The big facts page

152 car engine facts, all checked

Every fact on this site in one place, each linked to Encyclopaedia Britannica, the US Department of Energy or NASA. Our build checks each one against the source text; see the sources page.

How an engine works

1 In an internal-combustion engine the fuel and air burn inside the engine itself, and the hot gases push on a moving surface such as the face of a piston. Encyclopaedia Britannica: Internal-combustion engine
2 Internal-combustion engines are the most widely used power-generating devices in existence: petrol and diesel engines, gas turbines and rockets are all examples. Encyclopaedia Britannica: Internal-combustion engine
3 Internal-combustion engines come in two groups: continuous-combustion engines, such as a jet engine with its steady flame, and intermittent-combustion (reciprocating) engines, such as petrol and diesel piston engines. Encyclopaedia Britannica: Internal-combustion engine
4 Every internal-combustion engine burns its air-fuel mixture, takes work from the expanding hot gases, then lets the burnt gases out through the exhaust. Encyclopaedia Britannica: Internal-combustion engine
5 A steam engine is an external-combustion engine: its working fluid does not burn, and it gains energy only by heat passing into it through a heat exchanger. Encyclopaedia Britannica: Internal-combustion engine
6 The most common internal-combustion engine is the four-stroke, petrol-powered, spark-ignition engine, thanks to its performance in road transport. Encyclopaedia Britannica: Internal-combustion engine
7 Intake stroke: with the inlet valve open, the piston moves down and draws a mixture of petrol vapour and air into the cylinder. Encyclopaedia Britannica: Gasoline engine
8 Compression stroke: with both valves closed, the piston moves up and squeezes the mixture; near the top an electric spark sets it alight. Encyclopaedia Britannica: Gasoline engine
9 Power stroke: with both valves still closed, the expanding burnt gas presses the piston down. Encyclopaedia Britannica: Gasoline engine
10 Exhaust stroke: the rising piston pushes the burnt gases out through the open exhaust valve, and the cycle starts again. Encyclopaedia Britannica: Gasoline engine
11 Each four-stroke cycle takes four strokes of the piston (intake, compression, power and exhaust) and two turns of the crankshaft. Encyclopaedia Britannica: Gasoline engine
12 A four-stroke engine makes only half as many power strokes as a two-stroke, but it clears out the exhaust and refills the cylinders better. Encyclopaedia Britannica: Gasoline engine
13 The four-stroke cycle, the most important way of getting power from burning fuel so far, was first developed in the late 19th century. Encyclopaedia Britannica: Gasoline engine
14 In a piston-and-cylinder engine, the pressure of the burning fuel pushes the piston along the cylinder in a back-and-forth (reciprocating) motion. Encyclopaedia Britannica: Gasoline engine
15 The force on the piston passes down the connecting rod to the crankshaft, which turns the piston’s straight-line motion into turning motion. NASA Glenn Research Center: Engine mechanical operation
16 To raise the pressure in the compression stroke, the piston has to do work on the mixture, just as you do work to pump up a bicycle tyre. NASA Glenn Research Center: Engine mechanical operation
17 The Wright brothers’ 1903 Flyer was powered by a four-stroke engine with four cylinders, each piston joined to one crankshaft. NASA Glenn Research Center: Engine mechanical operation
18 The Wright brothers based their engine on early car engines that used the Otto cycle, developed by Nikolaus Otto in 1876. NASA Glenn Research Center: Internal combustion engine (Otto cycle)
19 Power is the work done in each cycle multiplied by the number of cycles each second. NASA Glenn Research Center: Internal combustion engine (Otto cycle)
20 A real engine always produces less work than the ideal cycle, which assumes no friction and no heat lost during compression and power. NASA Glenn Research Center: Internal combustion engine (Otto cycle)
21 Only about 12% to 30% of the energy in the fuel you put in a conventional car is used to move it down the road. US Department of Energy and EPA, fueleconomy.gov: Where the energy goes (petrol vehicles)
22 In a petrol car, most of the fuel’s energy is lost in the engine, mainly as heat. US Department of Energy and EPA, fueleconomy.gov: Where the energy goes (petrol vehicles)
23 Most cars have used four-stroke petrol piston engines, while diesel engines are widely used for lorries and buses. Encyclopaedia Britannica: Automobile
24 The petrol engine was first chosen for cars because it ran well over a wide range of speeds, gave reasonable power for its weight, could be mass-produced cheaply and used a readily available fuel. Encyclopaedia Britannica: Automobile
25 In the United States, bigger cars moved from long straight engines to compact V6 and V8 layouts, while smaller cars used four-cylinder engines. Encyclopaedia Britannica: Automobile
26 European car engines ranged from 1 to 12 cylinders; most had four cylinders in a straight line. Encyclopaedia Britannica: Automobile
27 To save fuel, some engines have as many as five valves per cylinder. Encyclopaedia Britannica: Automobile
28 Engine oil does more than reduce friction: it also cools, cushions noise and seals the gap between the piston rings and the cylinder walls. Encyclopaedia Britannica: Automobile
29 A gear-type pump sends filtered oil under pressure through drilled passages to the engine’s bearings. Encyclopaedia Britannica: Automobile

