Numerical investigation on the effect of water in the reduction of diesel engine exhaust emissions using a novel ionic chemical kinetics mechanism


This paper aims to investigate the role of water in the reduction of diesel exhaust emissions. To do so, a multi-zone thermodynamic model coupled to a novel semi-detailed ionic chemical kinetics mechanism is used. This mechanism includes 467 reactions and 105 species containing 51 ionic reactions and 15 ions. The mechanism contains 6 basic ionic reactions, 23 NOx-related ionic reactions, and 22 soot-related ionic reactions. Four different amounts of water are added to the in-cylinder mixture and the effects of water in the formation of soot and NOx are investigated. The results showed that water does not have a regular effect on diesel exhaust soot, but causes a significant reduction in exhaust NOx. Water has decreased the temperature of the combustion chamber and consequently has reduced the ionic current inside the combustion chamber. Reduction of the in-cylinder ion current decreases the mass of NOx-related ions and results in reduced exhaust NOx. Adding 5% water reduces the in-cylinder ion current by 47%. Five percent water also reduces engine exhaust NOx to 33%. Among NOx-related ions, water has the greatest effect on N+ ions and reduces its amount to less than 20%. Water affects the progress rate of ionic reactions, and 5% of water reduces the progress rate of the fastest reaction to 14% of its initial value.

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Data availability

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.



crank angle degree

c v :

specific heat constant at constant volume (J/kg K)

C D :

discharge coefficient

D :

cylinder diameter (m)

d n :

nozzle hole diameter (m)

H :

enthalpy (J/kg)

m :

mass (kg)

MW :

molecular weight

n :

number of zones

n n :

number of nozzle holes

n s :

number of species

P :

pressure (Pa)

Q :

heat (J)

R u :

universal ideal gas constant (J/mol K)

T :

temperature (K)

t :

time (s)

U :

internal energy (J)

u :

specific internal energy (J/kg)

V :

volume (m3)

W :

work (J)d

z :

distance between zone center and injector (m)

Y :

mass fraction


density (kg/m3)

\( \dot{\omega} \) :

molar rate of production (mole/m3s)




ith zone


jth species


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EN: study conception and design, data analysis and interpretation, drafting of the article, and critical revision of the article. MM: data collection and drafting of the article.

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Correspondence to Elaheh Neshat.

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Mohammadi, M., Neshat, E. Numerical investigation on the effect of water in the reduction of diesel engine exhaust emissions using a novel ionic chemical kinetics mechanism. Environ Sci Pollut Res (2021).

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  • Diesel engine
  • Exhaust emissions
  • NOx
  • NOx-related ions
  • Water addition
  • Ion current