Technical Report 62, c4e-Preprint Series, Cambridge
Investigating Cycle to Cycle Variations in an SI Engine Through Experiments and a New Computational Model
Reference: Technical Report 62, c4e-Preprint Series, Cambridge, 2008
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This paper presents experimental results and a new computational model that investigate Cycle to Cycle Variations (CCVs) in a Spark Ignition (SI) engine. An established Stochastic Reactor Model (SRM) previously used to examine Homogeneous Charge Compression Ignition (HCCI) combustion has been extended by spark initiation, flame propagation and flame termination sub-models in order to simulate combustion in SI engines. The model contains a detailed chemical mechanism but relatively short computation times are achieved. The flame front is assumed to be spherical and centered at the spark location, and a pent roof and piston bowl geometry are accounted for. The model is validated by simulating the pressure profile and emissions from an iso-octane fueled single cylinder research engine that showed low CCVs. The effects of key parameters are investigated. Experimental results that show cycle to cycle fluctuations in a four-cylinder naturally aspirated gasoline fueled SI engine are presented. The model is then coupled with GT-Power, a one-dimensional engine simulation tool, which is used to simulate the breathing events during a multi-cycle simulation. This allows investigation of the cyclic fluctuations in peak pressure. The four cylinder engine has been modified so that transition to HCCI operation is possible via cam profile switching. It is then demonstrated why the detailed exhaust composition obtained may be necessary to simulate the transition between SI-HCCI-SI engine operating modes in future work.
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