Exergy evaluation of equivalence ratio, compression ratio and residual gas effects in variable compression ratio spark-ignition engine using quasi-dimensional combustion modeling

Abstract

This study is founded on previously validated, in-house, comprehensive, two-zone, quasi-dimensional combustion model, predicting performance and emissions in spark-ignition engines. The model is extended to include exergy terms complementing the first-law analysis results, which provide further useful information by implementation on test results acquired from an experimental, Ricardo E6, variable compression ratio (VCR) gasoline engine at the authors’ laboratory, operated under various CR and equivalence ratio (EQR) values at wide-open throttle. The model consists of unburned and burned zones simulating the combustion process, following strictly the flame-front movement in combustion chamber. The eventual combustion of the unburned mixture turbulent entrainment into burned zone through the flame-front area is followed closely. The exergy terms of each simulated zone are identified and computed, considering also chemical exergy components (diffusion plus reactive). The accurate account of temperature and species histories in burned zone after entrainment from the unburned one, should lead to more precise evaluation. This is important if irreversibility is computed from balance of all other exergy terms. The investigation examines and compares exergy-wise various EQR, CR and residual gas fractions. Presented diagrams of exergy terms for each zone and cylinder charge provide detailed information for chemical exergy, irreversibility and exergy losses.