4.2 ENGINES AND MOTORS 80 Go online and find the possible positions and numbers of cylinders in a reciprocating engine. For example, what does Ferrari V12s mean? Piston rings are very important parts in an engine: they seal the combustion chamber to ensure minimal loss of gases, improve heat transfer from the piston to the cylinder wall, maintain the correct quantity of the oil between the piston and the cylinder wall, regulate engine oil consumption by scraping oil from the cylinder walls back to the oil sump. Top Dead Centre is the position of the piston when it is at the very top of its stroke inside the cylinder; Bottom Dead Centre is the opposite, when the piston is at the very bottom of its stroke. INTERNAL COMBUSTION ENGINES Engine vs motor An engine is a machine that can convert some form of energy, obtained from a fuel, into useful mechanical power or motion. If the engine produces kinetic energy from a fuel source, it is called a prime mover; if it produces kinetic energy from a preprocessed fuel , for instance electricity or compressed air, it is called a motor. Internal combustion engines (ICE) Internal combustion engines are the most common form of heat engines, i.e. engines that produce motion from heat, and they are used in vehicles, boats, ships, airplanes, and trains. They are named as such because they generate mechanical power from the chemical energy released by fuel combustion which occurs in a confined space called combustion chamber. Many of the automotive engines are four-stroke ICEs, which get their name from the four distinct phases that occur in the engine during operation. Main parts The engine block contains the cylinders. The more cylinders an engine has, the more power it is capable of producing and the engines are classified by the number usually from 1 to 12 and alignment of the cylinders. alignment: allineamento bottom dead centre: punto morto inferiore camshaft: albero a camme connecting rod: biella crank: manovella crankcase: carter motore, basamento crankshaft: albero a gomiti, albero motore displacement: cilindrata groove: gola, scanalatura Inside each cylinder, a piston, a cylindrical structure whose top surface is the crown, moves up and down: this movement is called reciprocating. Grooves are present on the circumference of each piston where some rings are placed, in order to prevent friction and leakage. Engine displacement is the volume generated by all the pistons inside the cylinders in a single movement from the top dead centre (TDC) to the bottom dead centre (BDC) . There is a connecting rod that has an I shape structure: one end is connected to each piston and the other one to the crankshaft, which converts the linear (up and down) motion of the piston into a rotational motion. A crankcase protects these parts and retains lubricating oil, which is pumped to the different engine parts. The engine head has openings for air to flow into the cylinders and out for burned gases expulsion. The intake and exhaust valves, placed in the cylinder heads and operated by a camshaft, allow fuel and air to enter the combustion chamber and let the exhaust fumes out. oil sump: coppa dell olio prime mover: motore primario reciprocating: a movimento alternativo ring: fascia elastica, segmento to seal: sigillare shaft: albero top dead centre: punto morto superiore 176 EnginEEring MechPower.indb 176 30/01/24 17:08