![]() ![]() EPA Doubles ‘Non-Conformance Penalties’ for Navistar 2012 Diesel Trucks,” Diesel Fuel News, Vol. 16, No. 34, Sept. 2012, pp. 4–5. Environmental Protection Agency, “ Non-Conformance Penalties for Heavy-Duty Diesel Engines Subject to the 2010 NOx Emission Standard,” Paper EPA-420-F-12-049, Office of Transportation and Air Quality, Washington, D.C., Aug. 2012. Based on the experimental and modeling results, a mechanism for thermoacoustic instability was proposed for ultra-lean premixed H 2 / air ignition by a hot turbulent jet. The physical significance of the instability modes and their behavior were identified using dynamic mode decomposition. To model the instability, 3D linearized Euler equations were solved in the frequency domain coupled with combustion response models. A phase-resolved measurement of strain rates along flame edge showed an oscillating strain along pressure perturbation cycle. Transverse and mixed modes were observed at lean conditions, ϕ < 0.4. However, a leaner flame was affected more due to stronger coupling between heat release and the pressure field perturbation. Classical acoustic resonator analysis and pressure spectra showed the longitudinal mode of acoustic disturbance as the primary instability mode for all equivalence ratios. Simultaneous schlieren and OH * chemiluminescence were used to visualize the unstable flame propagation and to characterize the instability. ![]() Thermoacoustic combustion instability was initiated for main-chamber equivalence ratio, ϕ < 0.5, and grew severe in the lean-burn regime, 0.22 < ϕ < 0.3. Prechamber combustion generated a hot turbulent jet that ignited the ultra-lean H 2 / air mixture in the main chamber. Unstable combustion was observed in a dual-chamber combustor that mimics heavy-duty gas engines utilizing prechamber jet ignition. ![]()
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