MXPA00005275A - No to no2 - Google Patents

Abstract

The invention is directed towards a method for adjusting the NO2 to NO content of a diesel engine's exhaust without affecting engine performance. The NO2 to NO ratio is adjusted by varying the amount and timing of secondary hydrocarbon injection during the engine's expansion stroke. The appropriate amount of secondary injected hydrocarbon and the appropriate injection timing are determined from calibration values obtained by direct engine measurements and the desired NO2:NO ratio.

Description

CONTROL OF THE CONVERSION OF NO TO NQ2 IN AN ENGINE OF COMPRESSION INJECTION FOR HYDROCARBON INJECTION DURING THE EXPANSION CAREER Field of the Invention The present invention relates, generally, to an improved method for operating a diesel engine. More particularly, the method relates to a process for the conversion of NO to N02 by the injection of hydrocarbons into the cylinder of the diesel engine during decompression.

BACKGROUND OF THE INVENTION In the normal operation of a diesel engine, atmospheric air is first compressed within the combustion chamber of the engine, at a pressure of approximately 3.5 kg / cm2. The compression of the air raises its temperature to approximately 538 ° C. Then the diesel fuel is injected into the compressed hot air, through a fuel injection nozzle. The fuel is atomized, inside the combustion bed, where it rises to its auto-ignition temperature, which results in the spontaneous ignition, burning and expansion of the gases inside the chamber. The expansion of the combustion products drives the cylinder downwards, thus supplying the motor power stroke. In order for a diesel engine to operate efficiently, that is, with minimum fuel consumption and maximum power, it is typically operated under air to fuel ratios that produce exhaust gases containing large amounts of oxygen and usually only minimum amounts of oxygen. unburned hydrocarbons. Unfortunately, the operation of a diesel engine with maximum power and efficiency also results in conditions that raise peak operating temperatures and, therefore, result in the formation of nitrogen and oxygen compounds, known as NOx compounds. A method to decrease the concentration of the compounds? Ox in the emissions of the exhaust gases is, of course, to put these exhaust gases in contact with a catalyst, capable of reducing the amount of the species of the? Ox in the stream soda. However, the catalysts known to be effective in the diesel exhaust environment, the catalytic catalysts, are usually more effective when the reduction species are present in the exhaust gas. In order to generate these species, the engine is operated under conditions of a low peak temperature, these conditions are directly opposite to those desired from the point of view of the general efficient operation of the engine. One way that the concentrations of oxygenated, unsaturated, unsaturated oxygenates and their mixtures can be increased in the exhaust is by the direct injection of a hydrocarbon into the cylinder of the diesel engine, during the expansion stroke (power) of the engine. This is referred to as the secondary injection. Many of the deNOx catalysts, capable of using such hydrocarbons to reduce the N0X species in the exhaust stream are most effective when the N02: NO ratio of the exhaust stream can be controlled to provide an optimum ratio, depending on the particular catalyst employed. Consequently, there is a need to control the ratio of N02: NO among the exhaust species of the NOx in the diesel engine that uses the secondary injection.

SUMMARY OF THE INVENTION In one embodiment, the invention relates to a method for converting the NO formed into a diesel fuel engine cylinder, during the engine expansion stroke, to the N02, without substantially reducing the power of the engine, this The method comprises: (a) determining, at one or more pre-selected points of operation of the engine, a hydrocarbon calibration quantity and a value of the calibration crank angle to inject the hydrocarbon into the cylinder of the diesel fuel engine, during a race of expansion, following the injection of the primary fuel charge into the cylinder, during an intake stroke, whereby the desired ratio of N02 to NO is obtained in the exhaust stream of the engine; and then, during engine operation, (b) measuring the engine operating point; (c) determining a value of the crank angle and the amount of hydrocarbons for injection, during the expansion stroke at the measured point of operation, from the calibration values of the crank angles and the quantities of calibration hydrocarbons in the pre-selected operating points, when the measured operating point is the same as one of the predetermined operating points and, when the measured operating point is different from the predetermined operating points, determine the amount of hydrocarbons and the crank angle for the injection, during the expansion stroke, interpolating between the values of the calibration crank angles and the quantities of calibration hydrocarbons, at predetermined operating points; (d) injecting the amount of hydrocarbons into the engine cylinder, during the expansion stroke in the crank angle; and (e) repeating steps (c) and (d), when the operating point in step (b) changes.

