Blowdown Interference on a V8 Twin-Turbocharged Engine

<div class="section abstract"><div class="htmlview paragraph">One-dimensional (1D) simulation tools, the computing speed of which is relatively fast, usually solve simple complexity problems. The solving process of 1D simulation is mostly based on one-dimensional dynamic equations and empirical laws and thus in some cases it cannot obtain a similar accuracy with the time-consuming three-dimensional (3D) simulation tools. The 1D-3D co-simulation, which combines the advantages of the two simulation tools while minimizes the disadvantages, is a method that integrates and runs the two simulation tools concurrently. The coupled simulation can offer a 3D analysis for which a detailed information is needed while offer system level information in the rest of the whole system where averaged results are sufficient. The approach not only minimizes the computational cost, but avoids demand for imposing accurate boundary conditions to the 3D simulation. But nowadays, a lot of paper only use the approach to obtain boundary condition from 1D environment, few study focus on the influence of 3D part on system. (e.g influence of intake or exhaust manifold on flow in cylinder in co-simulation).The objective of this study includes two aspects, one compares the difference between 1D and the 1D/3D coupling, the other studies the influence of the 4-1 and 4-2-1 exhaust manifold on in-cylinder residual fraction gas (RGF) based on the proposed 1D and 3D co-simulation approach.</div><div class="htmlview paragraph">It describes a detailed analysis of the integrated 1D-3D simulation for two different exhaust manifold geometries on a turbocharged gasoline engine. The research results show that the induction process of the original 1D model and the co-simulation model were nearly equal, but the exhaust pressure of the coupled model was smoother than that of the original 1D model. The 4-1 exhaust manifold has a larger residual gas fraction due to the more severe pulse interference and the 4-2-1 exhaust manifold is able to mitigate this phenomenon by separating the runner 1/runner 4 with runner 2/runner 3. Furthermore, by added a spacer plate at exit port of 4-2-1 manifold, it can further reduce in-cylinder RGF and enable more uniformity among four cylinders. Therefore, the 4-2-1 exhaust manifold can be used to enhance the engine performance to achieve the concept of downsizing and down-speeding, and also it can be adopted to optimize the fuel efficiency by advancing the spark timing.</div></div>

<div class="htmlview paragraph">The effects of the swirl level on the fresh air charge distribution is studied by using a multidimensional computer code for a uniflow type two-cycle diesel engine geometry. The flow is assumed to be axisymmetric. The inlet ports are simulated as an annular opening around the liner, and the exhaust valves are simulated as an annular slot in the cylinder head. Calculations are performed from exhaust valve opening to TDC for a large range of inlet port angles (10-30°). Results are presented in terms of velocity vector plots together with swirl velocity, and fresh charge contour plots.</div> <div class="htmlview paragraph">During the valves open period, the calculations indicate the presence of two vortices in the radial-axial flow plane as previously observed by Diwakar. The first one is near the liner wall (named as wall vortex) and the other is near the symmetry axis (named as the backflow vortex). The incoming fresh air tends to flow toward the cylinder head between these two vortices with reverse flows on the liner wall and near the symmetry axis. Increasing the swirl increases the strength and the region covered by the backflow vortex, redirects the upward fresh charge to a larger radius, and restricts the short-circuiting of the fresh air to the exhaust valves. This increases the trapping of fresh charge and the scavenging efficiency.</div> <div class="htmlview paragraph">Calculations from the exhaust valve closing to TDC show that: <ol class="list nostyle"> <li class="list-item"><span class="li-label">1)</span> <div class="htmlview paragraph">The size of the backflow vortex is reduced as the port is closed and diminishes immediately thereafter. The wall vortex is present up to 60° CA BTDC when the squish effects generated by the piston motion becomes dominant.</div></li> <li class="list-item"><span class="li-label">2)</span> <div class="htmlview paragraph">Fresh charge is not completely mixed with the residual gases even at TDC. There is about 11-17% difference in the fresh charge concentrations at the highest and lowest fresh charge locations at TDC. The inlet port angle (engine swirl level) seems to increase the magnitude of this stratification slightly, but more importantly, it changes the location of this charge stratification considerably. At low swirl levels (port angle 10°), the low fresh charge region is located near the mid-radius of the bowl, and the maximum fresh charge is in the clearance volume between the piston and the bowl. At high swirl levels (port angle 30°), the maximum fresh charge is compressed toward the bowl belly, and the low concentration region is both in the clearance volume and on the cylinder head near the axis. At medium swirl levels (port angle 20), the fresh charge covers the midsection of the bowl, while the residual gases are restricted only within the clearance between piston and engine head.</div></li> </ol></div> <div class="htmlview paragraph">For the diesel engine application and to enhance the mixing of the fuel spray with the fresh air, the residual gas-fresh air stratification pattern of the medium swirl case is better than both the high swirl and low swirl cases.</div> <div class="htmlview paragraph">In addition to the wall vortex (generated by flow separation above the port) and the Backflow Vortex (generated by the swirl velocity field), a new vortex pattern named as the Head Vortex is identified. The mechanism for the Head Vortex development is recognized as the stagnation of the fresh air jet on the cylinder wall rather than on the engine head. The presence of the head vortex changes the mixing rate between the residual gases and the fresh air considerably. The development of the concentration profiles to these final shapes is demonstrated. The effects of the engine swirl level on the mixing of the fresh charge with the residual gases are investigated in terms of the mixing rates and the maximum concentration difference within the flow field.</div>

