# Internal combustion engine

An internal combustion engine , also referred to as an internal combustion engine in the patent literature , is an internal combustion engine (also known as a heat engine) that converts chemical energy into mechanical work . For this purpose, an ignitable mixture of fuel and air (oxygen) is burned in a combustion chamber . All combustion engines are characterized by internal combustion , i.e. the generation of combustion heat in the engine . The thermal expansion of the resulting hot gas is used to set pistons ( rotors in Wankel engines ) in motion. The most common types of internal combustion engines are Otto (positive ignition) and diesel (compression ignition) engines . A typical application of these motors is the drive of motor vehicles ( motor vehicles for short) such as automobiles , motorcycles , ships and aircraft .

The continuously operating jet and rocket engines as well as gas turbines are usually not part of the internal combustion engine, although there too the fuel is burned inside the machine. Steam turbines , steam engines or the Stirling engine are not combustion engines because the heat required for their operation is generated outside.

Four-stroke gasoline engine as an example of an internal combustion engine. Designation of the work cycles:
1. Suction
2. Compression
3. Work
4. Ejection

## Basic functionality

In all engines with internal combustion , the gas involved is changed after each work cycle, i.e. exhaust gas is emitted and a fresh mixture (fresh gas) is supplied. The heat of combustion and frictional heat that is lost with the exhaust gas and the heat radiation is called power loss .

Modern engines compress the gas supplied to the work area , then combustion is started under pressure , which causes the gas to heat up considerably. The motor relaxes the hot gas (for example with a receding piston), the pressure and temperature of the gas decrease and the volume increases. It does mechanical work. Depending on the construction and function of the engine, these processes are implemented differently. Fundamental to the function as an engine is that because of the combustion of the fuel-air mixture, the expansion of the mixture takes place at a higher pressure than the compression. The maximum possible efficiency depends on the temperature level at which the heat of combustion is supplied and removed, and depends on the compression ratio . Modern vehicle petrol engines achieve an effective efficiency of 40% at their best operating point (roughly in the middle of the speed range and just below the full load curve). For automotive diesel engines, this is 43%. However, it must be taken into account here that the efficiency is lower in the partial load range and at high speeds, which is particularly important because motor vehicles in road traffic are mainly driven in the lower partial load range. The average efficiency of a vehicle is therefore much lower than the maximum values. For example, Crastan indicates an average efficiency of 20% for a conventional vehicle with a gasoline engine. The mechanical losses amount to approximately 10% of the full load power and are almost only dependent on the speed, so the mechanical efficiency decreases sharply with decreasing load. (see consumption map )

## Designations

In the first half of the 20th century, the Allgemeine Deutsche Sprachverein attempted to Germanize the compound foreign word explosion engine. “Explosion” became “Zerknall” (as is still the case today in “ Kesselzerknall ”) and “Motor” became, among other things, “Driver”. The proposed German name for an internal combustion engine was "Zerknalltreibling", which today has only survived as a joke.

## Classification

In the history of engine construction, many concepts have been devised and implemented that do not necessarily fit into the following grid, for example gasoline engines with direct injection or multi-fuel engines . For the sake of clarity, these special cases are not considered here.

These include the Wankel engine (gasoline engine with rotary piston and slot control) or marine diesel engines , which are often designed as two-stroke diesel engines with exhaust valves .