Brief Description of the Drawings Figure 1 is a schematic illustration of the main components of a cylinder in a diesel engine, necessary to understand the present invention. Figure 2 is a schematic illustration of a common rail injection system, configured for use in the present invention. Figure 3 shows the effect of the engine operating parameters on the fraction of the NO converted to the N02, as a function of the secondary injection angle, as measured from the start of the expansion stroke, according to the present invention. - Figure 4 is a graph, showing that the fraction of the NO converted to N02, as a function of the angular deviation of the angle corresponding to the peak conversion is approximately independent of the motor operating parameters.

Figure 5 illustrates the production of thermally decomposed products, formed from a secondary injection and the conversion of NO to N02, as a function of an ignition angle. The solid rectangles correspond to the performance of the thermally decomposed product, the open rectangles correspond to the NO conversion. Figure 6 shows. the dependence of the conversion of NO to N02 on the amount of secondary injected hydrocarbons.

Detailed Description The invention will now be described in greater detail with specific reference to a reciprocal four-stroke, compression-ignition internal combustion engine; however, it will be readily appreciated that the invention is equally applicable to other compression ignition engines, such as reciprocating compression internal combustion engines, of two strokes. Likewise, in the description that follows, similar reference numbers in the drawings apply to similar parts. Referring first to Figure 1, a diesel engine includes a motor block 12, in which there is a combustion chamber or cylinder 14. Inside the cylinder 14, there is a slideable piston 15, attached to the crank (not shown). shown) of the engine. In the upper part of the cylinder 14 there is a cylinder head 16, which closes one end of the cylinder 14. A fuel injection nozzle 17 is mounted on the cylinder head 16 for the synchronous injection of the diesel fuel directly into the chamber of combustion or cylinder 14. The engine also includes an exhaust valve 21, an exhaust port 24, an air valve 20 and an air door 18. In operation, when the piston 15 is in a position corresponding to a crank rotation angle of about 0 °, at the start of the cylinder intake stroke, the intake valve 20 opens and the atmospheric air is driven into the interior of the cylinder. the combustion chamber or cylinder 14, as the cylinder moves downwards. The valve 20 closes in or soon after the completion of the intake stroke, and the piston 15 rises in the compression stroke. The piston 15 begins its compression stroke in a position close to the bottom of the cylinder, which corresponds to an angle of rotation of the crank of 180 °, that is to say, the dead center position of the bottom. An optional pilot fuel charge is injected into the combustion chamber when the piston 15 reaches a position corresponding to a crank rotation angle of about 330 ° in the compression stroke. The air in the cylinder is compressed, increasing the temperature and pressure that causes any pilot fuel charge to undergo a chemical and physical reaction before ignition. As the compression continues, the primary diesel fuel is injected into the cylinder 14 by means of the injection nozzle 17, and the diesel fuel will ignite, causing all the mixture in the combustion chamber 14 to expand. The expansion stroke (or power) of the motor starts as the piston passes through a position corresponding to the crank angle of the upper dead center (0 °). According to the present invention, during the expansion of the cylinder 14 in the power stroke, a pre-selected amount of hydrocarbon fuel, based on the amount of the primary fuel, is injected into the cylinder at a predetermined angle of rotation, named the angle of secondary injection. This pre-selected fuel injection can be injected by means of the nozzle 17 or by a separate nozzle. The injection of hydrocarbons during the expansion, ie the power stroke, is referred to as the secondary injection, in order to distinguish it from the primary fuel injection. The hydrocarbons, injected during the expansion, are the secondary injected hydrocarbons. In general, the hydrocarbon fuel injected during the power stroke may be the same as the diesel fuel injected into the engine during the compression stroke or may be some other hydrocarbons or oxygenates. The amount of the fuel injected during the secondary injection should vary from about 0.5 to 5% by weight, preferably from 1 to 3% by weight, based on the weight of the primary fuel used for the main combustion. Desirably, the secondary injection is done in such a way as to cause the products to mix thoroughly with the NO formed during combustion. The angle of the secondary injection can be adjusted in order to provide a range of conversion values from NO to N02, as shown in Figure 3. The figure illustrates the conversion of NO to N02 in a turbocharged diesel engine, from 4 cylinders, 2.5 liters, directly injected, which has a compression ratio of 21: 1, which burns fuel from a mixture of iso, normal and cycle paraffins, designed to represent the aliphatic portion of a typical diesel fuel (the aliphatic portion) it is the main portion of a typical diesel fuel). The figure shows that the secondary injection angle, which corresponds to the peak conversion, varies with the engine load, speed and inlet pressure. The data is generated using a kinetic model to simulate the performance of such a motor. The points represented by rectangles correspond to a load of Break Mean Engine Pressure ("BMEP") (Average Pressure of the Motor to Braking) of 3.1 bar, a pressure of input of 1.4 bar, and a rotation speed of 2250 rpm; the diamond points correspond to a BMEP load of 1.5 bar, an inlet pressure of 1.4 bar and a rotation speed of approximately 2100 revolutions per ^ minute (rpm); star points corresponding to a load of 3.1 bar, an inlet pressure of 1.2 bar and a rotation speed of 1550 rpm; and circles corresponding to a BMEP load of 2.0 bar, an inlet pressure of 1.1 bar, and a rotation speed of 1550 rpm. In the simulation, illustrated in Figure 3, the amount of fuel injected during the secondary injection is 2% by weight of the amount of the primary fuel. In the present invention, the secondary injection occurs at an angle that depends on the load of the engine, the inlet pressure when a compressor is present and the speed of rotation. As explained above, the secondary injection results in the conversion of NO to N02 during the expansion stroke, and consequently reduces the presence of NO in the exhaust stream. As explained above, the conversion of NO to N02 decreases as the secondary injection angle deviates from the angle corresponding to the peak conversion of NO to N02. However, Figure 4 shows that the extent of the conversion reduction from the peak value is approximately independent of the engine load, the inlet pressure when a compressor is present, and the speed as the secondary injection angle deviates from