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The influence of piston geometry on the in-cylinder mixture distribution and combustion process in an optically-accessible, direct injection HCCI Diesel engine has been investigated. A new, purpose-designed piston which allows optical access directly into the combustion chamber bowl permitted the application of a number of optical diagnostic techniques. Firstly, laser-induced exciplex fluorescence (LIEF) has been applied in order to characterize the fuel spray and vapor development within the piston bowl. Subsequently a detailed study of the auto-ignition and two-stage Diesel HCCI combustion process has been conducted by a combination of direct chemiluminescence imaging, laser-induced fluorescence (LIF) of the intermediate species formaldehyde (CH2O) which is present during the cool flame and LIF of the OH radical later present in the reaction and burned gas zones at higher temperature.

This article investigates the fuel/air mixture homogeneity that may be achieved at part/low load using a conventional common rail Diesel fuel injector. The experiments are carried out with an optical, single cylinder, small bore Diesel engine equipped with a 6 hole, narrow angle, common rail injector and a bowl shaped piston. While the rate of combustion is essentially controlled in HCCI using very diluted mixtures achieved with Exhaust Gas Recirculation (EGR), the influence of mixture homogeneity on the onset of auto-ignition is also investigated here. Mixing between air and fuel is performed using several multiple injection strategies. Mixture homogeneity corresponding to these strategies is assessed using 2D Laser Induced Exciplex Fluorescence images. Fuel images indicate that the process is never fully homogeneous. Auto-ignition and combustion are also monitored using direct light emission observation.

This study is dealing with optical experiments in a common rail DI Diesel small-bore automotive engine. Its purpose is to investigate the influence on soot emissions of the location of the point of impact of the fuel jet on the piston bowl walls. The experiments are carried out in a single cylinder, 4 valves Diesel engine equipped with a common rail injector and a bowl shaped piston. A classic extended piston with piston-crown quartz window provides a first optical access to the combustion chamber. A transparent quartz cylinder also provides a second access to the chamber. Liquid and vapor phases of the fuel were visualized using Exciplex laser induced fluorescence while combustion and soot images were recorded with an intensified CCD camera by direct light emission monitoring. Soot emissions were also analyzed in the exhaust pipe with a standard smoke meter.

This paper describes the development and tests of a combined CO/O2 zirconia sensor for on-board diagnosis of oxidation catalysts. To achieve accurate measurements, preliminary model scale experiments have been carried out. These tests consist in careful calibrations with synthetic gases, measurements in exhaust gas from a laboratory scale lean premixed methane-air burner, and comparisons with classical and FTIR gas analyzers. Accordingly, a new sensor has been designed and prototyped. Held in a spark plug type housing, it simultaneously monitors the CO, and O2 content of the exhaust gas. Over the wide O2 range of interest, model scale tests of the sensor with burnt gases have shown good agreement with laboratory analyzers. Closed loop experiments carried out with the same burner also demonstrate the CO/O2 probe potential for combustion control.

This article describes the development and tests of a combined NOx/oxygen Zirconia sensor. To achieve accurate NOx and oxygen measurements under lean-burn conditions, preliminary model scale experiments with a premixed methane-air burner are carried out with current production oxygen sensors as well as with our own oxygen probe. It is found from these tests that accurate oxygen sensing requires sensor operating temperatures much lower than usually set, about 600°C. Moreover, this temperature is a good compromise for NOx sensitivity and time response of the sensor. Accordingly, a new NOx/O2 sensor has been designed and prototyped. Held in a spark plug type housing, it simultaneously monitors the NOx and oxygen content of the exhaust gas. Over the wide 02 range of interest, model scale tests of the sensor with burnt gases have shown promising agreement with laboratory analysers.