### According to the working procedure

Section through a motorcycle engine
Four-stroke process ( four-stroke engine )
Each of the four work steps takes place during one cycle. A stroke means a piston stroke , that is, a complete upward or downward movement of the piston. The crankshaft rotates twice during a four-stroke cycle. The gas hub is closed , i.e. fresh gas and exhaust gas are completely separated from each other. In practice, however, there is brief contact during the so-called valve overlap .
Scott two-stroke engine from 1912
Two-stroke process ( two-stroke engine )
Even with the two-stroke process, all four work steps take place, but during two piston strokes (= strokes). This is possible because some of the suction and compression (pre-compression) takes place outside the cylinder, in the crankcase under the piston or in a supercharger. The crankshaft rotates only once during a working cycle. The gas exchange is open , which means that the fresh gas and exhaust gas are partially mixed.
Compound engine
In the compound motor, the gases are compressed and expanded in stages. For this purpose, the compound engine has two combustion cylinders and a central cylinder that is used to pre-compress and expel the gases and whose piston is double-acting. The piston in the central cylinder sucks in the combustion air on its underside in upward gear and compresses it in downward gear. The compressed air is directed into one of the combustion cylinders where it is further compressed. When the piston of the combustion cylinder has reached top dead center, the fuel is injected. The fuel burns and the piston is pushed down by the expanding gases. In its upward gear, the piston does not push the gases into the exhaust, but back into the central cylinder, but on top. The gases that continue to expand push the piston downwards, thereby pre-compressing the air that has already been drawn in; the gases are then expelled when the piston moves upwards. At this point in time, the engine's work cycles have already started again. The central cylinder works in two-stroke, while the combustion cylinders work in four-stroke. Therefore, two combustion cylinders are required for a central cylinder. Rudolf Diesel had the compound motor patented under patent DRP 67207. Diesel hoped for a high degree of efficiency from the compound engine. In the course of 1896, a prototype based on Nadrowski's drawings made in 1894/1895 was created, which was not completed until 1897. The test runs showed that due to the high heat loss when the gases overflow from the combustion cylinder into the central cylinder, a high degree of efficiency could not be achieved. According to Diesel, the petroleum consumption when idling was 499 g · PS i · h −1 (678 g · kW i · h −1 ), for comparison, the first functioning diesel engine consumed only 238 g · PS · h −1 (324 g KW h −1 ) petroleum.
Split-cycle engine ( Scuderi engine )
The Scuderi engine works with four separate strokes, which are, however, divided between two cylinders. The four work steps suction, compression, combustion and ejection are distributed over two cylinders that are designed for their task. It is a well-known process, but it was only recently (2007) that a prototype was built. One of the earliest known engines of this type is the Puch two-stroke twin-piston engine .

### According to the mixture formation process

Mikuni round slide carburetor
Crank drive and common rail system

Otto engines usually work with an approximately constant combustion air ratio , that is, 13  to  15 mass units of air are added per unit of mass of fuel . 14.5 kg of air are required to burn 1 kg of gasoline; Such a fuel-air mixture is referred to as stoichiometric (air ratio ). If there is more air in the combustion chamber than necessary, the mixture is lean and lean ( ); if there is too little air in the combustion chamber, the mixture is under-stoichiometric, rich ( ). In order to detoxify the exhaust gases in a catalytic converter with maximum effect, an air ratio of 1 is required. Diesel engines work with a variable air ratio, roughly from 10 to 1.3. ${\ displaystyle \ lambda = 1}$${\ displaystyle \ lambda> 1}$${\ displaystyle \ lambda <1}$

The mixture formation can take place both inside and outside the combustion chamber, whereby the most important compression ignition engine, the diesel engine, only works with mixture formation within the combustion chamber.

External mixture formation
An ignitable gas mixture is fed into the cylinder via the intake tract and compressed there. This enables high speeds, as the combustion takes place without delay as soon as the ignition takes place. Excessive temperature (hot engine, high compression at full load) can lead to uncontrolled self-ignition . This effect, known as knocking , limits the compression ratio. The knock resistance of a fuel is indicated by its octane number and can be reduced by adding anti- knock agents . After ignition, the combustion can usually no longer be influenced. The external mixture formation can take place in two ways:
• Carburetors atomize the gasoline into fine droplets, creating an aerosol that is fed into the cylinders. They werecommonin automotive engineering until the 1990sand are now almost exclusively used in small engines.
• With indirect gasoline injection , the so-called manifold injection , the fuel is added to the air flow at a comparatively low pressure in the intake tract just before the inlet valve (s). Advantages over the carburettor include the faster and more precise control of the amount of fuel and the independence of position (important for example with aircraft engines ).
Internal mixture formation
Only air is sucked in and compressed by the cylinder. The fuel is only injected directly into the combustion chamber at high pressure immediately before combustion ( direct injection ), which is why the efficiency can be increased through higher compression. After the start of injection, the fuel needs time to evaporate and mix with the air. The combustion begins with a delay and thus limits the maximum engine speed.

