IGNITION OF CNG MIXTURES IN SPARK IGNITION ENGINES

Abstract

Nowadays in automotive industry, the applying of gaseous fuels and particularly compressed natural gas both in SI and CI engines is more frequent. Application of CNG in the spark ignition internal combustion engines is more real than never before. The paper describes a problem of ignition of CNG mixtures formed in SI engines with direct injection, which requires higher energy supplied by the ignition systems. The main topic of this problem was determined on the basis of the work in NICE project. The paper presents the mathematical model of ignition of CNG mixture and results of calculations. One presents dependencies between different thermal parameters on requiring electric energy. The paper shows also results of experimental results carried out in the caloric chamber done in Cracow University of Technology and chosen results of testing different ignition systems. It was modelled ignition process of the air-methane mixture in the part of combustion chamber with real spark plug. Simulation process was carried out for simple kinetic chemical reaction at initial pressure 20 bar and temperature 900 K. The paper presents calculation CFD model with high density tetrahedral mesh. Transient modelling enables obtaining of the flame spreading in the considered chamber by presenting temperature distribution and kinetic reaction rate for four times. Mass fractions of methane, carbon dioxide and water vapours are shown in dependence on time in the diagrams. The simple combustion model indicated high temperature above 3500 K in the ignition kernel at the beginning of sparking.