Direct petrol injection

Cutaway model of a gasoline engine with direct injection ( BMW N53 )

Gasoline direct injection is a process for internal mixture formation in engines that run on gasoline , especially gasoline engines . Compared to conventional methods, it enables increased engine output and reduces fuel consumption and thus carbon dioxide emissions. Gasoline direct injection differs from direct diesel fuel injection in that the injection pressure is lower because of the lower lubricity of the gasoline.

Gasoline direct injection was first used in 1916 in a Junkers aircraft engine, which later served as a boat drive. It was mass-produced for German aircraft engines in the 1930s and briefly found its way into automobiles in the 1950s. They almost completely replaced low fuel costs in the 1950s and 1960s; In the 1970s and 1980s, manifold injection was the dominant system. It was not until 1995 that Mitsubishi and later also other manufacturers reintroduced gasoline direct injection with stratified charge for large-scale car engines. The hoped-for savings in fuel consumption did not materialize, so that the pure stratified charge operation was increasingly abandoned by the engine manufacturers. Instead, the combustion process with a homogeneous mixture had established itself in almost all engine manufacturers by 2017 . Gasoline direct injection continues to offer great potential for reducing fuel consumption.

Designations

Wall-mounted direct injection in a Ford EcoBoost engine with a displacement of 3.5 liters , 309 kW

The term gasoline direct injection describes the injection of gasoline with an injection nozzle directly into the cylinder. Only air is sucked in through the inlet valves. In contrast to this, in the case of an intake manifold injection, the gasoline is injected into the intake manifold behind the throttle valve and a fuel-air mixture is sucked in. One speaks of internal mixture formation when the fuel is injected directly and of external mixture formation when it is mixed with the intake air outside a combustion chamber, for example in the intake pipe.

functionality

A distinction is made between various operating strategies for gasoline direct injection, which mainly differ in terms of throttle valve position, injection timing and mixture composition; Furthermore, the guidance of the fuel jet and the design of the air turbulence in the combustion chamber are also distinguishing criteria in stratified charge operation.

Operational strategies

Homogeneous operation
Stratified charge operation
Mixture of both operating modes

Injection jet guidance in stratified charge operation

Air-guided
Wall mounted
Beam guided

Operational strategies

Homogeneous operation

Mercedes-Benz M 198 , the first four-stroke gasoline engine for a passenger car with gasoline direct injection

Homogeneous operation means that a gasoline engine is operated with a homogeneous, stoichiometrically regulated fuel- air mixture ( combustion air ratio ). It works without low-sulfur fuel as it works with a conventional three-way catalytic converter . The focus here is not on the potential to save fuel consumption; instead, this process aims to achieve more torque and thus higher performance , but the process is also well suited for increasing efficiency by reducing displacement while increasing the specific displacement (so-called downsizing ). In homogeneous operation, the fuel is injected into the intake stroke, so that the fuel mixes with the air at an early stage and a homogeneous mixture is created in the combustion chamber. Today (2017) passenger car gasoline engines are designed with this operating strategy or converted to it by updating the engine control software. ${\ displaystyle \ lambda = 1}$

The homogeneous operation is the structurally much simpler variant of the gasoline direct injection, since it can also be implemented with a purely mechanical engine drive (i.e. without electronic control units). In the historic Mercedes-Benz M 198 engine from 1954, which will serve as an example here, homogeneous operation is therefore used, as is the case with comparable engines with manifold injection or carburettors . The torque is set via the throttle valve position (change in quantity ) and, as described above, the fuel is injected very early into the intake stroke. Even with a high crankshaft speed and thus high piston speed, there is still enough time for the gasoline to mix sufficiently well with the air and for the mixture formed to be evenly distributed in the combustion chamber; the injection time does not have to be adapted to the engine speed, which considerably simplifies the construction of the injection pump.

