High-speed engines can also be fitted as auxiliary power units parallel to the main propulsion engine. Medium- (300-1000 RPM) and high-speed (>1000 RPM) engines are mainly of the 4-stroke type and are used for passenger ships and naval vessels. High power and reliability are the top priorities for freighters. Marine low-speed (~100 RPM) propulsion engines are often 2-stroke engines operating with heavy fuel oil. Space is a critical variable: the more compact the engine, the more space there is for cargo, and the simpler it is to carry out maintenance. In a steam engine, steam pressure pushing on a piston makes the engine work.Īs well as meeting tough demands for accessibility and output, marine engines must be able to withstand huge stresses, depending on the load and climatic conditions. Steam engines, for example, have external combustion: a heat source separate from the engine heats a boiler, producing steam that makes the engine turn. In contrast, in an external combustion engine the combustion process heats a separate working fluid that then in turn does work. They appear in most autos, motorbikes and boats, and in a wide variety of aircraft, large ships and locomotives, mostly in the form of gas turbines. Internal combustion engines are most commonly used for mobile propulsion systems. The crankcase contains oil for lubrication. Exhaust : When the piston reaches the bottom of its stroke, the exhaust valve opens the exhaust gases leave the cylinder and are discharged via the tail pipe. The gasoline charge in the cylinder explodes, driving the piston down.Ĥ. Combustion : When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. Compression makes the explosion more effective.ģ. Compression : Then the piston moves back up to compress the fuel/air mixture. A mixture of air and fuel is then drawn into the cylinder through the intake valve.Ģ. Intake : The piston starts at the top the intake valve opens, and the piston moves down. The downward stroke that immediately follows the ignition of the air-fuel mix in the cylinder is known as the power stroke.Īll internal combustion engines depend on the exothermic chemical process of combustion: the reaction of a fuel, typically with air though other oxidizers such as nitrous oxide may be employed.įigure 7.1 The moving parts of a 4-stroke engine, which cause friction and heat. A single sweep of the cylinder by the piston in an upward or downward motion is known as a stroke. Both types of engines may have one or more cylinders, each with a spark plug, a piston and a connection to a crankshaft (see Figure 7.1). A 2-stroke engine may simply have an exhaust outlet and a fuel inlet instead of a valve system.
The key parts of a 4-stroke engine include the intake and exhaust valves. The most common engine types are 4- or 2-stroke internal combustion engines.
The parts of an engine vary depending on its type. These engines, called Wankel engines, are also known as Orbital engines or Quasiturbines. A few internal combustion engines use a rotary piston motion instead of the common reciprocating type. Classification by engine cycleĪll internal combustion engines are heat engines and thus have a physical upper limit on their efficiency achieved only by the theoretical Carnot heat engine. Engines operating with heavier fuel oil, biogas, landfill gas, coke gas, etc., are also available. High-powered engines are most commonly operated with distillates such as diesel or natural gas. Similarly, there is a wide range of ways to classify engines, some of which are listed below: There is a wide range of engines corresponding to their many varied applications. Practically every device from the industrial revolution was referred to as an engine.