the angle that corresponds to the peak conversion. The data in Figure 4 are generated using the data in Figure 3, and the representations of the rectangle, diamond, star and circle correspond to the same values of the operation parameter as in Figure 3. It should be noted that in cases where Using a compressor, the inlet pressure can be strongly correlated with the speed of rotation of the engine. In one embodiment, a desired secondary injection angle is obtained by measuring the conversion of NO to N02 as a function of the secondary injection angle, according to the operating conditions, such as the air-fuel ratio, the degree of recirculation of the exhaust gas , gas inlet pressure (air and EGR), when a compressor is present, the load of the motor and the speed of rotation are varied over the entire operating range of the motor. These measurements are recorded as a calibration. It should be noted that all motor parameters do not need to be measured as part of the calibration with all motors because, as those skilled in the art recognize, some motor operating parameters may be strongly correlated, depending on the configuration of the motor. particular engine and its use. In general, at least the load and the speed of rotation must vary in determining the calibration. During the actual use of the motor, according to this mode, the operating conditions of the motor are measured, and the corresponding record of the secondary injection angle is recovered. The motor injectors are then operated so that the secondary injection occurs at the optimum angle through the action of an injector controller. The optimum angle, as noted above, depends on the conversion of the NO to the N02 that is desired at each operating point. In a preferred embodiment, the calibration is obtained as follows: First, the synchronous secondary injection angle is determined at a reference point at which the conversion of NO to N02 is maximum. This angle of synchronism is called APr. Preferably, the reference point is selected to be within the range of all parameters used in the calibration. Once the APr is determined, the diesel engine measurements are made to determine the extent of the changes in the injection angle, necessary to maximize the conversion of NO to N02, according to engine parameters, such as the load , speed and gas inlet pressure, when a compressor is present, they are varied. The injection angle, which corresponds to the maximum conversion, is recorded for the operating conditions, which correspond to the engine operating range. This injection angle corresponds to the production in the peak reduction (AP) at the operating point (i) of the motor, which is different from the reference point (r), which is named APj .. The deviation in the angle The injection angle of the reference injection angle is, therefore, APX -APr. Those skilled in the art of the catalytic operation of exhaust from diesel engines will be aware that it may be advantageous for a portion of the NOx, in the exhaust stream, to be in the form of NO. In this situation, it may be desirable to decrease the conversion of NO to N0 from peak conversion to some desired conversion value. The desired secondary injection angle, at the reference operating point (r), which corresponds to the value of the desired conversion, ADr, is determined by direct motor measurements. It has been found that the desired deviation of the injection angle, which corresponds to the peak conversion at any motor operating point (i) equal to Di-APX is an approximately equal constant rl value of ADr-APr. See Figure 4. In other words, it has been found that the amount of deviation in the crank angle between the secondary injection angle, which corresponds to the generation of crest reduction at any operating point (i), and the angle that corresponds to the desired oxygenate / olefin ratio and the yield of the thermally decomposed total product at the same point (i), is approximately constant for all values of (i), and, consequently, can be evaluated at the value (r) reference. To summarize, in this mode, the parameters APr and ADr-APr and the vector APi are determined as a calibration, using direct measurements of the motor. The amount of the conversion from NO to N02 can then be optimized during the actual use of the motor, by determining the operating point (i) of the motor, which corresponds to a particular operating condition and then determining the desired crank angle for the injection secondary ADi from the relation ADi = APr + (AP_-APr) + (ADi-APj.), where ADi-APi is equal to ADr-APr for any (i). The calibration points are selected between those values of the motor load and the speed corresponding to the desired operating range of the motor. The particular points selected will depend on the particular catalyst used and the desired ratio of N02 to NO, present in the exhaust stream, before the exhaust catalyst as a function of the load and speed of the engine. The catalytic conversion of N0X species occurs at a temperature range where the exhaust catalyst is functional. The temperature of the exhaust catalyst at any particular speed is determined primarily by the operating load. Consequently, at any particular speed in the operating range, the minimum minimum load calibration point is selected in a load that corresponds to a temperature of the exhaust catalyst at the start of the functional range. The maximum load-speed calibration point at that speed is selected at a load corresponding to an exhaust catalyst temperature at the upper end of the functional temperature range of the catalyst, as long as the load does not exceed the maximum load of the motor for the selected speed. In practice, during the calibration of the diesel engine, the calibration points are selected at speeds that extend in the desired operating range and the value of the load, maximum and minimum, is determined for each speed, as noted above. Within the range of these load values, maximum and minimum, other calibration points will be selected,, when the increased production of N0X is observed. The exact number of calibration points will depend on both the type of the diesel engine and the manner in which the engine is used. For example, in cases where an engine is continuously operated at a constant load and speed, a single calibration point will be sufficient in the practice of the invention. In other cases, such as those in which an engine undergoes load and speed conditions that vary rapidly over a full range of engine operation, the calibration points may include minimum and maximum load values at representative speeds, as well as that the calibration points within these minimum and maximum values in load-speed points correspond to the increased production of NOx. The Elementary Urban Impulse Cycle - ^ the Extra-Urban Impulse Cycle (E.C.E.R15-E.U.D.C.) Is representative of that case. This impulse cycle is indicated in the directive brochure 91/441 / E.E.C. , as amended by 96/69 / E.C. as the Type 1 Test, the emission test cycle. It is not necessary to obtain a calibration value at each operating point in the engine operating range, which exhibits the production of NOx.

