Experimental and Numerical Investigations of the Engine Operational Conditions’ Influences on a Small Un-scavenged Pre-Chamber’s Behavior

Paper #:
  • 2017-24-0094

Published:
  • 2017-09-04
Abstract:
Ignition and combustion processes inside pre-chamber spark plugs employed in stationary gas engines exhibit considerably longer durations compared to conventional, open chamber ‘’G-type’’ capacitive discharge ignition systems. The strength and timing of the turbulent flame jets subsequently issuing into the main chamber strongly depend on the pre-chamber combustion process and, thus, high sensitivity with respect to the specific engine operating conditions it experienced. This poses considerable difficulties in optimizing engine operational conditions as well as controlling engine performance. This paper investigates the influence of engine operating conditions on the pre-chamber combustion event using both experimental and numerical methods. A miniaturized piezo-electric pressure transducer was designed and placed inside the engine cylinder head to record the pre-chamber inner volume pressure, in addition to conventional pressure indication inside the main chamber. The pressure difference between the main chamber and the pre-chamber (∆p = ppre-chamber -pmain chamber) served as an indicator of the pre-chamber combustion event by studying the crank angle resolved ∆p under different engine operating conditions. The variations include spark timing, air-fuel ratio and engine speed as well as engine intake air temperature and boost pressure, for which a single-parameter sensitivity approach was carried out. 3D-CFD simulation in the RANS context was further employed to estimate the turbulence and thermo-physical conditions inside the pre- and main chamber with respect to the distinct engine operating conditions. The results indicate that the ∆p peak value and its timing show the highest sensitivity to the air-fuel ratio variation, followed by the intake air temperature. And their sensitivities to the pressure difference and the absolute pressure level at the spark timing were considerably lower.
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