NO_x is a common pollutant in combustion engines that is responsible for smog, t
ID: 1061669 • Letter: N
Question
NO_x is a common pollutant in combustion engines that is responsible for smog, tropospheric ozone formation, and other negative environmental phenomena. (NO_x + energy from sun rightarrow NO + O + Smog). NO_X formation occurs from the dissociation of nitrogen mainly between temperatures of 2500-3000 degrees Celsius. For this reason, it is preferable to keep the temperature inside of 1C engines below this range to improve emission qualities. Research and give a detailed report on the usage of EGR as a means of reducing NO_x. Docs this seem like a good idea based on an efficiency point of view? Also, find and explain any other methods of reducing emissions currently in place in the automobile industry, compare methods based on effectiveness. For full credit tilde 1 page, 12 point Times New Roman, single space. Please type answers and use proper citations.Explanation / Answer
NOx Emissions
In many countries around the world, the emissions of NOx from diesel and gasoline vehicles are restricted by legislation. NOx is formed in the combustion chamber of engines, when high temperatures cause oxygen and nitrogen (both found in the air supplied for combustion) to combine.
Exhaust Gas Recirculation
A widely adopted route to reduce NOx emissions is Exhaust Gas Recirculation (EGR). This involves recirculating a controllable proportion of the engine's exhaust back into the intake air. A valve is usually used to control the flow of gas, and the valve may be closed completely if required.
The substitution of burnt gas (which takes no further part in combustion) for oxygen rich air reduces the proportion of the cylinder contents available for combustion. This causes a correspondingly lower heat release and peak cylinder temperature, and reduces the formation of NOx. The presence of an inert gas in the cylinder further limits the peak temperature (more than throttling alone in a spark ignition engine).
The gas to be recirculated may also be passed through an EGR cooler, which is usually of the air/water type. This reduces the temperature of the gas, which reduces the cylinder charge temperature when EGR is employed. This has two benefits- the reduction of charge temperature results in lower peak temperature, and the greater density of cooled EGR gas allows a higher proportion of EGR to be used. On a diesel engine the recirculated fraction may be as high as 50% under some operating conditions.
Advantages of EGR
Disadvantages and Difficulties of EGR
Although the term EGR usually refers to deliberate, external EGR, there is also a level of internal EGR. This occurs because the residual combustion gas remaining in the cylinder at the end of the exhaust stroke is mixed with the incoming charge. There is therefore a proportion of internal EGR which must be taken into account when planning EGR strategies. The scavenging efficiency will vary with engine load, and in an engine fitted with variable valve timing a further parameter must be considered.
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