Presented by:
Amit A. Pawar

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INTRODUCTION
Propulsion is defined as force causing movement. Vehicle propulsion refers to the act of moving an artificial carrier of people or goods over any distance. The power plant used to drive the vehicles can vary widely. Originally, humans or animals would have provided the means of propulsion, later being supplemented by wind power (e.g. sailing ship). Since the Industrial Revolution, mechanical propulsion has been possible, initially using steam engines. More recently, most vehicles use some form of internal-combustion engine, with various energy sources to power them.
It is broadly categorized as
Vehicle propulsion
 Air propulsion
 Ground propulsion
 Marine propulsion
 Spacecraft propulsion
In the following paper I have concentrated over unconventional methods that can be used for air propulsion and space propulsion.
 AIRCRAFT
Air propulsion is the act of moving an object through the air. The most common and now conventional types are propeller, jet engine, turboprop, ramjet, rocket propulsion, and, experimentally, scramjet, pulse jet, and pulse detonation engine. Animals such as birds and insects obtain propulsion by flapping their wings. The unconventional methods for air propulsion are:
• Wankel engine
The promising design for aircraft use was the Wankel rotary engine. The Wankel engine is about one half the weight and size of a traditional four stroke cycle piston engine of equal power output, and much lower in complexity. In an aircraft application, the power to weight ratio is very important, making the Wankel engine a good choice. Because the engine is typically constructed with aluminum housing and a steel rotor, and aluminum expands more than steel when heated, unlike a piston engine, a Wankel engine will not seize when overheated. This is an important safety factor for aeronautical use. Considerable development of these designs started after World War II, but at the time the aircraft industry favored the use of turbine engines. It was believed that turbojet or turboprop engines could power all aircraft, from the largest to smallest designs. The Wankel engine did not find many applications in aircraft. Wankel engines are becoming increasingly popular in homebuilt experimental aircraft, due to a number of factors. Most are Mazda 12A and 13B engines, removed from automobiles and converted to aviation use. This is a very cost-effective alternative to certified aircraft engines, providing engines ranging from 100 to 300 horsepower (220 kW) at a fraction of the cost of traditional engines. These conversions first took place in the early 1970s, and with hundreds or even thousands of these engines mounted on aircraft, as of 10 December 2006 the National Transportation Safety Board has only seven reports of incidents involving aircraft with Mazda engines, and none of these is of a failure due to design or manufacturing flaws. During the same time frame, they have reports of several thousand reports of broken crankshafts and connecting rods, failed pistons and incidents caused by other components which are not found in the Wankel engines.
• Diesel engine
The diesel engine is another engine design that has been examined for aviation use. In general diesel engines are more reliable and much better suited to running for long periods of time at medium power settings—this is why they are widely used in trucks for instance. Several attempts to produce diesel aircraft engines were made in the 1930s but, at the time, the alloys were not up to the task of handling the much higher compression ratios used in these designs. They generally had poor power-to-weight ratios and were uncommon for that reason but, for example, the Clerget 14F diesel radial engine (1939) has the same power to weight as a gasoline radial. Improvements in diesel technology in automobiles (leading to much better power-weight ratios), the diesel's much better fuel efficiency (particularly compared to the old gasoline designs currently being used in light aircraft) and the high relative taxation of AVGAS compared to Jet A1 in Europe have all seen a revival of interest in the concept. Competing new diesel engines may bring fuel efficiency and lead-free emissions to small aircraft, representing the biggest change in light aircraft engines in decades. Wilksch Airmotive build 2 stroke diesel engine (same power to weight as a gasoline engine) for experimental aircraft: WAM 100 (100 hp), WAM 120 (120 hp) and WAM 160 (160 hp).
• Precooled jet engines
For very high supersonic/low hypersonic flight speeds inserting a cooling system into the air duct of a hydrogen jet engine permits greater fuel injection at high speed and obviates the need for the duct to be made of refractory or actively cooled materials. This greatly improves the thrust/weight ratio of the engine at high speed. It is thought that this design of engine could permit sufficient performance for antipodal flight at Mach 5, or even permit a single stage to orbit vehicle to be practical.
