DE2657416A1 - EMISSION CONTROL - Google Patents

Description

The invention relates to an internal combustion engine and to a method for operating the machine. The invention is of great importance because it enables harmful exhaust emissions with CO, NO and unburned hydrocarbons (HC) to be kept as small as possible.

in U.S. Patent 3,776,212, a method and a Described machine for controlling harmful emissions, with which very lean air-fuel mixtures are burned. The engine differed in the construction of the combustion chamber from known internal combustion engines. The combustion chamber consisted of a main combustion chamber and a secondary combustion chamber. The secondary combustion chamber was only above one

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Communication port in communication with the main combustion chamber, which was sized so that a flame passed through and turbulence was generated. Valves ensured that an air-fuel mixture was only introduced into the main combustion chamber became. The main combustion chamber or the weave combustion chamber was provided with a spark plug. A quick burn of the lean air-fuel mixture was brought about by turbulence emitted from one of the secondary combustion chambers in the main combustion chamber exiting the combustion jet was generated.

"Ό as described in this patent specification existed Method for operating the machine from a) Filling in an only very lean combustion mixture (air-fuel ratio of at least 18: 1) only in the main combustion chamber, b) the compression of the combustion mixture in the main combustion chamber, a part of the mixture through the connection opening was pressed into the secondary combustion chamber to cause turbulence therein, c) the ignition of the combustion mixture in the combustion chamber by means of a single ignition source, d) generating a rapid pressure increase in the secondary combustion chamber due to the rapid combustion caused by the turbulence and e) one caused by the pressure The combustion products flow out of the secondary chamber through the connecting opening into the. Main combustion chamber, so a suitable one Turbulence to achieve substantially perfect combustion within an acceptable crankshaft angle to effect.

A further reduction in CO, NO and HC emissions

Ji.

can be achieved through improvements based on the combustion process described above. The procedure and the machine for making these improvements will now be described.

The amount of NO generation in the lean air-fuel mixture

ji

is a steeply increasing function of the flame temperature.

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For example, for 15 atmospheres pressure and 425 C mixture temperature before combustion is the calculated peak temperature of the flame and the amount of NO generated shown in the following table:

Air fuel
relationship Flame temperature NO amount formed 15th 2260 ° C 750-500 ppm / msec. 20th 1965 ° C 70-65 ppm / msec. 21.4 1800 ° C 9.5-7.0 ppm / msec.

This table shows that the flame temperature in

of the machine below about 1900 ° to 2000 ° C 15th

must in order to keep the formation of the amount of NO emissions low.

On the other hand, measurements show that the unburned hydrocarbon (HC) emissions are strongly influenced by the temperature of the exhaust gas. The HC emissions can even be in large machines are kept low if the exhaust gas temperature is not too low, for example about 750 ° C. The remaining hydrocarbons are at the end of the Burned during the combustion process, but only if the temperatures have not fallen so quickly that their combustion

is delayed too much.
25th

It was found that the machine and the process according to the introductory explanation along with certain significant changes to burning a very lean air-fuel mixture can be used within an acceptable crankshaft angle so that the flame peak temperature does not exceed about 1900 to 2000 ° C.

In short, according to the invention, the compression ratio of the air-fuel mixture and the Combustion rate controlled to a combined

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to create volume-constant-pressure-constant combustion cycle. Lei this cycle becomes part of the fuel burned roughly at top dead center with an almost constant volume, while the rest of it was burned just after top dead center, ζ.

. B. is burned within 30 ° C, at almost constant pressure. Because only part of the fuel is close to the When top dead center is burned, the flame peak temperatures be kept below a critical temperature for NO formation. At the same time this has combined Cycle good efficiency.

The combustion cycle with one at an almost constant volume and then at an almost constant one Pressure combustion is accomplished by increasing the rate of combustion in the main combustion chamber by applying the correct amount of turbulence during the Combustion process is controlled. As in the case mentioned at the beginning, the turbulence is generated by a connecting opening The combustion jet emerging from the secondary combustion chamber is generated in the main combustion chamber. The strength of the focal beam is controlled by the rate of combustion in the secondary combustion chamber. The rate of burn turbulent flames is under the influence of centrifugal force. By transferring a whirling motion to it during the compression stroke The air-fuel mixture entering the secondary combustion chamber slows down the rate of combustion in the secondary combustion chamber, the strength of the connection opening into the main combustion chamber decreases at the beginning exiting combustion jet and one avoids the formation of a pressure and temperature peak in the main combustion chamber. The duration of combustion in the main combustion chamber is extended, creating the correct level of turbulence for the Completion of combustion in the main combustion chamber is created. The strength of the vortex movement forms one additional, independent parameters for controlling the combustion process and for realizing the

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desired print cycle of the machine.