Stratified charge operation

The stratified charge operation means that a gasoline engine is operated with a layered, inhomogeneous, partly over-stoichiometric fuel-air mixture. The maximum global air-fuel ratio can exceed values of 8 ( ), while the mean air-fuel ratio is approximately at part load and at full load . As with a diesel engine, the torque is only adjusted via the amount of fuel injected; ideally, the throttle valve always remains wide open. ${\ displaystyle \ lambda> 8}$ ${\ displaystyle \ lambda = 3 \ ldots 5}$ ${\ displaystyle \ lambda = 1}$

Since the ignition can no longer be safely initiated if the mixture is too lean, the mixture must be stratified: unlike in homogeneous operation, where fuel and air are homogeneously distributed in the combustion chamber, in stratified charge operation the fuel is injected into the combustion chamber in such a way that only in An ignitable mixture is present in the area of the spark plug, while in the rest of the combustion chamber the mixture is very lean or consists of pure air or recirculated exhaust gas. Injection takes place in the compression stroke. In order to ignite the mixture, a high ignition energy of up to 0.14 J must be applied. With this operating mode, fuel consumption and thus carbon dioxide emissions can be reduced in particular; this applies in particular to operation with a low load. At full load, however, stratified charge no longer affects fuel consumption. As with a diesel engine, the overstoichiometric mixture produces nitrogen oxides during combustion , which make a storage catalytic converter necessary; this storage catalytic converter only works with sulfur-free fuel. Since the consumption advantage of stratified charging only has a limited effect in practice, but the system requires costly exhaust gas aftertreatment and special fuel, it was unable to prevail on a broad basis against homogeneous operation; if stratified charging is used, then only in conjunction with the spray-guided injection process (see below) .

Mixed operation

If both operating strategies are combined, this is done in order to circumvent the throttling of the mixture, which has a negative effect on the efficiency, as well as possible and to compensate for the disadvantages of stratified charging. For this purpose, stratified charge mode is used in the operating range of low load, while in the area of higher load, the system switches to lean or homogeneous operation. Since the throttle valve is wide open in homogeneous operation at full load, there is almost no more mixture throttling.

Injection jet guidance for mixture formation in gasoline engine stratified charge operation

Wall-guided method

Nose piston for wall-mounted travel of a Ford EcoBoost engine

The wall-guided method is a method with a large gap between the injection valve and the spark plug. The fuel is injected onto the nose-shaped piston crown and thus directed to the spark plug; this operation is by a targeted swirl (swirl) or tumble flow (tumble) supports the sucked air. Since individual hydrocarbon components of the fuel cannot burn properly, especially at low operating temperatures, by applying the fuel directly to the piston, they are ejected again unburned. If the engine changes from a low load to the medium partial load range, the gasoline has to be injected earlier, which can lead to it being injected outside the intended combustion chamber and into the pinch gap, where it does not burn and again as unburned hydrocarbon is expelled. Furthermore, the point in time of injection is linked to the piston speed and thus to the engine speed. The point of injection and ignition must therefore be precisely coordinated with one another, and the charge movement must be very stable due to the long transport time of the mixture from the piston to the spark plug.

Air-guided process

The air-guided method, like the wall-guided method, has a large distance between the injection valve and the spark plug, which is why the fuel must first be transported to the spark plug. In contrast to the wall-guided method, however, contact between the fuel and the combustion chamber wall is avoided, which prevents fuel deposits and, as a result, poor exhaust gas behavior. For this purpose, a swirl or roller-like charge movement is generated on the inlet side alone, which leads the fuel jet to the spark plug. This effect can be increased by using certain piston designs. The problem with this process is that the twisting or roller-like charge movement has to be maintained for a very long time (longer than with the other processes), which reduces the degree of delivery and thus the performance. In practice, air-guided methods are used in combination with wall-guided methods; there is only a purely air-guided process without this combination (as of 2017).

Beam-guided process

Ford EcoBoost 1.0 liter (cutaway model): The close proximity between the injection valve and the spark plug can be seen on the right cylinder. The yellow arrow shows the spark plug, the red arrow the injection valve.

With the jet-guided method, the spatial distance between the spark plug electrode and the injection valve is very small; both components are arranged between the inlet and outlet valves. The injection takes place late, namely in the compression stroke. The injected fuel mixes rapidly with the air that surrounds it due to aerodynamic effects, which leads to large stratification gradients : While the mixture in the jet core is very rich, the air ratio increases rapidly towards the edge, the fuel-air mixture is there so too lean to be sufficiently ignitable, only in the area between these two zones is the mixture sufficiently ignitable. The ignition, measured in ° CA , is initiated almost immediately after the injection, which improves the efficiency. The spark plug and injection valve must now be arranged in such a way that the ignitable mixture is present exactly in the area of the spark plug.

