Prechamber Equipped Laser Ignition for Improved Performance in Natural Gas Engines

Abstract

Lean-burn operation of stationary natural gas engines offers lower NOx emissions and improved efficiency. A proven pathway to extend lean-burn operation has been to use laser ignition (LI) instead of standard spark ignition (SI). However, under lean conditions, flame speed reduces, thereby offsetting any efficiency gains resulting from the higher ratio of specific heats, γ. The reduced flame speeds, in turn, can be compensated with the use of a prechamber to result in volumetric ignition and thereby lead to faster combustion. In this study, the optimal geometry of PCLI was identified through several tests in a single-cylinder engine as a compromise between autoignition, NOx, and soot formation within the prechamber. Subsequently, tests were conducted in a single-cylinder natural gas engine comparing the performance of three ignition systems: standard electrical spark ignition (SI), single-point laser ignition (LI), and PCLI. Out of the three, the performance of PCLI was far superior compared to the other two. Efficiency gain of 2.1% points could be achieved while complying with EPA regulation (BSNOx < 1.34 kWh) and the industry standard for ignition stability (coefficient of variation of integrated mean effective pressure (COV_IMEP) < 5%). Test results and data analysis are presented identifying the combustion mechanisms leading to the improved performance.

Estimates of the air-fuel ratio at the time of ignition in a pre-chamber using a narrow throat geometry

“…Pre-chamber combustion (PCC) is a promising concept that has been shown to improve the thermal efficiency of an internal combustion (IC) engine by enabling combustion at leaner conditions than with conventional spark-ignition engines, leading to improved combustion stability, reduced knock tendency, [1][2][3] and lower engineout NOx emissions. [4][5][6] The pre-chambers are suited for a wide array of alternative fuels, including hydrogen, [7][8][9] natural gas, [10][11][12] propane, 13 alcohol fuels, 14 and conventional gasoline.…”