CN107178418A - Preprocessor heat management control method based on air inlet system and exhaust system - Google Patents

Abstract

The invention discloses a thermal management control method of an after-processor based on an intake and exhaust system: the working condition point of the original engine steady-state experiment is determined by analyzing the test cycle and exhaust temperature, and according to the original engine in the WHTC test cycle Determine the target temperature based on the change trend of SCR temperature; determine the influence mechanism of the variable geometry turbocharger opening on the SCR temperature based on the WHTC test cycle; determine the influence mechanism of the intake valve late closing mechanism on the SCR temperature based on the WHTC test cycle; The WHTC cold start test was carried out, and the opening of the variable geometry turbocharger and the closing timing of the intake valve were changed at the same time to determine the optimal control strategy parameters of the variable geometry turbocharger-intake valve late closing mechanism. The invention can improve the exhaust gas temperature to improve the _NOx conversion efficiency of the aftertreatment system, and is suitable for diesel engines equipped with turbochargers with variable geometry sections.

Description

Thermal management control method of afterprocessor based on intake and exhaust system

technical field

The present invention relates to diesel engine exhaust post-treatment technology, variable geometry cross-section turbocharging technology and Miller cycle technology that delays intake valve closing late, more specifically, relates to a post-processor thermal management based on intake and exhaust systems Control Method.

Background technique

Diesel engines are widely used in the fields of commercial vehicles and passenger vehicles due to their outstanding features such as high efficiency, low fuel consumption, and low _CO2 emissions. However, in-cylinder oxygen-enriched combustion is usually accompanied by a large amount of nitrogen oxide emissions, mainly referring to nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ), which are collectively referred to as NO _x . Normally, NO in the exhaust of diesel engines accounts for the vast majority, and it can reach 90% in some working conditions. Medical research has shown that both NO and NO ₂ will have adverse effects on human health, and even endanger human life in severe cases. Therefore, how to effectively reduce engine NO _x emission levels has become a research hotspot for internal combustion engine workers worldwide.

At present, the post-treatment technologies used to reduce NO _x emissions from diesel engines mainly include: Lean NO _x Trap (LNT) technology, NO _x selective non-catalytic reduction, NO _x selective catalytic reduction and plasma-assisted catalytic reduction. Selective catalytic reduction (Selective Catalytic Reduction, SCR) technology, under the action of a catalyst, injects fuel or other reducing agents into the oxygen-rich exhaust gas to promote the reaction between the reducing agent and _NOx , reducing _NOx to harmless _N2 , which can reduce More than 90% of _NOx in diesel engine is currently considered to be the most effective technology to solve _NOx emission of diesel engine. Existing SCR technologies can be roughly divided into two types according to the types of reducing agents: urea-type SCR technology using NH ₃ produced by urea decomposition as reducing agent, and hydrocarbon-type SCR technology using hydrocarbon as reducing agent. In comparison, urea-based SCR technology is more mature and has been widely used in engineering practice. Compared with EGR technology, the use of urea-type SCR post-treatment technology is beneficial to the improvement of fuel economy, and the configuration of the fuel system does not need to be too high, and SCR is not very sensitive to sulfur in fuel, and low-required fuel quality can reduce the operation of diesel engines cost.

In the field of post-treatment technology for reducing NO _x of diesel engines, LNT and SCR are still the mainstream technology routes. Among them, SCR technology is more mature and has higher conversion of NO _x , and its application prospects are generally optimistic. Whether it is LNT technology or SCR technology, the conversion process requires the participation of a catalyst, and the activity of the catalyst is closely related to the temperature. Taking the copper-iron-based SCR system used in the test as an example, when the exhaust gas temperature is lower than 180°C, the SCR efficiency will be greatly reduced. With the improvement of diesel engine efficiency, the application of two-stage supercharging and low-pressure EGR technology, the exhaust temperature of diesel engines is also getting lower and lower, which brings challenges to the application of SCR systems, especially in the Euro VI stage, regulations on engine There are clear requirements for cold start, so it is of great significance to study the thermal management technology of the aftertreatment system.