The required precision means very low manufacturing tolerances, as the jet pattern can be changed significantly by the slightest impairment, which has a negative effect on the burning behavior. Since the fuel is liquid during injection and only evaporates in the combustion chamber, it cools the spark plug considerably, which, however, becomes very hot again due to the subsequent combustion, which means that the spark plug must be very resistant to thermal shock . If the piston speed is low, it is possible that the relative speed between fuel and air is not sufficiently great, which means that the fuel droplets are too large and do not evaporate sufficiently, as a result of which the mixture becomes too rich. Unburned fuel can coke the electrodes of the spark plug and the injection nozzle. Coking of the spark plug can lead to misfiring, while coking of the injection nozzle, as mentioned above, negatively affects the spray pattern. If the piston speed is too high with the jet-guided method, the fuel droplets are atomized more finely and are distributed more strongly in the combustion chamber, whereby the mixture stratification can be influenced so that there is no longer an ignitable mixture in the area of the spark plug. If the spark plug is positioned too close to the injection valve, the flow velocities in the spark plug gap increase so much that the spark duration is shortened and no longer enough energy can be transferred to ignite the fuel-air mixture.

Advantages and disadvantages in practical operation

advantages

Compared to gasoline engines with manifold injection or carburetors, engines with gasoline direct injection have a higher degree of efficiency, especially in the low load range, which is even improved in connection with stratified charge . There are also approaches to using direct gasoline injection to overcome the change in quantity of the gasoline engine and the associated throttle losses and instead to change the torque qualitatively . Direct injection cools the combustion chamber and thus reduces the engine's tendency to knock, which allows the compression ratio to be increased by around to . In addition, direct injection allows the gasoline to be injected centrally in the combustion chamber, which means that there is less heat loss through the cylinder wall. All of this has the effect of reducing gasoline consumption, with gasoline direct injection having the greatest potential for reducing consumption compared to other technologies. Reduced fuel consumption also means a reduction in carbon dioxide emissions. ${\ displaystyle \ varepsilon = 1 {,} 5}$ ${\ displaystyle \ varepsilon = 2 {,} 0}$

The performance of an engine with direct fuel injection is slightly better compared to an engine with external mixture formation. This is possible because the valve control times can be better utilized and therefore good residual gas purging can be achieved without fresh gas losses. Furthermore, the filling (and thus the power) is greater than the intake manifold injection with gasoline direct injection due to the higher degree of delivery, even when the same boundary conditions (throttle-free operation with fully open throttle valve) are present, because the gasoline is not already in the intake manifold but only in the combustion chamber evaporates and thereby extracts thermal energy from the gas in the combustion chamber. Theoretically, the delivery rate is around 9% higher, while the larger filling means that the performance can be increased by around 5–8% compared to the intake manifold injector.

Furthermore, due to the higher relative speed between fuel and air, the effect of pressure atomization occurs, which means that the amount of atomized fuel droplets is very large, which leads to better mixing of air and fuel and consequently faster mixture formation.

disadvantage

Gasoline direct injection requires more engineering effort than other systems and is therefore more expensive. If an engine is operated with gasoline direct injection according to the stratified charge strategy, the theoretical fuel consumption advantages do not occur in practice, especially at high load conditions, which makes the use of this technology doubtful. The Volkswagen group has therefore switched its engines with stratified charge operation back to homogeneous operation; Homogeneous operation is also generally used in series engines, with the gas exchange losses that occur being compensated for by variable valve control.

