DE19746855A1 - Operation of lean-burn fuel-injected diesel and petrol engines - Google Patents

Abstract

Following conventionally controlled, metered fuel injection into a cylinder, once the combustion phase is over, additional fuel is injected. This occurs in the region of bottom dead center, following expansion. Exhaust subsequently passes through one or more treatment stages (10,11) of mechanical (soot filter), chemical or catalytic nature, to remove pollutants. Preferred features: Additional fuel is injected, once the mean gas temperature in the cylinder is below the sooting temperature of 1300 deg K. The quantity is metered over time, such that neither gas in the cylinder, nor gas after leaving, reaches sooting temperature. Additional injection takes place at latest, 110 deg after bottom dead center. Additional fuel is metered, to relate exhaust NOx concentration, to a C1 equivalent (further detailed in text). Metering assures that the mean exhaust fuel air ratio is 0.95. Waste gas temperature before the soot filter is kept below 850 deg C. Of pollutants present, at least the NOx content is measured before treatment, allowing the engine management system (5) to determine the required additional quantity. Additional fuel injection quantities are entered as a matrix in the engine management unit, for each revolution of the engine.

Description

Direct-injection piston internal combustion engines, both direct-injection diesel engines and direct-injection gasoline engines, are operated in the excess air range, ie in the lean range. Accordingly, the nitrogen oxides (NO _x ) in the exhaust gas cannot be reduced due to a lack of the reducing agent.

The three-way catalyst technology is based on the fact that in the exhaust gas with an air ratio λ = 1 in a narrow air ratio concentrations of hydrocarbon (HC) and Carbon monoxide (CO) and nitrogen oxides in such a ver Ratio with each other that the nitrogen oxides through the existing hydrocarbons and carbon monoxide redu can be decorated and at the same time the hydrocarbons or the carbon monoxide are oxidized so far that the order degree of settlement for all components is about 90% and more.

This technique is used to reduce the nitrogen oxide content follow the excess air in the exhaust gas at lean Mo gors, especially with direct-injection piston combustion engines not possible.

To reduce the nitrogen oxides in the exhaust gas, so-called SCR catalysts (selected catalytic reduction) are used, which selectively reduce the nitrogen oxides with the aid of a reducing agent injected into the exhaust gas. Possible reducing agents here are, for example, ureas, ammonia or also hydrocarbons or hydrocarbon mixtures. These were previously mixed with the exhaust gas upstream of the catalytic converter through a separate nozzle in the exhaust system. To ensure NO _x reduction levels greater than 15%, especially in the case of direct-injection internal combustion engines, carbon dioxide also had to be mixed with the exhaust gas from the outside.

Another option for reducing nitrogen oxides are Nitrogen oxide storage catalysts. Here the stickoxi de accumulated in a storage phase in the catalyst and in a regeneration phase through a rich operation in the Be range from λ <0.95 through which then exist in the exhaust gas high concentrations of hydrocarbons, carbon monoxides and regenerated hydrogen again. The so-called enrichment in homogeneous gasoline engines by enriching the combustion air-fuel mixture reached in the combustion chamber. This technique leads however with direct injection internal combustion engines, which always have an inhomogeneous mixture in the combustion chamber ben, on intolerable soot emissions.

The soot emission from diesel engines can be achieved with the help of soot fil ters can be reduced by up to 90%. The diesel soot filter however, it must be regenerated periodically. This can be thermal by an additional burner in the exhaust gas or by a electrical ignition of the soot retained in the soot filter. There is also the option of using appropriate force Additives to effect regeneration. Significant is for the ignition and combustion of the soot retained soot that the soot is sufficiently high has adsorbed hydrocarbon amount, which leads to a simple Chen ignition and improved flame stability of the burning soot in the filter is necessary.

In summary, it can be said that both for Nitrogen oxide reduction in the exhaust gas of so-called lean engines as Nachbe also for particle reduction in diesel engines action facility intermittent or continuous must be regenerated and that this requires a certain coal hydrogen content in the exhaust gas is required and accordingly hydrocarbons must be added to the exhaust gas. The injection of additional fuel into the exhaust pipe is a possibility, corresponding  to supply additional amounts of hydrocarbon to the exhaust gas. Of the However, the disadvantage is that the hot exhaust gas flow lying nozzle tends to coke and that here next to one additional nozzle also an additional control of this Injector must be provided.

In the publication by Hiromitsu Ando et al in AVL conference "Motor und Umwelt"'97, pages 55 to 69, a method is described in which an additional quantity of fuel is injected after the injection of the quantity of fuel required for the work cycle. The injection is made here so early, however, that the injected fuel quantities burn ver during the expansion stroke in the cylinder chamber, so as to increase the exhaust gas temperature and achieve a faster warm-up of the downstream exhaust gas treatment device during the starting phase. However, since this additional amount of fuel is still burned, it is not available as a reducing agent for the downstream gas treatment devices, so that use of this method is unsuitable for continuous operation with the aim of reducing pollutants. This technology is derived from the catalyst heaters used in practice in the cold start, in which the catalyst temperature is brought up to the catalyst start-up temperature in a short time by post-oxidation in the combustion chamber (late ignition) or in the exhaust system. The goal is the exclusive reduction of all pollutants (NO _x + HC + CO) when starting the engine cold.

