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Numerical simulations of diesel engine combustion and emission formation have been performed using a detailed soot model. Operating conditions typical for modern truck-size engines have been investigated, and calculated results show encouraging agreement with experimental data for soot in engine exhaust gas. Predictions of details in the soot formation process compare well with detailed experimental data from the literature. The modelling of the soot/flow-field interaction is based on a flamelet approach. Source terms of the soot volume fraction are taken from a flamelet library using a presumed probability density function and integrating over mixture fraction space. In order to save computer storage and CPU time, the flamelet library of sources was constructed using a multi-parameter fitting procedure resulting in simple algebraic equations and a proper set of parameters.

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.

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.

For the simultaneous evaluation of the influence on engine knock of both chemical conditions and global operating parameters, a combined tool was developed. Thus, a two-zone kinetic model for SI engine combustion calculation (Ignition) was implemented into an engine cycle simulation commercial code. The combined model predictions are compared with experimental data from a single-cylinder test engine. This shows that the model can accurately predict the knock onset and in-cylinder pressure and temperature for different lambda conditions, with and without EGR. The influence of nitric oxide amount from residual gas in relation with knock is further investigated. The created numerical tool represents a useful support for experimental measurements, reducing the number of tests required to assess the proper engine control strategies.

In this work, constant volume combustion is studied using a zero-dimensional FORTRAN code, which is a wide-ranging chemical kinetic simulation that allows a closed system of gases to be described on the basis of a set of initial conditions. The model provides an engine- or reactor-like environment in which the engine simulations allow for a variable system volume and heat transfer both to and from the system. The combustion chamber is divided into two zones as burned and unburned ones, which are separated by an assumed thin flame front in the combustion model used for this work. Equilibrium assumptions have been adopted for the modeling of the thermal ionization, where Saha's equation was derived for singly ionized molecules. The investigation is focused on the thermal ionization of NO as well as for other species. The outputs generated by the model are temperature profiles, species concentration profiles, ionization degree and an electron density for each zone.

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.

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 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.

Full cycle simulations of a spark ignition engine running on a primary reference fuel have been performed using a two-zone model. A detailed kinetic mechanism is taken into account in each of the zones, while the propagating flame front is calculated from a Wiebe function. The initial conditions for the unburned gas zone were calculated as a mixture of fresh gas and rest gas. The composition of the burned gas zone at the end of the last engine cycle, including nitric oxide emissions, was taken as rest gas. The simulations confirm that the occurrence of autoignition in the end gas is sensitive on the amount of nitric oxide in the rest gas of the spark ignition engine. The comparison of autoignition timings calculated for a single cylinder test engine are getting more accurate if the nitric oxide in the initial gases is taken into account.

A 0.5 liter optical HCCI engine firing a mixture of n-heptane (50%) and iso-octane (50%) with air/fuel ratio of 3 is studied using large eddy simulation (LES) and laser diagnostics. Formaldehyde and OH LIF and in-cylinder pressure were measured in the experiments to characterize the ignition process. The LES made use of a detailed chemical kinetic mechanism that consists of 233 species and 2019 reactions. The auto-ignition simulation is coupled with LES by the use of a renormalized reaction progress variable. Systematic LES study on the effect of initial temperature inhomogeneity and turbulence intensity has been carried out to delineate their effect on the ignition process. It was shown that the charge under the present experimental condition would not be ignited without initial temperature inhomogeneity. Increasing temperature inhomogeneity leads to earlier ignition whereas increasing turbulence intensity would retard the ignition.

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.

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.

A major trend in current automotive research is hybridization of the power supply. This combination of electrical machine and combustion engine results, in some hybridization topologies, in a total decoupling of the combustion engine from the transmission. When the engine is decoupled from the transmission a new degree of freedom arises in engine design. The piston movement does not have to follow an evenly rotating shaft any more. It can be altered by the generator to achieve a movement found to be better from the point of efficiency or environmental concerns. Modelling work showed a potential of lowered NO emissions if the expansion could be delayed. The experimental study, conducted in a two piston Alvar engine, showed that the state of the art electrical machine (EM) propelling one of the crankshafts was too weak to change the crankshaft speed in an extent to give the fast volume changes required to change the emissions of the internal combustion engine (ICE).

A stochastic model based on a probability density function (PDF) was developed for the investigation of different conditions that determine knock in spark ignition (SI) engine, with focus on the turbulent mixing. The model used is based on a two-zone approach, where the burned and unburned gases are described as stochastic reactors. By using a stochastic ensemble to represent the PDF of the scalar variables associated with the burned and the unburned gases it is possible to investigate phenomena that are neglected by the regular existing models (as gas non-uniformity, turbulence mixing, or the variable gas-wall interaction). Two mixing models are implemented for describing the turbulent mixing: the deterministic interaction by exchange with the mean (IEM) model and the stochastic coalescence/ dispersal (C/D) model. Also, a stochastic jump process is employed for modeling the irregularities in the heat transfer.

Hydrogen has been proposed as a possible fuel for automotive applications. Methanol is one of the most efficient ways to store and handle hydrogen. By catalytic reformation it is possible to convert methanol into hydrogen and carbon monoxide. This paper reports an experimental investigation of Reformed Methanol Gas as Homogeneous Charge Compression Ignition (HCCI) engine fuel. The aim of the experimental study is to investigate the possibility to run an HCCI engine on a mixture of hydrogen and carbon monoxide, to study the combustion phasing, the efficiency and the formation of emissions. Reformed Methanol Gas (RMG) was found to be a possible fuel for an HCCI engine. The heat release rate was lower than with pure hydrogen but still high compared to other fuels. The interval of possible start of combustion crank angles was found to be narrow but wider than for hydrogen. The high rate of heat release limited the operating range to lean (λ>3) cases as with hydrogen.

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 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.

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.

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.