The exhaust gas behavior changes due to direct injection with stratified charge, the conventional three-way catalytic converter no longer works because of the high air ratio and more nitrogen oxides and hydrocarbons are produced , which make the use of a special exhaust gas cleaning system absolutely necessary in car engines because it is not possible to clean through constructive measures to sufficiently reduce pollutant emissions. This can only be avoided by the less fuel-saving homogeneous operation, the exhaust gas aftertreatment of which works sufficiently well with a conventional three-way catalytic converter . If the engine is operated according to the stratified charge process, sulfur-free fuel ( Super Plus in general or in Germany all types of petrol according to DIN EN 228) must be used, as otherwise the storage catalytic converter would be excessively poisoned with sulfur. Sulfur poisoning can be counteracted by increased storage catalytic converter regeneration, which, however, increases fuel consumption and reduces the consumption advantage. The stratified charge operation also produces more soot , which has to be removed from the exhaust gas with a soot particle filter due to stricter exhaust gas limits, but the particle emissions are significantly lower than with comparable diesel engines. It is less the total particle mass than the high number of ultrafine particles that is important.

Because gasoline has no lubricating effect, the injection pressure cannot be significantly greater than 20 MPa, as otherwise the injection pump and the injector would wear out too much. However, a high injection pressure is required to ensure good droplet formation and rapid evaporation of the fuel in order to prevent misfires and, above all, soot formation.

Injection systems

In direct injection technology there are various approaches to constructing a functioning injection system for gasoline. Such a system primarily consists of a (high pressure) fuel injection pump and the injection nozzles. The first mechanical gasoline direct injection systems for aircraft engines suitable for series production were derived from mechanical in- line injection pumps of the type used for diesel engines. The design of the injection nozzles was also initially similar to that of diesel engines, before special multi-hole nozzles were developed. The main problem was that gasoline, unlike fuel for diesel engines, does not have particularly good lubricating properties, which greatly increases the wear and tear on the injection system. The injection pressure of the first gasoline direct injection system for four-stroke passenger car engines is therefore only 1.0-4.9 MPa to minimize wear. Newer engines with gasoline direct injection, however, no longer have purely edge-controlled injection pumps, but either air-assisted low-pressure direct injection or common rail injection , the latter system being the more modern of the two.

Low pressure direct injection

The low-pressure direct injection with air assistance or also low-pressure mixture injection is a system that was largely developed by Orbital . Its structure is relatively simple. It is mainly used in two-stroke engines such as outboard engines. Four-stroke engines with this process are mainly operated with a stoichiometric mixture and work with the jet-guided process.

Low-pressure direct injection is characterized in that it is injected into the intake stroke and that air and fuel are partially mixed with one another before they even enter the combustion chamber. For this purpose, the actual injection nozzle has a kind of upstream chamber that is under pressure (up to 0.5 MPa). The fuel is injected into this prechamber at a pressure of up to 0.8 MPa. A large part of the fuel already breaks down and evaporates in this upstream chamber. If the injection valve is opened, an already ignitable fuel-air mixture is blown into the combustion chamber, the remaining still liquid fuel droplets disintegrate and evaporate during the injection when they are accelerated by the expanding air. The necessary pressure is generated with an external air compressor. Since the fuel droplets have already evaporated or are very small when they are injected, the depth of penetration of the fuel into the combustion chamber is not very great and relatively high exhaust gas recirculation rates can be achieved with smooth running. In order to distribute the fuel / air mixture appropriately in the combustion chamber, a swirl or roller flow is sometimes generated via the air inlet.

The injection nozzle is usually a so-called A-nozzle, an injection nozzle that opens outwards and has a wide jet cone due to the annular opening cross-section. This allows a good stratification of the charge when the back pressure in the combustion chamber is low, which is the case on the intake stroke. Since the injection pressure is very low, injection cannot be performed in the compression stroke where the cylinder pressure is high. The disadvantage of this is that by the time of ignition the mixture cloud can be blown away again, which also makes the charge stratification unstable, particularly in operating areas with low loads.

Common rail high pressure injection

Schematic representation of the common rail system. The fuel cooler is not shown here.

Common rail injection is actually intended for diesel engines. It was mainly developed by ETH Zurich from 1976 onwards and brought to series production readiness by Bosch in the 1990s. It was used on a trial basis in the diesel engine from 1985, and in series production in the gasoline engine from 1995. The name-giving component is the rail, a fuel distribution line that is constantly under high pressure. It supplies all injection nozzles with fuel and at the same time serves as a storage and damping volume for the system pressure generated by the high-pressure fuel pump. Injection of the fuel is initiated by opening electronically controlled solenoid injection valves or piezoelectric injection valves and is possible at any time. For this reason, common rail injection is well suited for gasoline engines with direct injection, and in terms of atomization quality, jet penetration depth and frequency of injections within a work cycle, it is best suited for the requirements of a gasoline engine.

