In recent years, the Cooling Exhaust Gas Recirculation (EGR) and Indirect Intercooler (iCAC) systems developed by Bessie (reducing NOx emissions from diesel engines) do not require an exhaust after-treatment system such as Selective Catalytic Reduction (SCR) or Another additional urea station will meet Euro 5 emission requirements. When this technology is combined with the latest engine and injection technology, while satisfying Euro 5, it will not increase fuel consumption, and it will reduce the overall vehicle quality. What is better is that these new solutions can be applied flexibly. This system has been further developed by Bellows to meet the potential of the Euro 6 standard.
The exhaust gas recirculation process is basically based on the principle that the exhaust gas has a higher heat capacity and a lower oxygen content than air, which leads to a decrease in the combustion temperature inside the cylinder. The cooled exhaust gas and the charge air charged into the cylinder (these air are both boosted by the turbine and then charged into the cylinder, hereinafter referred to as boosted air) cause the combustion temperature to further decrease due to the exponential function of the NOx generation and temperature change. Combine exhaust gas recirculation with turbocharger with intercooler (CAC) to meet Euro 4 standards. In order to meet the more stringent requirements of the Euro 5 standard, it is possible to increase the exhaust gas recirculation rate or reduce the temperature of the exhaust gas and the charge air.
Euro 5 Engine Cooling System
In recent years, Bellow has been studying how to improve the engine cooling system to meet increasingly stringent standards. In particular, the effective cooling of the charge air and the exhaust gas can reduce NOx generation and fuel consumption. The two Euro 5 engine cooling systems and their components newly developed and ready for production are described in detail below and compared with the selective catalytic reduction system.
1. Single-stage exhaust cooling and two-stage turbocharged engine cooling system
Figure 1 is a schematic of this cooling system. It consists of an exhaust gas recirculation cooler (cooled by the engine coolant) and a cryogenic cooling circuit consisting of two intercoolers and a cryogenic radiator. Since the low-temperature radiator is installed at the forefront, the car's oncoming wind directly cools it, and the low-temperature coolant in the loop cools the second-stage intercooler to obtain a lower post-intercooling temperature. This type of intercooler is called an indirect intercooler.
The exhaust gas discharged from the exhaust manifold of the engine is cooled by the exhaust gas recirculation cooler and then enters into the intake manifold along with the charge air. After mixing, the intake air temperature is further reduced to reduce the generation of NOx. However, the application of a single-stage exhaust gas recirculation cooling system can only reach Euro 4 standards and cannot meet Euro 5 requirements. As mentioned before, reaching Euro 5 requires a stronger cooling effect or a higher exhaust gas recirculation rate. However, increasing the exhaust gas recirculation rate will definitely reduce the concentration of oxygen in the cylinder. In order to ensure the concentration of sufficient oxygen in the cylinder, a higher boost pressure must be used, and secondary cooling with medium cooling can achieve this goal. Although the exhaust gas recirculation rate is increased, the secondary turbocharging can still ensure that the output power of the engine does not decrease, and it does not increase the particulate emissions.
In the two turbochargers, the pressurized air is increased in two compression temperatures, cooled in the intercooler, and part of the heat is transferred to the cooling fluid. This part of the heat in the low-temperature radiator is emitted to the air. . The radiator is installed in the front of the vehicle, which is the location where we see the intercooler on the diesel truck today. The traditional intercooler is connected to the turbocharger and the engine intake manifold through many pipes. The use of indirect intercoolers eliminates these pipes, which saves space and simplifies the assembly.
Compared with the traditional intercooler, the indirect intercooler has high heat exchange efficiency and compact structure and can be installed between the turbocharger and the intake manifold. This also makes it possible to use a straight pipeline for the charge air line. In this way, the loss of air pressure inside the pipe will be reduced by 50%, and the inflation pressure will increase accordingly. The increase in the air charge in the cylinder and the simplification of the gas exchange process, these two factors enable the engine to reduce fuel consumption at the same output power.
Due to the use of indirect intercoolers, the volume of air ducts can be reduced.
For example, in a 12L diesel engine, the air duct volume can be reduced by more than 50%, so the system responds to the load faster. Although commercial vehicles do not respond quickly to torque like passenger cars, emissions problems are inevitable, such as particulate emissions. As is known to all, when a driver without a particulate trap suddenly accelerates, the turbocharger cannot provide enough air because it responds slowly, resulting in insufficient combustion of the fuel in the cylinder due to lack of oxygen, and the particulates rapidly increase. Reducing the volume of the air duct increases the response speed of the charge air and reduces the discharge of particles into the atmosphere or into the particle trap.
The intercooled charge air increases the secondary pressurization efficiency. Currently, in the case of single-stage turbocharging, the inflation pressure can be as high as 3.6 bar, and in the case of two-stage turbocharging plus intermediate cooling, the absolute pressure of inflation can reach 4 to 5 bar. As described above, it makes it possible to increase the exhaust gas recirculation rate without increasing the particulate emission without lowering the engine performance.