<div class="htmlview paragraph">The present work concerns the study of the potentialities of high-boost small-displacement C.R. (Common Rail) diesel engines where the compressor and the expander are mechanically disengaged for the purpose of power cogeneration from the exhaust gas. This objective can be achieved by means of advanced concept electrical devices capable of delivering the energy produced by the expander either to the drivetrain transmission or to the even more power-demanding auxiliary equipment of both the engine and the vehicle.</div> <div class="htmlview paragraph">The performance of a small-displacement boosted diesel engine with a common-rail injection system has been predicted by means of a computational code obtained by integrating different in-house non-commercial codes that simulate the intake, combustion and exhaust processes.</div> <div class="htmlview paragraph">The model validation has been carried out by means of the experimental data obtained at Fiat Research Center on a commercial small-displacement C.R. turbocharged diesel engine. The data related to: in-cylinder pressure time-histories, injection-rate distributions, air- and fuel-flow rates, EGR (Exhaust Gas Recirculation) mass fraction, discharge flow coefficients of the intake and exhaust valves, intake- and exhaust-gas pressures as well as engine performance at different speeds and loads. The computational code requires the heat-release distribution and the heat-transfer coefficients as inputs for the simulation of the engine cycle. Therefore, a heat release analysis of the measured in-cylinder pressure was performed and the heat-transfer coefficients in the model were adjusted so that the computed in-cylinder pressure matched the measured one.</div> <div class="htmlview paragraph">After calibration, the model was applied to the analysis of the engine performance at <b>A/F</b><sup><span class="xref">1</span></sup> of approximately 19 for different boosting and exhaust pressures as well as for different engine speeds and loads. The compressor and the expander were taken as mechanically disengaged and the maximum boost pressure was chosen so as to comply with an in-cylinder pressure limit of ≈ 180 bar. The engine performance were characterized in terms of the following main parameters: engine torque, power and fuel consumption, expander power output and overall system efficiency. This latter was evaluated as the ratio between the available net power of the whole system, including the supercharger, and the energy supplied by the fuel. It was ascertained that an overall efficiency of the system higher than 45% can be achieved. Moreover, an insight was given into the CO2 and pollutant exhaust emissions.</div>

