Autoignition and knock

Autoignition and knock in internal combustion engines are phenomena primarily governed by the temperature and pressure history of the unburned gas mixture as well as on their chemical composition. The onset of autoignition is almost exclusively governed by the chemical kinetics, but its timing strongly depends on the velocity of the thermodynamic properties of the gases. A useful numerical tool to model such a complex phenomenon should be able to simulate all possible engine operating conditions and the effects of the fundamental engine parameters and fuel characteristics, on the basis of a deep understanding of both thermodynamic and chemical mechanisms which control the combustion process. To achieve this result a mutual interactive coupling between a thermo-fluid dynamic model and an advanced kinetic code is required.

In recent works, a detailed kinetic code, DSMOKE, developed at Dept. of Industrial Chemistry & Chemical Engineering, has been embedded into an engine simulation model based on a 1D schematization of the intake and exhaust system and a thermo-dynamic approach for the combustion process (GASDYN). The kinetic modeling of oxidation and autoignition of hydrocarbon fuels requires careful analysis of both low and high temperature mechanisms. A very general detailed kinetic scheme, consisting of more than 300 species and 6000 reactions, is available since several years.

Validation has been performed and is still ongoing, considering spark ignition engines (w and w/o optical access) with commercial and reference fuels and HCCI engines. This work is based on a collaboration with the Istituto Motori CNR of Naples, where the conducted experiments include spectroscopic investigations of natural emissions were performed in several locations of the chamber. In order to investigate the spatial evolution of OH and HCO, chemiluminescence measurements were performed to measure the overall emission intensity of both radicals and compare the acquired data with the results of the simulations.

Publications:
1 - G. D'Errico, T. Lucchini, A. Onorati, M. Mehl, T. Faravelli, S. Merola, B. Vaglieco, Development and Experimental Validation of a Combustion Model with Detailed Chemistry for Knock Predictions, SAE Technical Paper 2007-01-0938, 2007.
2 - M. Mehl, A. Tardani, T. Faravelli, E. Ranzi, G. D'Errico, T. Lucchini, A. Onorati, D. Miller, N. Cernansky, A Multizone Approach to the Detailed Kinetic Modelling of HCCI Combustion, SAE Technical Paper 2007-24-0086, 2007.
3 - M. Mehl, T. Faravelli, E. Ranzi, T.Lucchini, A. Onorati, F. Giavazzi, P. Scorletti, D. Terna, Kinetic Modeling of Knock Properties in Internal Combustion Engines, SAE Technical Paper 2006-01-3239, 2006.