On Comparative Performance Testing of Prechamber and Open Chamber Laser Ignition

Abstract

Laser ignition is a potential ignition technology to achieve reliable lean burn ignition in high brake mean effective pressure (BMEP) internal combustion engines. The technology has the potential to increase brake thermal efficiency and reduce exhaust emissions. This submission reports on engine testing of a Caterpillar G3516C stationary natural gas fueled engine with three types of ignition approaches: i) non-fueled electric prechamber plug with electrodes at the base of the prechamber (i.e., conventional ignition), ii) non-fueled laser prechamber plug with laser spark in the middle of the prechamber, and iii) open chamber plug with laser spark in the main chamber. In the second configuration, a stock non-fueled prechamber plug was modified to incorporate a sapphire window and a focusing lens to form a laser prechamber plug. A 1064 nm Q-switched Nd:YAG laser was used to create laser sparks. For these tests, a single cylinder of the engine was retrofitted with the laser plug while the remaining cylinders were run with conventional electric ignition system at baseline ignition timing of 24 degree before Top Dead Center (BTDC). The performances of the three plugs were compared in terms of Indicated Mean Effective Pressures (IMEP), Mass Burn Fraction Duration and Coefficient of Variation (COV) of IMEP, and COV of Peak Pressure Location. Test data show comparable performance between electric and laser prechamber plugs, albeit with a lower degree of variability in engine’s performance for electric prechamber plug compared to the laser prechamber plug. The open chamber plug exhibited poorer variability in engine performance. All results are discussed in the context of prechamber and engine fluid mechanics.

Resonant dual-pulse laser ignition technique based on oxygen REMPI pre-ionization

“…LI systems are potentially attractive in this regard, for example, when applied to industrial reciprocating natural gas engines, LI has shown reduction in NO x emissions and extension of the lean limit 1 – 3 . The technology is of interest to a variety of combustion applications including reciprocating engines, aero-turbines, and rocket engines 4 – 10 . System level features of LI, as contrasted to conventional igniter technology, include: the lack of electrodes (which tend to act as heat sinks) within the combustion chamber, the ability to achieve fine control over ignition timing, flexibility in locating the ignition source (based on focusing optics), and potentially systems with favorable cost, packaging and reliability parameters.…”