Chemistry in Everyday Life (Fuel Types)

Fuel Types
Unleaded Petrol (ULP) ULP has a Research Octane Number (RON) of between 91 and 93.
Premium Unleaded Petrol (PULP)
PULP is a special blend of petrol designed to bring high octane, and hence high engine power, as well as knock-free performance to unleaded cars with a high-octane requirement. Most petrol companies have a specially named varsion of PULP PULP has a Research Octane Number (RON) of 95.
Diesel
Diesel engines are usually very efficient engines, offering better fuel economy in comparison to equivalent petrol models. Diesel engines emit very low levels of exhaust hydrocarbons and carbon monoxide when correctly tuned and maintained. The main concern diesel engines raise is the smoke they emit, which can be a health hazard.
Liquefied Petroleum Gas (LPG)
LPG, most commonly a blend of propane and butane, is an environmentally cleaner fuel compared to petrol and diesel. It is the most widely accepted alternative fuel for the automotive sector.
Despite LPG cars having lower fuel economy compared to petrol-powered vehicles, fuel costs will usually be
98 RON
98 RON has a Research Octane Number (RON) of 98. It is a high-octane unleaded fuel that maximizes engine power and performance, as well as producing less pollution. It is more commonly used by imported and high performance vehicles
98 RON is promoted as providing excellent fuel economy. It has low levels of benzene, sulphur and lower aromatics and a sulpur content which is 10 times lower than the national standard for unleaded fuels.
Biodiesel and Biodiesel Blends (B20 diesel)
Biodiesel is 100% biodiesel fuel and is referred to as B 100 or "neat biodiesel". Biodiesel is made from natural renewable sources and can be blended in almost any ratio with petroleum based diesel. Biodiesel blends are often known by the ratio of biodiesel to regular diesel i.e. B20 means 20% biodiesel and 80% petroleum based diesel. The most common blends available internationally are B5 (a mix of 5% biodiesel and 95% petroleum based diesel) and B20 (a mix of 20% biodiesel and 80% petroleum based diesel).
Ethanol
Ethanol is made form natural renewable sources and can be blended with petroleum based unleaded fuels. Ethanol is pure 100% ethanol, referred to as E100 or "neat ethanol". Ethanol blends are often known by the ratio of ethanol to regular petrol i.e. E10 means a mix of 10% ethanol and 90% unleaded petrol.
Lead Replacement Petrol (LRP)
Now phased out, LRP (96 RON) was introduced as an environmental alternative for cars that used leaded petrol. LRP was refined to contain no lead, along with lower concentrations of benzene and sulphur, respectively identified as health hazards and pollutants. Lead was historically added to petrol as a cost-effective way of increasing octane and hence engine power rating and providing a measure of engine protection by way of its lubricating qualities.
Rocket propellant
Rocket propellant is mass that is stored, usually in some form of propellant tank, prior to being used as the propulsive mass that is ejected from a rocket engine in the form of a fluid jet to produce thrust.
Chemical rocket propellants are most commonly used, which undergo exothermic chemical reactions which produce hot gas which is used by a rocket for propulsive purposes.
The first stage will usually use high-density (low volume) propellants to reduce the area exposed to atmospheric drag and because of the lighter tankage and higher thrust/weight ratios. Thus, the Apollo-Saturn V first stage used kerosene-liquid oxygen rather than the liquid hydrogen-liquid oxygen used on the upper stages (hydrogen is highly energetic per kilogram, but not per cubic metre).
Chemical propellants
There are three main types of propellants: solid, liquid, and hybrid.
Solid propellants
The earliest rockets were created hundreds of years ago by the Chinese, and were used primarily for fireworks displays and as weapons. They were fueled with black powder, a type of gunpowder consisting of a mixture of charcoal, sulfur and postassium nitrate (saltpeter). Rocket propellant technology did not advance until the end of the 19th century, by which time smokeless powder had been developed, originally for use in firearms and artillery pieces. Smokeless powders and related compounds have seen use as double-base propellants.