• Air breathing nuclear engine
Nuclear-powered air-cushion vehicles using lightweight nuclear powerplants such as those being investigated for nuclear aircraft may be able to achieve transoceanic cargo cost rates per metric ton-kilometer (ton-n mi) comparable to rail transport rates independent of the distance traveled. Cargo rates for 7420 kilometers (4000 n mi) (typical of transatlantic routes) are expected to be less than one-half those for similar fossil-.fueled air- cushion vehicles. For 11 130-kilometer (6000-n mi) nonstop distances, the rates are expected to be less than one-sixth as much.The technical problems associated with providing containment of fission products in the worst conceivable accidents are much easier to solve for nuclear air-cushion vehicles than for nuclear aircraft. This is because (1) the operating speed is much lower, (2) the operation is at zero altitude, and (3) the operation is over water.
There are no fundamental technical reasons why subsonic nuclear aircraft cannot be made to fly successfully providing the aircraft is large enough. The weight of a completely shielded nuclear aircraft reactor varies about as the square root of the reactor power. Hence, the larger the aircraft the less is the weight fraction of the nuclear power system. Aircraft of 0.45 million kilograms (1 million lb) or greater are required to make the payload fraction greater than 15 percent of the gross weight. 
 SPACECRAFT
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the back/rear of the vehicle at very high speed through a supersonic de Laval nozzle. This sort of engine is called a rocketengine.
All current spacecraft use chemical rockets (bipropellant or solid-fuel) for launch, though some (such as the Pegasus rocket and SpaceShipOne) have used air-breathing engines on their first stage. Most satellites have simple reliable chemical thrusters (often monopropellant rockets) or resistojet rockets for orbital station-keeping and some use momentum wheels for attitude control. Soviet bloc satellites have used electric propulsion for decades, and newer Western geo-orbiting spacecraft are starting to use them for north-south stationkeeping. Interplanetary vehicles mostly use chemical rockets as well, although a few have used ion thrusters and Hall effect thrusters (two different types of electric propulsion) to great success.the spacecraft propulsion is classified as:
1. Chemical rockets
2. Electric thrusters
3. Nuclear propulsion
4. Miscellaneous
• Chemical rockets
Propulsion by means of chemical reactions happening due to the properties of propellant is termed as chemical propulsion. Rockets utilizing such propulsion are called chemical rocklets
 Hybrid rocket
A hybrid rocket is a rocket with a rocket motor which uses propellants in two different states of matter - one solid and the other either gas or liquid. The Hybrid rocket concept can be traced back at least 75 years. Hybrid rockets exhibit advantages over both liquid rockets and solid rockets especially in terms of simplicity, safety, and cost. Because it is nearly impossible for the fuel and oxidizer to be mixed intimately (being different states of matter), hybrid rockets tend to fail more benignly than liquids or solids. Like liquid rockets and unlike solid rockets they can be shut down easily and are simply throttle-able. The theoretical specific impulse (Isp) performance of hybrids is generally higher than solids and roughly equivalent to hydrocarbon-based liquids. Isp as high as 400s has been measured in a hybrid rocket using metalized fuels.[3] Hybrid systems are slightly more complex than solids, but the significant hazards of manufacturing, shipping and handling solids offset the system simplicity advantages.
Basic concepts
In its simplest form a hybrid rocket consists of a pressure vessel (tank) containing the liquidpropellant, the combustion chamber containing the solid propellant, and a valve isolating the two. When thrust is desired, a suitable ignition source is introduced in the combustion chamber and the valve is opened. The liquid propellant (or gas) flows into the combustion chamber where it is vaporized and then reacted with the solid propellant. Combustion occurs in a boundary layer diffusion flame adjacent to the surface of the solid propellant. Generally the liquid propellant is the oxidizer and the solid propellant is the fuel because solid oxidizers are problematic and lower performing than liquid oxidizers. Furthermore, using a solid fuel such as HTPB or paraffin allows for the incorporation of high-energy fuel additives such as aluminium, lithium, or metal hydrides.
Common oxidizers include gaseous or liquid oxygen or nitrous oxide. Common fuels include polymers such as polyethylene, cross-linked rubber such as HTPB or liquefying fuels such as paraffin