Search Results

In this paper the development approach and the results of numerical and experimental investigations on homogeneous charge compression ignition in a free piston engine are presented. The Free Piston Linear Generator (FPLG) is a new type of internal combustion engine designed for the application in a hybrid electric vehicle. The highly integrated system consists of a two-stroke combustion unit, a linear generator, and a mass-variable gas spring. These three subsystems are arranged longitudinally in a double piston configuration. The system oscillates linearly between the combustion chamber and the gas spring, while electrical energy is extracted by the centrally arranged linear generator. The mass-variable gas spring is used as intermediate energy storage between the downstroke and upstroke. Due to this arrangement piston stroke and compression ratio are no longer determined by a mechanical system.

In this paper experimental measurements and simulations of the gas flow inside the combustion chamber of a free piston engine are presented. This combustion unit is integrated into a power train concept, named free-piston linear generator (FPLG), which is designed as a new type of gasoline engine for hybrid electric vehicles. By combining a two stroke combustion chamber, a linear alternator and an adjustable gas spring the engine design aims at a highly efficient conversion of chemical energy into electrical energy. In this context a high system efficiency can only be reached if a two stroke combustion cycle is applied. Efficiency advantages are expected due to the missing mechanical link to a crank which enables a new flexibility in terms of stroke and compression ratio. Instead of scavenging ports the presented FPLG combustion unit has poppet valves which are actuated by a variable electro-magnetic valve train.

This article presents a detailed kinetic mechanism for the combustion of surrogate gasoline fuels (mixtures of primary reference fuels and toluene) that has been developed by modification of a previous mechanism (Andrae et al., 2007). The modifications introduced were: (i) revision of the sub-mechanisms associated with H2, CO and CH4 oxidation and (ii) retuning of rate coefficients of reactions involved in the i-octane oxidation sub-mechanism. The first set of modifications made use of new kinetic parameters evaluated by the CODATA project (Baulch et al. 2006), whereas the second was prompted by a sensitivity analysis of the mechanism obtained after implementation of (i). The resulting mechanism, which describes the low, intermediate and high temperature combustion regimes, is used to study pre-ignition of surrogate gasoline fuels. Comparison of the simulation data with experimental measurements over a wide range of conditions reveals a good agreement.

In this work, the spark-ignition (SI) of a methane/air mixture contained in a constant-volume chamber is investigated by numerical simulations. A cylinder-shaped vessel filled with a methane/air mixture containing two electrodes is used as simulation model. The impact of an electrical discharge at the electrodes on the surrounding gas is simulated, with detailed treatment of the ignition process involvig chemical kinetics, transport phenomena in the gas-phase and electrodynamical modeling of the interaction between spark and fuel/air mixture. For the calculations, a 2D-code to simulate the early stages of flame development, shortly after the breakdown discharge, has been developed. Computational results are shown for ignition of a methane air-mixture.