Soilid propellants (and almost all rocket propellants) consist of an oxidizer and a fuel. In the case of gunpowder, the fuel is charcoal, the oxidizer is potassium nitrate, and sulfur serves as a catalyst. (Note: sulfur is not a true catalyst in gunpowder as it is consumed to a great extent into a variety of reaction products such as K2S. The sulfur acts mainly as a sensitizer lowering threshold of ignition.) During the 1950s and 60s researchers in the United States deveveloped what is now the standard high-energy solid rocket fuel. The mixture is primarily ammonium perchlorate powder (an oxidizer), combined with fine aluminium powder (a fuel), held toigether in a base of PBAN or HTPB (rubber-like fuels). The mixture is formed as a liquid, and then cast into the correct shape and cured into a rubbery solid. Solid fueled rockets are much easier to store and handle than liquid fueled rockets, which makes them ideal for military application. In the 1970s and 1980s the U.S. switched entirely to solid-fuelled ICBMs: the LGM-30 Minuteman and LG-118A Peacekeeper (MX). In the 1980s and 1990s, the USSR/Russia also deployed solid-fuelled ICBMs (RT-23, RT-2PM, and RT-2UTTH), but retains two liquid-fuelled ICBMs (R-36 and UR-100N). All solid-fuelled ICBMs on both sides have three initial solid stages and precision maneuverable liquid-fuelled bus used to fine tune the trajectory of the reentry vehicle.
Their simplicity also makes solid rockets a good choice whenever large amounts of thrust are needed and cost is an issue. The Space Shuttle and many other orbital launch vehicles use solid fuelled rockets in their first stages (solid rocket boosters) for this reason.
However, solid rockets have a number of disadvantages relative to liquid fuel rockets. Solid rockets have a lower specific impulse than liwuid fueled rockets. It is also difficult to build a large mass ratio solid rocket because almost the entire rocket is the combustion chamber, and must be built to withstand the high combustion pressures. If a solid rocket is used to go all the way to orbit, the payload fraction is very small. (For example, the Orbital Sciences Pegasus rocket is an air-launched three-stage solid rocket or bital booste. Launch mass is 23,130 kg, low earth orbit payload is 443kg, for a payload fraction of 1.9%. Compare to a Delta IV Medium, 249,500 kg, payload 8600 kg, payload fraction 3.4% without air-launch assistance.)
A drawback to solid rockets is that they cannot be throuttled in real time, although a predesigned thrust schedule can be created by altering the interior propellant geometry.
Solid rockets can often be shut down before they run out of fuel. Essentially, the rocket is vented or an extinguishant injected so as to terminate the combustion process. In some cases termination destroys the rocket..
Liquid propellants
Liquid fueled rockets have better specific impulse than solid rockets and are capable of being throttled, shut down, and restarted. Only the combustion chamber of a liquid fueled rocket needs to withstand combustion pressures and temperatures. On vehicles employing turbopumps, the fuel tanks carry very much less pressure and thus can be built far more lightly, permitting a larger mass ratio. For these reasons, most orbital launch vehicles and all first-and second-generation ICBMs use liquid fuels for most of their velocity gain.
The primary performance advantage of liquid propellants is the oxidizer. Several practical liquid oxidizers (liquid oxygen, nitrogen teroxide, and hydrogen peroxide) are available which have much better specific impulse than ammonium perchlorate when paired with comparable fuels.
Most liquid propellants are also cheaper than solid propellants. For orbital launchers, the cost savings do not, and histrorically have not mattered; the cost of fuel is a very small protion of the overall cost of the rocket, even in the case of solid fuel.
The main difficulties with liquid propellants are also with the oxidizers. These are generally at least moderately difficult to store and handle due to their high reactivity with common materials, may have extreme toxicity (nitric acids), moderately cryogenic (liquid oxygen), or both (liquid fluorine, FLOX - a fluorine/LOX mix). Several exotic oxidizers have been proposed: liquid ozone (O3), CIF3, and CIF5, all of which are unstable, energetic, and toxic.
Liquid fuelled rockets also require potentially trublesome valves and seals and thermally stressed combustion chambers, which increase the cost of the rocket. Many employ specially designed turbopumps which raise the cost enormously due to difficult fluid flow patterns that exist within the casings.
