A phenomenological description, or “conceptual model,” of how direct-injection (DI) diesel combustion occurs has been derived from laser-sheet imaging and other recent optical data. To provide background, the most relevant of the recent imaging data of the author and co-workers are presented and discussed, as are the relationships between the various imaging measurements. Where appropriate, other supporting data from the literature is also discussed. Then, this combined information is summarized in a series of idealized schematics that depict the combustion process for a typical, modern-diesel-engine condition. The schematics incorporate virtually all of the information provided by our recent imaging data including: liquidand vapor-fuel zones, fuel/air mixing, autoignition, reaction zones, and soot distributions. By combining all these elements, the schematics show the evolution of a reacting diesel fuel jet from the start of fuel injection up through the first part of the mixing-controlled burn (i.e. until the end of fuel injection). In addition, for a “developed” reacting diesel fuel jet during the mixingcontrolled burn, the schematics explain the sequence of events that occurs as fuel moves from the injector downstream through the mixing, combustion, and emissions-formation processes. The conceptual model depicted in these schematics also gives insight into the most likely mechanisms for soot formation and destruction and NO formation during the portion of the DI diesel combustion event discussed.

A Conceptual Model of DI Diesel Combustion Based on Laser-Sheet Imaging*

Ignition of turbulent non-premixed flames

Cyclic Variability in Spark Ignition Engines A Literature Survey

This paper proposes a structure for the diesel combustion process based on a combination of previously published and new results Processes are analyzed with proven chemical kinetic models and validated with data from production-like direct injection diesel engines The analysis provides new insight into the ignition and particulate formation processes, which combined with laser diagnostics, delineates the two-stage nature of combustion in diesel engines Data are presented to quantify events occurring during the ignition and initial combustion processes that form soot precursors A framework is also proposed for understanding the heat release and emission formation processes

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Diesel combustion: an integrated view combining laser diagnostics, chemical kinetics, and empirical validation

Effect of fuel injection timing and pressure on combustion, emissions and performance characteristics of a single cylinder diesel engine

Three Dimensional Modelling of Flow and Turbulence In a Four-valve Spark Ignition Engine - Comparison with LDV Measurements

Spray and Self-Ignition Visualization in a DI Diesel Engine

Development of a Three Dimensional Model of Wall Fuel Liquid Film for Internal Combustion Engines

Cycle-to-Cycle Correlations Between Flow Field and Combustion Initiation in an S.I. Engine

Fuel/air mixing is analysed on an optical gasoline direct-injection engine. The fuel concentration field is measured using a laser-induced fluorescence technique. Three conditions, which vary injection timing while keeping constant the ignition timing, are investigated. A qualitative correlation is made between the local fuel/air ratio near the spark plug with ignition and combustion in chamber. It is found that the mean concentration at the ignition point is high when the delay between injection and ignition is short. In some cycles, liquid fuel covers the electrodes resulting in frequent misfires. The best operating point is achieved with near-stoichiometric conditions at the ignition point, and a moderate concentration cyclic variability. On the contrary, early injection timing gives lean conditions and large cyclic variations at the ignition point. Moreover, the mixture is more dilute in the chamber, and combustion is slow and unstable. Cycle to cycle correlation between fuel concentration near the spark gap and combustion initiation shows that locally lean conditions give very slow combustion.

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J. F. Le Coz

Papers

Three Dimensional Modelling of Flow and Turbulence In a Four-valve Spark Ignition Engine - Comparison with LDV Measurements

Spray and Self-Ignition Visualization in a DI Diesel Engine

Development of a Three Dimensional Model of Wall Fuel Liquid Film for Internal Combustion Engines

Cycle-to-Cycle Correlations Between Flow Field and Combustion Initiation in an S.I. Engine

Fuel/Air Mixing Process and Combustion in an Optical Direct-Injection Engine