A common rail injection can be divided into high pressure and low pressure circuits. The former is on the engine side and essentially consists of a distributor pipe (rail), a high-pressure piston pump, a pressure regulating valve, a rail pressure sensor, a fuel cooler and an injection valve for each cylinder. The high-pressure piston pump is fed from the low-pressure circuit that is installed on the tank side. A fuel pressure of around 0.4 MPa is built up in it with an electric fuel feed pump, and there is also a mechanical pressure regulator. The power that has to be applied to drive the high-pressure piston pump depends on the speed and injection pressure and is between 600 W at 5 MPa and 2000 min ⁻¹ and 3000 W at 15 MPa and 6000 min ⁻¹ . The injection pressure is between 5 and 20 MPa. In the case of common rail injection, swirl nozzles, multi-hole nozzles or outward-opening A nozzles with a mushroom valve can be used as injection nozzles.

Development history

First Junkers engine with gasoline direct injection in the First World War

In 1916, a gasoline direct injection system was installed in a Junkers aircraft engine for the first time . From 1914 Junkers planned to develop a diesel engine with direct injection for commercial aviation ready for series production, as the diesel engine was considered more economical and less fire-prone than a gasoline engine. At first, the attempts with the diesel engine failed, but the opposed piston engines Jumo 205 and Jumo 207 with diesel process were finally developed in the 1930s until they were ready for series production. During the First World War, however , the Prussian War Ministry required the use of gasoline or benzene ( petrol ) for aircraft engines, which led to the development of an aircraft engine with gasoline as a fuel at Junkers. First test bench runs with a newly designed six-cylinder two-stroke engine with 14,137 cm ³ displacement in November 1915 showed that the mixture flushing, which was chosen as the flushing method for the engine, was unsuitable because the fuel-air mixture ignited in an uncontrolled manner in the crankcase, which is why Engine damage led; otherwise the engine was too heavy. From 1916 onwards, under the direction of Otto Maders , an enlarged new engine with 17,105 cm ³ displacement was developed, which had a better mass-performance ratio . In order to prevent the uncontrolled ignition in the crankcase, the engine was equipped with direct injection, as had already been used in the experimental opposed piston diesel engine. The engine's exhaust and scavenging ducts were arranged tangentially in order to generate a swirl of air that supports mixture formation with direct injection.

After initial difficulties with the pistons , the load control turned out to be problematic, but could be made manageable by optimizing the injection pump. From 1917, the engines, now called Fo.2 , were produced in small series and initially planned to drive speedboats of the Imperial Navy . Since the electrodes and ceramic insulators of the spark plugs overheated, they were cooled with water after reducing the compression ratio from to unsatisfactory. From 1918, a Mercedes D IVa was also converted to direct injection. This engine started better, had a mixture formation without misfiring or retarded ignition and its idling speed of 300 min ⁻¹ could be maintained without any problems; its full load performance compared to the basic model with carburettor was increased by approx. 15%. ${\ displaystyle \ varepsilon = 10}$ ${\ displaystyle \ varepsilon = 6}$

Developments inspired by the Reich Aviation Ministry

In Germany, however, further development ceased in the 1920s. It was not until the 1930s that the development of gasoline direct injection was resumed, again for use in aircraft engines. German companies (Bosch, Junkers, L'Orange) were familiar with the specialist knowledge of metering small amounts of fuel through the development of diesel engines. In various test series, gasoline engines for flight operations were equipped with modified diesel injection pumps in order to inject the gasoline directly. In the case of the BMW Va aviation gasoline engine , tests with direct injection showed an increase in output of 17% and a consumption advantage of 3%, so that the Reich Aviation Ministry encouraged the German aircraft industry to develop gasoline engines with direct injection for use in aircraft; However, the actual development work was mainly done by the injection system suppliers.

