Search Results

In most optimization strategies of combustion processes in gasoline IC engines, spatial inhomogeneities of the temperature, of the residual exhaust gas and of the fuel-air distribution play a major role. Hence, the development of experimental methods for the simultaneous quantification of both, concentration and temperature fields, is highly desirable. One method which is in particular suitable for measuring these quantities is the technique of two-laser excitation of the fluorescence of ketones like 3-pentanone and acetone. Different groups have used 3-pentanone for the measurement of fuel concentration. In this work we present the determination of the exhaust gas concentration field simultaneously with the temperature field using acetone as an intake air tracer. Acetone is a more suitable gas tracer than 3-pentanone due to its higher vapor pressure and its better stability regarding thermal decomposition.

This paper presents calibration results of the two excitation laser wavelength fluorescence of acetone for the determination of temperature fields. The calibration was performed under engine relevant conditions and comprises the simultaneous variation of temperature and pressure in the range of 293 K to 750 K and of 0.1 MPa to 2 MPa, respectively. The influence of different gas compositions, e.g., resulting from exhaust gas recirculation, was checked by calibrating for pure nitrogen, synthetic air and carbon dioxide and for a certain extend for water as bath gas. The two excitation wavelengths used were 248 nm and 308 nm.

The direct view into the combustion chamber of a direct injection (DI) Diesel engine allows a fast, comprehensive analysis of the influence of different engine parameters on the combustion process. Therefore and in order to acquire a maximum amount of information from one engine cycle, a combination of four non-intrusive temporally and spatially highly resolving optical measurement techniques were applied simultaneously to a passenger car DI Diesel transparent engine. These measurement techniques include the detection of the flame luminosity in the UV-range as well as the detection of thermally excited soot radiation in the visible range, the visualization of the distribution of the liquid fuel phase by the Mie scattering technique and the laser-induced incandescence (LII) technique for the characterization of the two-dimensional soot distribution inside a selected plane of the combustion chamber.

The intention of the presented work was to develop a new simulation tool that fits into a CFD (computational fluid dynamics) workflow and provides information about the soot particle size distribution. Additionally it was necessary to improve and use state-of-the-art measurement techniques in order to be able to gain more knowledge about the behavior of the soot particles and to validate the achieved simulation results. The work has been done as a joint research financed by the European Community under FP5.

The application of exhaust gas aftertreatment systems is currently discussed to be the most suitable solution to significantly reduce soot and nitrogen oxide emissions of modern diesel engines. Nevertheless, an improvement of the engine combustion process reducing the raw emissions must be seen in combination with such systems or as a replacement. In this study, the influence of nozzle geometry, rail pressure and pre-injection on injection, vaporisation and combustion was analysed in a transparent single-cylinder diesel engine equipped with a common rail injection system by means of optical measurement techniques. The results show that a high-speed fuel intake into the combustion bowl, in combination with high rail pressures, forces the injection jets to break-up close to the wall of the combustion bowl. The engine swirl and the influence of the wall improve the mixture formation.

Increasing decentralization of production combined with just-in-time delivery of products and components calls for a flexible and reliable transportation system. So far, trucks offer the most versatile and efficient solution to those problems. In consideration of increasingly strict emission standards and customer demands for more engine power and less fuel consumption, further selective developments and optimization of DI-diesel engines are necessary. One step in this direction is the application of 4 valves per cylinder in heavy-duty diesel engines to improve mixture formation of fuel and air to get a cleaner combustion and a higher power output. For visualizing the combustion processes inside the engine, an optically accessible heavy-duty DI-diesel engine was used. This engine is a slightly modified conventional heavy-duty MAN engine based on the D0824 LFL 06 series.

Future exhaust gas limits for diesel-driven passenger cars will force the automotive industry to significantly improve the design of the vehicles respectively of the drive assemblies. Especially the contributions of soot and nitrogen oxide will be the main problems in the future. One possible solution could be the application of suitable exhaust gas aftertreatment systems, but since modern common rail injection systems deliver more degrees of freedom referring to the injection process, again the optimisation of the injection process could offer a possibility to meet the exhaust gas limits. In this study, a passenger car common rail system, applied to an optically accessible transparent engine based on the AUDI V6 TDI engine, was investigated using a solenoid-driven and a piezo-driven injector, both equipped with the same injection nozzle.

A central point for the further development of direct injection engines is the optimization of the mixture formation process, because all subsequent processes as ignition, combustion and pollutant formation are mainly influenced by the local air/fuel-ratio inside the cylinder. Especially for passenger car engines the interaction between the spray and the combustion chamber walls is an important issue for mixture formation. For that reason this interaction was object of the investigation described. The investigations were carried out in a heatable high pressure high temperature chamber under typical diesel engines conditions of 450°C temperature and 50 bar pressure. A passenger car common rail system was used as injection system equipped with a 6 hole nozzle with common rail specific seat geometry, mini-sac hole geometry and double needle guide.

