DETERMINATION OF OPTIMAL OPERATIONAL PARAMETERS OF BIOGAS ENGINES CONVERTED FROM DIESEL ENGINES BY MODELLING AND EXPERIMENTAL STUDIES

Using biogas to run generators in rural areas is an efficient solution to save fossil fuel and environment protection. Diesel engines can be converted to biogas engines by two different ways: biogas diesel dual fuel engine or biogas spark ignition engine. The structural and operational parameters of engine and biogas composition have considerable effects on performance of biogas enginDETERMINATION OF OPTIMAL OPERATIONAL PARAMETERS OF BIOGAS ENGINES CONVERTED FROM DIESEL ENGINES BY MODELLING AND EXPERIMENTAL STUDIESes.
CO₂ on biogas reduces burning velocity so we should increase advanced ignition angle in comparison with gasoline engine to ensure normal operation of the engine. However the presence of CO₂ in biogas fuel reduces combustion temperature so biogas engine can operate at higher compression ratio.
This paperpresents the results of modeling and experimental study of effects of engine operating parameters such as advanced ignition angles, compression ratio, engine speed… and fuel composition to performance of a spark ignition engine converted from diesel ZH1115 engine.
Combustionprocess in engine is simulated by FLUENT software. Dynamic meshing method is applied for modeling of piston movement. k-eand partial premixed combustion models have been used for modeling of turbulence and combustion of biogas-air mixture. Different compositions of fuel are introduced to the calculation by establishing thermodynamic tables.
The experimentwas conducted with a hydraulic dynamometer Froude. Compression ratio of the engine is changed by cutting the piston head. Biogas fuel is adjusted to different CH₄ composition by mixing fuel from different filtration resources.
The simulation resultsfitted well with experiment data. Optimal compression ratio of engine running with biogas is e=12.With this compression ratio, power of biogas engine can reach to maximum power of diesel engine at speed of 2200 rpm. Optimum advanced ignition angle of the engine when running with biogas is varied from 34°to 42°before TDC. Within nominal speed region, engine power increases an average of 15% when CH₄ component in biogas increased from 60% to 87%.