EGR (Exhaust Gas Recirculation) Systems Flashcards
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What does the acronym EGR stand for in automotive exhaust systems?
Answer: Exhaust Gas Recirculation
EGR stands for Exhaust Gas Recirculation, the process of routing a portion of exhaust gases back into the engine's intake manifold.
What is the primary purpose of an EGR system?
Answer: Reduce oxides of nitrogen (NOx) emissions
EGR systems dilute the intake charge with inert exhaust gas, lowering peak combustion temperatures and primarily reducing the formation of oxides of nitrogen (NOx).
During which engine operating condition is EGR flow typically at its maximum?
Answer: Light to moderate load at cruise speed
EGR flow is maximized during light-to-moderate cruise conditions when NOx formation is highest and the engine can tolerate charge dilution without severe driveability impact.
How does EGR primarily reduce NOx formation in the combustion chamber?
Answer: By introducing inert exhaust gas that lowers peak combustion temperature
EGR dilutes the incoming air-fuel charge with inert exhaust gases, absorbing heat and lowering the peak combustion temperature at which NOx forms.
What are the two main EGR system configurations classified by where exhaust gas is extracted?
Answer: High-pressure and low-pressure EGR
EGR systems are classified as high-pressure (exhaust tapped before the turbocharger) or low-pressure (exhaust tapped after the DPF), each offering different flow control characteristics.
What engine symptom most commonly results from an EGR valve stuck in the open position?
Answer: Rough idle, misfires, and stalling at low speeds
A stuck-open EGR valve allows excessive inert exhaust gas into the intake at idle and low speeds, diluting combustion and causing rough running, misfires, and stalling.
What is the primary function of an EGR cooler?
Answer: Reduce exhaust gas temperature before it enters the intake manifold
The EGR cooler uses engine coolant to lower exhaust gas temperature before intake, increasing charge density and improving the NOx reduction effectiveness of recirculation.