The force resulting from the vortex movement keeps the burning gases and the hot combustion products in the axial direction Area of the secondary combustion chamber. As a result, the heat losses on the side walls of this chamber are kept small.

Furthermore, the centrifugal force allows by including the gases in the axial area of the secondary combustion chamber that the Flame moves along the axis. Consequently, a combustion jet can even then leave the secondary combustion chamber shortly after ignition exit when the sparkover has occurred at the end of the secondary combustion chamber.

The invention is explained in more detail below with reference to the drawing using an exemplary embodiment:

Fig. 1 shows a cross section through a cylinder of a

machine according to the invention, 20

Fig. 2 shows the plan view of the connection opening

a secondary combustion chamber in a machine according to the invention, with guide surfaces for turbulence being shown,
25th

Fig. 3 shows a pressure-volume diagram, which is used to explain the operational sequence of an inventive Internal combustion engine is used.

In Fig. 1, a combustion chamber is shown, which is formed by cylinder walls 1, a cylinder head 2 and a piston 3 is limited. The cut is made so that an inlet or Exhaust valve is shown. The main combustion chamber of the combustion chamber is equipped with a secondary combustion chamber or combustion cartridge connected via a connection opening 6. In the secondary fuel kaitroer 5 is at the end opposite to the connection opening 6

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Ignition electrode C spark plug) shown. At the connection opening 6 bordering surfaces 9 are shown.

As shown in the patent described above, in a conventional engine with a compression ratio of 10: 1 operating on a very lean air-to-fuel ratio of about 20: 1 creates turbulence within an acceptable crankshaft angle without any loss of energy and without risk of extinction Flame allows the mixture to burn. The problem was getting the turbulence needed at the right time deliver. The turbulence can occur because of the speed with which the kinetic energy of the vortex motion is absorbed and not because of the amount of turbulence required for rapid combustion of lean air-fuel mixtures are introduced or generated ahead of time. Turbulence must be created when it is needed.

According to the invention, turbulence is caused by the small secondary combustion

Chamber of the combustion chamber generated via the connection opening communicates with the main combustion chamber.

The kinetic energy of the pressed through the connection opening into the secondary combustion chamber during the compression stroke The air-fuel mixture is quickly converted into turbulence. A strong turbulence of the mixture is for example also of those arranged in the vicinity or in the connection opening Baffles caused. When ignited, the very turbulent mixture burns with one of turbulence and swirl controlled speed. Shortly after ignition, the pressure in the secondary combustion chamber exceeds the pressure in the Main combustion chamber and a jet shoots into the combustion chamber at high speed. The jet is generated in the main combustion chamber of the combustion chamber the turbulence necessary for rapid completion of the combustion.

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The process within the sub-combustion chamber will now be described. A secondary combustion chamber is considered with a Air-fuel mixture that swirls around an axis executes. Centrifugal force will greatly influence the spread of the turbulent flame. The speed of propagation the flame increases when the flame moves against the direction of the centrifugal force, as small bubbles burned Gases move in the denser, unburned gas against the direction of the centrifugal force. The speed of propagation the flame diminishes when the flame is in Direction of centrifugal force moves because the buoyancy force of the centrifugal force field tends to be caused by the turbulent Currents caused wave surges of the combustion wave to calm down or. to smooth out.

After ignition, the burning and burnt gases will be concentrated on the axis of the secondary combustion chamber, there the centrifugal force will move the cold unburned mixture outside. Consequently it will be very shortly after ignition a jet of flame emerge from the secondary combustion chamber.

The speed of combustion in the secondary combustion chamber can be adjusted by the speed of the vortex movement v / earth. Furthermore, it is possible to control the combustion speed of the filling in the main combustion chamber in such a way that that pressure and temperature peaks are avoided and the combustion at an acceptable crankshaft angle, for example 30 after top dead center is completed.

