Activity 2

Read the following text. Create a mind map using examtime to identify clearly how combustion engines can be classified. Add some images to your mindmap.

COMBUSTION ENGINES CLASSIFICATION

External combustion engines

1. Steam engines They started to be used about 300 years ago. In a chamber outside the engine called the boiler (or furnace), fossil fuels were burned to boil water, resulting in the production of steam. Since steam takes up to 1,500 times more space than water, the pressure generated could be used to move a piston, transforming heat energy into mechanical energy (movement). It was used in industry (for instance the textile industry) in the 19th and the first half of the 20th centuries. It was used in steam trains and in steam boats as well.

2. Steam turbines Steam turbines transform pressurized steam, turning its blades in a rotation movement This rotation movement is generally used to generate electricity. It is used in electric power stations.

Internal combustion engines

1. Piston engines (Reciprocating engines)

Fossil fuel combustion (usually the fuel is in gas or vaporized liquid state) is produced inside the engine and the explosion achieved, and gases that appear, are used to move a piston with a lineal and repetitive up-and-down or back-and-forward motion.

1.1. Spark-ignition engines. Engines that need a spark (produced by the spark plug) to produce the combustion reaction.

1.1.1. The four-stroke engine: Nikolaus Otto, a German engineer, designed the four-stroke engine in1876. (Following the thermodynamic cycle with his name (Otto)). A four-stroke engine completes the thermodynamic cycle in four movements of the piston (between the moment in which petrol come inside the cylinder and it is repeated this action, piston has four movements); for this reason is called four-stroke engine. Use petrol as a combustible. Used in the most of the petrol cars.

1.1.2. The two-stroke engine: Dugald Clerk, a Scottish engineer, is thought to have invented the 2 stroke engine in 1878 and in 1881 patented his design. The two-stroke engines follow the Otto thermodynamic cycle as well, but this engine complete the cycle in two movements of the piston; for this reason is called two-stroke engine. Two-stroke engines require a specific oil to gas ratio. It is used in some motorbikes.

1.2. Compression-ignition engines. Designed by the German engineer Rudolf Diesel in 1897. Follow the thermodynamic cycle with his name (Diesel). It is a four-stroke engine that uses the heat of compression to initiate ignition, so that is not necessary the spark plug. Use diesel (gasoil) as a combustible.

2. Rotary engines. Developed during the years shortly before and during the World War I. Rotary engines are internal combustion engines in which the combustion generates directly a rotary movement. It is not necessary the use of pistons. In these engines, the crankshaft remained stationary and the entire cylinder block rotated around it.

2.1. Wankel engine. Invented by the German engineer Felix Wankel in the 1950s. This engine uses a rotary design to convert pressure into a rotating movement. The engine follows the thermodynamic Otto cycle, so that, it is possible to say that Wankel engine is a four-stroke engine as well. For instance, some cars such as some Mazda use this type of engine.

2.2. Gas turbines and jet engines. Gas turbines are rotary engines that extract energy from a flow of combustion gas. In the combustion, the hot gases produced are forced into the turbine to move its blades and so, it is possible to generate electricity in electric power stations. Jet engines are used in different machines such as the aircrafts. Jet engines create force by releasing a high speed jet of a liquid or a gas, pushing the plane through the air. Turbojet and turbofan engines are similar, but turbofan has a big fan in the front of the turbine that promotes its turn achieving to use less fuel, noise, and speed.