Contents of the invention

The purpose of the present invention is to provide a post-processor thermal management control method based on the intake and exhaust system, aiming at low-load conditions of the diesel engine and the low conversion efficiency of the SCR system during the cold start process, which can increase the temperature of the exhaust gas and improve the efficiency of the after-treatment system. _NOx conversion efficiency.

The purpose of the present invention is achieved through the following technical solutions.

The postprocessor thermal management control method based on the intake and exhaust system of the present invention comprises the following steps:

Step 1. Determine the operating point of the original engine steady-state experiment by analyzing the test cycle and exhaust temperature, and determine the target temperature reached by the cycle within a certain period of time according to the change trend of the SCR temperature of the original engine in the WHTC test cycle ;

The second step is to modify the original engine: one is to replace the fixed geometry turbocharger with a variable geometry turbocharger, and the other is to add a variable geometry turbocharger between the cylinder and the fixed geometry turbocharger. Cross-section turbocharger; based on the WHTC test cycle, the influence of the opening of the variable geometry turbocharger on the SCR temperature and engine performance was studied, and the mechanism of the influence of the opening of the variable geometry turbocharger on the SCR temperature was determined;

Step 3, install a variable valve timing device on the original engine, specifically install an intake valve late closing mechanism on the cylinder intake valve; study the influence of the intake valve late closing mechanism on the SCR temperature and engine performance based on the WHTC test cycle, To determine the influence mechanism of intake valve late closing mechanism on SCR temperature;

Step 4: After the original engine is equipped with a variable geometry turbocharger and a late intake valve closing mechanism, the WHTC cold start test is carried out. According to the relationship between the opening of the variable geometry turbocharger determined in step 2 and the SCR temperature The influence mechanism and the influence mechanism of the intake valve late closing mechanism determined in step 3 on the SCR temperature, while changing the opening of the variable geometry turbocharger and the closing timing of the intake valve, matching the two technologies, and confirming that after modification The optimal variable geometry turbocharger-intake valve late closing mechanism control strategy parameters when the engine reaches the target temperature of step one.

The target temperature mentioned in step 1 should be greater than the minimum light-off temperature of the SCR processor installed.

The intake valve late-closing mechanism described in step 3 includes a hydraulic tappet assembly, a pressure source and a regulating valve. The hydraulic lifter assembly slides up and down to control the valve timing.

Compared with the prior art, the beneficial effects brought by the technical solution of the present invention are:

(1) VGT is added in the present invention, through the flexible regulation and control to engine intake air volume, can produce important effect to combustion temperature and exhaust gas temperature in cylinder, increase VGT opening degree and improve combustion temperature in cylinder in many respects to promote Post-treatment temperature has a direct effect;

(2) The RIVCT installed in the present invention has a very fast response speed, and can be switched and used within one cycle, effectively increasing the combustion temperature and exhaust temperature;

(3) The present invention determines the optimal VGT-RIVCT control strategy parameters by comparing the SCR temperature rise corresponding to different VGT openings and intake valve closing timings, temperature response rates, and engine performance; The control strategy realizes the control of the intake air volume and the heat capacity of the gas in the cylinder, which can significantly increase the temperature of the SCR system, greatly advance the SCR ignition time, and have a fast response effect;

(4) The present invention adopts the combination of VGT and RIVCT technology, and improves the NO _x conversion efficiency of the aftertreatment system by changing the charge heat capacity and affecting the combustion process in the cylinder, increasing the SCR temperature.

Description of drawings

Fig. 1 is a schematic diagram of the post-treatment thermal management system of the present invention with VGT and RIVCTD installed simultaneously;

Fig. 2 is the influence figure of VGT opening degree to SCR temperature under the test condition of the present invention;

Fig. 3 is the figure of influence of VGT opening degree on BSFC under the test working condition of the present invention;

Fig. 4 is the figure of influence of RIVCT on SCR temperature under the test working condition of the present invention;

Fig. 5 is a diagram showing the influence of the SCR temperature and the post-treatment thermal management control strategy of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

Selective catalytic reduction systems include catalysts that assist in the reduction of nitrogen oxides in the exhaust. A catalyst works effectively when it reaches an operating temperature known as the light-off temperature. With the application of technologies such as two-stage supercharging and low-pressure EGR technology, the exhaust temperature of diesel engines has been greatly reduced at this stage, especially in the cold start stage of the engine, the efficiency of the after-treatment SCR system has been significantly reduced, resulting in worsening emissions. In the Euro VI stage, emission regulations have clear requirements for engine cold start, so it is of great significance to study the thermal management technology of the aftertreatment system.

