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Cycle-resolved end-gas temperatures were measured using dual-broadband rotational CARS in a single-cylinder spark-ignition engine. Simultaneous cylinder pressure measurements were used as an indicator for knock and as input data to numerical calculations. The chemical processes in the end-gas have been analysed with a detailed kinetic mechanism for mixtures of iso-octane and n-heptane at different Research Octane Numbers (RON'S). The end-gas is modelled as a homogeneous reactor that is compressed or expanded by the piston movement and the flame propagation in the cylinder. The calculated temperatures are in agreement with the temperatures evaluated from CARS measurements. It is found that calculations with different RON'S of the fuel lead to different levels of radical concentrations in the end-gas. The apperance of the first stage of the autoignition process is marginally influenced by the RON, while the ignition delay of the second stage is increased with increasing RON.

A detailed analysis of the end-gas temperature and pressure in gasoline engines has been performed. This analysis leads to a simplified zero-dimensional model, that considers both, the compression and the expansion of the end-gas by the piston movement, and the compression by the flame front. If autoignition occurs in the end-gas the sudden rise of the pressure and the heat release is calculated. The rate form of the first law of thermodynamics for a control volume combined with the mass conservation equation for an unsteady and a uniform-flow process are applied. The heat of formation in the end-gas due to the chemical activity has been taken into account. In addition, a chemical kinetic model has been applied in order to study the occurrence of autoignition and prediction of knock.

SI Engine knock is caused by autoignition in the unburnt part of the mixture (end-gas) ahead of the propagating flame. Autoignition of the end-gas occurs when the temperature and pressure exceeds a critical limit when comparatively slow reactions-releasing moderate amounts of heat-transform into ignition and rapid heat release. In this paper the difference in the heat released in the end-gas-by low temperature chemistry-between lean, rich, stochiometric, and stoichiometric mixtures diluted with cooled EGR was examined by measuring the temperature in the end-gas with Dual Broadband Rotational CARS. The measured temperature history was compared with an isentropic temperature calculated from the cylinder pressure trace. The experimentally obtained values for knock onset were compared with results from a two-zone thermodynamic model including detailed chemistry modeling of the end-gas reactions.

The influence of variable air-fuel ratio inside a spark ignition engine is examined by the use of an ionization sensor. The measured ion currents are used for predicting the local air-fuel ratio in the vicinity of the spark plug. In order to support the results, a theoretical analysis has been made. An instationary chemical kinetic model burning a mixture of iso-octane and n-heptane is used for the calculations. The results are used to reconstruct the crank angle resolved ion current that has been measured in an engine. This technique has been developed in order to offer a supplementary low-cost facility of controlling the air-fuel ratio within the combustion chamber of an engine.

This paper reports an one–dimensional modeling procedure of the hot spot autoignition with a detailed chemistry and multi–species transport in the end gas in an SI engine. The governing equations for continuity of mass, momentum, energy and species for an one–dimensional, unsteady, compressible, laminar, reacting flow and thermal fields are discretized and solved by a fully implicit method. A chemical kinetic mechanism is used for the primary reference fuels n–heptane and iso–octane. This mechanism contains 510 chemical reactions and 75 species. The change of the cylinder pressure is calculated from both flame propagation and piston movement. The turbulent velocity of the propagating flame is modeled by the Wiebe function. Adiabatic conditions, calculated by minimizing Gibb's free energy at each time step, are assumed behind the flame front in the burned gas.