Flame Propagation Study in a Single-Cylinder Research Engine with Gaseous Fuel

Pressures on vehicle manufacturers to reduce emissions have resulted in an increased interest to improve fuel economy and enable use of fuels developed from renewable sources that can achieve a net reduction in the CO₂ output per vehicle. The use of bio-gas fuels in internal combustion engines has become a real alternative to traditional liquid fuels derived from petroleum. To extract the maximum benefits from these emergent fuels through optimized engine design and calibration, a deep understanding of the behavior is necessary. The combustion process of a single cylinder research engine with optical access, four stroke PFI-SI, was experimentally investigated. High spatial resolution cycle resolved digital imaging, in the visible and UV spectral range was used to characterize the flame front propagation. A post-processing routine was developed to evaluate flame areas and various local and global morphology characteristics to have a detail understanding of the flame behavior in an engine combustion chamber. The engine was fueled with Methane as baseline fuel and compared with an equivalent syngas mixture (blend of hydrogen, methane, carbon monoxide, carbon dioxide and nitrogen). It was operated at 900 rev/min, under partial load condition. For the equivalent syngas blend the results suggest an increase in the combustion duration. The flame speed propagation was higher to methane, with a difference of 1.9 m/s. Also both fuels present a preferential flame center movement in direction of the intake valves, and the average curvature was negative. The cyclic variations in the combustion process were around 1% for syngas and 0.5% for methane, indicating a stable combustion process.