### After the ignition process

Functional principle of a diesel engine
Model engine with homogeneous mixture and compression ignition

Spark ignition is a feature of various engines, including the gasoline engine. The ignition of the fuel-air mixture is initiated by an ignition aid, usually shortly before top dead center. Otto engines have spark plugs for this . If there is no spark plug and if the spark ignition is uncontrolled, it is called glow ignition. The first Daimler engines worked with glow ignition. A glow-igniter engine that was popular in the past is the glow-head engine , also known as the acroyd engine after its inventor . In Germany it is best known from the Lanz Bulldog farm tractors , and in Scandinavia as the engine of fishing boats, including Bolinders . With these engines, a part of the cylinder head called a glow head has to be heated, for example with a blowtorch, before ignition can start. The fuel is injected into the glow head during the compression stroke. Today glow igniter engines (which, however, do not work according to the Akroyd method) are mainly used in model making. In the case of gasoline engines, glow ignitions can occur in rare cases after the engine has been switched off, but they have a harmful effect on the engine and are therefore undesirable.

Compression ignition is a feature of various engines, the most famous compression ignition being the diesel engine. No ignition aids are used in a compression-ignition engine; instead, ignition is initiated solely by compression heat. The way compression-ignition engines work depends on their functional principle: in a diesel engine, clean air is first strongly compressed and thereby heated. Shortly before top dead center (TDC), the diesel fuel is injected, which ignites by itself due to the heat. Since the fuel in the diesel engine ignites due to the late injection before a homogeneous mixture can form, the diesel engine is called a heterogeneous mixture . In so-called HCCI engines, on the other hand, a homogeneous mixture is formed that is only supposed to ignite through the heat of compression. In contrast to the diesel engine, the fuel must be injected early so that the mixture is well mixed (homogeneous) until ignition. This results in better emission values. Some model construction engines also work with homogeneous compression ignition, the mixture is formed here with a carburetor, the compression ratio can be adjusted with a screw.

### After the firing process

With combustion process or combustion process in internal combustion engines is called the sequence in which the fuel burns in the engine.

turbocharger

### After the cooling process

• Liquid cooling
• Evaporative cooling
• Air cooling
• Oil cooling
• Combinations of air / oil cooling (SAME)
• Nitrogen cooling

### According to the degree of speed

In earlier years the degree of speed was determined by the piston speed , later increasingly by the speed . There are three classes of large engines (ships, trains, power generators):

• Slow runners up to 300 rpm, which work in the two-stroke process and are suitable for heavy fuel oil
• Medium-speed runners between 300 and 1200 rpm, which are mainly four-stroke engines suitable for heavy oil
• High-speed four-stroke engines from 1000 rpm, which are no longer suitable for heavy fuel oil.

According to further definitions there are

• Center runner up to 2000 rpm for boat and inland waterway engines, auxiliary units and the like
• High-speed runners over 2000 rpm as gasoline and diesel engines for vehicles
According to Schrön

In the 1942 published work The Internal Combustion Engine, Hans Schrön distinguishes between three different types, the slow runners, the middle runners and the fast runners. Schrön uses the piston speed as a distinguishing feature . He sees the fact that not all motors are designed as high-speed runners in points that play a more important role than high speeds in the design. The slow runners and middle runners should have a long service life and freedom from interference, including stationary engines and ship engines. Schrön also points out the advantage of high efficiency in marine engines. Other central runners include railcar, truck, tractor and combat vehicle engines. High-speed runners should have low mass, little volume and good installation capabilities; the highest possible performance may still play a role. Speed ​​boats, airplanes and light vehicles come into consideration as areas of application. Both diesel and gasoline engines can run fast.

