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In Spark Ignition engines, the heat release rate is not only piloted by the mixture reactivity but also by its sensitivity to stretch effects. Only few results can be found in the literature about flame stretch effect in SI engine configurations. For this study, three different fuels (Methane, Propane, Iso-octane) were studied, but at different air-fuel lean mixture conditions, to present almost equivalent laminar flame speeds and thermo-dynamical properties at ignition timing condition. Besides those mixtures present different Lewis numbers which are relevant parameters to describe flame-stretch interactions. Mie-scattering tomography was then performed in an optical Spark Ignition (S.I.) engine. Using a high speed camera, flame propagation images were acquired through the piston. Thermodynamic analyses based on in-cylinder pressure traces were performed to estimate in-cylinder temperature and burnt mass fraction during the engine cycle.

Increasingly stringent pollutant emission regulations have constrained car manufacturers to reduce the fuel consumption and pollutant emissions of internal combustion engines. Downsized engines appear to be the most promising way to achieve this in terms of emission reduction as well as investment minimization. The design of downsized internal combustion engines requires the understanding and quantification of thermo-fluid-dynamic processes at high pressure, high temperature and with high dilution rate. This study aims to carry out preparatory work in a fan-stirred spherical combustion vessel at conditions representative of those occurring in downsized engines. First, experimental correlations giving the laminar burning velocity from the initial pressure, the initial temperature, the dilution rate and the equivalence ratio are proposed.

As an alternative to second generation ethanol, valeric esters can be produced from lignocellulose through levulinic acid. While some data on these fuels are available, only few experiments have been performed to analyze their combustion characteristics under engine conditions. Using a traditional spark ignition engine converted to mono-cylinder operation, we have investigated the engine performances and emissions of methyl and ethyl valerates. This paper compares the experimental results for pure valeric esters and for blends of 20% of esters in PRF95, with PRF95 as the reference fuel. The esters propagate faster than PRF95 which requires a slight change of ignition timing to optimise the work output. However, both the performances and the emissions are not significantly changed compared to the reference. Accordingly, methyl and ethyl valerate represent very good alternatives as biofuels for SI engines.

The current decrease in fossil energy resources requires a diversification of the liquid and gaseous fuels potentially consumable in internal combustion engines. The use of these fuels modifies the combustion process and the heat released as well. In a Spark Ignition (SI) engine, the heat released is mainly piloted not only by the mixture reactivity but also by its sensitivity to stretch effects. Only a few results can be found in the literature about stretch effects for SI engine configurations. The purpose of the present paper is to evaluate stretch effects on the flame front propagation in an optical SI engine and to investigate the relative importance of these effects depending on the fuel considered. Different air-fuel mixtures presenting different flame stretch sensitivities were selected. Four different engine regimes (1400, 1600, 1800 and 2000 rpm) were studied for all the mixtures in order to evaluate the impact of different turbulence intensities.

An experimental investigation was conducted in an optical mono-cylinder Spark-Ignition engine in order to explore the influence of the fuel and of the dilution rate on the initial stages of flame propagation. Images of flame radiation were acquired through the transparent piston crown with a high speed CMOS camera operating at 6000 frames/second. Experiments were performed under stoichiometric and lean conditions (0.8 of equivalence ratio), and two engine speeds (1200 rpm and 2000 rpm). The spark ignition timing was set at 30 (iso-octane) and 25 (methane) crank angle degrees before top dead center. Image acquisition was synchronized with in-cylinder pressure to allow simultaneous evaluation of the Indicated Mean Effective Pressure (IMEP) and of the heat release rate. Image post-processing was performed to obtain the temporal evolution of the projected flame area.

Quantitative planar laser-induced fluorescence (PLIF) of gaseous acetone as a fuel-tracer has been used in an optically accessible engine, fueled by direct hydrogen injection. The purpose of this article is to assess the accuracy and precision of the measurement and the associated data reduction procedures. A detailed description of the acetone seeding system is given as well. The key features of the experiment are a high-pressure bubbler saturating the hydrogen fuel with acetone vapor, direct injection into an optical engine, excitation of acetone fluorescence with an Nd:YAG laser at 266 nm, and detection of the resulting fluorescence by an unintensified camera. Key steps in the quantification of the single-shot imaging data are an in-situ calibration and a correction for the effect of local temperature on the fluorescence measurement.