EXPERIMENTAL AND DETAILED KINETIC INVESTIGATION ON THE EFFECTS OF NATURAL GAS COMPOSITION ON EMISSION OF THE GAS FUELLED SI ENGINES

摘要

The market demand for developing new gas engines in stationary and automotive applications is increasing due to its advantageous situation concerning resources and its potential to meet strict engine emission regulations. On the other hand, the changes in carbon content and combustion characteristics due to the diversity in composition of CNG, makes the prediction of emission in CNG engines complex. Today, conventional solutions through the development of numerous prototypes are not economically feasible. Numerical models can now be powerful tools to meet the rapid responses required by the regulatory agenda during the IC engine development processes. The experiments are carried out using AVL single cylinder gas test engine. Pure methane and three different compositions of natural gas (NG), which can be found in Iran, are used. AVL Boost is employed to develop a comprehensive engine model, which is fully calibrated against experiment. A validated detailed chemical scheme is used to simulate the combustion. Species transport equations are solved inside all the pipes and engine components and the results are compared with the experimental findings. The amounts of the formed CO, CO_2 and NO_x during the performance of the test engine under different loads with different natural gases at 2000 rpm are observed experimentally and compared with the results obtained from coupling detailed chemistry with one-dimensional gas dynamics equations. Natural gas may contain species up to C_5, however the amounts of the larger hydrocarbons, i.e. C_4 and C_5 species, are very low. In this research, these small amounts are incorporated into propane to restrict the size of the reaction set. In spite of attempts on employing chemical schemes to model the emission from SI engines, most of these works which are related to gas engines only consider a single component as NG and hence the effect of NG composition is not studied. On the other hand, despite the fact that NG seems to be a good choice for Iran due to its large reservoirs, there are still many uncertainties in its usage as engine fuel considering its composition variation and doubts about the engine performance. There is a need to study ICE performance with different NG compositions found in Iran, which has not been previously done. The simulation results agree well with experimental findings, showing that the deviation in the amount of emissions when using each of Iranian local CNG fuels and pure methane does not exceed 5%.