From prototype to series engine at Daimler-Benz

Daimler-Benz DB 601 with gasoline direct injection

At Daimler-Benz, the DB 600 aircraft engine was equipped with direct fuel injection from March 1934 in a series of tests by Hans Scherenberg under the direction of Fritz Nallinger . A diesel injection pump and a needle injection nozzle were also used here. It was found that the fuel is best injected during the intake stroke into the zones of the combustion chamber in which the strongest air movements prevail, in order to achieve better mixing of fuel and air. The needle injection nozzle was quickly replaced by a multi-hole nozzle, with which the effect of the stronger air movement can be better exploited, which greatly reduced fuel consumption and the engine's tendency to knock . Since hole nozzles react more sensitively to impurities in the fuel, a small gap filter has been integrated into the injection nozzle. This made it possible to dispense with mixed lubrication, which would have a negative effect on the knock resistance. The construction of the injection pumps for the later series engines ( DB 601 , DB 603 , DB 605 ) was similar to that of comparable diesel engines; The DB 601 A was built in series from 1937 and was, alongside the Junkers Jumo 210 G used in the Messerschmitt Bf 109 and the BMW 132 F, one of the first three gasoline engines with direct fuel injection to be mass-produced. In order to regulate the ratio of the supercharger and thus the boost pressure, the combustion air ratio , the throttle valve position, the ignition point and, if necessary, the blade position of the variable-pitch propeller , these aircraft engines had a mechanical "command device " with which they were operated, which was used for the pilot and correct setting of the motor should simplify and prevent incorrect operation.

Performance increase in historical aircraft engines

In-line injection pump of a Daimler-Benz DB 605

In the course of development it quickly became apparent that gasoline direct injection offered great potential for increasing performance. In contrast to an engine with a carburetor or intake manifold injection, in which fuel and air are mixed outside the combustion chamber, with a direct injection engine with mixture formation, large valve timing overlaps of up to 100 ° CA can be achieved within the combustion chamber at the optimal point in time , since there is no fuel- air mixture from the exhaust can be pressed (so no flushing losses occur). This is used in conjunction with a supercharger to completely blow residual gases out of the cylinder (residual gas purging) and to cool the combustion chamber, which has a positive effect on the performance of an engine. Since the limitation of the residual gas content is a prerequisite for good idling behavior, the intake manifolds of a gasoline engine with direct injection must be precisely calculated. The fuel is individually metered to each cylinder with high accuracy and injected shortly after the exhaust valve is closed at a pressure of approx. 5 MPa; the fuel only has a short time to mix with the fresh gas before the controlled spark ignition is initiated. In this way, the tendency of an engine to knock could be reduced even with inferior fuels and the compression ratio selected to be relatively high. All these measures resulted in an increase in performance of almost 100% within a period of less than ten years.

Vehicle engines after the Second World War

Gutbrod Superior

Mercedes-Benz W 196 from 1954 with an eight-cylinder in - line engine

In two-stroke engines, especially for vehicle use, gasoline direct injection offers an even greater potential for reducing fuel consumption, as the flushing losses mentioned in the previous section occur in principle in two-stroke engines with external mixture formation and Otto processes and are a cause of the high fuel consumption. Bosch developed an injection system for the DKW master class during the 1930s . However, developments came to a standstill as a result of the Second World War and did not resume until 1949. Since a two-stroke engine only has two work cycles, the fuel has to be injected more often per unit of time, which requires a higher pump speed. In addition, two-stroke engines cover larger speed ranges, which must be taken into account when designing the injection pump; In addition, the operating noise of the injection pump and the nozzles is high, which required new approaches in the development. The injection cam was replaced by an eccentric, the injection nozzle was positioned in such a way that the injection jet is directed in the opposite direction to the flushing flow and the injection pump is equipped with an overrun cut-off . The outward-opening injection nozzles have a conical valve seat and no leakage lines. The optimal position of the spark plugs also had to be determined and was not known at the beginning of the development.

In autumn 1951 Goliath presented the GP 700 and Gutbrod the Superior , both of which have two-stroke engines with direct injection; the engines had been developed in cooperation with Bosch and the first mass-produced passenger car gasoline engines with direct injection. Compared to the carburettor variant of the Gutbrod 600 cm ³ engine type, the injection engine has more than 10% more power and, especially in the partial load range, a very much reduced fuel consumption. Since the injection system caused high production costs and the low fuel consumption only played a subordinate role in the early 1950s, the two-stroke engine with direct injection could not establish itself.