A sufficient number of calibration points has been obtained when standard interpolation methods, known to those skilled in the art, can be used to determine the crank angle for secondary injection, which corresponds to the generation of the crest reduction in any point of operation of the engine. In the preferred embodiment, the invention is carried out as shown in Figure 2. Figure 2 shows a fuel tank (1) connected to a fuel pump (2). The fuel leaves the fuel pump at a high pressure and is delivered to a common rail (3). A control unit (5) of the injector detects the information of the load and speed by means of the sensors (7). The control unit of the injector determines the point (i) of operation of the engine and calculates the desired injection in the angle ADi. The control unit of the injector produces a signal (6) which activates the injectors (4) of the engine at an appropriate crank angle so that the secondary injection occurs at the desired crank angle AD ± in each cylinder of the engine. As it should be easily appreciated, diesel engines come in several models. For each engine model, the relationship between the fuel consumption condition and the characteristics of the exhaust gas can be easily determined. Of these, any person skilled in the art is able to adjust the composition of the exhaust gas, by injecting a preselected amount of hydrocarbons into the cylinder, during its expansion or power stroke, at a predetermined time. This allows the engine to be optimized from the point of view of supplying maximum power and efficiency and, at the same time, being able to have an exhaust gas having the appropriate ratio of N02 to NO, present in the catalytic converter. Those skilled in the art are aware that many catalytic converters in their use decompose the NOx exhaust species more efficiently in the presence of an optimal ratio of N02 to NO, found in the exhaust species of the N0X. When these catalytic converters are present, the timing of secondary hydrocarbon injection and the quantity must be adjusted for the appropriate ratio. It should be noted that NO and N02 count substantially on all N0X compounds produced in the engine. It should also be noted that the conversion of NO to N02 is also affected by the spread of the mixture of nO formed during the primary combustion of fuel with the secondary injected fuel. The more intimate the mixture between the NO and the secondary injected fuel, the greater the conversion of NO to N02. This peak conversion from NO to N02 resulting from the secondary injection at a given crank angle and under given engine operating conditions, will occur when the NO and the secondary injection product are completely intermixed. The secondary injection results in the formation of thermally decomposed products, comprising oxygenates, unsaturated and oxygenated unsaturates. Those skilled in the art will be aware that these compounds can function as reducing agents for NOx compounds. Figure 5 shows that at some engine operating points it is possible to select a secondary injection angle corresponding to both a high reducer formation and a high conversion of NO to N02. The amount of secondary hydrocarbons injected will depend, in part, on the amount of hydrocarbons needed in the exhaust as a NOx reducer. This amount will generally vary from about 0.5 to 5% by weight of the injected primary fuel. The amount of the secondary injection product depends on the desired ratio of NO to N02. Figure 6 illustrates the relationship between the conversion of NO to N02 as a function of the molar ratio of the hydrocarbon to NO. The figure shows that if, for example, 75% conversion of NO to N02 is desired over the motor operating range, then the minimum molar ratio of hydrocarbons to NO will be 5: 1. A molar ratio of 5: 1 corresponds to an amount of the secondary injection product of about 1.5% by weight, based on the weight of the primary fuel charge. In Figure 6, the rectangle, diamond and star points correspond to the same motor parameters as in Figures 3 and 4. However, the points correspond to a BMEP load of 2.0 bar, inlet pressure of 1.1 bar , and rotation speed of 1550 rpm, are represented by unshaded rectangles and no circles, as in Figures 3 and 4. The molar ratio is that of component Ci of the fuel to NO in the exhaust stream.