<div class="htmlview paragraph">An accelerated comparative exhaust system cycling durability test has been developed at the Ford Motor Company Research and Engineering Center Dynamometer facility. This paper is a summary of events leading up to the development of the test, a description of the test procedures and conditions, the equipment, the actual test results and usage of the test.</div> <div class="htmlview paragraph">The initial design of an exhaust manifold for a new four cylinder engine successfully passed a rather long thermal cycling test program on an engine dynamometer, a test traditionally used in design verification. However, vehicle test results proved unacceptable and necessitated an immediate redesign of the exhaust manifold. Time constraints required a rapid comparative test to evaluate this redesign. Simply modifying the test parameters of the existing thermal cycling test procedure proved inadequate. It was necessary to combine periodic physical loading of the outlet system with thermal cycling to produce the desired results.</div> <div class="htmlview paragraph">Time limitations, equipment availability and economic considerations eliminated a “state of the art” approach to this problem. A more practical method was derived. System loading was accomplished by mounting the test engine on soft vehicle engine mounts and allowing the engine to rock during periodic changes in the engine RPM. The test room exhaust orifice plate and flex hosing [approximately 10.4 Kg (23 lb.)] were mounted on the vehicle exhaust manifold header pipe and partially supported by a spring. During engine rock, the weight would load the exhaust manifold header which, in turn, would load the exhaust manifold. The springs were used to prevent undesirable impact loading of the system.</div> <div class="htmlview paragraph">In an effort to evaluate this mechanical loading, a triaxial accelerometer was mounted on the exhaust manifold for comparative purposes. Five different mounting configurations of the engine were tested for severity and the most severe was used on the test cycle (<span class="xref">Appendix A</span>).</div> <div class="htmlview paragraph">The consistent results of the accelerated durability test supports the continued use of mechanical loading and thermal cycling in comparing exhaust system components and revealing system weaknesses and potential failure modes.</div>

<div class="htmlview paragraph"> </div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">A computer simulation of a high performance two-stroke engine has been validated by a transient test method. The simulation included unsteady gas dynamics, together with detailed mechanical models for the reed valve, etc. The combustion model used Vibe coefficients derived directly from measured cylinder pressures. Cylinder scavenging characteristics which were measured on The Queen's University of Belfast (QUB) single-cycle rig were also incorporated in the simulation.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">Validation of the model involved use of an inertial dynamometer and data acquisition system which has been developed at QUB. This dynamometer incorporates a flywheel which is directly coupled to the engine. During a test, the engine is accelerated, and the torque and power are calculated from the flywheel speed characteristics. Further, at pre-determined engine speed intervals, the cylinder and exhaust pressures may be recorded. This testing system provided a convenient and rapid experimental method to acquire data.</div> <div class="htmlview paragraph"> </div> <div class="htmlview paragraph">Measurement of power, pressures and temperatures during transient testing are discussed. Also presented are methods which reduce the errors arising from the slow response of thermocouples. The measured results are compared with the computer predictions for power and exhaust pressure. Excellent correlation was achieved.</div> <div class="htmlview paragraph"> </div>

<div class="htmlview paragraph">At Mitsubishi Motors, a thin-walled exhaust manifold, made of stainless cast-steel, has been developed with the aim of achieving higher heat-resisting reliability as well as weight reduction. The new exhaust manifold is made of ferritic stainless cast-steel, employing an advanced vacuum casting (CLAS). Its geometry was designed using finite element analysis and its durability was confirmed by testing both on various test devices and on a vehicle.</div> <div class="htmlview paragraph">The exhaust manifolds has been adopted on a production engine model and has proven the following advantages over a conventional cast-iron ones; <ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">excellent heat resistance. weight reduction of over 20%.</div></li> <li class="list-item"> <div class="htmlview paragraph">possible exhaust emission reduction as a result of lower heat-capacity of the exhaust manifold.</div></li></ul></div>

