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The high compression ratio in the auxiliary combustion chamber causes the auto-ignition of the homogeneous lean air-fuel mixture therein (no spark plug required); the burnt gas bursts - through some "transfer ports", just before the TDC - into the main combustion chamber triggering its auto-ignition.
Snowmobiles Usually have one to four cylinders and can be both 2-stroke or 4-stroke, normally in the in-line configuration; however, there are again some novelties that exist with V-4 engines; Small portable appliances such as chainsaws, generators, and domestic lawn mowers most commonly have one cylinder, but two-cylinder chainsaws exist.
Free-piston engine used as a gas generator to drive a turbine. A free-piston engine is a linear, 'crankless' internal combustion engine, in which the piston motion is not controlled by a crankshaft but determined by the interaction of forces from the combustion chamber gases, a rebound device (e.g., a piston in a closed cylinder) and a load device (e.g. a gas compressor or a linear alternator).
The free-piston linear generator generally consists of three subsystems: combustion chamber, linear generator and return unit (normally a gas spring), which are coupled through a connecting rod. In the combustion chamber, a mixture of fuel and air is ignited, increasing the pressure and forcing the moving parts (connection rod, linear generator ...
Many two-stroke engines use a crankcase-compression design, where a partial vacuum draws the fuel/air mixture into the engine as the piston moves upwards. Then as the piston travels downward, the inlet port is uncovered and the compressed fuel/air mixture is pushed from the crankcase into the combustion chamber.
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A variation of the opposed-piston design is the free-piston engine, which was first patented in 1934. Free piston engines have no crankshaft, and the pistons are returned after each firing stroke by compression and expansion of air in a separate cylinder. Early applications were for use as an air compressor or as a gas generator for a gas turbine.
Two-stroke engines which use crankcase compression do not require a crankcase ventilation system, since all of the gases within the crankcase are then fed into the combustion chamber. Many small four-stroke engines such as lawn mower engines and electricity generators simply use a draught tube connected to the intake system.