Exhaust Gas Recirculation (EGR) – Useful information
Posted on 22. Nov, 2011 by paulr542 in Technology
What is it for? When the engines combustion temperatures exceed 2500 degree F., atmospheric nitrogen begins to react with oxygen during combustion. The result is various compounds called nitrogen oxides (NOX), which play a major role in air pollution. To reduce NOX the combustion temperatures must be kept below the NOX threshold. .
How does it work? The NOX combustion temperature is kept below the NOX threshold by recirculating a small amount of exhaust through the “exhaust gas recirculation,” or EGR. valve. The EGR valve controls a small passageway between the intake and exhaust manifolds. When the valve opens, intake vacuum draws exhaust through the valve. This dilutes the incoming air/fuel mixture and has a quenching effect on combustion temperatures which keeps NOX within acceptable limits. As an added benefit, it also reduces the engine’s octane requirements which lessens the danger of detonation (spark knock).
The EGR valve consists of a poppet valve and a vacuum diaphragm. When vacuum is applied to the EGR valve diaphragm, it pulls the valve open allowing exhaust to pass from the exhaust manifold into the intake manifold. Some engines have “positive backpressure” EGR valves, while others have “negative backpressure” valves. Both types contain a second diaphragm that modulates the action of the valve. This prevents the valve from opening unless there is a certain level of exhaust backpressure in the system. EGR valves are calibrated for specific engine applications. The wrong valve may flow too much or not enough exhaust and cause emission, driveability and detonation problems.
Do I need to do anything different when servicing my vehicle? EGR valves do not normally require maintenance or replacement for preventative maintenance. But the valve can become clogged with carbon deposits that cause it to stick or prevent it from closing properly. Dirty EGR valves can sometimes be cleaned, but replacement is necessary if the valve is defective.
Do I need to have the EGR fitted to my vehicle? More and more vehicle owners are looking to remove the engines EGR valves from their vehicles as they are getting tired of replacing them regularly. The problem is, once you do this, you run into problems… If you simply remove the EGR system from the car, but do not disable it in the vehicles ECU, you will likely run into many problems: (Poor running, lack of power, excessive temperature, ECU fault light on dashboard, detonation of sparks as the ECU is still actively telling the engine to action the cycle.
If unsure whether your vehicle’s symptoms are a direct cause of EGR or you wish to generally know more about the subject them contact one of our highly skilled technicians on 0845 643 6898 or email info@black-code.co.uk
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