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A optical investigation of injection, and combustion process has been performed in order to understand auto-ignition phenomena into a small 4 cylinder DI Diesel optical engine. Measurements were obtained a representatives partial load condition, corresponding to a motored TDC temperature and density of 800 K and 20 kg/m3. A better comprehension of cyclic fluctuation of auto-ignition sites was provided by a double optical diagnostics set up. Laser induced fluorescence was applied on Diesel fuel liquid phase along with synchronous natural flame imaging. The auto-ignition process has been investigated by a new experimental set up. A spectrally resolved imaging of the first chemical reaction was performed and revealed errors induced by a pressure transducer analysis. A photomultiplier tube, sensible to the OH* radical emission's band was employed to approach the real auto-ignition delay.

The concept of lean-burn combustion in spark ignition engines had been developed for reducing both exhaust emissions and fuel consumption. However the operation of engines in this mode is limited due to the misfire phenomenon. Several studies have been conducted to improve the understanding of the interaction between flow-field, mixture preparation and the progress of combustion. Multidimensional optical diagnostics are an important tool and in the other hand, the work done on combustion modelling in engine becomes more and more relevant but mainly in the case of stoichiometric mixture. The objective of the present work is to provide new information on the flame structure in lean mixtures under different flow field configurations, particularly when the flame is in the laminar-turbulent transition. Classical Mie scattering tomography of flames was performed in a transparent 4-valve Spark Ignition engine.

The paper presents a new firing concept for internal combustion engines. This concept attempts to merge the best of both Spark Ignition and Compression Ignition engine worlds. The concept is called APIR in French, standing for ‘Auto-inflammation Pilotée par Injection de Radicaux’, meaning Self-ignition Triggered by Radical Injection. The application of this concept to a standard SI engine, leads to a consequent improvement of the firing and combustion performances. A dramatic cycle variability decrease is pointed out. Initiation and combustion develop with a speed and a repeatability incomparable with the spark plug firing case. The use of the APIR device leads to an increase of the engine operating range in terms of Lean Operating Limit and thus Lean Burn Torque Range. An interesting gain on fuel consumption for idle and low load operating points is pointed out.