Diesel engines according to Mau

Günter Mau differentiates the degree of speed of diesel engines as follows:

• Slow speed: up to 300 min -1
• Medium-speed: less than 1000 min -1
• High speed: greater than or equal to 1000 min -1

### According to types and number of cylinders

Depending on the number of cylinders , gasoline and diesel engines or four-stroke and two-stroke engines are / were built as:

Cross-sectional drawing of a six-cylinder - V-type engine
The in-line radial engine
Zvezda M503 with 42 cylinders in seven cylinder banks of six cylinders each.

The types and numbers of cylinders in bold are common in motor vehicles today. The combustion engine with the highest number of cylinders ever built is the Zvezda M520 in-line star engine with 56 cylinders in seven cylinder banks of eight cylinders each.

Four-stroke radial engines always have an odd number of cylinders per star. The reason for this is that in a four-stroke engine each cylinder is only fired in every second revolution, so that a continuous firing sequence, which is necessary for the smooth, vibration-free running of the engine, can only be achieved with an uneven number of cylinders. Multiple radial engines such as the 14-cylinder double radial engines BMW 801 and Wright R-2600 or the P & W R-4360 (28 cylinders in four stars of seven each) have an even number of cylinders.

This is to be distinguished from the in-line radial engines , in which several cylinder banks are arranged in a star shape around the crankshaft . These were, for example, the Daimler-Benz DB 604 , Rolls-Royce Vulture and Allison X-4520 ( X-engines with four cylinder banks of six cylinders each = 24 cylinders), Junkers Jumo 222 and Dobrynin WD-4K (also 24 cylinders, however as a hexagon with six cylinder banks of four cylinders each) and the twelve-cylinder Curtiss H-1640 Chieftain engine with six cylinder banks of two cylinders each.

In motorsport , V-engines with an uneven number of cylinders (three or five) are occasionally built despite the higher unbalance.

As slow-running marine diesel engines, there are in-line engines with up to 14 cylinders and V-engines with 20 or 24 cylinders.

## Unusual designs

The rotary engine is a rotary piston engine that was invented by Felix Wankel and named after him. Two kinematic forms are possible with the Wankel engine: On the one hand the rotary piston engine , in which an arched-triangular piston ( constant thickness ) in an oval-disc-shaped housing revolves on a circular path determined by the eccentric shaft. On the other hand, the rotary piston engine, in which both the arched-triangular rotor and the oval-disk-shaped shell figure ( trochoid ) rotate around their centers of gravity on slightly offset axes.

The Stelzer engine , named after its inventor Frank Stelzer , is a two-stroke free-piston engine with a moving part called a “stepped piston”. It consists of three pistons rigidly connected by a piston rod. The middle one is a double-acting disc piston as a flushing pump for the two outer working pistons, which work as pistons in a slot-controlled, direct-current flushed two-stroke engine. Because of the piston rod, the combustion chambers of these two-stroke engines are ring-shaped. The outer ends of the stepped piston move out of the engine block and can be part of a work machine, for example a compressor or an electric generator .

The Mederer motor and the cross-loop motor have a slightly different piston movement.

The spherical motor : The first patented spherical motor was developed by Frank Berry in 1961 in the USA. Another model followed, which was developed by the physicist Wolfhart Willimczik after 1974 and works according to the two-stroke principle. Herbert Hüttlin developed a spherical motor that works with curved pistons that move against each other. This engine is known in the literature under the generic term rotary piston machine. Arnold Wagner developed the Hiteng spherical motor. The Hiteng spherical motor works with two double pistons that rotate in a spherical housing. The inventor calls this engine an oscillating piston machine.

In the first half of the 20th century a number of exotic constructions were designed, but they did not exceed the prototype stage. Advances in materials research have made it possible to solve problems of old designs.