The thermal management control method of the afterprocessor based on the intake and exhaust system of the present invention utilizes an intake valve late tube mechanism (RIVCT), a variable geometry turbocharger (VGT), a _NOx sensor, a temperature sensor, and an SCR post Processing, establish the SCR thermal management model, and control the temperature of the after-processor by adjusting the parameters of the intake side, so that the after-treatment system can run efficiently, specifically including the following steps:

Step 1. Determine the operating point of the original engine steady-state experiment by analyzing the test cycle and exhaust temperature, and determine the target temperature reached by the cycle within a certain period of time according to the change trend of the SCR temperature of the original engine in the WHTC test cycle . The target temperature should be greater than the minimum light-off temperature of the installed SCR processor.

Step 2, if the original engine is not equipped with a variable geometry turbocharger (VGT), the original engine should be modified: one is to use a variable geometry turbocharger (VGT) instead of a fixed geometry turbocharger ( WGT); the other is a two-stage supercharging setup, retaining the fixed geometry turbocharger (WGT) while adding a variable geometry turbocharger between the cylinder and the fixed geometry turbocharger (WGT) Transformer (VGT), the modification method is determined according to the engine type.

The VGT can play an important role in the combustion temperature and exhaust temperature in the cylinder through the flexible regulation of the intake air volume of the engine. Increasing the opening of the VGT can improve the combustion temperature in the cylinder in many ways and have a direct effect on increasing the aftertreatment temperature. Based on the WHTC test cycle, the influence of VGT opening on SCR temperature and engine performance was studied, and the related influence mechanism of VGT opening on SCR temperature was determined, such as the influence of VGT opening on SCR temperature rise, temperature response rate and engine performance.

Step 3, add a variable valve timing device to the original engine, specifically install a slide valve type two-mode intake valve late closing mechanism (RIVCT) on the cylinder intake valve, and the intake valve late closing mechanism (RIVCT) includes Hydraulic tappet assembly, pressure source and regulating valve, the hydraulic tappet assembly is installed on the push rod connected to the camshaft, and the hydraulic tappet assembly slides up and down by controlling the flow of hydraulic oil to realize the control of valve timing control.

Using RIVCT to delay the closing time of the intake valve, part of the air entering the cylinder is pushed out by the upward piston, which reduces the amount of air participating in the combustion and the total heat capacity of the charge in the cylinder. Based on the WHTC test cycle, the influence of the intake valve late closing mechanism (RIVCT) on the SCR temperature and engine performance was studied, and the relevant influence mechanism of RIVCT on the SCR temperature was determined, such as the influence of RIVCT on the SCR temperature rise, temperature response rate and engine performance.

Step 4: The original engine is equipped with VGT and RIVCT at the same time. By controlling the intake air volume and the heat capacity of the gas in the cylinder, the temperature of the SCR system can be significantly increased, and the ignition time of the SCR can be greatly advanced. Carry out WHTC cold start test, according to the influence mechanism of VGT opening on SCR temperature determined in step 2 and the influence mechanism of RIVCT on SCR temperature determined in step 3, while changing the VGT opening and intake valve closing timing, the two technologies are tested Matching work to determine the optimal VGT-RIVCT control strategy parameters when the refitted engine reaches the target temperature of step 1.