Since the flow rate into the secondary combustion chamber and consequently the

If turbulent strength and centrifugal acceleration change together with the changing engine speed, this control of the combustion speed is automatically set for each engine speed.
35

Fig. 3 shows a volume-pressure diagram of one cycle,

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the desired volume constant-pressure constant combustion made clear. Between points 11 and 12 there is a Fresh air fuel filling compressed adiabatically. at At point 12 the ignition takes place. Part of the filling will be approximately constant between points 12 and 13 Volume burned, the pressure at point 13 increasing to approximately 1.5 to 2.5 times the pressure at point 12 will. The rest of the filling is burned at almost constant pressure between points 13 and 14. Between Points 14 and 15 complete the expansion of the filling. The flame temperature is also between points 13 and 14 almost constant.

Calculations show that, for example, a machine with a compression ratio of 10: 1 is possible is a mixture with an air-fuel ratio of to be incinerated in such a way that the above requirements are met with the following numerical results:

A third of the filling burns with an almost constant volume, where P ~ / P ₁₂ = 2.

Two thirds of the filling burns at almost constant pressure.
25th

Flame temperature T ₁₃ = T ... = 19 6O ⁰ C. NO generation rate = 70 ppm / msec.

Complete combustion within a crankshaft angle of around 30 °.

The NO _x concentration is frozen at a crankshaft angle of 45 ° or the ISD formation is complete at this angle.

Flue gas temperature T ₁ _ = 930 ° C.

Increasing the air-fuel ratio from 20 to 21 could reduce NO _x formation by a factor of 3.

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The following abbreviated calculations show the strength of the burn rate control in the Secondary combustion chamber required turbulence in the secondary combustion chamber. The centrifugal force acceleration C of the vortex mass at a point within the secondary combustion chamber corresponds to the Circumferential speed U and the Padius r in relation as follows:

r (1)

The amount of the centrifugal force acceleration C, which can counteract the effect of the turbulence on the flame propagation, can be developed as follows: If the degree of turbulence / L cm, and the turbulence strength u ¹ cm / sec. the characteristic turbulence time t ₂ can be represented as follows:

₂ 'see. (2)

The characteristic time t_ in the centrifugal force field is the time / which ^{is required to reduce the root mean square value of the turbulence speed u 1} down to 0 by centrifugal force acceleration C, so:

t ₃ = u VC (3)

In the critical state, when the characteristic times t 1 and t 1 are the same, the effect is the turbulence balanced on the flame propagation speed by the centrifugal force. In this state:

i / u ¹ = u '/ C
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C = n ' ² / JL (4)

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The required optical acceleration to reduce the speed of fiber propagation in the Secondary combustion chamber to the desired speed will be a fraction of the critical value mentioned above. The above equations can be combined as follows to determine the critical condition:

If U is the peripheral speed and r is the radius of the Vortex motion is / then results in 10

^U V

(5)

The following numerical example is considered. If = 10 (a typical value) then applies to the critical condition

and therefore

^Ü V

Accepted

u ¹ = 1400 cm / sec. (a typical value) U _v = 4200 cm / sec.

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The ratio of the circumferential speed U _v to the axial flow through the connection opening is a characteristic parameter (tgc _v ) for the deflection that the guide surfaces must generate in order to form the desired vortex movement. With an axial flow velocity of U = 32,000 cra / sec. and ü "= 4200 cm / sec. will

^Ü V

tg <* - = = i ^ - = 0.13.

U 32,000

For a machine with cylinders that are approximately 60 ecm

Total compression volume, a secondary combustion chamber with about 6 cm volume and a connecting opening with a diameter of 5 mm between the main and the secondary combustion chamber should have a guide surface angle of approximately 20 to 30 (as shown in Fig. 3) provide the correct swirl strength.

In order to keep the harmful emissions as small as possible, the secondary combustion chamber allows for vortex formation designed connection opening the operation of an internal combustion engine as follows: With the compression ratio selected for reasonably good efficiency of, for example 10: 1 and using a lean air-fuel mixture of, for example, 18: 1 or leaner, the ignition point (near top dead center) can be selected and the turbulence can be generated so that the desired pressure constant-volume constant Combustion curve is obtained.

The ratio of the pressure at the beginning of the constant volume combustion to the pressure at the end of the constant volume combustion can be around 1: 2. Such a combustion curve keeps the flame peak temperature and the exhaust gas temperatures in the areas of the lowest possible NO formation or a breakdown or elimination of the hydrocarbon residues.

