Development of Thermodynamic Model for Conventional SI Engine Simulation and Detailed Testing Analysis of a Lean Combustion in PFI SI Engine.

The research presented in this thesis consists of two parts. The first one proposed to perform a detailed testing analysis of lean combustion in a PFI equipped SI engine and find out its operational envelope. The second one presented development of simplified thermodynamic model for conventional SI engine simulation, which can further be extended to lean burn operations. The first part focuses on conducting an experimental investigation of parameters that facilitate lean burning and their implications on cyclic variability, exhaust emissions. The magnitudes of cyclic variability and exhaust emissions decide the operational range of lean burn. An air fuel ratio swing is carried under different loads and compression ratios from 14:1 to 22:1. The cyclic variability results have been presented in terms of normalised COV in IMEP. The results show an increment trend in COV with leaner mixtures for each load. The COV values reduce with the increase in loads. The CR findings indicate that increase in compression ratio substantially reduces cyclic variability. The NOx emissions increase significantly up to 5 times from AFR 14:1 to 22:1 for 3.36 bar load and CO emissions decrease with leaner mixtures drastically. The second part focuses on developing in house MATLAB code for simulation of a conventional SI engine, which can be used as a teaching tool. A detailed thermodynamic quasi dimension model for each process and sub process that occurs in SI engine operation has been formulated and validated against experimental results from the literature. The model is developed on the basis of first law and second law of thermodynamics. The working fluid is considered as an ideal gas and combustion is modelled as a two zone model. The results show that the model gives quite a good match for in-cylinder pressure trace and mass fraction burned curve with that of the experiment. Also, results for performance parameters against speed show the shortcomings in the model for predicting the performance under variable speed conditions