Though all the early rocket theorists proposed liquid hydrogen and liquid oxygen as propellants, the first liquid-fuelled rocket, launched by Robert Goddard on March 16, 1926, used gasoline and liquid oxygen. Liquid hydrogen was first used by the engines designed by Pratt and Whitney for the Lockheed CL-400 Suntan reconnaissance aircraft in the mid-1950s. In the mid-1960s, the Centaur and Saturn upper stages were both using liquid hydrogen and liquid oxygen.
The highest specific impulse chemistry ever test-fired in a rocket engine was lithium, and fluorine, with hydrogen added to improve the exhaust thermodynamics (making this a tripropellant). The combination delivered 542 seconds (5.32 kN.s/kg, 5320 m/s) specific impulse in a vacuum. The impracticality of this chemistry highlights why exotic propellants are not actually used: to make all three components liquids, the hydrogen must be kept below-252 °C (just 21 K) and the lithium must be kept above 180 °C (453 K). Lithium and fluorine are both extremely corrosive, lithium ignites on contact with air, fluorine ignites on contact with most fuels, and hydrogen, while not hypergolic, is an explosive hazard. Fluorine and the hydrogen fluoride (HF) in the exhaust are very toxic, which damages the environment, makes work around the launch pad difficult, and makes getting a launch license that much more difficult. The rocket exhaust is also ionized, which would interfere with radio communication with the rocket.
The common liquid propellant combinations in use today:
- LOX and kerosene (RP-1). Used for the lower stages of most Russian and Chinese boosters, the first stages of the Saturn V and Atles V, and all stages of the developmental Falcon 1 and Falcon 9. Very similar to Robert Goddard's first rocket. This combination is widely regarded as the most practical for civilian orbital launchers.
- LOX and liquid hydrogen, used in the Space Shuttle, the Centaur upper stage, Saturn V upper stages, the newer Delta IV rocket, the H-IIA rocket, and most stages of the European Ariane rockets.
- Nitrogen tetroxide (N2O4) and hydrazine (N2H4), MMH, or UDMH. Used in military, orbital and deep space rockets, because both liquids are storable for long periods at reasonable temperatures and pressures. This combination is hypergolic, making for attractively simple ignition sequences. The major inconvenience is that these propellants are hightly toxic, hence they require careful handling. Hydrazine also decomposes energetically to nitrogen, hydrogen, and ammonia, making it a fairly good monopropellant.
Gas propellants
A gas propellant usually involves some sort of compressed gas. However, due to the low density and high weight of the pressure vessel, gases see little current use.
Hybrid propellants
A hybrid rocket usually has a solid fuel and a liquid or gas oxidizer. The fluid oxidizer can make it possible to throttle and restart the motor just like a liquid fuelled rocket. Hybrid rockets are also cleaner than solid rockets because practical high-performance solid-phase oxidizers all contain chlorine, versus tha more benign liquid oxygen or nitrous oxide used in hybrids. Because just one propellant is a fluid, hybrids are simpler than liquid rockets.
Hybrid motors suffer two major drawbacks. The first, shared with solid rocket motors, is that the casing around the fuel grain must be built to withstand full combustion pressure and often extreme temperatures as well. However, modern composite structures handle this problem well, and when used with nitrous oxide or hydrogen peroxide relatively small percentage of fuel is needed anyway, so the combustion chamber is not especially large.
The primary remaining difficulty with hybrids is with mixing the propellants during the combustion process. In solid propellants, the oxidizer and fuel are mixed in a factory in carefully controlled conditions. Liquid propellants are generally mixed by the injector at the top of the combustion chamber, which directs many small swift-moving streams of fuel and oxidizer into one another. Liquid fuelled rocket injector design has been studied at great length and still resists reliable performance prediction. In a hybrid motor, the mixing happens at the melting or evaporating surface of the fuel. The mixing is not a well-controlled process and generally quite a lot of propellant is left unburnd[citation needed], which limits the efficiency and thus the exhaust velocity of the motor. Additionally, as the burn continues, the hole down the center of the grain (the 'port') widens and the mixture ratio tends to become more oxidiser rich.
There has been much less development of hybrid motors, than solid and liquid motors. For military use, ease of handling and maintenance have driven the use of solid rockets. For orbital work, liquid fuels are more efficient than hybrids and most development has concentrated there. There has recently been an increase in hybrid motor development for nonmilitary suborbital work.