NoX Production: Endothermic or Exothermic?

Hello, fellow diesel enthusiasts.

As someone who disables the AGR (Abgasrückführung) system and therefore produces NOx emissions, I have the following question:

Everyone knows that energy is released through the oxidation of carbon (Nona).
But what about the oxidation of nitrogen?
If this were an exothermic reaction, it would provide an additional power gain.
by disconnecting the AGR.
If it were endothermic, there would be a loss of power, but that would likely be compensated by...
would compensate for the improved combustion of hydrocarbons.

What do you think?

Hi! That's an interesting question.

As a general rule for reactions: If a reaction can only occur at high pressure and high temperature, and the product also has a higher density than the average density of the two reactants under normal pressure and the same temperature, then it is likely an endothermic reaction. Therefore, one would need to look up the densities of the gases N2, O2, NO, and possibly NO2.

To definitely figure it out, you would need to consider the delta EN (electronegativity) of the elements involved in the reaction. However, I'm not a chemistry expert and I'm too lazy to look that up right now . In any case, the EN values are listed in the periodic table.

NOx is also produced in electric arcs, naturally for example during lightning. When NOx is catalytically decomposed into N2 and H2O using ammonia (NH3), heat is generated – an exothermic process. Therefore, it would be possible to use ammonia and nitrogen oxides to power a heating system. What actually exists are automotive catalytic converters that operate on this principle. However, instead of ammonia, urea is used as an auxiliary substance because ammonia is too dangerous. The urea is then directly converted into ammonia within the catalytic converter through an auxiliary reaction, and this ammonia then facilitates the elimination of NOx.

Sure, here is the translation of the text from German to English:

'Hello'

If it were endothermic, there would be a power loss, but that would probably be compensated by...
would compensate for the improved combustion of hydrocarbons.

Yes, you are definitely right. But it's not just that: At full load, very little oxygen is available for NOx formation because the combustion of the fuel has already consumed most of the O2 before N2 can react. Therefore, the NOx problem only arises in partial load operation, where there is a relatively high excess of O2 because only a small amount of fuel is being burned. Consequently, a loss of power due to NOx at full load is not an issue.

Hello.

The nitrogen reaction in the combustion chamber (N2 + O2 -> 2NO) is highly endothermic. However, this does not need to be taken into account in the energy balance, as the effect is simply too small.

At full load, very little oxygen is available for NOx formation because the combustion of the fuel has already consumed most of the O2 before N2 can react. Therefore, the NOx problem actually only arises during partial load operation, where there is a relatively high excess of O2 because only a small amount of fuel is being burned.


While it is true that there is less O2 available throughout the entire combustion chamber, the production of NO in the combustion chamber is still significantly higher at full load compared to partial load.
For comparison: The gasoline engine produces the highest NOx emissions just above the stoichiometric air-fuel ratio (i.e., with only a very slight excess of air). The high temperature at this air-fuel ratio is the decisive factor.

In diesel engines, the temperature is significantly higher under full load compared to partial load, which results in a considerably higher production of NOx.
The EGR system for NOx reduction is particularly important in the partial load range because today's emission tests (maximum speed 120 km/h) are only conducted in this partial load range.

While modern TDIs produce significantly more NOx during highway driving with higher loads compared to their partial-load emissions (regardless of whether they have an EGR system or not), the performance loss due to NOx production is still negligible.



Best regards, Ernst.

ideeAlist wrote:

Under full load, very little oxygen is available for NOx formation because the combustion of the fuel has already consumed most of the O2 before N2 can react.

To the best of my knowledge, a TDI engine operates with a 40% excess of oxygen even under full load to reduce soot emissions.

Urea in the exhaust .
It's unlikely that highways will soon start smelling like train stations.

Okay, thanks for the information. So, if that's the case, then the benefit of the AGR is even smaller than it already was.

Example: City driving: Every acceleration, even in the city, is often a short period of full load, especially with a 'sporty' driving style. Does the AGR (which only works at partial load) actually lead to a noticeable improvement in the overall NOx emissions?

"Ah... I think the function of a non-functional EGR system is not limited to just reducing fuel consumption."
Compelling arguments in favor of this include a cleaner engine and improved turbocharger response.
Not to be forgotten is the rally whistle during the thrust phase .


Lately, a lot of things have been seeming blue to me.
city, money, car, tires, eBay, parts, etc.

Well...