Petrol and diesel

30 A petrol engine burns a volatile liquid fuel, petrol or a petrol mixture such as ethanol, and an electric spark starts the burning. Encyclopaedia Britannica: Gasoline engine
31 Four-stroke petrol engines power the vast majority of cars, light vans, medium and large motorcycles and lawn mowers. Encyclopaedia Britannica: Gasoline engine
32 Two-stroke petrol engines are less common, but they run small outboard boat motors and handheld garden tools such as chainsaws, hedge trimmers and leaf blowers. Encyclopaedia Britannica: Gasoline engine
33 In a diesel engine, air is squeezed until it is hot enough to set alight the diesel fuel sprayed into the cylinder. Encyclopaedia Britannica: Diesel engine
34 Diesel engines power freight lorries, large tractors, locomotives and ships, as well as a limited number of cars. Encyclopaedia Britannica: Diesel engine
35 Unlike a petrol engine, a diesel engine takes in only air on its intake stroke. Encyclopaedia Britannica: Diesel engine
36 Diesel engines usually have compression ratios between 14:1 and 22:1. Encyclopaedia Britannica: Diesel engine
37 The air in a diesel cylinder is usually hotter than 526 °C (979 °F), hot enough for the fuel to catch fire by itself. Encyclopaedia Britannica: Diesel engine
38 Diesel engines are also called compression-ignition engines, because the fuel is lit by air heated by squeezing, not by a spark. Encyclopaedia Britannica: Diesel engine
39 Diesel fuel is sprayed in at 7 to 70 megapascals (1,000 to 10,000 pounds per square inch) as the piston nears the top of its stroke. Encyclopaedia Britannica: Diesel engine
40 Diesel engines are often turbocharged and aftercooled, which can improve both power and efficiency. Encyclopaedia Britannica: Diesel engine
41 The diesel engine’s most outstanding feature is its efficiency: by squeezing air alone it can use higher compression ratios than a spark-ignition engine. Encyclopaedia Britannica: Diesel engine
42 Diesel engines are generally about one-third more efficient than petrol engines. US Department of Energy and EPA, fueleconomy.gov: Where the energy goes (petrol vehicles)
43 A diesel does not throttle its intake to control power, so it is much more efficient than a petrol engine when idling or at low power. Encyclopaedia Britannica: Diesel engine
44 The main drawback of diesel engines is air pollution: they give off more soot, nitrogen compounds (NOx) and smell than spark-ignition engines. Encyclopaedia Britannica: Diesel engine
45 Small diesel engines make less than 188 kilowatts (252 horsepower) and are the most commonly made kind; they power cars, light vans and small generators. Encyclopaedia Britannica: Diesel engine
46 Medium diesel engines, from 188 to 750 kilowatts, mostly power heavy lorries. Encyclopaedia Britannica: Diesel engine
47 Large diesel engines, over 750 kilowatts, power ships and locomotives and generate electricity; some turn as slowly as 500 revolutions a minute. Encyclopaedia Britannica: Diesel engine
48 Diesel engines with cylinders wider than 600 mm (24 inches) are almost all two-strokes. Encyclopaedia Britannica: Diesel engine
49 Diesel fuel is made of heavier hydrocarbons, with at least 12 to 16 carbon atoms per molecule, that boil at 177 to 343 °C. Encyclopaedia Britannica: Diesel engine
50 The cetane number describes how readily a diesel fuel ignites. Encyclopaedia Britannica: Diesel engine
51 The simplest way to start a diesel is to blow high-pressure air into each cylinder in turn; others use an electric starter motor or even a small petrol engine. Encyclopaedia Britannica: Diesel engine
52 The diesel engine became the main power for submarines in the First World War, because it was economical and reliable and its fuel was less volatile than petrol. Encyclopaedia Britannica: Diesel engine
53 The first commercial diesel engine in America was installed in St. Louis by the brewer Adolphus Busch, who had seen one at an exhibition in Munich. Encyclopaedia Britannica: Diesel engine
54 Rudolf Diesel first planned to run his engine on powdered coal; after his experimental engine was destroyed by an explosion, he turned to liquid petroleum. Encyclopaedia Britannica: Diesel engine
55 A fuel’s octane number measures how well it resists knocking in an engine cylinder. Encyclopaedia Britannica: Octane number
56 The octane number is the percentage of iso-octane, which resists knocking, in a blend with heptane, which knocks readily, that matches the fuel in a test engine. Encyclopaedia Britannica: Octane number
57 In the 21st century regular petrol in the United States was rated 87 octane and high-test about 93. Encyclopaedia Britannica: Automobile
58 Ethanol is often blended with petrol (15 parts to 85) to raise its octane rating, but it holds less energy, so a tank goes less far. Encyclopaedia Britannica: Automobile
59 In a spark-ignition engine the fuel is mixed with air in the combustion chamber, and a spark from the spark plug lights the mixture. US Department of Energy, Alternative Fuels Data Center: How do gasoline cars work?

