets are much more sensitive to deposits, as described above. Thus, the kerosene system generally requires more teardown and overhaul, creating operations and labor costs. This is a problem for disposable machines, as well as reusable ones, since the machine must be fired several times before it is launched. Even cold flow tests, in which the propellant is not turned on, can leave residue.

On the upper side, under a space pressure of about 1000 psi (6.9 MPa), kerosene can produce soot deposits inside the nozzle and chamber liner. It acts as a significant insulation layer and can reduce heat flow to the wall by approximately two factors. Most modern hydrocarbon engines, however, go above this pressure, therefore this has no significant effect on most machines.

The recent heavy-hydrocarbon engines have modified new components and operating cycles, in an effort to manage better fuel, achieve a more gradual cooldown, or both. This still leaves the issue of oil residue that is not separated. Other new machines have tried to get through the problem completely, by switching to light hydrocarbons like methane or propane gas. Both are volatile, so the residue of the machine just evaporates. If necessary, other solvents or laxatives can be run through the machine to complete the dispersion. The short-chain propane carbon backbone (C ₃ Ãƒ, molecule) is very difficult to destroy; methane, with a single carbon atom (C ₁), technically not a chain at all. The product of solving both molecules is also a gas, with fewer problems due to phase separation, and less possibility of polymerization and deposition. However, methane (and to a lesser extent propane) reintroduces the discomfort driving the kerosen in the first place.

Low-pressure steam kerosenes provide security for the ground crew. However, in a kerosene tank flight requires a separate pressure system to replace the volume of fuel as it flows. Generally, this is a separate tank from an inert or high-pressure inert gas, such as nitrogen or helium. This creates extra costs and weights. Cryogenic or volatile propellants generally do not require a separate pressurant; instead, some propellant is expanded (often with engine heat) into a gas of low density and redirected to the tank. Some highly unstable propellant designs do not even require a gas loop; some liquids automatically evaporate to fill their own containers. Some rockets use gas from gas generators to suppress fuel tanks; Normally, it's a waste of turbo. Although this saves on a separate gas system, the loop must now handle hot and reactive gases rather than cold and inert ones.

Apart from the chemical constraints, RP-1 has supply constraints, due to the size of the vehicle launching industry that is very small compared to other oil consumers. While the price of materials such as very fine hydrocarbons is still less than many other rocket propellants, the number of RP-1 suppliers is limited. Some machines have tried to use more standard and widely distributed petroleum products such as jet fuel or even diesel. By using alternative or optional engine cooling methods, some can tolerate non-optimal formulations.

Any hydrocarbon-based fuel when burned will produce more air pollution than hydrogen. Burning hydrocarbons produces carbon dioxide (CO ₂), toxic carbon monoxide (CO) emissions, hydrocarbons (HC), and nitrogen oxides (NO _{x ), while hydrogen (H ₂) reacts with oxygen (O ₂) to produce only water (H ₂ O), with some not react H ₂ also released.}

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BBM like -RP-1

Early rocket Robert H. Goddard uses gasoline.

John Drury Clark mentions in Ignition! that when the RP-1 specification is being developed, Rocketdyne experiments with diethyl cyclohexane. However, it offers several advantages over RP-1, and is dropped. In addition, the military (NASA does not exist) prefers RP-1 as it is processed with jet fuel at the same refinery.

The Soviet formulation is discussed above. In addition, the Soviets briefly used syntin (Russian: ?????? ), a higher energy formulation, used in the upper stage. Syntin is 1-methyl-1,2-dicyclopropyl cyclopropane ( C
₁₀ H
₁₆ ). Russia also announced plans to replace Soyuz-2 from RG-1 to "naphthyl" or "naphthyl".

After the RP-1 standard, RP-2 was developed. The main difference is the lower sulfur content. However, since most users receive RP-1, there is little incentive to produce and store a second, rarer and more expensive formulation.

The OTRAG Group launches test vehicles using a more general mix. At least in one instance, the rocket is driven by diesel fuel. However, no OTRAG rockets are even close to orbit.