According to the invention the above problems are ge solves by a method of operating a piston internal combustion engine machine, in which the individual cylinders each by means of an injector that is required for the respective work cycle amount of fuel depending on the load requirement dimensioned via an engine control and injected directly is, and furthermore after the injection of the for The fuel quantity measured via the injection nozzle an additional force after completion of the combustion phase amount of substance is injected when the piston is each  during its expansion stroke in the area of the bottom dead center lung, and in which the emerging from the cylinder Exhaust gases from at least one mechanically, chemically and / or Catalytic exhaust treatment device for elimination distribution of pollutants.

The advantage of this procedure is on the one hand that the introduction of additional hydrocarbons for the Exhaust aftertreatment does not have an additional injection nozzle but via the already existing injection nozzle under ent speaking control via the existing motor control he follows. Another advantage is that the additional fuel quantities intermittently, d. H. in the exhaust stroke of a cylinder in the exhaust gas, so that here too there is the possibility of the additional injected Amounts of fuel each for operation in the respective Adjust the metered amount of fuel so that a much more precise dosage is possible here. A white Another advantage of the method according to the invention is that that the additional fuel to be supplied only after the Combustion phase is introduced. This phase depends on the Operating conditions reached at the end of the expansion stroke. Each after control and operating conditions can still be in the Extension stroke the additional fuel quantity introduced the. The gas temperatures in the cylinder are in this range below the soot formation temperature of 1300 ° K. The additional che amount of fuel must be measured so that this tempe temperature is not exceeded, neither in the cylinder still in the exhaust duct. The additionally injected fuel quantities are cracked and processed in the hot exhaust gas tet, so that hydrocarbons in corresponding in the exhaust gas Quantities and are available in a form as they are Regeneration of nitrogen oxide catalysts or particulate film tern are needed. By influencing the injection time in relation to the expansion phase and the out shift phase and through the injection duration can both Composition as well as the amount of hydrocarbons and of hydrogen adapted to the respective requirements  the. Another advantage is that the injector se can not coke, because before the post-injection much larger amount of fuel for each engine load setting Inject the lung and thereby the nozzle with every work cycle due to the increased fuel quantity of any coke residues which is being liberated.

This is done in that a total λ of <0.95 is set for the regeneration of storage catalysts, but under the boundary condition that the post-injection quantity is controlled so that the gas / exhaust gas temperature remains <1300 K. In DeNO _x catalysts with continuous NO _x reduction by hydrocarbons, the post-injection amount is set so that the hydrocarbon / NO _x ratio is expressed by the equivalent C ₁ amount of total hydrocarbons is greater than or equal to 2. For the diesel filter regeneration, the post-injection quantity must be dimensioned so that the exhaust gas temperature before the filter does not exceed 900 ° C.

The required amount of post-injection can be made by corresponding exhaust gas sensors are regulated. But it is also one Map control possible in the engine control for a corresponding post-injection menu for each load / speed point ge depending on the exhaust gas aftertreatment device is saved.

With diesel engines, the injection of the additional Amounts of fuel are also made so that these additional Amounts of fuel in the expansion phase during ejection burn before and thus for thermal regeneration of the soot filter cause the necessary temperature increase.

This can prevent the additional force amount of substance still burns in the cylinder. Rather, it is si made that this additional amount of fuel only ge is cracked and corresponding hydrocarbon substances and hydrogen with the exhaust gas flow into the exhaust gas action facility are held. By choosing this  Injection time is ensured that the in the Zy Linder introduced additional amount of fuel also completely dig with the exhaust gas into the exhaust pipe and thus to the exhaust gas action facility is held.

As for the supply of the additional fuel quantities injection nozzle available for each cylinder anyway and the amount of fuel required for the work cycle are specified by the engine control, gives the inven the possibility of adding the additional fuel quantity of the power required for the respective work cycle adjust amount of fabric.

The method according to the invention in its various versions events made possible by the injection of additional Amounts of fuel at the end of the expansion phase until the end shift phase a supply of hydrocarbon / Hydrogen mixtures in the exhaust gas. Leave these mixtures in the exhaust gas thus for the most diverse forms of exhaust gas use action facilities, so for intermittent Regeneration of nitrogen oxide storage catalysts, for continuous Nuclear reduction of nitrogen oxides in SCR catalysts (SCR = selected catalytic reduction), for thermal and / or catalytic regeneration of particle filters, as well as to support the regeneration of particles filter with the help of external energy.

The invention is explained in more detail with the aid of a flow diagram.

The drawing schematically shows two cylinders I, II of a four-stroke cylinder internal combustion engine with spark ignition. Accordingly, the individual cylinders are each provided with at least one gas inlet channel 1 and at least one gas outlet channel 2 . The gas inlet channel 1 can be closed by a gas inlet valve 3 and the gas outlet channel 2 by a gas outlet valve 4 . The Gaseinlaßven tile 3 and gas outlet valves 4 of each cylinder are connected to a correspondingly controllable drive, for example a camshaft or an electromagnetic actuator, via which the opening and closing times of the individual valves can be controlled freely via a motor controller 5 .

