Thermal fl uid energy machines 3 Internal gunt

Basic knowledge Internal combustion engines

Internal combustion engines are thermal fl uid energy machines: Small single- engines are perfect for demonstrating the Comparison of engines: 2- petrol , 4-stroke petrol engine, 4-stroke they generate mechanical energy by burning a mixture of fundamentals of engine technology. GUNT offers various internal and air. All work processes take place inside a working area: the combustion engines with capacities of up to 75kW, including 2-stroke petrol engine 4-stroke petrol engine 4-stroke diesel engine cylinder. Since the force/energy within the cylinder is trans- real engines with a volumetric displacement of up to two ferred by means of a variable volume, internal combustion litres. Among these engines are four-stroke diesel and petrol Load air/fuel mixture air/fuel mixture pure air engines are part of the group of positive displacement machines. engines, petrol engines with variable compression and two- stroke petrol engines. Fuel supply carburettor carburettor injector nozzle Motors or engines are often used to power motor vehicles, ships or . They are also used for drives that must be Ignition ignition spark ignition spark compression reliable and independent of the electrical power supply, such as 5...8 5...12 14...21 emergency backup generators, construction machines or agri- cultural machinery. Fuel-air ratio 0,8...1,2 0,8...1,2 1,5...10 Fuel petrol petrol diesel

2-stroke engine: one work cycle = one revolution Indicator diagram of a 2-stroke engine

1st stroke: compression/ 2nd stroke: power /precompression

The moves upward: from bottom dead centre to top Downward motion of the piston: from top dead centre to p dead centre bottom dead centre 1st stroke (0 -1): the cylinder is charged with the fuel/air mixture, 3 (1-2): compression of the mixture, Processes above the piston: Processes above the piston: The resulting pressure forces 2 The precompressed mixture is further compressed above the piston downward and opens fi rst the outlet channel and (2-3): ignition and combustion of the mixture, the piston. The compressed mixture is ignited shortly then the transfer port. The precompressed mixture under 2nd stroke (3-4): expansion of the combustion gases, before the top dead centre is reached. the piston pushes the accumulated exhaust fumes out and 4: exhaust opens, expansion is fi nished fi lls the cylinder. 4’: transfer port opens, purging starts 4 1’: purging is fi nished Compression Top dead centre: Expansion Bottom dead 4' 0 1: exhaust closes and compression starts and intake ignition centre pU gas exchange: 1 1' exhaust and purging VC VH V

Processes below the piston: Processes below the piston: The transfer port is closed as the piston travels upwards. The mixture that was sucked in is precompressed by the intake, compression, power, exhaust; Due to the resulting negative pressure the inlet valve upward motion of the piston and pressed into the transfer pU ambient pressure, V volume, opens: The fuel and air mixture is drawn in. port. The positive pressure closes the inlet valve. VH displaced volume, Vc compression volume

4-stroke engine: one work cycle = two crank revolutions Indicator diagram of a 4-stroke engine

st nd rd th 1 stroke: intake 2 stroke: compression 3 stroke: power – 4 stroke: exhaust st ignition and expansion p 1 stroke (0 -1): intake • of the fuel and air mixture in a petrol engine, 3 • of pure air in a diesel engine 2 2nd stroke (1-2): compression • of the fuel and air mixture in a petrol engine, • 4 of air to a least 700°C in a diesel engine 3 rd stroke (2-3): ignition and combustion 4' pU 0 • of the fuel and air mixture in a petrol engine 1 (spark plugs), • injection of diesel oil, ignition caused by high air V VH The piston moves from the top The piston moves from the bot- The compressed fuel and air The piston moves from the temperature to the bottom dead centre. As tom to the top dead centre. As mixture is ignited shortly bottom to the top dead centre. (3-4): expansion of the combustion gases it does, the fuel and air mixture it does, the fuel and air mixture before the top dead centre As it does, the exhaust gases 4 th stroke (4-4’): exhaust of the combustion gases are discharged. is sucked in. is compressed. is reached. The resulting (4’-0): expulsion of the remaining combustion gases pressure presses the piston downwards.

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