The purpose of an Exhaust Gas Recirculation (EGR) system in a diesel engine is primarily to reduce nitrogen oxide (NOₓ) emissions, which are a major pollutant from diesel combustion. Here’s a detailed explanation:
1. Main Purpose
A. Reduce NOₓ Emissions
- Diesel engines operate with high combustion temperatures due to lean air-fuel mixtures and high compression.
- NOₓ forms when nitrogen (N₂) and oxygen (O₂) in the air react at temperatures above ~1500°C:
N2+O2→2NO
- High NOₓ levels contribute to smog, acid rain, and respiratory problems.
- EGR recirculates a portion of exhaust gas back into the intake manifold, diluting the air-fuel mixture and lowering peak combustion temperature, which reduces NOₓ formation.
B. Improve Engine Efficiency
- By recirculating exhaust gases, the combustion process becomes more controlled, especially under partial loads.
- Can slightly improve fuel efficiency and reduce knocking.
C. Assist in Meeting Emission Standards
- Diesel engines must comply with Euro 6, BS-VI, and EPA Tier 3 emission norms.
- EGR is a key technology enabling diesel engines to meet these stringent regulations.
2. How EGR Works in Diesel Engines
- Exhaust gases exit the combustion chamber.
- EGR valve opens, allowing a controlled portion of exhaust gas to enter the intake manifold.
- Exhaust gas mixes with fresh air → reduces oxygen concentration and absorbs heat, lowering combustion temperature.
- Engine continues combustion with less NOₓ formation, while maintaining power output.
3. Benefits of EGR in Diesel Engines
| Benefit | Description |
|---|---|
| Reduces NOₓ emissions | Primary purpose; prevents formation of harmful pollutants |
| Lowers combustion temperature | Reduces engine knocking and thermal stress |
| Helps meet emission standards | Essential for Euro/BS-VI compliant engines |
| Slight fuel efficiency improvement | By moderating combustion at partial load |
4. Limitations
- Excessive EGR can increase soot and particulate matter → DPF may be needed.
- Clogging of EGR valve or cooler due to carbon deposits → maintenance required.
In Short
The purpose of an EGR in a diesel engine is to reduce NOₓ emissions by recirculating exhaust gases to lower combustion temperature, helping the engine meet emission regulations while maintaining efficiency and performance.
Is EGR used in petrol engine?
Yes — EGR (Exhaust Gas Recirculation) is used in petrol engines to reduce NOx emissions by recirculating a small portion of exhaust gas back into the intake to lower combustion temperature.
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