Daimler-Benz AG recognized the potential of direct injection for use in passenger cars and from 1952 tested a direct injection system for a six-cylinder in-line engine with a displacement of three liters. It came from Bosch and was similar to the system for the two-stroke engines. From 1954 Daimler-Benz used this system as standard in the Mercedes-Benz M 198 ; it works exclusively in homogeneous operation and with an injection pressure of 4.5 MPa. The performance is increased by around 10% compared to the carburettor version, but the fuel consumption is significantly reduced. Daimler-Benz also used gasoline direct injection in the W 196 racing car in racing . Another German manufacturer is NSU, whose attempts with direct injection of gasoline did not go into series production. Due to the low fuel prices and the increasing emergence of manifold injection , the development of gasoline direct injection for gasoline engines was not pursued in the 1960s and 1970s.

Different concepts from the 1960s and 1970s

The development of direct fuel injection in the 1960s and 1970s was not concentrated on a specific working process, but some concepts for hybrid combustion processes, i.e. neither gasoline nor diesel processes, were brought to series production with direct injection in some cases. Engines with this method are often suitable for operation with gasoline, but can also be operated with other fuels. A problem with all of these methods turned out to be that dynamic load control, as required for a vehicle engine, does not work well enough, since the coordination between injection, mixture formation and combustion was only possible for certain operating ranges, but not the entire speed range.

Texaco developed the Texaco Controlled Combustion System (TCCS), a multi-fuel stratified charge concept that has a consumption advantage of 30% in partial load operation compared to a comparable engine . It was further developed until 1986. From the M process , a combustion process for diesel engines, MAN developed the FM process, which was used from the end of the 1960s to the mid-1980s. It is also a stratified charge process. Since the 1950s, Ford worked on the Ford Combustion Process (FCP), which was later developed into the PROCO process. The further developments extend into the 1980s. The FCP process divides the combustion process according to the engine load: At full load, fuel is injected at bottom dead center, while at part load and idling, fuel is injected just before top dead center and the mixture is stratified ( stratified charge ). In contrast to the Otto process, the intake air does not have to be throttled.

Klöckner-Humboldt-Deutz tried to design a diesel engine with direct injection for operation with fuels that were particularly unwilling to ignite and followed a similar approach to MAN with the FM process. In order to ensure the ignition in all operating states of the engine, a special spark plug was used here. From 1972 the process went into series production as an all-substance direct injection (AD process). In 1976 Mitsubishi introduced the Mitsubishi Combustion Process (MCP process), the specialty of which is the variable geometry of the injection jet: At low load, a hollow cone-shaped fuel jet with small droplets and a large jet angle is injected; at high load, the jet angle is reduced and a full jet is injected, which penetrates deep into the combustion chamber to prevent local over-greasing. This was achieved with a pin nozzle with variable needle lifts. Such MCP motors were used in Japanese harvesting machines.

Development since the 1980s

In the 1980s, technical articles and publications by Orbital, Subaru , Toyota and the AVL List on two-stroke engine concepts with direct injection appeared, so that gasoline injection in gasoline engines was once again the focus of developments. In outboard and motorcycle engines, gasoline direct injection was made ready for series production. Orbital was working on an air-assisted low-pressure direct injection. The gasoline direct injection ( GDI ) introduced by Mitsubishi in 1995 , on the other hand, is a high-pressure common rail system and was the first gasoline direct injection system for a mass-produced automobile with a four-stroke engine. It is beam-guided and a stratified charge process. In order to achieve good mixing of air and fuel, a roller-shaped air vortex is generated here. To do this, the air is drawn into the combustion chamber through a particularly steep intake duct, which sweeps over the lower part of the sloping inlet valve and the combustion chamber wall before it hits the specially shaped piston and is then swirled in a roller-like manner.

Later, Toyota, Nissan and the Volkswagen Group also introduced the spray- guided direct injection process for gasoline engines with stratified charge operation , which, however, did not become widely accepted. The reasons for this are the consumption savings that can hardly be achieved in practical driving and the cost-intensive exhaust gas aftertreatment using NO _x storage catalytic converters and soot particle filters ; at Nissan and Toyota, the exhaust gas behavior of the engines was so bad, despite exhaust aftertreatment, that the engines could not be launched in Europe and the USA. In modern gasoline engines with direct injection, operation with a homogeneous stoichiometrically regulated mixture has therefore prevailed over operation with an inhomogeneous stratified mixture at almost all engine manufacturers . There is a trend from air and wall-guided processes to jet-guided processes.

