An engine is a machine that converts fuel into energy in the form of mechanical work, which can be used to power other machines or vehicles.  The most common types of engines are internal combustion engines and external combustion engines.  Engines play a critical role in modern society, powering transportation, industry, and many other applications.

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Engine Design Requirements

Internal Combustion Engine  -  These work by burning fuel inside the engine, which creates high pressure and temperature, driving a piston or rotor that is connected to a mechanical system.  This mechanical energy can be used to power cars, motorcycles, boats, generators, and other machines.

• Cycle
  • Two Stroke Engine  -  A two stroke engine completes a power cycle in two strokes of the piston.  In this engine, the crankcase and the combustion chamber are both integrated into one chamber, which is sealed by the piston.
  • Four Stroke Engine  -  A four stroke engine completes a power cycle in four strokes of the piston.  The four strokes are intake, compression, combustion, and exhaust.
• Thermodynamics Cycle
  • Otto Cycle  -  Describes the functioning of a spark ignition piston engine.
  • Diecel Cycle  -  Used in diesel engines.  It is a combination of two isentropic processes (compression and expansion) and two constant pressure processes (heat addition and rejection).
  • Dual Cycle  -  Used to model the operation of internal combustion engines, such as gasoline engines and diesel engines.  It is a combination of two processes: a constant volume heat addition process and a constant pressure heat rejection process.
• Fuel
  • Diesel  -  A type of liquid fuel used in diesel engines.  It is made from crude oil and is heavier and less refined than gasoline.  Diesel fuel is composed of hydrocarbons, which are molecules that contain only hydrogen and carbon atoms.  The chemical composition of diesel fuel varies depending on the source and refining process, but it typically contains long chain hydrocarbons with between 10 and 20 carbon atoms.
  • Gas  -  A gaseous fuel that is used as a source of energy.  Natural gas, which is primarily composed of methane, is the most common type of gas fuel.  Other types of gas fuel include propane, butane, and hydrogen.
  • Petrol  -  Also known as gasoline, is a liquid fuel used in internal combustion engines.  It is primarily derived from crude oil through a refining process.  Petrol contains a mixture of hydrocarbons with different boiling points, which allows it to ignite and burn efficiently in a gasoline engine.
• Engine Speed
  • High Speed Engine  -  An engine that is designed to operate at high speeds.  High speed engines typically have a higher power-to-weight ratio and a smaller size than low speed engines, which makes them more suitable for applications where space and weight are at a premium.  They can also be more fuel efficient and environmentally friendly than low speed engines due to their ability to operate at higher speeds with lower fuel consumption. 
  • Medium Speed Engine  -  These engines that operate at medium speeds, typically ranging from 300 to 1000 revolutions per minute (RPM).  Medium speed engines can be further classified based on their fuel type, such as diesel or gas, and their ignition system, such as spark ignited or compression ignited.  Compared to high speed engines, medium speed engines are larger and heavier, but they offer better fuel efficiency and durability. 
  • Low Speed Engine  -  They are also known as slow speed engines or two stroke engines.  These engines operate at a low speed of around 60 to 120 revolutions per minute (RPM) and are known for their fuel efficiency and reliability.  They are designed to use heavy fuel oil (HFO) as their primary fuel, which is cheaper than other types of fuel.
• Arrangement of cylinder
  • Horizontal Engine  -  An engine where the cylinders are arranged in a horizontal orientation.  These engines are often used in applications where space is limited and a vertical engine cannot fit.  Horizontal engines can be either two stroke or four stroke, and they may run on gasoline, diesel, or other fuels.  One of the advantages of horizontal engines is that they have a lower center of gravity than vertical engines, which can make them more stable and easier to handle.
  • Vertical Engine  -  An engine where the crankshaft is oriented vertically, with the cylinder block and piston moving up and down in a vertical direction.  In a vertical engine, the valves are usually positioned at the top of the cylinder head, which can improve the engine's breathing and combustion efficiency.  The main advantage of a vertical engine is its compact size, which makes it well suited for use in applications where space is limited.
  • Radial Engine  -  An engine in which the cylinders are arranged in a circular pattern around the crankcase, with the crankshaft at the center.  The pistons are connected to the crankshaft by rods and the crankshaft is fixed to the airframe, while the cylinders rotate around it.  The radial engine is known for its reliability and ability to produce high power output, but has largely been replaced by more modern engine designs in most applications.