Claims (7)

1. CLAIMS 1. A method for varying the relative concentration of the compounds of N02 to NO, formed in a cylinder of a diesel fuel engine, without substantially reducing the power of the engine, this method comprises: (a) determining, in one or more pre-selected engine operating points, a hydrocarbon calibration quantity and a calibration value of the angle of the crank to inject the hydrocarbon into the cylinder of the diesel fuel engine, during an expansion stroke, followed by the injection of the fuel charge. primary fuel inside the engine cylinder, during an intake stroke, whereby the desired ratio of N02 to NO is obtained in the engine exhaust stream; and then, during engine operation, (b) measuring the engine operating point; (c) determining a value of the crank angle and an amount of hydrocarbons for the injection, during the expansion stroke, followed by the injection of the primary fuel load during the intake stroke, at the point of operation measured from the values of the calibration crank angle and the quantities of calibration hydrocarbons, at preselected operating points, when the measured operating point is the same as one of the predetermined operating points and, when the measured operating point is different from the points of predetermined operation, determining the amount of hydrocarbons and the angle of crank for injection, during the expansion stroke, interpolating between the values of the calibration crank angles and the quantities of calibration hydrocarbons, at predetermined operating points; (d) injecting the amount of hydrocarbons into the engine cylinder, during the expansion stroke in the crank angle; and (e) repeating steps (c) and (d), when the operating point in step (b) changes.
2. 2. The method of claim 1, wherein the engine operating point is determined at least one of the engine load, engine speed and inlet gas pressure, when an inlet gas compressor is present.
3. 3. The method of claim 1, wherein the crank angle in the injection varies from about 20 ° after the upper dead center, to 180 °, after this upper dead center.
4. 4. The method of claim 3, wherein the amount of hydrocarbons injected during the expansion stroke varies from about 0.5 to 5% by weight, with ase in the weight of the primary fuel charge of the engine.
5. 5. The method of claim 4, wherein the injected hydrocarbons are the same as the primary fuel. The method of claim 5, wherein the injected hydrocarbons are different from the primary fuel, and wherein these hydrocarbons are selected from the group consisting of iso, cyclo and normal paraffins, and mixtures thereof. 7. A method to vary the relative concentration of the compounds of N02 to NO in a cylinder of a diesel fuel engine, without substantially reducing engine power, this method comprises: (a) determining at one or more operating points of the engine. Pre-selected engine: a calibration amount of a hydrocarbon for injection into the cylinder, during an expansion stroke, followed by the injection of a primary fuel charge into the cylinder, during an intake stroke, the amount varies from approximately 0.5 at 5% by weight, with ase in the weight of the primary fuel charge of the engine and the hydrocarbon is the same as that of the primary fuel; and a value of the calibration crank angle, which varies from about 20 °, after the upper dead center, to about 180 °, after this upper dead center, whereby the desired ratio of N02 to NO is obtained, in the motor exhaust current; and then, during engine operation, (b) measure the engine operating point; (c) determining a value of the crank angle and an amount of hydrocarbons for injection, during the expansion stroke, at a point of operation measured from the values of the calibration crank angle, and the quantities of calibration hydrocarbons in the pre-selected operating points, when the measured operating point is the same as one of the predetermined operating points and, when the measured operating point is different from the predetermined operating points, determine the amount of hydrocarbons and the crank angle for the injection, during the expansion stroke, by the interpolation between the values of the calibration crank angles and the quantities of calibration hydrocarbons at the predetermined operating points; (d) injecting the amount of hydrocarbons into the engine cylinder, during the expansion stroke, at the crank angle; and (e) repeating steps (c) and (d), when the operation point in step (b) changes.