In addition, in theory, high inflation pressure has the following advantages:
Increase engine power density (liter power). In the same displacement condition, the output power of the engine can be increased or the engine displacement can be reduced ("miniaturization") under the same output power condition. Miniaturization reduces friction in the engine, which has a positive effect on fuel consumption.
• Increase the excess air in the cylinder, because the higher the oxygen content in the cylinder, will reduce the formation of carbon deposition. In other words, the generation of particles is reduced due to complete combustion of the fuel.
2. Secondary exhaust cooling and single-stage turbocharged engine cooling system
In this system, the exhaust gas to be recirculated from the engine is first sent to an exhaust gas cooler, which is cooled by the circulating water of the engine, and then enters another exhaust gas cooler next to the intercooler. With air cooling, the air flow rate is determined by the speed of the fan or vehicle.
The secondary exhaust gas cooling is applied in this system, which effectively reduces the exhaust gas temperature. Therefore, the single-stage turbocharging plus intermediate cooling can meet Euro 5 requirements. The intercooler is a conventional air-cooling method in which the exhaust gas and the pressurized gas can reach a similar temperature level, and the temperature of the mixed gas in the intake manifold can be significantly reduced.
In Fig. 3, there is an intercooler and an exhaust gas cooler installed in one module, and an exhaust gas cooler not included in this module is called an integrated cooler.
Product Innovation
1. Integration of exhaust cooler and intercooler
The system connects multiple exhaust gas coolers in series, applying a variety of different cooling media: engine coolant and air. Integrating an air-cooled exhaust gas recirculation cooler and an intercooler, this form of integration is the world's first.
Exhaust cooling process: Exhaust gas flows out of the cylinder into the exhaust manifold, and part of the exhaust gas flows into the first-stage exhaust gas cooler. This exhaust cooling is cooled by engine coolant. This portion of the exhaust gas then flows into the second stage air-cooled exhaust gas cooler, which is integrated with the upper portion of the charge air cooler. When the ambient temperature is low, the exhaust gas does not pass through the secondary exhaust cooler but through the bypass pipe into the engine intake manifold in order to prevent the cooler from freezing. In both cases, the cooled and intercooled gases are mixed in the mixing chamber into the intake manifold. Therefore, the gases entering the respective cylinders have the same composition and temperature, which is very important to ensure the consistency of combustion in each cylinder.
When the first stage exhaust gas cools, its temperature drops to 200~150°C. In the second stage of cooling (low temperature), the temperature drops to only 25~20°C higher than the ambient air temperature. The degree of reduction in the temperature of the charge gas depends on the mixing ratio of the charge air and the exhaust gas.
The core of the air-cooled exhaust gas recirculation cooler is an exhaust gas pipe, and there is a corrugated heat-dissipation belt between the exhaust gas pipes. The exhaust pipe has a turbulence generating winglet, and the pipe and the corrugated heat-dissipation band are brazed together. The exhaust pipe and The exhaust chamber is welded together. The cooler consists of corrosion-resistant pipes, corrugated heat sinks and exhaust chambers, all of which are made of stainless steel.
Integrated charge air/exhaust cooler module features:
·Optimize pressure loss in exhaust gas and charge air coolers
Better mixing of charge air and exhaust gas in the mixing chamber
Exhaust gas cooler with bypass to prevent it from freezing
· No condensate back into the intercooler
Corrosion-resistant EGR cooler
2. Indirect intercooler with integrated thermostat
Compared with Euro 5 and Euro 4, Euro 5 requires a higher exhaust gas recirculation rate which inevitably requires more supercharging pressure. As a result, the charge air temperature rises. Therefore, the required intercooler must be able to withstand 220°C or more. The temperature and absolute pressure exceeding 5.1bar. Based on pressure and temperature loads, changes in the design of the intercooler can reduce stress levels and can withstand higher loads. For example, the CAC/EGR module uses finite element analysis (FEM) to test its stress analysis.
An indirect intercooler is a lamination system that includes a charge air duct and a cooling water duct. In order to meet the requirements of heat transfer performance, temperature and pressure, it is necessary to optimize the design of the turbulence plates in the charge air and coolant. In addition, the gas-liquid fluid in the intercooler runs in the opposite direction, and the flow of the coolant is controlled by a thermostat mounted in the outlet of the intercooler. By quickly adjusting the flow of coolant through the quick-response wax component in the thermostat, complex control systems can be avoided.
3. Fan assembly and its operation
The latest NFX750 fans have increased air flow. The newly adjusted blade shape and increased number of blades (from 8 to 11) greatly increase the fan output air flow. The original axial structure is almost unchanged, and the same air volume is output. The fan power consumption is reduced by approximately 10%. The fan is driven by the ViscoERS250 fan clutch. The transmission torque of the electronically controlled clutch can transmit 40% more torque than the fan clutch used now. At the same time, its controllability and dynamic clutch response speed are significantly improved, and unnecessary fans can be eliminated. noise.
In order to fully cool the Visco fans running at various speeds, the fan hub is optimized for fan clutch cooling requirements, further improving the cooling of the clutch oil, greatly reducing the sliding power deviation, and preventing overheating of the silicone oil in the clutch. .
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