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The liquid and vapor phases penetrations are important improvement parameters of DI Diesel combustion chamber conception. In this study the effects of the pilot injection timing on the main injection evolution and combustion are investigated using laser based optical diagnostics and 3D modeling. The pilot injection timing is shown to have a strong effect on the main liquid and vapor phases development and these results are more precisely depicted using 3D calculations. The mixing stated derived from laser induced fluorescence and thus the pilot injection combustion process are studied and are also shown to influence the main injection inflammation. These tendencies provide interesting insights in the comprehension of the physical phenomena occurring in a DI Diesel engine of production size.

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.

Many studies were done about the link between the flame kernel behavior and the global combustion stability. It was shown that aerodynamics and mixture preparation are predominant for flame propagation. Multidimensional optical diagnostic techniques have become an important tool to study combustion inside engines. One-point measurements of flow field have been done in order to look at the impact on global combustion analysis. But the effect of the instantaneous flow field at the vicinity of the spark plug and at the spark timing on the flame kernel was not well explored. It is the objective of this paper: to quantify as well as possible, the effects of the instantaneous local velocity field at the vicinity of the spark plug and just prior spark, on the flame kernel propagation.

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.

This paper follows a former one (Robinet [1]) which underlined the spark kernel hazardous development due to residual gas in the spark plug vicinity. A new igniter called FSP (Fueled Spark Plug) has been designed and compared to conventional spark plug. Its purpose is to sweep away the residual gas from the spark vicinity. This investigation has been performed in a standard research engine and an optical accesses engine. A faster heat release development and a more repeatable combustion for low-load operating conditions have been observed when firing with the FSP. The lean operating range is extended. The idle performances (IMEP covariance, ISC) have been improved as well as the emissions (CO and NOX). Unburned hydrocarbons emissions are raised due to non-optimal feed line design. Contrary to previous alternative igniter designs, residual gas sweeping can be switched on or off at will: in the latter case the FSP falls back to conventional spark plug operation.