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In internal combustion engines operating in Controlled Auto Ignition (CAI) mode, combustion phasing and heat-release rate is controlled by stratification of fuel, fresh air, and hot internally recirculated exhaust gases. Based on the Representative Interactive Flamelet (RIF) model, a two-dimensional flamelet approach is developed. As independent parameters, firstly the fuel mixture fraction and secondly the mixture fraction of internally recirculated exhaust gases are considered. The flamelet equations are derived from the transport equations for species mass fraction and total enthalpy, employing an asymptotic analysis. A subsequent coordinate transformation leads to the phase space formulation of the two-dimensional flamelet equations. By the use of detailed chemical reaction mechanisms, the effects of dilution, temperature, and chemical species composition due to the internally recirculated exhaust gases are represented.

In order to reduce engine out CO2 emissions, it is a main subject to find new alternative fuels from renewable sources. For identifying the specification of an optimized fuel for engine combustion, it is essential to understand the details of combustion and pollutant formation. For obtaining a better understanding of the flame behavior, dynamic structure large eddy simulations are a method of choice. In the investigation presented in this paper, an n-heptane spray flame is simulated under engine relevant conditions starting at a pressure of 50 bar and a temperature of 800 K. Measurements are conducted at a high-pressure vessel with the same conditions. Liquid penetration length is measured with Mie-Scatterlight, gaseous penetration length with Shadowgraphy and lift-off length as well as ignition delay with OH*-Radiation. In addition to these global high-speed measurement techniques, detailed spectroscopic laser measurements are conducted at the n-heptane flame.

To understand how laminar burning velocities of standard unleaded gasoline-air-mixtures change by varying the concentration of oxygen in the combustible mixture, experimentally and numerical investigations are conducted in this work. Experiments were performed using a heatable pressure vessel which enables optical access. A monochromatic high-speed Schlieren cinematography measurement system combined with a high-speed CCD camera were used to track the propagating spherical flame fronts in the vessel. Numerically, freely propagating one dimensional laminar steady flame calculations were conducted for Primary-Reference-Fuel Air Mixtures (PRF87 or RON87), corresponding for standard gasoline combustible mixtures. Two combustible mixtures were investigated: (1) with air as oxidizer; (2) oxidizer consisting of 15% O2 and 85% N2 by mole fractions. The initial temperature for all investigated mixtures was 373 K.