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ic engine emission
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Posted by: ravindra.patil

01/09/2006, 04:34:13

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nitrogen oxides (nox) is formed during combustion process by combinng n2 & o2. But this process takes place at high temperature only !!!

Now to restrict temperature to reach high value in cylinder rich mixture is used i.e. f/a ratio increased.

but my question is that incrasing the amount of fuel will increase d amount of heat released & hence increase in temperature which will led to formation of nox.

So how d solution is justified ????








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Re: ic engine emission
Re: ic engine emission -- ravindra.patil Post Reply Top of thread Forum
Posted by: sam_mas47

09/02/2007, 00:35:47

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I don't think increasing the temperature is the solution. We use catylitic converters to reduce NOx.






Modified by Administrator at Sun, Sep 02, 2007, 08:50:00


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Re: ic engine emission
Re: ic engine emission -- ravindra.patil Post Reply Top of thread Forum
Posted by: Kelly_Bramble Cragyon, Cragyon

01/09/2006, 08:24:31

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It has been a long time, however I did work / design / testing automotive exhaust emmissions controls systems in the mid 1980's. If I remember right, by adding more fuel, at some point a large part of the fuel does not burn. This is due to the lack of oxygen available for a particular engine induction system. So, no oxygen left to form NOx and a reduction in combustion temperature due to an excess of unburned fuel. Keep in mind that to burn gasoline, that a endothermic process must first occur to "crack" the gasoline into other cumbustable compounds. The amount of heat energy required to do this significant. So, all or a lot of the unburned fuel has absorbed heat energy to break down into H2, CO, etc.., however has not burned (creates heat). This process of unburned fuel also lowers the peak combustion temperature, and reduces the produced NOx.

By the way, NOx is Oxides of Nitrogen, and is any nitrogen atom combined with any number of oxgen atoms, NO2, NO3, NO4 and so on.






Modified by Kelly_Bramble at Mon, Jan 09, 2006, 08:49:12


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Re: Re: ic engine emission -- Kelly_Bramble Post Reply Top of thread Forum
Posted by: ravindra.patil

01/09/2006, 22:38:35

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Thnx kelly !!!

but my qustion remains same !!!!

your alowing fuel to be unburned which will be coming out in the exhaust & increasing d pollution. So reduction in nox has led to d unburned hc & co formation !!!!

Den how d control system is justified !!!!








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Re: ic engine emission
Re: Re: ic engine emission -- ravindra.patil Post Reply Top of thread Forum
Posted by: Kelly_Bramble

01/09/2006, 23:23:49

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I'm not exactly sure I understand your question.

When adjusting an internal combustion engine F/A ratio to optimize for exhaust emissions there are several challenges. The more fuel you put in, the less NOX, and more hydrocarbons and CO the engine puts out. The less fuel you put in and you get more NOx however less CO and hydrocarbons. Either way the engine pollutes in a bad way. The goal is to find the right balance to produce minimal exhaust emissions.

In modern cars this is accomplished by F/A feedback control systems. Normally, temperature, exhaust oxygen, rpm and a bunch of other engine operating parameters are monitored. With this information, a optimal F/A, ignition timing, etc is delivered to the engine to produce the right exhaust chemicals and feed the catalytic converters the right chemicals to operate in a optimal manner. Normally, there are two types of catlytic converters, one to break down the NOx, and one to complete the burning of the hydrocarbons into water and CO2. Idealy, with the right F/A mixture, a engine will produce the correct balance of hydrocarbons and NOx so that the converters can clean up the excess pollutants.

Other exhaust emmission control devices are the EGR valve, is it still called this? This valve recirculates exhaust gas into the intake normally during high demand acceration. The idea of introducing already burned exhaust gas is to introduce a unburnable medium, which will dilute the oxygen/fuel and reduce peak combustion temperature, and thus NOx (which only forms at very high temperatures).

Now, it is possible to get the combustion temperature high enough above the temperature where NOx does not form. NOx only forms within a window (low and high temperature). However, when the engine is subjected to such high tempertures many materials used within the engine tends to , well burn up.

I do know that in the mid 1970's, a engine/fuel system was developed called a "Lean Burn" or somthing by the Chrysler Corp.. The engine was designed to run on very lean F/A ratio. Additionally the engine was insulated to retain as much heat energy as possible. Even the exhaust system was modified to slow the exit of gasses. This engine was actualy pretty efficient, however impractical and very exspensive as it turns out.







Modified by Kelly_Bramble at Mon, Jan 09, 2006, 23:30:41


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Re: Re: ic engine emission -- Kelly_Bramble Post Reply Top of thread Forum
Posted by: ravindra.patil

01/10/2006, 02:34:18

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thnxxx !!!!







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