Individual evidence

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↑ ^a ^b ^c p. 563
↑ ^a ^b p. 565

Konrad Reif (Ed.): Otto engine management. 4th edition, Springer, Wiesbaden 2014, ISBN 978-3-8348-1416-6 , pp. 117-137.

↑ ^a ^b ^c p. 123
↑ ^a ^b p. 121
↑ ^a ^b ^c p. 122
↑ p. 124
↑ p. 119

Richard van Basshuysen, Fred Schäfer: Handbook internal combustion engine. 8th edition, Springer, Wiesbaden 2017, ISBN 978-3-658-10901-1 , Chapter 12, pp. 647-656.

↑ ^a ^b ^c p. 647

Kyrill von Gersdorff, Kurt Grasmann: aircraft engines and jet engines. Volume 2 of the series Die Deutsche Luftfahrt. Bernard & Graefe, Munich 1981, ISBN 3-7637-5272-2 .

↑ p. 76

Further references

↑ ^a ^b Gert Hack : The future belongs to lean operations. FAZ, August 18, 2007, accessed on August 21, 2018.
↑ VDI 3782 sheet 7: 2018-09 (draft) Umweltmeteorologie; Vehicle emissions determination; Air pollution. Beuth Verlag, Berlin, p. 12.
↑ Peter Diehl: Auto Service Praxis , issue 06/2013, p. 100 ff.

This article was added to the list of articles worth reading on January 11, 2019 in this version .

[vB1-6] ↑ ^a ^b ^c ^d ^e p. 2

[vB29-7] . 31

[vB52n-8] . 52

[vB25-9] . 27

[vB43-11] . 45

[vB69-12] . 76

[vB52-13] . 59

[vB54-15] . 61

[vB30-16] . 32

[vB79-17] . 90

[vB195-18] . 223

[vB55-22] . 62

[vB56-23] . 63

[vB60-25] . 67

[vB62-26] . 69

[vB63-27] . 70

[vB194-29] . 222

[vB44-31] . 46

[vB12-32] . 14

[vB46-33] . 48

[vB45-34] . 47

[vB50-36] . 51

[vB363-37] . 393

[vB237-38] . 270

[vB240-39] . 275

[vB245-40] . 245

[vB71-42] . 78

[vB7-43] . 9

[vB9-44] . 11

[vB8-45] . 10

[vB18-46] . 20

[vB118-48] . 138

[vB122-49] . 142

[vB120-50] . 140

[vB121-51] . 141

[vB119-52] . 139

[vB131-54] . 152

[vB123-55] . 143

[vB133-57] . 154

[vB6-58] . 8

[vB10-59] . 12

[vB11-61] . 13

[vB14-62] . 16

[vB15-63] . 17

[vB13-64] . 15

[vB17-65] . 19

[vB20-66] . 22

[vB24-67] . 26

[vB21-68] . 23

[vB22-69] . 24

[vB23-70] . 25

[vB41-71] . 43

[vB388-72] . 418

[LM64-1] . 64

[LM61-14] . 61

[LM60-30] . 60

[LM62-47] . 62

[BL86-2] . L 86

[BL92-19] . L 92

[BL91-28] . L 91

[B563-3] . 563

[B565-24] . 565

[R123-4] . 123

[R121-5] . 121

[R122-20] . 122

[R124-35] . 124

[R119-56] . 119

[vBF647-21] . 647

[vGG_76-60] . 76

[Hack-10] Gert Hack : The future belongs to lean operations. FAZ, August 18, 2007, accessed on August 21, 2018.

[VDI3782-7-41] VDI 3782 sheet 7: 2018-09 (draft) Umweltmeteorologie; Vehicle emissions determination; Air pollution. Beuth Verlag, Berlin, p. 12.

[Diehl-53] Peter Diehl: Auto Service Praxis , issue 06/2013, p. 100 ff.