Optical study of active narrow throat pre-chamber assisted internal combustion engine at lean limit

Abstract

The pre-chamber assisted ignition offers several much-needed upgrades to gas engines, ranging from improved combustion efficiency and stability to extended lean limits. The concept has received intermittent attention from researchers over the past century, and the concept's fundamental understanding remains segmented. This study investigates pre-chamber assisted combustion (PCC) in a heavy-duty gas engine fueled by methane at the lean limits. The engine is operated at two lean limits at intake pressures of 1.2 and 1.4 bar. At lower intake pressure, global excess air ratio (λglobal) is 2.4, while at higher intake pressure λglobal is 2.6. The comparison of two lean limits through experimental data and GT-Power 1D model reveals the underlying ignition and combustion. Using a combination of acetone PLIF (N-PLIF) and OH* chemiluminescence imaging allows visualization of both the reacting and non-reacting part of the pre-chamber jet. The results suggest that pressure differential across the pre-chamber and main chamber controls the reacting jet growth speed. The combustion chamber boundaries affect the main combustion through the wall jet part of the impinging pre-chamber jets as higher OH* concentrations are observable at stagnation points of the jet. In addition, the study reports the appearance of post-combustion jets and dispersed OH* pockets as the combustion dwindles. The narrow throat pre-chamber shows a spectral pressure signature reminiscent of the Helmholtz oscillator, and circumferential resonant modes dominate the main chamber combustion. Although the PCC offers great ignitibility, the main chamber mixture cannot sustain prolonged combustion at a lean limit lambda value.