<div class="htmlview paragraph">The second generation methanol lean burn system has been developed. The power unit is a new, 4 valve 1.6L in-line four with compact combustion chambers. Lean misfire limit was extended by using a swirl control valve in the intake port which improves combustion under partial load. Lean mixture control is made by using a signal from lean mixture sensor provided in the exhaust manifold. An EGR system has been newly adopted to reduce NOx emissions and a under-floor type catalyst is also used to reduce formaldehyde emission in the cold transient mode in addition to the manifold type catalyst.</div> <div class="htmlview paragraph">Permissible excess air ratio range (PEXARR) was defined and used to indicate the potential for reducing vehicle NOx emissions in engine dynamometer tests to optimize compression ratio, valve timing and swirl ratio and to evaluate the effect of the EGR.</div> <div class="htmlview paragraph">Test results indicate 0.4g/mile NOx at low mileage, and about 11% better fuel economy than stoichiometric feed back under FTP (Federal Test Procedure) driving cycle. The optimized second generation vehicle has an inertia weight of 2750 lbs. which is 500 lbs. heavier than the first generation one. The driveability is still in need of improvement. Although low formaldehyde emission was obtained at low mileage using this system, further study on the stability of this level during mileage accumulation is necessary.</div>

<div class="htmlview paragraph">The 1975 federal CVS test procedure and emission standards have placed a heavy emphasis on minimizing the time required after engine start up to begin converting exhaust emissions. Four major improvements in catalytic HC/CO converters have been made in the past year to reduce catalyst ignition time:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">1.</span> <div class="htmlview paragraph">Use of low thermal capacity monolithic catalyst supports.</div> </li> <li class="list-item"> <span class="li-label">2.</span> <div class="htmlview paragraph">Locating converter after thermal reactor and/or closer to the exhaust manifold.</div> </li> <li class="list-item"> <span class="li-label">3.</span> <div class="htmlview paragraph">Development of catalysts with superior stability to long exposure at high temperatures.</div> </li> <li class="list-item"> <span class="li-label">4.</span> <div class="htmlview paragraph">Development of catalysts with improved low temperature activity.</div> </li> </ol> </div> <div class="htmlview paragraph">Small laboratory samples of potential HC/CO oxidation catalysts were screened for activity in a “laboratory simulated cold-start” test with exhaust from a 2-cyl engine. Several improved catalyst candidates were evaluated in a full-size converter “cold-start” test with exhaust from a 351 in<sup>3</sup> engine.</div> <div class="htmlview paragraph">Locating the converters closer to the exhaust manifold results in higher catalyst operating temperatures which require greater stability at high temperatures in the presence of trace contaminants. Stability, when exposed to wide temperature variations and changes from oxidation to reduction environments, has been evaluated in a thermal-cycling test for several improved catalysts. Catalyst stability to long-term exposure has also been evaluated in an engine dynamometer mileage accumulation test operated under simulated road conditions.</div> <div class="htmlview paragraph">Unfortunately, the rapid thermal-chemical response of the improved catalyst, operated closer to the exhaust manifold, increases the occurrences of excessive catalyst temperatures. Mathematical model studies of the effect of the improved catalyst properties on thermal response indicate a need to prevent unexpected high CO or HC concentration peaks in the engine exhaust, or to improve properties of existing catalysts. System changes, such as moving the low temperature catalyst farther from the exhaust manifold, may be required to obtain some protection from catalyst overtemperatures. These changes increase emission levels and require a breakthrough in engine control of raw emissions or improved catalysts.</div>

