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The estimation of wall heat losses is difficult in combustion chambers, and particularly in piston engines, because current heat transfer models are not universally applicable. And yet, heat losses are of great interest for engine thermal balance or Computational Fluid Dynamics (CFD). Thus, unlike previous correlations that are based on macroscopic Fluid Mechanics, an innovative model is elaborated from an atomic-scale study of gas-wall interaction. This model is validated for turbulent combustion in piston engines, and also for laminar combustion in two spherical vessels. The theoretical basis of this model is confirmed by the variety of operating conditions investigated, such as pressure.

Direct Injection Spark Ignition (DISI) engines are known to be sensitive to injector fouling. To evaluate the effectiveness of detergent additives and the influence of fuel parameters on injector fouling, a new DISI engine test has been developed, using a 2.0 l stoichiometric homogeneous DI engine on a test bench. Severe engine running conditions have been found to lead to a high amount of deposits on the injector nozzle over a short period of time (“one day” procedure). Injector fouling is measured using a fuel flow measurement procedure representative of injector operating conditions (opening time and pressure). This procedure has proved to be reliable and repeatable with different gasoline fuels and additives being evaluated. The influence of the base fuel and the effect of the composition and the dosages levels of detergent additives (keep-clean and clean-up properties) are demonstrated with the test method.

The purpose of this study is to outline the effects of aerodynamics on the heat losses of a S.I. multivalve engine and to link these results with the energetic efficiency of the engine. For that aim, we measured the local and instantaneous heat transfer in a 1.6 1 spark-ignited engine with several heat flux probes inserted in the cylinder head and in the liner of the combustion chamber. Two different cylinder heads were instrumented. They allowed to create distinct air motion configurations (baseline without structured flow, swirl and two levels of tumble). Furthermore, the pressure history was determined in the same cylinder than the heat transfer measurements. For all these configurations, we used a large range of operating conditions including several part loads, distinct equivalence ratios and two different engine speeds.