Engine parts

60 A spark plug fits into the cylinder head and has two electrodes with a small air gap; current jumps the gap as a spark that lights the air-fuel mixture. Encyclopaedia Britannica: Spark plug
61 A spark plug’s insulator must stand up to high temperatures and up to several thousand volts. Encyclopaedia Britannica: Spark plug
62 A car’s ignition system turns the battery’s low voltage, usually 12 volts, into some 40,000 volts for the spark plugs. Encyclopaedia Britannica: Ignition system
63 The distributor sends each burst of high-voltage current to the right spark plug in the firing order. Encyclopaedia Britannica: Ignition system
64 Many modern engines have no distributor: a coil sits on top of each spark plug (coil-on-plug). Encyclopaedia Britannica: Ignition system
65 A carburettor supplies a spark-ignition engine with its mix of fuel and air; its choke gives a fuel-rich mixture to start a cold engine. Encyclopaedia Britannica: Carburettor
66 In a carburettor, a narrow venturi in the air flow lowers the pressure and draws fuel from the main jet into the air stream. Encyclopaedia Britannica: Carburettor
67 From the 1970s, computer-controlled fuel injection replaced the carburettor in almost all petrol engines except two-strokes and small engines like those in lawn mowers. Encyclopaedia Britannica: Carburettor
68 Fuel injection uses a pump to put fuel into the cylinders, instead of relying on the suction of the moving pistons. Encyclopaedia Britannica: Fuel injection
69 Fuel injection shares fuel more evenly between the cylinders than a carburettor, so more power can be made and fewer unwanted emissions. Encyclopaedia Britannica: Fuel injection
70 A supercharger is an air compressor that raises the pressure of the air going into the engine, so more fuel can be burnt each cycle and the engine makes more power. Encyclopaedia Britannica: Supercharger
71 A turbocharger is a blower driven by a small turbine that is spun by the engine’s own exhaust gases. Encyclopaedia Britannica: Supercharger
72 In aircraft piston engines, supercharging makes up for the thinner air at high altitude. Encyclopaedia Britannica: Supercharger
73 The camshaft turns at a fixed ratio to the crankshaft, and its cams open each valve at exactly the right moment, with pauses while the valves stay shut. Encyclopaedia Britannica: Cam
74 If a cam’s follower is not held in a groove, a spring keeps it pressed against the cam. Encyclopaedia Britannica: Cam
75 The Wright brothers’ 1903 engine opened its intake valve “automatically” by suction; modern engines use cams and rocker arms for better timing. NASA Glenn Research Center: Engine mechanical operation
76 A flywheel is a heavy wheel on a turning shaft that smooths out the delivery of power and stores energy. Encyclopaedia Britannica: Flywheel
77 In a car engine the flywheel smooths out the pulses from the cylinders and gives energy for the pistons’ compression strokes. Encyclopaedia Britannica: Flywheel
78 Double a flywheel’s speed and its stored energy goes up four times. Encyclopaedia Britannica: Flywheel
79 In a car, the clutch is built into the engine’s flywheel. Encyclopaedia Britannica: Gasoline engine
80 In a modern petrol car an electronic control module controls the fuel mixture, the ignition timing and the emissions system. US Department of Energy, Alternative Fuels Data Center: How do gasoline cars work?
81 A catalytic converter passes the exhaust through a honeycomb or pellets coated with a catalyst, turning hydrocarbons and carbon monoxide into water vapour and carbon dioxide. Encyclopaedia Britannica: Catalytic converter
82 A catalytic converter also turns nitrogen oxides back into nitrogen and oxygen. Encyclopaedia Britannica: Catalytic converter

