Laser ignition and flame kernel characterization of HCNG in a constant volume combustion chamber
Abstract
Laser ignition of gaseous fuels leads to improved lean-burn combustion, which is a key technology in reducing engine out emissions for meeting stringent future emission legislations. Hydrogen enriched natural gas (HCNG) promotes lean-burn combustion due to higher flammability limits of constituent hydrogen. HCNG is a promising gaseous fuel for spark ignition (SI) engines prior to development and deployment of dedicated hydrogen fueled engines. In this study, laser ignition of HCNG was compared with baseline natural gas for different lambdas (λ) ranging from 1.1, 1.3, to 1.5 using a Q-switched Nd:YAG laser in a constant-volume combustion chamber (CVCC). Experiments were conducted at different ambient pressures, i.e., initial chamber filling pressures of 5 bar and 10 bar. These pressures simulated the in-cylinder pressures identical to that at the time of spark ignition in an engine cycle. Flame kernel evolution in HCNG blends of different compositions (10%, 20%, and 30% v/v hydrogen) were compared with baseline natural gas for a specified Lambda (λ). A high speed CCD camera was used for triggering the laser and thus the flame kernel evolution in the CVCC, which was recorded using shadowgraphy technique. Images captured were further analyzed to obtain temporal propagation of flames in different directions. Flame kernel propagated faster in ambient pressure of 5 bar compared to 10 bar. Both, flame speed and peak CVCC pressure increased, and combustion duration shortened with increasing hydrogen fraction in HCNG.