Thermal Effect Essay

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Thermal effect results from the change in the heat capacity of the gases in the combustion chamber. It is worth mentioning that EGR contains water and CO2 which have higher specific heat capacity than air. The change in absorbing heat is proportional to the added mass, to the heat capacity at constant pressure and to the difference in temperature between the EGR and the combustion temperature.
ΔQ=Δm*Cp*(Tcom-Tegr)
The change in specific heat capacity results from charge dilution and represents the thermal effect. The added-mass effect is represented by the change in mass Δm. To achieve higher NOx emissions reductions, gases of higher specific heat capacity are ideal.
Chemical effect
The Chemical effect can affect and alter the combustion temperature
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The formation of NO during equation 1 is much slower than by equation 2. NO formation is strongly dependent on temperature therefore it is called a ‘kinetically controlled reaction’. In other words, the chemical reaction kinetics at the temperatures in the combustion chamber are slow compared to the physical time-scale of the flow field and equilibrium cannot be achieved.
Prompt NO formation
The formation of NO is related to the formation of CH-radicals. Prompt NO formation by Fennimore is expressed by the equation
CH+N2→HCN+N→⋯→NO

In this equation the forward reaction coefficient, Kg,r, is obtained by the equation
Kg,r=4.4*〖10〗^9*exp⁡(-11060/T) (m^3/(Kmol*s))
Prompt NO formation amount is smaller when compared to Thermal NO formation due to lower activation temperature and it is associated with local fuel concentration. Moreover, Prompt NO formation requires low energy for the reaction, since the formation of NO begins before

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