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The optimization of the vaporization and mixture formation process is of great importance for the development of modern gasoline direct injection (GDI) engines, because it influences the subsequent processes of the ignition, combustion and pollutant formation significantly. In consequence, the subject of this work was the development of a measurement technique based on the laser induced exciplex fluorescence (LIF), which allows the two dimensional visualization and quantification of the in-cylinder air/fuel ratio. A tracer concept consisting of benzene and triethylamine dissolved in a non-fluorescent base fuel has been used. The calibration of the equivalence ratio proportional LIF-signal was performed directly inside the engine, at a well known mixture composition, immediately before the direct injection measurements were started.

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.

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.

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.

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.

Detailed experimental investigation of fuel sprays are of utmost importance for the development of appropriate injection systems for gasoline direct injection (GDI) engines. A number of laser based techniques have been developed to study the spray formation. The temperature of the gas phase surrounding the fuel droplets was not accessible up to now. In this work for the first time, to the best of our knowledge, gas-phase temperatures were measured within the vaporizing spray of a high pressure GDI injector using pure rotational coherent anti-Stokes Raman spectroscopy (CARS). Results from an isooctane fuel spray of a multi-hole injector in a heated injection chamber are presented with the probe volume located at a distance of 70mm downstream the injector nozzle in the centre of the spray cone.

Planar laser-induced fluorescence (PLIF) has been successfully used for the investigation of the mixture formation process in hydrogen engines. Detailed information has been obtained about the process development (qualitative measurements) and on the fuel/air-ratio (quantitative measurements) in the combustion chamber. These results can be used for further optimization of the mixture formation and the combustion process concerning emissions and fuel consumption. The measurement technique used here is not limited to hydrogen and can also be applied to other fuel gases like natural gas. The main topic of this paper is the experimental verification of the PLIF data by simultaneous Raman scattering measurements. By Raman scattering the fuel/air-ratio can directly be determined from the direct concentration measurements of the different gas species.

The influence of the injector temperature on the spray distribution and fuel volatility of a high-pressure swirl injector of the type used in direct-injection gasoline engines and thus of flash boiling effect was investigated in a pressure chamber with optical access. Laser-induced (exciplex) fluorescence was used to visualize the liquid phase and the vapour phase of the spray. The experiments were conducted at a chamber pressure of 50 kPa and a chamber temperature of 323 K by varying the injector temperature (323 K, 343 K, 363 K and 381 K) at a constant rail pressure of 8 MPa. Three single-component fuels with different boiling points (n-hexane: Tb = 339 K, iso-octane: Tb = 372 K and n-octane: Tb = 398 K) and a non-aromatic multi-component fuel (mcf) (Tb = 303 K - 473 K) were chosen for the investigations. The dopant was a combination of 2% by mass TEA (triethylamine) and 3.4% by mass benzene in the non-fluorescing substitutional fuels.

Two-dimensional Mie and LIEF techniques were applied to investigate the spray propagation, mixture formation and charge distribution at ignition time inside the combustion chamber of a direct injection SI engine. The results obtained provide the propagation of liquid fuel relative to the piston motion and visualize the charge distribution (liquid fuel and fuel vapor) throughout the engine process. Special emphasis was laid on the charge distribution at ignition time for stratified charge operation. By means of a LIEF technique it was possible to measure cyclic fluctuations in the fuel vapor distributions which explain the occurrence of misfiring.

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.

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.

In spark-ignition engines, high exhaust gas recirculation (EGR) rates have demonstrated their potential in reducing fuel consumption and emissions. However, irregular combustion at high residual gas concentrations limits the EGR rates. The following study presents a strategy that has been developed to investigate the influence of complex charge motion on mixture formation and combustion for high residual gas concentrations with the aim of extending these limits. An optically accessible single-cylinder SI Engine with direct injection was used to measure the charge distribution by means of laser induced fluorescence (LIF). A special device inside the inlet pipe gave the possibility to generate a defined swirl motion overlaying a tumble motion given by the design of the inlet ports.

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.

Laser-based measurements of charge temperature and exhaust gas recirculation (EGR) ratio in an homogeneous charge compression ignition (HCCI) engine are demonstrated. For this purpose, the rotational coherent anti-Stokes Raman spectroscopy technique (CARS) was used. This technique allows temporally and locally resolved measurements in combustion environments through only two small line-of-sight optical accesses and the use of standard gasoline as a fuel. The investigated engine is a production-line four-cylinder direct-injection gasoline engine with the valve strategy modified to realize HCCI-operation. CARS-measurements were performed in motored and fired operation and the results are compared to polytropic calculations. Studies of engine speed, load, valve timing, and injection pressure were conducted showing the strong influence of charge temperature on the combustion timing.

Combustion processes with partially or fully premixed cylinder load combined with self-ignition provide high combustion efficiency and low emissions of Nitrogen Oxides (NOx) and particulate matter at the same time. Since the number of diesel operated passenger cars is still rising, it would be interesting, if such a combustion concept can be realized in an ordinary DI-Diesel engine which is operated with conventional diesel fuel. In this study, the influence of nozzle geometry, Tintake, pTDC and injection timing on the functioning chain of combustion was analyzed in a transparent single-cylinder diesel engine equipped with a common rail injection system by means of optical measurement techniques. Simultaneously, different optical diagnostics (laser-based and non laser-based) were used to study the fuel distribution, ignition and combustion in the combustion chamber of the optically accessible diesel engine. The liquid fuel was visualized by Mie scattering at 532nm.

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.

Measurements of ignition behavior, homogeneous reactor simulations employing detailed kinetics, and quantitative in-cylinder imaging of fuel-air distributions are used to delineate the impact of temperature, dilution, pilot injection mass, and injection pressure on the pilot ignition process. For dilute, low-temperature conditions characterized by a lengthy ignition delay, pilot ignition is impeded by the formation of excessively lean mixture. Under these conditions, smaller pilot mass or higher injection pressures further lengthen the pilot ignition delay. Similarly, excessively rich mixtures formed under relatively short ignition delay conditions typical of conventional diesel combustion will also prolong the ignition delay. In this latter case, smaller pilot mass or higher injection pressures will shorten the ignition delay. The minimum charge temperature required to effect a robust pilot ignition event is strongly dependent on charge O2 concentration.

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.

Biofuels and alternative fuels are increasingly being blended with conventional gasoline fuel to decrease overall CO₂ emissions. A promising way to achieve this is the use of DISI (direct-injection spark-ignition) technology. However, depending on temperature, pressure, chemical composition and the spark timing, unwanted pre-ignition may occur. Despite higher compression ratios, this engine knock can be decreased by lowering the mixing temperature. This results from the larger fuel evaporation enthalpy of certain biofuels which provides a non-homogeneous mixture throughout the combustion chamber. This work focuses on estimating the biofuel evaporation rate from absolute local vapor temperature and concentration. Measurements conducted in a high temperature/pressure cell using a multi-hole injector are carried out by applying planar, 2-line, laser-induced fluorescence and phase doppler interferometry.