## Particulate emissions from combustion

Particles in the exhaust gas from internal combustion engines (10–1000 nm) are smaller than others, for example those caused by tire abrasion (15,000 nm). Like them, however, they consist of soot and hydrocarbons ( e.g. PAH ). The exhaust gas nanoparticles obtain their presumed health relevance for humans due to their surface area and size. They can damage cell membranes (soot) or react with them (PAH). Due to their size ( nano refers to everything below 100 nm) they manage to overcome the upper airways and the lung wall and thus enter the bloodstream ( cf. ). Dose, exposure time, projectability of animal experiments on humans and accompanying circumstances such as smoking by study participants form the objectives of current research. In anticipation of this, the Euro 6 emission standard for 2014 limits the amount of particles for the first time (draft value: 6 × 10 11 pieces per km) and no longer just their mass. The mass is only influenced by the decisive nanoparticles by 20%, but with diesel the total mass is already reduced by 97% by closed particle filters. This shows that the accumulation of filtrate there also traps relevant quantities of nanoparticles well below the actual filter pore size of 1000 nm. With this reduction, the filter also minimizes the climate impact of the particles. The dark soot color turns the particles into heat absorbers. In this way, they directly heat the soot-polluted air and, after deposition, also areas of snow in the Arctic, which they reach through air currents from Europe, for example.

Gasoline and diesel engines produce comparable quantities and sizes of particles during full load and cold start phases. In both phases, more fuel is injected than the oxygen can burn in the cylinder (“enriched mixture”). In cold start phases, this is done to warm up the catalytic converter, under full load to cool the engine. While gasoline engines only produce particles when they are in rich operation due to a lack of oxygen, they are produced in diesel engines even in lean operation and thus during all operating phases. Therefore, the total amount of particles in the gasoline engine is still at the low level of a diesel with a closed filter system.

The reason for the diesel soot is its twice as long-chain aromatics ( compare petrol ). They have a significantly higher boiling point (from 170 to 390 ° C instead of 25 to 210 ° C). At the same time, however, the combustion temperature of the diesel is 500 ° C below that of the gasoline engine. Gasoline therefore evaporates more completely than diesel. Its components, which boil earlier, evaporate first, which also keeps the remaining droplets of aromatics with higher boiling points at a lower temperature ( cf. ). The aromas that have not evaporated are cracked into their components during the auto-ignition phase due to the temperature . One of these is carbon , i.e. soot.

The particle composition differs due to the chemistry of both fuels. In the case of gasoline engines, PAH particles predominate, in diesel engines it is soot particles. The particles only become visible when they are stacked together. Visible particles are no longer respirable and are usually filtered out and broken down in the upper airway. Deposits take place in the exhaust and especially in the particle filter. The accumulation of the filtrate there also traps particles far below the actual filter pore size (1 µm). This reduces the number of particles to the level of a gasoline engine. The accumulation of particles in the exhaust becomes recognizable. If this is missing, a diesel has a closed filter system and a gasoline engine has only a few parts of cold start and full load phases.

## Prohibitions

Many countries are planning to ban passenger cars with internal combustion engines. The following table gives an overview.

country region Beginning diesel petrol Type of prohibition
Belgium Brussels 2030 Driving ban
People's Republic of China Hainan Province 2019 Ban on sale
Denmark nationwide 2030 Ban on sale
France nationwide 2040 Ban on sale
United Kingdom nationwide 2040 Ban on sale
Ireland nationwide 2030 Admission ban
Iceland nationwide 2030 Admission ban
Israel nationwide 2030 Ban on sale
Italy Rome 2024 Driving ban
Netherlands nationwide 2030 Admission ban
Norway Oslo 2025 Driving ban
Spain nationwide 2050 Driving ban
Sweden nationwide 2030 Ban on sale
Taiwan nationwide 2040 Driving ban
United States California 2040 Driving ban