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The choice of the size of the secondary combustion chamber and the Connection opening is basically based on the teachings of the patent described above, with the exception that an additional, independent parameter, namely the turbulence, must be taken into account.

The invention relates to an internal combustion engine and a method for operating this machine, which has a combustion chamber with main and secondary combustion chamber. The air-fuel mixture compressed in the combustion chamber causes turbulence and swirling of the mixture in the secondary combustion chamber. When ignited, it becomes the initial combustion speed limited in the secondary combustion chamber by the effect of centrifugal force on the flame. The one from the The gas jet ejecting from the secondary combustion chamber controls the combustion speed in the main combustion chamber Reduction of the flame peak temperature and consequently a reduction in CO, NO and HC emissions.

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Claims (8)

■ Young of the remainder of the mixture, v / above the temperature peak in the cycle is limited and NO emissions are reduced. 2. The method according to claim 1, characterized in that the compression ratio has the usual value of 10: 1 and the ratio of the pressure at the beginning of the constant volume combustion to the pressure at the end of the constant volume Combustion has a typical value of 1: 2. 3. The method according to claim 1, characterized in that the ignition (5) a'n that of the connecting opening (6) opposite The end of the secondary combustion chamber (5) begins. 4. The method according to claim 1, characterized in that that the part pushed through the connection opening (6) of the mixture for generating the turbulence through guide surfaces (9) located near the connecting opening (6) pressed v / ird. 5. Internal combustion engine with at least one cylinder and a reciprocating piston, which has a combustion chamber limit, which is divided by a device into a main and a secondary combustion duct, v / obei the secondary combustion chamber is only connected to the main combustion chamber and the device for dividing a connecting opening determined between the chambers, with means for filling the combustion mixture only into the main combustion chamber of the combustion chamber, where the volume ratio of the main and secondary combustion chamber and the size of the connecting opening are as follows selected, are that during the compression stroke a part the combustion mixture of fuel and air into the secondary combustion chamber depressed and causing turbulence, the improvement being characterized in that it comprises means (9) to swirl the gases in the secondary combustion chamber (5) in the area of the axis of the secondary combustion chamber and a spark plug (8) in the combustion chamber, so that after 709848/0694 B 7837 Claims 1. Method for operating an internal combustion engine with Spark ignition and at least one cylinder and one reciprocating piston that delimit a combustion chamber, which is divided into a main and a secondary combustion chamber, with one between the main and secondary combustion chamber Connection opening is characterized by the following steps: a) Filling in a very lean fuel mixture with an air-fuel ratio of at least 18: 1 only in the main combustion chamber (4) of the combustion area, b) Compressing the combustion mixture in the main combustion chamber (4) of the combustion chamber, with part of the Mixture with a vortex flow through the connector Application opening (6) pressed into the secondary combustion chamber (5) and in the area of the axis of the secondary combustion chamber (5) causing turbulence and swirling of the gases, c) ignition of the combustion mixture in the combustion chamber by means of a single ignition source (8), d) generating a pressure increase in the secondary combustion chamber (5) due to the rapid combustion caused by the turbulence and by the eddying is controlled and causes a focal beam · through the connection opening (6) in the Main combustion chamber exits and there is enough tur- _. Bulenz generated that part of the mixture at im burns with a substantial constant volume, followed by an essentially pressure-constant combustion 709848/0694 - y> - B 7837 Ignition the combustion in the secondary combustion chamber strives in the direction of the vortex axis until a substantial part of the air-fuel mixture is consumed, V7obei the turbulence is an independent parameter for controlling the combustion process forms. 6. Internal combustion engine according to claim 5, characterized in that that the spark plug (8) is arranged at the end of the secondary combustion chamber (5) opposite the connection opening (6) is. 7. Internal combustion engine according to claim 5, characterized in that that near the connecting opening (6) guide surfaces (9) are arranged, around the pressed into the secondary combustion chamber (5) To provide mixture with the VJirbelstromung. 8. Internal combustion engine according to claim 7, characterized in that that the size of the connection opening (6), the size of the secondary combustion chamber (5) and that through the guide surfaces (9) generated turbulence strength selected v / ground to turbulence to be introduced into the main combustion chamber (4) and to achieve essentially constant volume combustion, followed by constant pressure Combustion, to achieve. 709848/0694