Gears and power

83 A gear is a toothed wheel on a shaft; gears work in pairs to pass on turning motion and torque (turning force) without slipping. Encyclopaedia Britannica: Gear
84 If the driven gear has twice as many teeth as the small driving gear, it turns at half the speed with twice the torque. Encyclopaedia Britannica: Gear
85 When the smaller gear of a pair drives, the pair slows the speed and multiplies the torque. Encyclopaedia Britannica: Gear
86 Spur and helical gears join parallel shafts, bevel gears join shafts that meet, and a worm and gear is usually used for shafts that do neither. Encyclopaedia Britannica: Gear
87 A worm gear can have just one thread (tooth), but a spur or helical pinion needs at least five teeth. Encyclopaedia Britannica: Gear
88 A differential lets the two driving wheels turn at different speeds round a corner while sharing the engine’s force equally between them. Encyclopaedia Britannica: Differential gear
89 On a corner the outside wheel has farther to go, so it turns faster than the inside wheel. Encyclopaedia Britannica: Differential gear
90 The car differential was invented in 1827 by a Frenchman, Onésiphore Pecqueur, and was first used on steam vehicles. Encyclopaedia Britannica: Differential gear
91 Jack up both driving wheels in neutral, turn one, and the other turns the opposite way at the same speed. Encyclopaedia Britannica: Differential gear
92 If one wheel slips on ice or mud, an ordinary differential gives the other wheel less torque too; a limited-slip differential helps with this. Encyclopaedia Britannica: Differential gear
93 A car’s transmission passes the mechanical power from the engine to drive the wheels. US Department of Energy, Alternative Fuels Data Center: How do gasoline cars work?
94 The fully automatic transmission was introduced in 1939, and it changes gear by itself as the car speeds up and slows down. Encyclopaedia Britannica: Automatic transmission
95 An automatic’s fluid coupling works like two fans facing each other: oil spun by one turbine turns the other. Encyclopaedia Britannica: Automatic transmission
96 An automatic transmission does its shifting with planetary gears and a speed-sensitive governor. Encyclopaedia Britannica: Automatic transmission
97 One horsepower is 33,000 foot-pounds of work a minute: enough to lift 33,000 pounds one foot in one minute. Encyclopaedia Britannica: Horsepower
98 James Watt chose the value of the horsepower in the late 18th century after tests with strong dray horses; it is about 50 percent more than an average horse can keep up all day. Encyclopaedia Britannica: Horsepower
99 One horsepower is 746 watts. Encyclopaedia Britannica: Horsepower
100 A metric horsepower is a little smaller: 0.9863 of an imperial horsepower. Encyclopaedia Britannica: Horsepower
101 Brake horsepower, measured at the output shaft, is less than indicated horsepower by the power lost to friction inside the engine, which can be 10 percent or more. Encyclopaedia Britannica: Horsepower
102 Energy is also lost in the transmission and the rest of the driveline, and to brakes, wind resistance and the tyres’ rolling resistance. US Department of Energy and EPA, fueleconomy.gov: Where the energy goes (petrol vehicles)

