The combustion products expand in the nozzle and flow into the environment with great speed. The outflow of gases from the nozzle is the cause of jet engine thrust. Positive feature of jet engines should be considered that the reactive thrust them almost independent of the speed of installation, and the power of its speed increases with the air entering the engine, ie, with increasing speed. This property used in the application of turbojet engines in aviation. The main disadvantages of jet engines – a relatively low cost and relatively short lifespan.
Composite engine Internal combustion engines are called, consisting of reciprocating parts and multiple compression and expansion machines (or devices), as well as devices for the supply and removal of heat, combined with each other common working body. As part of the combined piston engine uses piston internal combustion engine. The energy in this setting is passed to the consumer side of the piston shaft, the shaft or other expansion engine, or both shafts simultaneously. The number of compression and expansion machines, their styles and designs, their connection with the piston part and each defined purpose of the combined engine and its scheme and operating conditions. The most compact and economical engines are combined, in which the continued expansion of the exhaust gas piston parts is carried out in a gas turbine, and the preload fresh charge is made in a centrifugal or axial flow compressor (the latter has not yet received a distribution), and the power of the consumer is usually transmitted through the crankshaft of the piston. Piston engine and gas turbine in the combined engine successfully complement each other: the first is most effective when mechanical work is converted heat small volumes of gas at high pressure, and the second best used heat large volumes of gas at low pressure. Combined (MARINE) consists of a piston part, which is used as a piston internal combustion engine, gas turbine and compressor. Exhaust gases after the piston engine having a still higher temperature and pressure, results in rotation of the impeller blades of a gas turbine, which transmits the torque of the compressor.
Compressor sucks in air from the atmosphere and under a certain pressure pumps it into the cylinder piston engine. Increased filling cylinder air by raising the pressure at the inlet is called supercharging. When pressurization air density increases and, consequently, the fresh charge of filling the cylinder at intake, compared with a charge of air in the same naturally aspirated engines. The combustion of fuel introduced into the cylinder is required certain mass of air (for the complete combustion of 1 kg of liquid fuel theoretically need about 15 kg of air). Therefore, the more air goes into the cylinder, the more fuel you can burn it, ie, get more power. The main advantages of the combined engine – small volume and mass per I kW, as well as high cost, often exceeding the cost conventional piston engine. Most economical piston, and combined internal combustion engines are widely used in transportation and stationary power. They have a fairly long life, relatively small dimensions and weight, high efficiency, their characteristics are in good agreement with the characteristics of the consumer. The main disadvantage of engines to be considered reciprocating piston associated with the presence of crank mechanism, complicates the design and limiting the possibility of increasing the speed, especially when large size of the engine. Source: ship supplies.