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A program of development and experimental validation of a multidimensional spray prediction method, based on the discrete droplet model, has been broadened to include computational investigations of the effects of random perturbations of the injection velocity on the spray characteristics, and further detailed examination of the spray structure and development. The results demonstrate strong dependence of the predicted spray penetration length on the precise start-of-injection time and injection velocity data, and relative insensitivity to subsequent variations of the injection velocity. Specifically, it is found that under imposition of random variations of the injection velocity, the variation of the spray-tip penetration and velocity remain smooth, bearing no correspondence to the instantaneous spray injection velocity.

Gasoline direct injection is one of the main issues of actual worldwide SI engine development activities. It requires a comprehensive system approach from the basic considerations on optimum combustion system configuration up to vehicle performance and driveability. The general characteristics of currently favored combustion system configurations are discussed in this paper regarding both engine operation and design aspects. The engine performance, especially power output and emission potential of AVL's DGI engine concept is presented including the interaction of advanced tools like optical diagnostics and 3D-CFD simulation in the combustion system development process. The application of methods like tomographic combustion analysis for investigations in the multicylinder engine within further stages of development is demonstrated. The system layout and operational strategies for fuel economy in conjunction with exhaust gas aftertreatment requirements are discussed.

Gasoline direct injection and turbocharging enable the progress of clean and fuel efficient SI engines. Accessing potential efficiency benefits requires very high power density to be achieved across a broad rpm range. This imposes risks which in conventional engines are rarely met. However, at torque levels exceeding 25 bar BMEP, the thermal in-cylinder conditions together with chemical reactivity of any ignitable matter, require major efforts in combustion system development. The paper presents a methodology to identify and locate sporadic self ignition events and it demonstrates non contact surface temperature measurement techniques for in-cylinder and exhaust system components.

The exploitation of full load capabilities of DI gasoline engines requires at least the same degree of effort as in MPFI engine development. An optics based sensor and sensing technique is presented, which together with conventional pressure indicating provides identification of self ignition centers as the engine is operated under knock or borderline knock conditions. The knock location sensor is configured as a spark plug providing the relevant spark plug properties together with the multichannel optical access into the upper part of the combustion chamber. Functionality and sensitivity of this sensing technique are demonstrated and results for combustion system development are shown.

The combined requirement of achieving CAFE values between 32 to 38 mpg plus LEV/ULEV emission standards to comply with US legal requirements between 1995 and 2000 represents the most demanding challenge for engine engineering. Thus all possible methods of engine improvement towards fuel economy and emissions have to be considered. Besides using new ideas also the methods of engine development have to be modernized to cope with the challenge. The paper presents advanced combustion and exhaust gas aftertreatment systems which combine high power output, favourable torque characteristics and high fuel economy with the potential for obtaining LEV/ULEV emission values, as well as improved development techniques.

Traditional power train development work is concentrated mainly on test bed and on chassis dyno. Though we can simulate a lot of real world conditions on testbed and chassis dyno today, on road application work willis gaining more attention. This means that strategies and tools for invehicle testing under real world conditions are becoming more important. Emission, performance, fuel economy, combustion noise and driving comfort are linked to combustion quality, i.e. quality of fuel mixture preparation and flame propagation. The known testing and research equipment is only partly or not at all applicable for in-vehicle development work. New tools for on the road testing are required. Following, a general view on in-vehicle power train testing will be given. Additionally, new ways to investigate cylinder and cycle specific soot formation in GDI engines with fiber optic tools will be presented.

An optical imaging technique has been developed which allows the visual observation of fuel vapour within selected planes in optically accessed combustion chambers of Spark Ignition engines. The technique utilises fluorescence radiation of hydrocarbon molecules to image fuel vapour distribution. This fluorescence radiation is induced by a pulsed laser light sheet projected into the transparent combustion chamber and it can be observed with an intensified camera gated synchronously with the pulsed laser at any selected time instant of the engine cycle. In addition to recording mixture distribution, the camera arrangement also allows visualisation of the gasoline flame propagation. These imaging methods are used for he investigation of mixture formation and flame development in a transparent, disc-shaped combustion chamber under low speed and low load conditions.

Formation, ignition and combustion of diesel fuel sprays have been observed in the combustion chamber of an optically accessed single cylinder diesel engine. Two different combustion chamber geometries allowed the fuel sprays to be studied under quiescent and cross flow conditions. The study of the spatial distribution with different single shot photography techniques is complemented with an investigation of the temporal development of spray and flame propagation by an electronic high-speed line-scan technique. This continuous, time resolved analysis technique allows to resolve the influence of temporal variations imposed on the spray propagation and combustion by the fuel injection schedule. The application of these methods to the investigation of diesel sprays highlights mechanisms which govern the propagation and distribution of fuel sprays, fuel evaporation and the formation of a combustible fuel-air mixture.

In order to facilitate the analysis of SI engine combustion phenomena, we have developed a fiber optic system which allows the observation of combustion in essentially standard engines. Optical access to the combustion chamber is achieved with micro-optic elements and optical fibers in the cylinder head gasket. Each fiber views a narrow cone of the combustion chamber and transmits the light seen within this acceptance cone to the detector and recorder unit. A large number of such fiber optic detectors have been incorporated in a cylinder head gasket and this multichannel system was arranged in a geometric configuration which allowed the reconstruction of the spatial flame intensity distribution within the observed combustion chamber cross-section. The spatial information was gained from the line-of-sight intensity signals by means of a tomographic reconstruction technique.

An optical sensor system provides access to standard SI engine combustion chambers via the cylinder head gasket. Flame radiation within the plane of the gasket is observed with optical fibers which are arranged to allow the tomographic reconstruction of flame distribution. The effect of convective in-cylinder air motion generated by variations of inlet ports and combustion chamber geometries on flame propagation is directly visible. A high degree of correlation between flame intensity distribution and NOx emission levels yields a useful assessment of combustion chamber configurations with minimum emission levels. The location of knock centers is identified.

The performance of SI engines is substantially influenced by the degree of fuel atomization that occurs within the mixture preparation system. With a measuring device, based on laser Sight diffraction, it is possible to determine droplet size spectra with high temporal and spatial resolution, even if the droplets are moving with high velocity. However, with such a measuring device, the influence of density gradients within the measuring volume, as that created by fuel vapor or temperature differences, can be critical and must be taken into consideration to provide satisfactory results. The degree of atomization depends on the engine operating conditions, namely engine speed and load.

Current legislation trends for Heavy Duty and Off-Road engines show an increased contribution of transient cycles for engine homologation. For the HD EURO 3 and EURO 4 regulations, effective from the year 2000 and 2005 respectively, the new ESC (European Steady State Cycle), the new ETC (European Transient Cycle) and also the new ELR (European Load Response) Opacity test must be carried out, as well as the old ECE R 24 test procedure. A highly sophisticated new Opacimeter, designed according to the latest state of the art, is described. This instrument, certified to conform to the old and new legal homologation test procedures and to international standards, has proved to be also a powerful tool for engine R & D as well as production testing, as shown in several application examples.