## literature

• Hans-Hermann Braess Vieweg Handbook Automotive Technology 6th edition Vieweg + Teubner Verlag, Wiesbaden ISBN 978-3-8348-1011-3 .
• Wolfgang Kalide: Pistons and flow machines. 1st edition. Carl Hanser Verlag, Munich / Vienna 1974, ISBN 3-446-11752-0 .
• Jan Drummans: The car and its technology. 1st edition. Motorbuchverlag, Stuttgart 1992, ISBN 3-613-01288-X .
• Hans Jörg Leyhausen: The master craftsman's examination in the automotive trade. Part 1, 12th edition, Vogel Buchverlag, Würzburg 1991, ISBN 3-8023-0857-3 .
• Wilfried Staudt: Vehicle technology manual. Volume 2, 1st edition. Bildungsverlag EINS, Troisdorf 2005, ISBN 3-427-04522-6 .
• Peter A. Wellers, Hermann Strobel, Erich Auch-Schwelk: Vehicle technology expertise. 5th edition. Holland + Josenhans Verlag, Stuttgart 1997, ISBN 3-7782-3520-6 .
• Gernot Greiner: Internal combustion engines in car and airplane model construction. Poing near Munich, Franzis Verlag, 2012, ISBN 978-3-645-65090-8 .
• Helmut Hütten: Engines: Technology - Practice - History. 10th edition, Motorbuch Verlag Stuttgart, 1997, ISBN 3-87943-326-7 .

Wiktionary: Internal combustion engine  - explanations of meanings, word origins, synonyms, translations

## Individual evidence

1. According to the definition of IPC class F02 “ Internal combustion engines; engine systems operated with hot gas or exhaust gases ", subgroup F02B" internal combustion engines with internal combustion with displacement effect ; Internal combustion engines in general ”, inventions of internal combustion engines are classified in these classes by the patent offices.
2. Vieweg Handbook Motor Vehicle Technology p. 162, ISBN 978-3-8348-1011-3
3. See Peter Hofmann, hybrid vehicles . Vienna 2010, p. 72f.
4. Valentin Crastan , Electrical Energy Supply 2 . Berlin Heidelberg 2012, p. 57.
5. ^ Rudolf CK Diesel: The emergence of the diesel engine , Springer, Berlin 1913, ISBN 978-3-642-64940-0 , p. 85; 130-140
6. See GP Merker, R. Teichmann (Ed.), “ Basics of Combustion Engines ”, 7th edition 2014, Section 3.8 “ Large Diesel Engines ”, Springer Fachmedien Wiesbaden, ISBN 978-3-658-03194-7
7. Harald Maass: Design and main dimensions of the internal combustion engine , Springer-Verlag, 1979, ISBN 978-3-7091-8569-8 , pp. 81–82 [1]
8. Hans Schrön: The dynamics of the internal combustion engine . In: Hans List (Ed.): The internal combustion engine . No. 8 . Springer, 1942, ISBN 978-3-662-01905-4 , pp. 9 , doi : 10.1007 / 978-3-662-02200-9 .
9. Günter Mau: Manual Diesel Engines in Power Plant and Ship Operation . Vieweg. Braunschweig / Wiesbaden. 1984. ISBN 978-3-528-14889-8 . P. 15
10. Passability of exhaust gas nanoparticles ( Memento of February 8, 2008 in the Internet Archive ).
11. page can no longer be accessed , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. .
12. ↑ Number of particles limited from Euro 6 ( Memento of February 22, 2014 in the Internet Archive ).
13. page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
14. Page no longer available , search in web archives: p. 16: 97% reduction in the total number of particles through a closed filter .
15. page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
16. Page no longer available , search in web archives: p. 17 Nanoparticle reduction by closed filter by 99.5% .
17. Same particle quantities and sizes in diesel and gasoline engines at full load and cold start phases ( Memento from July 8, 2012 in the web archive archive.today )
18. page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. .
19. Xiangdong Chen, Dave OudeNijeweme, Richard Stone, Philip Price: Cold Start Particulate Emissions from a second generation DI Gasoline Engine . No. 2007-01-1931 . SAE Technical Paper, Warrendale, PA July 23, 2007 ( sae.org [accessed March 10, 2019]).
20. a b
21. page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. .
22. Planned registration bans and driving restrictions for combustion engines worldwide ACE, accessed on November 7, 2019