Functionality of Exhaust Gas Recirculation (EGR) Valve
An Exhaust Gas Recirculation (EGR) Valve is a device which is put to use in internal combustion engine of your vehicle. EGR valve reduces the nitrogen oxide content from the exhaust emissions of the automobile, and therefore, plays a very crucial role in containing the environmental pollution.
As you start-up the engine of your car, it starts burning the fuel which leads to rise in the combustion temperatures. Resultant oxygen emission begins to react with atmospheric nitrogen to form Nitrogen Oxides – a major cause of air pollution in the metros, today. As the emissions pass through the car naturally in a small passageway between car parts (intake and exhaust manifolds), the EGR valve opens and pushes them back through the system. It re-circulates almost 5 to 15 percent of the vehicle’s engine’s exhaust gas back to the engine cylinders. During this process, the oxygen level in the incoming air stream gets diluted which leads to a fall in peak in-cylinder temperatures. Now, since formation of nitrogen oxide essentially requires mixing of nitrogen and oxygen at a high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of nitrogen oxide. The arrangement in turn leads to fall in the level of nitrogen oxide and enables the EGR to aid in environment protection.
If you know that efficiency of your vehicle’s engine depends upon the rate at which it combusts the fuel, then by now, you must be thinking that won’t an EGR valve slow my vehicle down? Well, the answer is No! Although EGR does reduce the cylinder temperature leading to slower rate of combustion, this gets largely compensated if you get the spark timing advanced accordingly. And yes, the impact of EGR on engine efficiency would considerably depend upon the specific engine design too. So, a compromise between efficiency and NOx emissions can never be ruled out.
What follows naturally from the discussion above, is that most modern engines now require an EGR valve to meet emissions standards. However, one should always keep in mind that EGR valves are car parts that are calibrated for specific engine applications only. A wrong EGR valve fitted in your vehicle may flow too much or inadequate exhaust and can in fact cause high emission levels instead of keeping them down. Also, some latest automobiles engines come fitted with such mechanism that prevents generation of nitrogen oxide altogether, and hence do not require an EGR valve at all.
As the EGR valves work in very demanding and challenging conditions, they are subject to high level of wear and tear. Being very prone to become faulty, they should be regularly get checked by expert technicians. While most faults can be detected from an error code reader, you can also get to know about an EGR valve failure through an MOT emissions failure. Loss of engine power and a poor fuel economy are some of the other symptoms, hinting towards an under-performing EGR valve in your vehicle. They can also become clogged with carbon deposits, preventing it from opening or getting closed properly. Dirty EGR valves can sometimes be cleaned but this usually gives only a month or two of extra use till they again start malfunctioning. Although, EGR valves do not normally require maintenance or replacement for preventative maintenance, but replacement becomes necessary if the EGR valve is defective. Another thing worth knowing here is that in most of the vehicles, it’s the electronic solenoid which activates the EGR valve by sensing the correct vacuum. So, it would not be a bad idea to check this part, before you start considering the EGR valve to be defective.