The development of new generations of internal combustion engines requires appropriate measurement techniques for all relevant limited exhaust gas species and particulates. However, because of stricter future emission limits, there is a severe lack especially with respect to soot particles. Conventional methods, like gravimetric sampling, have substantial deficiencies in sensitivity and temporal resolution, which is strongly required for transient tests. Furthermore, artifacts arise from other exhaust components, like sulfuric acid, water vapor and volatile hydrocarbons. In contrast to the state-of-the-art techniques, laser induced incandescence (LII) has been proved to be a favorable technique, which overcomes these deficiencies and offers additional information, which allows new insight into combustion phenomena. Besides soot mass concentration, also the soot primary particle size is accessible by this technique.

The linear Raman scattering has been applied for the investigation of the influence of fuel properties on the mixture formation of high pressure swirl injectors. The measurements have been performed in an optically accessible high pressure high temperature chamber with a multi-component fuel consisting of benzene and n-decane. The local air/fuel-ratio and the composition of the fuel vapor phase were detected simultaneously with high spatial and local resolution along a line inside the spray region of the injector. In addition to the measurements performed with this two-component fuel mixture formation of the injector has also been studied by the separate use of the fuel components alone. Furthermore the influence of injector cooling on mixture formation has been investigated.

Improved understanding of the active combustion chain “injection - vaporisation - mixture formation - ignition - combustion - exhaust gas emissions” is important for the further development of IC engines with respect to fuel consumption and pollutant emissions. By means of multidimensional optical, mostly laser-based measurement techniques, a modern passenger car common rail system, applied to an optically accessible engine, was investigated. The utilisation of a new optical detection system allowed a simultaneous detection of the liquid phase by Mie scattering, the flame propagation from flame luminosity and the soot formation by laser-induced incandescence inside the combustion bowl of the engine. By such simultaneous measurements, direct dependencies of single combustion phenomena on fuel injection parameters can be resolved, and in particular soot formation and oxidation can be correlated to the actual combustion situation.

The transport of goods is mainly realised by the use of heavy-duty vehicles equipped with diesel engines as a drive assembly. Considering the high flexibility and reliability as well as the growing interest in saving environmental resources, a further optimisation of DI-diesel engines regarding fuel consumption and exhaust emissions is necessary. Current discussions on the application of different injection systems for passenger cars (distributor pump, common-rail, …) are also of great significance with regard to heavy-duty vehicles. Optical measurement techniques are a valuable tool to evaluate the quality and the potential of modern DI-diesel injection systems. In this work a conventional heavy-duty engine (MAN) was modified to carry out optical investigations inside the combustion bowl, concerning spray propagation and flame luminosity for different injection nozzles. With respect to the current discussions, it was equipped with a modern common-rail system.

Many details of the diesel spray breakup in real technical applications are still quite unknown because of the difficulties in the measurement techniques to obtain data inside the dense spray within the first millimeters downstream the nozzle exit. At the LTT-Erlangen the time-resolved Mie scattering technique in combination with a high resolving long distance-microscope is used to investigate this region. In contrast to previous works published by the LTT, the presented investigations have been carried out using a passenger car common-rail injection system equipped with six different injection nozzles. The aim of the presented investigations is to identify the influence of the nozzles geometry on the primary spray break up. With the taken 2D Mie scattering images many information can be extracted according to this topic, e. g., the development of the microscopic spray angle and local droplet size distributions.

In previous work, time-resolved laser-induced incandescence (TIRE-LII) has been introduced as a favorable and easy-to-use technique for accurate online measurements of soot within the exhaust gas of production engines without modifications and first experimental results have been presented. The method relies on the detection of the thermal radiation of the particles after heating with a high power laser pulse. Additionally to soot concentration measurements, a simultaneous determination of soot primary particle sizes and, derived from these, also of the particle number concentrations is possible. Basic features of the technique are the high temporal resolution, which also makes transient tests feasible, and its high sensitivity and selectivity. These aspects suggest its application as a standard method for exhaust measurements with enhanced performance, which also leads to considerable new insight into internal combustion phenomena.

Ultrafine particles within Diesel exhaust gases have gained increased attention within the last few years, as especially the particle size is expected to be the key property for possible toxicity and carcinogenicity from Diesel engine emission. Various exhaust aftertreatment systems like oxidizing catalysts or soot filters have been applied for a significant reduction of soot mass concentration, but their influence on particle sizes and number concentration also has to be considered. This enhances the need for new measurement techniques which allow to measure relevant morphological parameters of soot particles. Laser-induced incandescence (LII) is presented as a favorable optical technique for soot measurements.

Two-dimensional images of fuel distributions have been recorded in the intake of a fired 6-cylinder-4-valve spark ignition engine. As markers for the fuel a new exciplex-seed combination of triethylamine (TEA) and benzene was developed. Mixture formation and fuel evaporation of two different types of fuel injectors were compared inside the intake. The images were coupled with measurements of unburnt hydrocarbons (UHC) emissions of the two injectors in the exhaust gas. The behaviour of the fuel vapour distribution was examined at different times during the engine cycle. Instantaneous and averaged fuel distributions are shown and discussed in their influence on mixture formation.