Thursday October 28, 2010 4:00 – 5:00 p.m.
ME-EM Building, Room 112
Argonne National Laboratory
Lean-burn operation is very popular with natural gas fueled stationary engines as it offers simultaneous low-NO,emissions and high engine efficiencies, while not requiring the use of any aftertreatment devices. Though enginesoperating on lean-burn operation are capable of even better performance, they are currently limited by the inability tosustain reliable ignition under lean conditions. Addressing such an issue, Argonne has evaluated the use of laser ignitionas an alternative to the conventional Capacitance Discharge Ignition (CDI). Initial tests in a static chamber and a rapidcompression machine have shown laser ignition to be capable of ignition at very higher pressures and leaner conditionsthan those ignitable using CDI. Subsequent tests in a lean burn single cylinder engine have shown NO, reductions up to70% for a given efficiency, or efficiency improvements up to 3% for a given NO, emission. Though efforts continueworldwide to reduce laser ignition to practice, further improvement in fiber optics’ performance and laser technologyare required.In the meantime, two diagnostics were developed as a part of this effort:The first diagnostic relies on measuring the flame chemiluminescence, which has been acknowledged in premixedturbulent flames to be correlated to local? global heat release rate. Results from tests conducted in a single-cylinderengine equipped with a EGR system show that over 90% of the luminous signal can be attributed to CO2 emission.Also, the effect of dilution on ’2CO chemiluminescence intensities was studied, by varying the global equivalence ratio(0.6 — 1.0) and by varying the Exhaust Gas Recirculation rate. The flame luminosity signals, did not correlate on a crankangle resolved basis with temperatures and heat release rates obtained from in-cylinder pressure measurements.However, the peak luminous signals correlated very well with both peak cycle heat release rates as well as peak cycletemperatures. Such observations point towards the potential use of flame chemiluminescence to monitor peak bulk gastemperatures as well as peak heat release rates in natural gas fired reciprocating engines.A second diagnostic based on Laser Induced Breakdown Spectroscopy (LIBS) was developed to measure in-cylinderequivalence ratio. Following the laser induced spark ignition event, the broadband emission from the spark kernel wascollected and spectrally resolved. The peaks corresponding to H,,, N and 0 atoms were measured for a range ofconditions with global equivalence ratios ranging between 0.6 and 1.0, and for Exhaust Gas Recirculation fractions up to29%. The (H,,/O) and (H,,/N) peak intensity ratios from the spectral scans correlated extremely well (R’ > 0.97) with localoxygen based equivalence ratios. From the flow relations, it appears that for homogenous intake charge, such a LIBSdiagnostic enables estimation of EGR rate with the knowledge of the global equivalence ratio.