Conventional Otto type engine

The conventional Otto type engine is a four-stroke (4T) reciprocating type engine, although the two-stroke (2T) engine was widely used in outboards and two-wheeled vehicles up to a certain displacement. The thermal performance of modern Otto engines is limited by several factors, including energy loss due to friction, cooling, and lack of consistency in operating conditions.

Thermodynamics tells us that the performance of a reciprocating engine depends to a first approximation on the degree of compression "Compression ratio (engines)"). This ratio is usually 8 to 1 or 10 to 1 in most modern Otto engines. Higher ratios, such as 12 to 1, can be used, thus increasing engine efficiency, but this design requires the use of high octane fuels to avoid the detonation phenomenon "Knock (reciprocating engine)"), which can cause serious engine damage. The average efficiency or performance of a good Otto motor is 20 to 25%: only a quarter of the heat energy is transformed into mechanical energy.

Almost all engines of this type are manufactured for transportation and must work by supplying different powers at all times.

Due to this, their performance drops sharply when working with partial load, since, when this happens, the compression chamber maintains its volume, giving a low final compression and transforming a large part of the energy into heat.

Operation (Figure 1).

1. Intake timing - Mixed air and fuel enter through the intake valve.

2. Compression time - The air/fuel mixture is compressed and ignited by the spark plug.

3. Combustion time - The fuel ignites and the piston is pushed down.

4. Exhaust Time - Exhaust gases are directed out through the exhaust valve.

There is also a variation of the Otto cycle that improves engine efficiency by increasing the expansion time with respect to the compression time known as the Miller Cycle.

diesel engines

In theory, the diesel cycle differs from the Otto cycle in that combustion in the latter takes place at a constant volume rather than at a constant pressure. Most diesel engines are also four-stroke cycle, except for very large, railway or marine ones, which are two-stroke. The phases are different from those of gasoline engines.

In the first stroke, the intake stroke, the piston comes out, and air is absorbed into the combustion chamber. In the second stroke, the compression phase, in which the piston approaches. The air is compressed to a part of its original volume, which causes its temperature to rise to about 850 °C. At the end of the compression phase, the fuel is injected at high pressure through fuel injection, which atomizes it inside the combustion chamber, causing ignition due to the high air temperature. In the third phase, the working phase, the combustion gases push the piston outward, transmitting the longitudinal force to the crankshaft through the connecting rod, transforming it into engine torque. The fourth phase is, as in Otto engines, the exhaust phase, when the piston returns inward.

Some diesel engines use an auxiliary ignition system to ignite the fuel when starting the engine and while it reaches the proper temperature.

The efficiency or performance (proportion of fuel energy that is transformed into work and not lost as heat) of diesel engines depends on the same factors as Otto engines, that is, on the initial and final pressures (and therefore temperatures) of the compression phase. Therefore, it is higher than in gasoline engines, reaching over 40%. in large two-stroke naval propulsion engines. This value is achieved with a compression ratio of approximately 20 to 1, versus 9 to 1 in the Otto. Therefore, greater robustness is necessary, and diesel engines are generally heavier than Otto engines. This disadvantage is offset by higher performance and the use of cheaper fuels.

Large 2-stroke diesel engines are usually slow engines with crankshaft speeds of 100 to 750 revolutions per minute (rpm or r/min) (large ships), while 4-stroke engines run up to 2500 rpm (trucks and buses) and 5000 rpm (cars).

two stroke engine

With a suitable design, an Otto or diesel engine can be made to operate at two strokes, with a power stroke every two phases instead of every four phases. The efficiency of this type of engine is lower than that of four-stroke engines, but since they only need two strokes to perform a complete cycle, they produce more power than a four-stroke engine of the same size.

The general principle of the two-stroke engine is the reduction of the duration of the fuel absorption and gas expulsion periods to a minimum part of one of the strokes, instead of each operation requiring a complete time. The simplest two-stroke engine design uses, instead of valves in the cylinder head, ports, orifices (which are exposed as the piston rises and falls). In two-stroke engines, almost always lubricated by adding oil to gasoline, the fuel-air mixture enters the cylinder through the intake port when the piston is in the farthest position from the cylinder head. The first stroke is the compression-ignition, in which the combustion of the air/fuel/oil mixture charge begins when the piston advances to the end of that stroke (TDC). The piston is then withdrawn in the explosion phase, opening the ejection port and allowing the gases to exit the chamber. Of the two procedures for 'scavenging' inside the cylinders of two-stroke engines, a process by which the new charge enters and the gases from the combustion of the working mixture are expelled into the exhaust, it has been demonstrated (SAE) that the so-called: 'Loop scavenging' always gives better results than the system called: 'Unidirectional' ('Uniflow scavenging' in English).