The pioneers

103 The French inventors Nicéphore and Claude Niépce built an early internal-combustion engine, the Pyréolophore, in 1807. Encyclopaedia Britannica: Étienne Lenoir
104 Étienne Lenoir, a Belgian inventor, devised the first commercially successful internal-combustion engine, patented on 24 January 1860. Encyclopaedia Britannica: Étienne Lenoir
105 Lenoir’s engine was a converted double-acting steam engine that burnt coal gas and air, lit by a spark from a battery. Encyclopaedia Britannica: Étienne Lenoir
106 Lenoir’s engine did not compress its fuel and turned only about 4 percent of its fuel into work. Encyclopaedia Britannica: Étienne Lenoir
107 More than 500 Lenoir engines were at work across Europe in the 1860s, pumping water from mines and printing. Encyclopaedia Britannica: Étienne Lenoir
108 In 1863 Lenoir drove his three-wheeled Hippomobile 7 miles (11 km) in about three hours. Encyclopaedia Britannica: Étienne Lenoir
109 Lenoir patented nearly 80 inventions, from engines to leather tanning. Encyclopaedia Britannica: Étienne Lenoir
110 The four-stroke cycle was patented in 1862 by the French engineer Alphonse Beau de Rochas. Encyclopaedia Britannica: Nikolaus Otto
111 In 1876 Nikolaus Otto built an engine using the four-stroke cycle; because he was the first to build one, it is called the Otto cycle. Encyclopaedia Britannica: Nikolaus Otto
112 Otto and Eugen Langen’s improved engine won a gold medal at the Paris Exposition of 1867. Encyclopaedia Britannica: Nikolaus Otto
113 More than 30,000 Otto engines were built in the next 10 years, but Otto’s patent was revoked in 1886 when Beau de Rochas’s earlier patent came to light. Encyclopaedia Britannica: Nikolaus Otto
114 Otto’s four-stroke engine was the first practical alternative to the steam engine as a power source. Encyclopaedia Britannica: Nikolaus Otto
115 The British engineer Dugald Clerk, born in Glasgow, patented his two-stroke engine in 1881; it fires once every two strokes instead of once every four. Encyclopaedia Britannica: Sir Dugald Clerk
116 Clerk’s two-stroke cycle was widely used on light motorcycles and other small machines. Encyclopaedia Britannica: Sir Dugald Clerk
117 In 1872 Gottlieb Daimler became technical director at Nikolaus Otto’s firm; in 1882 he and Wilhelm Maybach left to start their own engine shop. Encyclopaedia Britannica: Gottlieb Daimler
118 Daimler and Maybach patented one of the first successful high-speed internal-combustion engines in 1885, and a carburettor that allowed petrol to be used as fuel. Encyclopaedia Britannica: Gottlieb Daimler
119 Daimler and Maybach fitted their engines to a bicycle (1885), a carriage (1886) and a boat (1887). Encyclopaedia Britannica: Gottlieb Daimler
120 Wilhelm Maybach’s carburettor design was widely used from 1893. Encyclopaedia Britannica: Wilhelm Maybach
121 Maybach was chief designer of the first Mercedes cars (1900–01), for which he improved a 24-horsepower engine. Encyclopaedia Britannica: Wilhelm Maybach
122 In 1909 Maybach and his son Carl set up a company to build aircraft engines, including engines for Zeppelin airships. Encyclopaedia Britannica: Wilhelm Maybach
123 Karl Benz built the world’s first practical car powered by an internal-combustion engine; his three-wheeled Motorwagen first ran early in 1885. Encyclopaedia Britannica: Karl Benz
124 Benz’s company, founded in Mannheim in 1883, first made stationary internal-combustion engines. Encyclopaedia Britannica: Karl Benz
125 Rudolf Diesel, a German engineer born in Paris in 1858, invented the engine that bears his name. Encyclopaedia Britannica: Rudolf Diesel
126 Diesel obtained a German patent in 1892 and in 1893 published a description of his engine. Encyclopaedia Britannica: Rudolf Diesel
127 In 1897 Diesel demonstrated a 25-horsepower, four-stroke, single-cylinder engine. Encyclopaedia Britannica: Rudolf Diesel
128 Diesel wanted an engine more efficient than the Otto engine, and saw that squeezing air hard enough would make the spark unnecessary. Encyclopaedia Britannica: Diesel engine
129 Diesel’s engine was an immediate commercial success, thanks to its high efficiency and simple design. Encyclopaedia Britannica: Rudolf Diesel
130 Charles Kettering developed the first electric starter, introduced on Cadillacs in 1912. Encyclopaedia Britannica: Charles F. Kettering
131 Kettering founded Delco with Edward A. Deeds to design electrical equipment for cars, including better lighting and ignition. Encyclopaedia Britannica: Charles F. Kettering
132 Felix Wankel, a German engineer, invented the Wankel rotary engine; he never earned an engineering degree or held a driving licence. Encyclopaedia Britannica: Felix Wankel
133 Wankel completed his first rotary engine design for NSU in 1954; prototypes were tested in 1957 and 1958. Encyclopaedia Britannica: Felix Wankel
134 In 1961 the Japanese company Mazda agreed with NSU to develop the Wankel engine; rotary Mazdas reached America in 1971. Encyclopaedia Britannica: Felix Wankel