  • V-type Engine  -  An engine configuration in which the cylinders are arranged in a "V" shape, typically at an angle of 60 or 90 degrees to each other, and mounted on a common crankshaft.  The V-shape design allows for a more compact engine size and can also provide a better balance of the reciprocating parts, resulting in less vibration.
• Ignition
  • Spark Ignition  -  A method of igniting a fuel-air mixture in the combustion chamber of an internal combustion engine.  It is the most common type of ignition system used in gasoline engines, where a spark is generated by an ignition system to ignite the fuel-air mixture in the combustion chamber.  In a spark ignition engine, the fuel and air mixture is compressed by the piston, and then a spark plug generates a spark to ignite the mixture, causing it to combust and drive the piston down.
  • Compression Ignition  -  A method of igniting a fuel-air mixture in the combustion chamber of an internal combustion engine.  It is the most common type of ignition system used in diesel engines, where the fuel-air mixture is ignited by the heat generated by the compression of the air in the combustion chamber.  In a compression ignition engine, the fuel is injected into the combustion chamber at the end of the compression stroke, and the heat generated by the compressed air ignites the fuel. 
• Cooling
  • Air Cooling  -  It is cooled by air rather than by liquid coolant.  In an air-cooled engine, the hot air generated by the combustion process is directed over and around the engine components, and the heat is dissipated into the surrounding air.  They are generally simpler and lighter than liquid cooled engines, as they do not require a radiator, coolant pump, or other complex cooling system components.  They are also less prone to leaks and other cooling system failures. 
  • Water Cooling  -  An engine that is cooled by a liquid coolant, usually a mixture of water and antifreeze.  In a water cooled engine, the coolant is circulated through the engine block and cylinder head, where it absorbs heat generated by the combustion process, and then flows through a radiator to dissipate the heat into the surrounding air.  They are generally more efficient than air cooled engines, as they can maintain a more consistent operating temperature, which can improve fuel efficiency and reduce emissions.
• Use
  • Stationary Engine  -  It is used to power equipment that is fixed in place, rather than being mounted on a vehicle or mobile equipment.  Stationary engines are used in a wide variety of applications, including generators, water pumps, compressors, sawmills, and industrial machinery.  Stationary engines can be either gasoline or diesel powered, and they can be air cooled or water cooled.
  • Automobile Engine  -  It is used to power a vehicle.  Automobile engines are typically designed to run on gasoline, diesel, or alternative fuels such as compressed natural gas or electric power.  Automobile engines can be classified based on their configuration, such as inline, V-shaped, or horizontally opposed.  They can also be classified based on their number of cylinders, with four cylinder and six cylinder engines.
  • Portible Engine  -  Is designed to be easily moved and transported from one location to another.  Portable engines can be powered by gasoline, diesel, propane, or other fuels, and they are commonly used for a wide range of applications, including powering small equipment and tools, providing backup power, and running small generators.  Portable engines are typically lightweight and compact, and they may be air cooled or water-cooled. 
  • Aero Engine  -  Also known as an aircraft engine, is an internal combustion engine that is designed and used to propel an aircraft through the air.  Aero engines can be classified into different types based on their design, size, and the aircraft they are used on.

External Combustion Engine  -  This work by heating a fluid, such as steam or gas, outside the engine, which generates pressure and causes mechanical movement.  Examples of external combustion engines include steam engines, Stirling engines, and gas turbines.

• Heat Source  -  Require a heat source to produce the heat that will be used to generate power.  This heat source can be a variety of fuels, including coal, wood, oil, or natural gas.
• Working Fluid  -  A substance that absorbs the heat from the heat source and converts it into mechanical energy.  The working fluid can be a gas, such as air or helium, or a liquid, such as water.
• Heat Exchanger  -  Is the device that transfers heat from the heat source to the working fluid.  This can be done through direct contact between the heat source and the working fluid, or through a separate device, such as a boiler or a heat exchanger.
• Engine Components  -  They have various components, such as pistons, turbines, and generators, that work together to convert the heat from the working fluid into mechanical energy.
• Control Systems  -  They require control systems to regulate the flow of heat and working fluid through the engine, as well as to monitor and adjust the engine's performance.
• Fuel and Emissions Control  -  Must meet environmental regulations regarding emissions of pollutants, such as nitrogen oxides and particulate matter.  This requires the use of control systems that limit the production of these pollutants and ensure compliance with regulatory standards.