four stroke engine

Around 1879 Nicolaus August Otto designed and built an engine with double expansion, a concept proposed by the English Jonathan Hornblower and Artur Woolf in 1781, before Watt put the steam engine into practice. The first expansion was made in the cylinder where the combustion took place, and a second in another piston, this one at low pressure, with the aim of harnessing the energy of the exhaust gases; Even triple expansion engines have been built, such as the Troy, and the principle was used in many marine engines. In 1906, the EHV company based in Connecticut, USA, manufactured a three-cylinder, double-expansion internal combustion engine that they mounted in a car. Like the engine built by Otto, whose buyer returned it, the EHV engine did not demonstrate in practice the expected lower fuel consumption benefits. In Spain there are two patents granted for engines with a similar principle, one from 1942 to Francisco Jimeno Cataneo (OEPM No. 0156621) and another from 1975 to Carlos Ubierna Laciana (OEPM No. 0433850), at INTA a prototype of an aviation engine with star cylinders and a similar principle was built, designed by the engineer J Ortuño García, patents 0230551 and 0249247 and to which very low fuel consumption was attributed, is exhibited in the Air Museum in Cuatro Vientos, Madrid. In 2009, the British company ILMOR presented a 5-stroke engine prototype at an international motor exhibition in Stuttgart, according to a patent granted in the US to Gerhard Schmitz. For this engine they announced a specific consumption of 215 g/kWh, an effective compression ratio of 14.5/1 and a weight 20% lower than equivalent conventional engines.[2][3][4]​.

Wankel engine

In the 1950s, German engineer Felix Wankel completed the development of an internal combustion engine with a revolutionary design, currently known as the Wankel Engine. It uses a triangular-lobe rotor inside an oval chamber, instead of a piston and cylinder.

The fuel and air mixture is absorbed through a suction hole and is trapped between one of the faces of the rotor and the wall of the chamber. The rotation of the rotor compresses the mixture, which is ignited by a spark plug. The gases are expelled through an exhaust hole with the movement of the rotor. The cycle takes place once on each face of the rotor, producing three phases of power with each turn.

The Wankel engine is compact and lightweight compared to piston engines, which is why it gained importance during the oil crisis in the 1970s and 1980s. In addition, it operates almost without vibrations and its mechanical simplicity allows for cheap manufacturing. It doesn't require much cooling, and its low center of gravity increases driving safety. However, except for some practical examples such as some Mazda vehicles, it has had durability problems.

Stratified charge engine

A variant of the spark plug ignition engine is the stratified charge engine, designed to reduce emissions without the need for a recirculation system for the gases resulting from combustion and without using a catalyst. The key to this design is a double combustion chamber inside each cylinder, with an antechamber containing a rich mixture of fuel and air while the main chamber contains a lean mixture. The spark plug ignites the rich mixture, which in turn ignites that of the main chamber. The maximum temperature reached is low enough to prevent the formation of nitrogen oxides, while the average temperature is sufficient to limit carbon monoxide and hydrocarbon emissions.

Conventional Otto type engine

The conventional Otto type engine is a four-stroke (4T) reciprocating type engine, although the two-stroke (2T) engine was widely used in outboards and two-wheeled vehicles up to a certain displacement. The thermal performance of modern Otto engines is limited by several factors, including energy loss due to friction, cooling, and lack of consistency in operating conditions.

Thermodynamics tells us that the performance of a reciprocating engine depends to a first approximation on the degree of compression "Compression ratio (engines)"). This ratio is usually 8 to 1 or 10 to 1 in most modern Otto engines. Higher ratios, such as 12 to 1, can be used, thus increasing engine efficiency, but this design requires the use of high octane fuels to avoid the detonation phenomenon "Knock (reciprocating engine)"), which can cause serious engine damage. The average efficiency or performance of a good Otto motor is 20 to 25%: only a quarter of the heat energy is transformed into mechanical energy.

Almost all engines of this type are manufactured for transportation and must work by supplying different powers at all times.

Due to this, their performance drops sharply when working with partial load, since, when this happens, the compression chamber maintains its volume, giving a low final compression and transforming a large part of the energy into heat.

Operation (Figure 1).

1. Intake timing - Mixed air and fuel enter through the intake valve.

2. Compression time - The air/fuel mixture is compressed and ignited by the spark plug.

3. Combustion time - The fuel ignites and the piston is pushed down.

4. Exhaust Time - Exhaust gases are directed out through the exhaust valve.

There is also a variation of the Otto cycle that improves engine efficiency by increasing the expansion time with respect to the compression time known as the Miller Cycle.

diesel engines

In theory, the diesel cycle differs from the Otto cycle in that combustion in the latter takes place at a constant volume rather than at a constant pressure. Most diesel engines are also four-stroke cycle, except for very large, railway or marine ones, which are two-stroke. The phases are different from those of gasoline engines.

In the first stroke, the intake stroke, the piston comes out, and air is absorbed into the combustion chamber. In the second stroke, the compression phase, in which the piston approaches. The air is compressed to a part of its original volume, which causes its temperature to rise to about 850 °C. At the end of the compression phase, the fuel is injected at high pressure through fuel injection, which atomizes it inside the combustion chamber, causing ignition due to the high air temperature. In the third phase, the working phase, the combustion gases push the piston outward, transmitting the longitudinal force to the crankshaft through the connecting rod, transforming it into engine torque. The fourth phase is, as in Otto engines, the exhaust phase, when the piston returns inward.

Some diesel engines use an auxiliary ignition system to ignite the fuel when starting the engine and while it reaches the proper temperature.