Example:

Figure 1 is a schematic diagram of the aftertreatment thermal management system of the present invention, the main component is the engine, Table 1 is the main parameters of the engine of this embodiment, which burns air-fuel mixture to generate driving torque. Air is drawn into the intake manifold through the inlet using supercharging technology or naturally aspirated. The air circuit system of the engine in this embodiment adopts a two-stage supercharging system and a low-pressure exhaust gas recirculation system (LP-EGR). The compressor is a fixed geometry turbocharger, and the air in the intake manifold is distributed to the cylinders. An intake valve late closing mechanism is installed at the intake valve, and what the engine of this embodiment adopts is a slide valve type two-mode intake valve late closing mechanism (RIVCT). Although the figures depict six cylinders, the invention is equally applicable to engines that may include more or fewer cylinders. The following table is the main parameters of the engine of this embodiment, which can be used as a reference. The maximum common rail pressure of the fuel system used is 180MPa, the combustion chamber has a BUMP ring, and the combustion technology uses a high-density low-temperature combustion (HD-LTC) strategy. The SCR used in this embodiment is a copper-iron-based SCR catalytic converter, and the minimum allowable urea injection temperature is 180°C.

The main parameter of table 1 embodiment engine

parameter value Bore (mm) 126 Stroke(mm) 155 Displacement (L) 11.596 compression ratio 17:1 Intake swirl ratio 1.2 combustion chamber Open ω type (with BUMP ring) Intake method Turbocharged Injector hole number×hole diameter×cone angle 8×0.217×143 Maximum speed(rpm) 2200 Maximum power (kW) 353(2100rpm) Maximum torque (Nm) 1970(1200-1500rpm) Maximum burst pressure (MPa) 16.5

In the present invention, firstly, the typical working condition points that need to shorten the SCR light-off time are determined, so as to determine the load range mainly targeted by the present invention. First, the operating point of the engine steady-state experiment was determined by analyzing the test cycle and exhaust temperature, and the target temperature reached within 600s of the cycle was determined according to the change trend of the SCR temperature of the original engine in the WHTC test cycle. The target temperature should be greater than the minimum light-off temperature of the installed SCR processor.

In order to realize the thermal management method mentioned in the present invention, it is necessary to carry out technical modification on the original machine, while retaining the fixed geometry turbocharger (WGT), increase the capacity between the cylinder and the fixed geometry turbocharger (WGT). The variable geometry cross-section turbocharger (VGT) adopts a two-stage supercharging system in the embodiment of the present invention, the low-pressure stage adopts WGT, and the high-pressure stage adopts VGT. VGT can play an important role in in-cylinder combustion temperature and exhaust temperature by flexibly regulating the intake air volume of the engine. FIG. 2 is a diagram showing the influence of VGT opening on SCR temperature of an example engine at the operating point of 1300 rpm/25% load (a typical operating point of the example engine). It can be seen from the figure that with the increase of the VGT opening, reducing the intake air volume reduces the heat capacity in the cylinder, and when the total heat released by combustion remains unchanged (the circulating oil volume remains unchanged), the average temperature in the cylinder is significantly improved Boost, higher in-cylinder combustion temperature has a direct effect on boosting aftertreatment temperature. It can also be found from Figure 2 that when the opening of the VGT exceeds a certain opening, the rising trend of the SCR temperature with the increase of the opening of the VGT gradually slows down. This is mainly because the intake air volume has basically decreased to The stable value, the change of the maximum average temperature in the cylinder is already very small, so other auxiliary heating measures are needed. In addition, as shown in Figure 3, under low-load conditions, the increase of VGT opening is beneficial to the improvement of fuel consumption.

A variable valve timing device is added to the original engine, specifically, a sliding valve type two-mode intake valve late closing mechanism (RIVCT) is added to the cylinder intake valve. This patent uses a sliding valve type two-mode intake valve late closing mechanism Mechanism (RIVCT), the hydraulic lifter assembly is installed on the push rod connected with the camshaft of the original machine, the hydraulic lifter assembly includes the push rod connected with the engine camshaft, the oil circuit structure, the oil A pressure chamber, the oil pressure chamber is provided with a piston connected with the rocker arm of the valve. The center of the oil passage structure is formed with an oil passage connected to the oil pressure chamber, and the periphery of the oil passage structure is formed with an oil inlet hole of the assembly connected with the oil passage, a main oil drain hole of the assembly and a secondary oil drain of the assembly. hole, the oil passage is provided with a spring and an inner spool from bottom to top, and the push rod can be the original engine push rod. By controlling the flow of hydraulic oil, the hydraulic tappet assembly reciprocates up and down with the rotation of the engine camshaft to realize the control of valve timing.