Each cylinder also has an ignition device 6 and an injection nozzle 7 designed as a controllable valve, the actuator of which is connected to the engine control 5 .

Via the electronic engine control 5 , the amount of fuel required for the respective operation is supplied by corresponding actuation of the injection valve 7 in accordance with the predetermined load request (for example by the accelerator pedal 8 ). In the engine control system, other information required for operation is usually taken into account in addition to the load request by the accelerator pedal 8 , for example the crankshaft speeds, the engine temperature, etc., which, in addition to the load specification of the accelerator pedal 8, are also included in the fuel metering via the injection valves 7 be taken into account. The ignition device 6 of the individual cylinders is also controlled via the engine control 5 .

The exhaust pipes 2 of the individual cylinders, which are only indicated for further cylinders, are combined to form an exhaust duct 9 , to which at least one exhaust treatment device 10 is assigned. In diesel engines, for example, this is a particle filter. In the case of gasoline engines, this is a storage catalytic converter or an SCR catalytic converter and possibly also a downstream oxidation catalytic converter 11 .

In order to provide the amount of hydrocarbon required for the operation of the exhaust gas treatment device in the exhaust gas, the individual injection valves 7 of each cylinder or even just selected individual cylinders are connected to the respective operating cycle or alternatingly via the engine control 5 every two th, third or nth work cycle additionally controlled so that an additional amount of fuel is injected into the respective cylinder. As described in detail above, this additional quantity of fuel is only injected into the respective cylinder when the piston has almost reached the end of the expansion stroke or the extension stroke has already begun. Thus, according to the injection cycle predetermined by the engine control 5 after each working stroke of each cylinder, or in a correspondingly different distribution, predeterminable amounts of hydrocarbons / hydrogen / carbon monoxides via the exhaust gas lines into the exhaust gas channel 9 , so that they are used for regeneration of the downstream exhaust gas treatment device 10 be available.

The ratio of the additional amount of fuel to be injected ge to the amount of fuel supplied to the cylinder in the respective work cycle and required for the work stroke can now be predefined via the engine control. However, it is also possible to detect the actual content of nitrogen oxides in the exhaust gas by the arrangement of a nitrogen oxide probe 12 in the gas duct 9 in front of the exhaust gas treatment device 10 , so that both the injection timing and the injection duration and thus also the injection quantity are not via the engine control 5 more is additionally injected depending on the amount of fuel required for operation, but only such an additional amount of fuel that is necessary for regeneration of the downstream exhaust gas treatment device 10 as a function of the detected nitrogen oxide content in the exhaust gas. This method is particularly advantageous when an SCR catalytic converter that works continuously is used as the exhaust gas treatment device.

With a diesel engine as a so-called compression ignition engine the ignition device and the engine control as well as a any map are appropriate to the diesel process fits.

Claims (9)

1. Method for operating a piston internal combustion engine, at that in each cylinder by means of an on spray nozzle required for the respective work cycle Fuel quantity depending on the load request an engine control is dimensioned and directly injected and in which, furthermore, after the injection, for the work cycle the measured amount of fuel via the injector according to Ab end of the combustion phase an additional amount of fuel is injected when the piston is at his Expansion stroke in the area of the bottom dead center position det and in which the exhaust gases emerging from the cylinders by at least one mechanically, chemically and / or catalyzed Table-acting exhaust treatment device for elimination of pollutants are passed through. 2. The method according to claim 1, characterized in that the additional fuel is injected when the mitt lower gas temperature in the cylinder below the soot formation temperature temperature of 1300 K. 3. The method according to claim 1 or 2, characterized in that the additional amount of fuel is timed is that the gas in the cylinder or the exhaust gas after the Zylin which does not reach the soot formation temperature of 1300 K. 4. The method according to claim 1 or 2, characterized in that the additional amount of fuel is injected at the latest when the piston has reached a position that is the maximum 110 ° KW after the bottom dead center position. 5. The method according to any one of claims 1 to 4, characterized in that the additional amount of fuel is dimensioned so that it - based on a C ₁ equivalent - corresponds to twice the NO _x concentration in the exhaust gas. 6. The method according to any one of claims 1 to 5, characterized ge indicates that the additional amount of fuel is measured in this way is that the average fuel-air ratio in the exhaust gas λ < Is 0.95. 7. The method according to any one of claims 1 to 6, characterized ge indicates that the additional amount of fuel is measured in this way is that the exhaust gas temperature upstream of the soot filter is not 850 ° C exceeds. 8. The method according to any one of claims 1 to 7, characterized ge indicates that of the damage contained in the exhaust gas flow substances at least the content of nitrogen oxides before the exhaust gas action facility recorded and depending on it the engine control system the additional fuel to be injected amount is measured. 9. The method according to any one of claims 1 to 8, characterized ge indicates that the additional fuel to be injected quantity as a function of the exhaust gas aftertreatment device for each load / speed point as a matrix in the motor control is placed.