EMPIRICAL MODEL TO ASSESS NITROGEN OXIDES CONCENTRATION WHEN ADDING HYDROGEN TO THE FUEL-AIR MIXTURE OF SPARK IGNITION ENGINES

The article presents the empirical model to assess nitrogen oxides concentration when adding hydrogen to the fuel-air mixture of piston spark ignition engines. The authors used the results of experiments carried out on the UIT-85 single-cylinder engine. The phenomenon of hydrocarbon flame electrical conduction was used to get the information on the combustion process in the cylinder of experimental engine. On the basis of the moments of ion current origination at the ionization detector electrodes, the authors got the values of velocity of the flame front propagation and the turbulent combustion zone width in the combustion chamber area remote from the ignition spark plug. The article displays the diagrams of dependencies of flame velocity and combustion zone width on the lambda (equivalence ratio) at various rotation rates of a crankshaft and the tempering air quantity in the fuel-air mixture. Using pressure indicator installed in the combustion chamber of experimental engine, the authors got the values of the crank angle based indicated pressure. The article presents the dependence of the combustion master phase duration on the flame propagation velocity and the turbulent combustion zone width. It was shown that the flame characteristics determine considerably the time for the combustion process scenario. The authors carried out the analysis of significant parameters influencing origination of the nitrogen oxides when adding hydrogen to the fuel-air mixture of the spark ignition engines. On the basis of dimensionless number of parameters, an empirical model was developed allowing the assessment of nitrogen oxides concentration when adding hydrogen to the fuel-air mixture and changing the crankshaft rotation frequency and the spark angle in the spark ignition engines. The proposed model allows assessment of the nitrogen oxides concentration during heat calculation of the designed engine.