Other engines

135 In the original two-stroke cycle of 1878, the engine does the compression and power strokes without separate intake and exhaust strokes, so one turn of the crankshaft completes the cycle. Encyclopaedia Britannica: Gasoline engine
136 A simpler two-stroke that uses the crankcase to pump in the fresh mixture was introduced in 1891. Encyclopaedia Britannica: Gasoline engine
137 In loop scavenging, the simplest way to swap exhaust for fresh mixture, the top of the piston steers the new charge up one side of the cylinder and down the other. Encyclopaedia Britannica: Gasoline engine
138 Many two-stroke machines are noisy and polluting, and some places have banned devices such as two-stroke leaf blowers. Encyclopaedia Britannica: Gasoline engine
139 Lenoir’s 1860 engine used an early two-stroke cycle, a process still used in some mopeds and lawnmowers. Encyclopaedia Britannica: Étienne Lenoir
140 An opposed-piston engine has two pistons moving in opposite directions in the same cylinder, with a crankshaft at each end joined by gears. Encyclopaedia Britannica: Gasoline engine
141 A Wankel rotary engine has no pistons going up and down: a curved triangular rotor orbits inside a closed casing. Encyclopaedia Britannica: Wankel engine
142 In a Wankel engine the output shaft turns three times as fast as the rotor, and one turn of the rotor completes intake, compression, expansion and exhaust. Encyclopaedia Britannica: Wankel engine
143 The only moving parts of a Wankel engine are the rotor and the output shaft. Encyclopaedia Britannica: Wankel engine
144 Experimental Wankel engines were built and tested by a German firm from 1956. Encyclopaedia Britannica: Wankel engine
145 A Wankel engine is small and light for its power, smooth, quiet and cheap to make; fuel economy and the cost of meeting emission standards have limited its use, with Mazda the only maker to sell large numbers. Encyclopaedia Britannica: Gasoline engine
146 A Wankel engine’s apex seals are oiled by adding a little oil to the fuel, as little as 1 part in 200. Encyclopaedia Britannica: Gasoline engine
147 A hybrid car has a petrol or diesel engine and one or more electric motors; the battery is charged by regenerative braking and by the engine, not by plugging in. US Department of Energy, Alternative Fuels Data Center: How do hybrid electric cars work?
148 The extra push from a hybrid’s electric motor can allow a smaller engine. US Department of Energy, Alternative Fuels Data Center: How do hybrid electric cars work?
149 An all-electric car has an electric motor instead of an internal-combustion engine, with no tailpipe exhaust and no fuel pump, fuel line or fuel tank. US Department of Energy, Alternative Fuels Data Center: How do all-electric cars work?
150 Hybrids, plug-in hybrids and electric cars use regenerative braking to win back some of the energy normally lost as heat in the brakes. US Department of Energy and EPA, fueleconomy.gov: Where the energy goes (petrol vehicles)
151 Hybrid-style stop-start systems switch the engine off when the car stops and restart it when the accelerator is pressed. US Department of Energy and EPA, fueleconomy.gov: Where the energy goes (petrol vehicles)
152 Rockets are internal-combustion engines too, and they are the one kind that does not take in air. Encyclopaedia Britannica: Internal-combustion engine