RIVCT is used to regulate the combustion temperature in the cylinder. As shown in Figure 4, after the RIVCT is turned on, the reduced intake air flow will greatly reduce the pressure in the cylinder during the combustion process, and the average combustion temperature in the cylinder will increase, so that RIVCT has an important impact on the SCR temperature. RIVCT can be used as a supplement to VGT technology. When the VGT opening is too large, VGT has little effect on adjusting the intake air volume. Using RIVCT at a large opening can further reduce the intake air volume and further increase the SCR temperature.

The engine is subjected to WHTC cold start test, and the VGT opening and intake valve closing timing are changed at the same time. The two technologies are matched and the optimal VGT-RIVCT control strategy is determined through the SCR temperature rise, temperature response rate and the impact on engine performance. parameter. The effect of the VGT-RIVCT strategy on the SCR temperature of the WHTC cycle is shown in Figure 5. Compared with several thermal management strategies, the VGT-RIVCT control strategy can significantly increase the temperature of the SCR system, so that the SCR light-off time is greatly advanced, and there is a rapid Responsive effect. Taking the engine of this embodiment as an example, increasing the VGT opening degree under low-load conditions by 10% to 15% in conjunction with the opening of RIVCT can advance the SCR light-off time to 540s, realizing the rapid light-off of the SCR system and making the cold start The emission of NO _x in the WHTC test cycle was reduced from 1.78g/kWh to 0.929g/kWh, and the fuel consumption of the engine was only deteriorated by about 1.4%.

Although the function and working process of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific functions and working process, and the above-mentioned specific implementation is only illustrative, rather than limiting. Under the enlightenment of the present invention, those skilled in the art can also make many forms without departing from the spirit of the present invention and the scope protected by the claims, and these all belong to the protection of the present invention.

Claims (3)

1. A postprocessor thermal management control method based on intake and exhaust system, characterized in that, comprising the following steps: Step 1. Determine the operating point of the original engine steady-state experiment by analyzing the test cycle and exhaust temperature, and determine the target temperature reached by the cycle within a certain period of time according to the change trend of the SCR temperature of the original engine in the WHTC test cycle ; The second step is to modify the original engine: one is to replace the fixed geometry turbocharger with a variable geometry turbocharger, and the other is to add a variable geometry turbocharger between the cylinder and the fixed geometry turbocharger. Cross-section turbocharger; based on the WHTC test cycle, the influence of the opening of the variable geometry turbocharger on the SCR temperature and engine performance was studied, and the mechanism of the influence of the opening of the variable geometry turbocharger on the SCR temperature was determined; Step 3, install a variable valve timing device on the original engine, specifically install an intake valve late closing mechanism on the cylinder intake valve; study the influence of the intake valve late closing mechanism on the SCR temperature and engine performance based on the WHTC test cycle, To determine the influence mechanism of intake valve late closing mechanism on SCR temperature; Step 4: After the original engine is equipped with a variable geometry turbocharger and a late intake valve closing mechanism, the WHTC cold start test is carried out. According to the relationship between the opening of the variable geometry turbocharger determined in step 2 and the SCR temperature The influence mechanism and the influence mechanism of the intake valve late closing mechanism determined in step 3 on the SCR temperature, while changing the opening of the variable geometry turbocharger and the closing timing of the intake valve, matching the two technologies, and confirming that after modification The optimal variable geometry turbocharger-intake valve late closing mechanism control strategy parameters when the engine reaches the target temperature of step one. 2. The thermal management control method of the afterprocessor based on the intake and exhaust system according to claim 1, wherein the target temperature in step 1 should be greater than the minimum light-off temperature of the SCR processor installed. 3. The thermal management control method of the afterprocessor based on the intake and exhaust system according to claim 1, characterized in that the intake valve late closing mechanism in step 3 includes a hydraulic tappet assembly, a pressure source and a regulating valve , the hydraulic lifter assembly is installed on the push rod connected to the camshaft, and the hydraulic lifter assembly slides up and down by controlling the flow of hydraulic oil to control the valve timing.