1.What is EGR?
EGR (Exhaust Gas Recirculation) is an emission control technology.
It guides part of the exhaust gas and the incompletely burned mixture back into the intake system, so that the exhaust gas is mixed with fresh air and enters the combustion chamber, which can reduce the combustion temperature and thus reduce the generation of nitrogen oxides, thus achieving the purpose of reducing emissions.
2.What does DOC mean? What functions does it have?
DOC (Diesel Oxidation Catalyst) literally means diesel oxidation catalyst
Generally, metal or ceramic is used as the carrier of the catalyst, and the main active components in the coating are precious metals such as platinum and palladium. When the exhaust gas passes through the catalyst, HC (hydrocarbons) and CO (carbon monoxide) can quickly react with the oxygen in the exhaust gas at the set temperature to generate pollution-free water and carbon dioxide, while raising the temperature for DPF/SCR, etc., to achieve the purpose of purifying the exhaust gas.
3.What does DPF mean? What is its function?
DPF (Diesel Particulate Filter) is a device used to capture and filter solid particles (such as smoke and soot) in diesel engine exhaust.
Main functions
Reduce particulate matter emissions: Reduce air pollution by filtering particulate matter in the exhaust.
Meet emission standards: Help diesel engines meet strict environmental regulations
Regeneration strategy
Active regeneration
The fuel is injected into the cylinder after injection or outside the cylinder, and the injected fuel is oxidized by DOC to generate heat to provide exhaust temperature to trigger regeneration.
C+O2=CO2(>600℃)
Passive Regeneration
Completely dependent on vehicle driving conditions to provide the right conditions to trigger regeneration
2NO+02=2NO2
C+2NO2=C02+2NO(250℃-450℃)
4.What does SCR do? How does it relate to EGR?
SCR (Selective Catalytic Reduction) is a technology used to reduce NOx emissions from diesel engines.
It reduces NOx emissions by injecting urea (DEF) into the exhaust system, which reacts chemically with NOx to produce nitrogen and water.
SCR works together with EGR, where EGR reduces the amount of NOx generated in the combustion chamber and SCR further processes the residual NOx in the exhaust to meet higher emission regulations.
5.What are the main components of EGR? What are their functions?
The EGR system mainly consists of the following parts:
EGR valve
Function: Regulate the flow of exhaust gas and control the proportion of exhaust gas returning to the intake system.
EGR cooler
Function: Cool the returning exhaust gas and reduce its temperature, thereby reducing the heat load on the intake system and improving the mixing efficiency with the fresh intake air.
EGR pipeline
Function: Connect the various parts of the EGR system and transport the exhaust gas from the exhaust system to the intake system.
EGR control unit
Function: Usually controlled by the engine control unit (ECU), adjust the opening of the EGR valve to achieve the best exhaust gas recirculation efficiency.
6.Are all EGRs the same? Are there any differences in type?
There are two main types of EGR systems
High-pressure EGR (HP-EGR)
Features: Exhaust gas is introduced directly from the exhaust manifold without being processed by the turbocharger
Applicable scenarios: Commonly used in urban/suburban conditions, and also in high-speed conditions.
Low-pressure EGR (LP-EGR)
Features: Exhaust gas is introduced from the rear of the turbocharger, and then returned to the intake system after being processed.
Applicable scenarios: More suitable for high-speed conditions
- How does EGR work?
The EGR system works through the following steps
Exhaust gas introduction
Part of the exhaust gas is returned to the intake system through the EGR valve
Exhaust gas cooling
The returned exhaust gas is cooled by the EGR cooler to reduce the impact on the intake temperature.
Mixed intake
The cooled exhaust gas is mixed with fresh air and enters the combustion chamber,
Reducing the combustion temperature
The inert gas in the mixed gas can reduce the combustion temperature in the cylinder, thereby reducing the generation of NOx.
- Which engine components are connected to EGR?
Intake system
The exhaust gas enters the intake system through the EGR system and mixes with fresh air.
Exhaust system
The EGR system extracts exhaust gas from the exhaust system.
Turbocharger
In a low-pressure EGR system, the exhaust gas flow is linked to the air flow of the turbocharger.
Engine Control Unit (ECU)
The ECU controls the opening of the EGR valve to ensure the optimal ratio of exhaust gas recirculation.
- What is “regeneration”
“Regeneration” usually refers to the cleaning process of the particle filter in the DPF.
Over time, the DPF will accumulate particulate matter discharged from the combustion in the engine cylinder. In order to avoid DPF clogging and ensure efficient engine operation, these particulate matter needs to be burned through the regeneration process to restore the performance of the filter. Regeneration can be performed passively or actively, depending on the system design.
- How to properly maintain the EGR system?
Regular cleaning: Clean the EGR valve and cooler regularly to prevent carbon deposits from clogging.
Use high-quality fuel: High-quality fuel, especially low-sulfur fuel, can reduce the formation of carbon deposits and the corrosion of sulfides on metal materials, and extend the service life of the EGR system.
Regularly replace the air filter: Keep the intake system clean and reduce exhaust pollutants from entering the EGR system.
Check the cooling system: Make sure the EGR cooler works properly to avoid overheating.
11.Will EGR failure immediately limit speed and torque?
EGR system failure will not immediately cause speed and torque limitation: but it may trigger the engine control unit (ECU) to enter protection mode to prevent further damage. In protection mode, engine performance may be limited, resulting in power loss and worse fuel economy.
- What are some common problems with EGR and how to solve them?
EGR valve stuck
Problem: The exhaust gas flow is unstable or completely blocked.
Solution: Check the fault diagnosis code, clean or replace the EGR valve.
EGR cooling efficiency is low
Problem: The cooling effect is reduced, and the exhaust gas temperature mixed with the fresh intake air is too high.
Solution: Check the water circuit, clean or replace the EGR cooler.
Carbon deposit problem
Problem: Too much carbon deposit in the EGR valve and pipeline causes system blockage
Solution: Check the combustion in the cylinder, clean the EGR system regularly, and use clean fuel additives.
- How to solve the EGR fault light?
Read the fault code
Use the diagnostic instrument to read the fault code and determine the specific problem
Check the EGR system
Check the relevant components according to the fault code and perform necessary cleaning or replacement
Reset the fault light
After the problem is fixed, follow the instructions in the service manual to turn off the fault light
- Does EGR have any requirements for the selection of fuel and urea?
Fuel: Use high-quality diesel to reduce carbon deposit formation and sulfide corrosion, and extend the life of the EGR system.
Urea: Urea solution (DEF) is mainly used in the SCR system and has no direct relationship with the EGR system. However, in comprehensive emission control, choosing high-quality urea solution is beneficial to both the SCR system and the overall emission control.
- Can EGR be forced to shut down if it is so troublesome?
Forced shutdown of the EGR system is not feasible and legal. The reasons include:
Environmental regulations: Forced shutdown of EGR will lead to excessive emissions and violate environmental regulations.
Engine life: The combustion parameters matched by the EGR system can reduce the cylinder explosion pressure and pre-turbo pressure to a certain extent. Shutting down the EGR system may increase the cylinder pressure and the risk of supercharger speed overspeed under certain conditions, reducing the engine life.
Performance and economy: EGR is designed to optimize performance and emissions. Shutting it down may lead to worse fuel economy and increased system failure rate. Further OBD fault codes and engine torque reduction and speed reduction will further affect the vehicle’s operating efficiency and driving needs.
- What should we pay attention to in driving behavior to ensure the smooth operation of EGR?
Maintain the vehicle on time, add fuel and engine oil according to the required grades, and maintain normal and safe driving behavior.
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