The efficiency or performance (proportion of fuel energy that is transformed into work and not lost as heat) of diesel engines depends on the same factors as Otto engines, that is, on the initial and final pressures (and therefore temperatures) of the compression phase. Therefore, it is higher than in gasoline engines, reaching over 40%. in large two-stroke naval propulsion engines. This value is achieved with a compression ratio of approximately 20 to 1, versus 9 to 1 in the Otto. Therefore, greater robustness is necessary, and diesel engines are generally heavier than Otto engines. This disadvantage is offset by higher performance and the use of cheaper fuels.

Large 2-stroke diesel engines are usually slow engines with crankshaft speeds of 100 to 750 revolutions per minute (rpm or r/min) (large ships), while 4-stroke engines run up to 2500 rpm (trucks and buses) and 5000 rpm (cars).

two stroke engine

With a suitable design, an Otto or diesel engine can be made to operate at two strokes, with a power stroke every two phases instead of every four phases. The efficiency of this type of engine is lower than that of four-stroke engines, but since they only need two strokes to perform a complete cycle, they produce more power than a four-stroke engine of the same size.

The general principle of the two-stroke engine is the reduction of the duration of the fuel absorption and gas expulsion periods to a minimum part of one of the strokes, instead of each operation requiring a complete time. The simplest two-stroke engine design uses, instead of valves in the cylinder head, ports, orifices (which are exposed as the piston rises and falls). In two-stroke engines, almost always lubricated by adding oil to gasoline, the fuel-air mixture enters the cylinder through the intake port when the piston is in the farthest position from the cylinder head. The first stroke is the compression-ignition, in which the combustion of the air/fuel/oil mixture charge begins when the piston advances to the end of that stroke (TDC). The piston is then withdrawn in the explosion phase, opening the ejection port and allowing the gases to exit the chamber. Of the two procedures for 'scavenging' inside the cylinders of two-stroke engines, a process by which the new charge enters and the gases from the combustion of the working mixture are expelled into the exhaust, it has been demonstrated (SAE) that the so-called: 'Loop scavenging' always gives better results than the system called: 'Unidirectional' ('Uniflow scavenging' in English).

four stroke engine

Around 1879 Nicolaus August Otto designed and built an engine with double expansion, a concept proposed by the English Jonathan Hornblower and Artur Woolf in 1781, before Watt put the steam engine into practice. The first expansion was made in the cylinder where the combustion took place, and a second in another piston, this one at low pressure, with the aim of harnessing the energy of the exhaust gases; Even triple expansion engines have been built, such as the Troy, and the principle was used in many marine engines. In 1906, the EHV company based in Connecticut, USA, manufactured a three-cylinder, double-expansion internal combustion engine that they mounted in a car. Like the engine built by Otto, whose buyer returned it, the EHV engine did not demonstrate in practice the expected lower fuel consumption benefits. In Spain there are two patents granted for engines with a similar principle, one from 1942 to Francisco Jimeno Cataneo (OEPM No. 0156621) and another from 1975 to Carlos Ubierna Laciana (OEPM No. 0433850), at INTA a prototype of an aviation engine with star cylinders and a similar principle was built, designed by the engineer J Ortuño García, patents 0230551 and 0249247 and to which very low fuel consumption was attributed, is exhibited in the Air Museum in Cuatro Vientos, Madrid. In 2009, the British company ILMOR presented a 5-stroke engine prototype at an international motor exhibition in Stuttgart, according to a patent granted in the US to Gerhard Schmitz. For this engine they announced a specific consumption of 215 g/kWh, an effective compression ratio of 14.5/1 and a weight 20% lower than equivalent conventional engines.[2][3][4]​.

Wankel engine

In the 1950s, German engineer Felix Wankel completed the development of an internal combustion engine with a revolutionary design, currently known as the Wankel Engine. It uses a triangular-lobe rotor inside an oval chamber, instead of a piston and cylinder.

The fuel and air mixture is absorbed through a suction hole and is trapped between one of the faces of the rotor and the wall of the chamber. The rotation of the rotor compresses the mixture, which is ignited by a spark plug. The gases are expelled through an exhaust hole with the movement of the rotor. The cycle takes place once on each face of the rotor, producing three phases of power with each turn.

The Wankel engine is compact and lightweight compared to piston engines, which is why it gained importance during the oil crisis in the 1970s and 1980s. In addition, it operates almost without vibrations and its mechanical simplicity allows for cheap manufacturing. It doesn't require much cooling, and its low center of gravity increases driving safety. However, except for some practical examples such as some Mazda vehicles, it has had durability problems.

Stratified charge engine

A variant of the spark plug ignition engine is the stratified charge engine, designed to reduce emissions without the need for a recirculation system for the gases resulting from combustion and without using a catalyst. The key to this design is a double combustion chamber inside each cylinder, with an antechamber containing a rich mixture of fuel and air while the main chamber contains a lean mixture. The spark plug ignites the rich mixture, which in turn ignites that of the main chamber. The maximum temperature reached is low enough to prevent the formation of nitrogen oxides, while the average temperature is sufficient to limit carbon monoxide and hydrocarbon emissions.