<div class="htmlview paragraph">The paper describes the experimental and simulation work recently carried out to investigate the effects of secondary air injection on the emission conversion in the exhaust after-treatment system of a S.I. automotive engine. The modeling of the 1D unsteady reacting flows in the complete exhaust system of a spark ignition engine, designed to satisfy the Euro IV limits, has been performed including the secondary air injection system, to predict the possible shortening of catalyst light-off time and the speed-up of the after-treatment system warm-up. The transport of chemical species with reactions in gas phase (post-oxidation of unburned HC in the exhaust manifold) and in solid phase (conversion of pollutants in the catalyst) with and without secondary air has been simulated by the 1D thermo-fluid dynamic model <i>GASDYN</i>, developed by the authors. The code has been extended to simulate the injection of air in the exhaust manifold and predict the consequent post-oxidation of pollutants in the ducts. The main chemical reactions arising in gas phase, in the upper part of the exhaust manifold, have been included, considering the oxidation of C<sub>3</sub>H<sub>6</sub>, C<sub>3</sub>H<sub>8</sub> and CO and the steam-reforming of C<sub>3</sub>H<sub>6</sub> and C<sub>3</sub>H<sub>8</sub>. The heat released in the gas due to the exothermal reactions has been taken into account, to evaluate the exhaust gas temperature along the ducts with injection of air.</div> <div class="htmlview paragraph">A Fiat-Alfa Romeo four-stroke, four-cylinder 2.0L automotive S.I. engine complying with the Euro IV regulations has been modeled, in order to predict the chemical specie concentration along the exhaust system. A large set of experimental data concerning this engine (cylinder pressure, pressure pulses, wall and gas temperatures, gas chemical composition along the system) with different secondary air mass flows has enabled a comprehensive comparison between predictions and measurements, in order to validate the model in different operating conditions.</div>

<div class="section abstract"><div class="htmlview paragraph">Some SI (spark-ignition) engines fueled with gasoline for industrial machineries are designed based on the conventional diesel engine in consideration of the compatibility with installation. Such diesel engine-based SI engines secure a combustion chamber by a piston bowl instead of a pent-roof combustion chamber widely applied for SI engines for automobiles.</div><div class="htmlview paragraph">In the development of SI engines, because knocking deteriorates the power output and the thermal efficiency, it is essential to clarify causes of knocking and predict knocking events. However, there has been little research on knocking in diesel engine-based SI engines. The purpose of this study is to elucidate knocking phenomena in a gasoline engine with a re-entrant piston bowl and swirl flow numerically and experimentally. In-cylinder visualization and pressure analysis of knock onset cycles have been experimentally performed. Locations of autoignition have been predicted by 3D-CFD analysis with detailed chemical reactions. The prediction accuracy of the location of autoignition has been examined by comparing with experimental results. Initial and boundary conditions for 3D-CFD are obtained by TPA (Three Pressure Analysis), which is a 1D engine cycle simulation using measured intake/exhaust and in-cylinder pressures as the input data. Locations and timing of autoignition have been observed through an endoscope attached to the cylinder head. The visualization area through the endscope is determined based on the location of autoignition predicted by 3D-CFD analysis. The in-cylinder pressure is also measured simultaneously, and the maximum amplitude of the pressure oscillations after applying a high-pass filter to the in-cylinder pressure is used as knock intensity (KI) to determine knock onset cycles. From results of the in-cylinder pressure measurements and analysis by TPA, the relationships between in-cylinder conditions and KI are analyzed. The comparison between visualized and calculated location of autoignition have been shown good agreement in the case that both the maximum and the low engine speed conditions.</div></div>

<div class="htmlview paragraph">The paper presents an original review and extension of existing mathematical models for on-line residual gas fraction estimation. The resulting model has first of all been extended to take into account also the presence of externally recirculated exhaust gas (external EGR), and then critically analyzed to highlight the importance of a correct Intake Valve Opening and Exhaust Valve Closing effective position identification. As shown in the paper, such quantities may be evaluated by using experimental data, either acquired in the test-cell or on a valve flow bench.</div> <div class="htmlview paragraph">The main objective is to obtain a simple and reliable model (that could be run in real time within the engine control unit) also in presence of Variable Valve Timing (VVT, both on intake and exhaust valves) and external Exhaust Gas Recirculation (EGR) systems. In fact, the two main contributions to residual gas fraction (backflow of the burned gas during the valve overlap period, and amount of gas trapped within the cylinder) are strongly affected by intake and exhaust valves timing, and EGR flow should be taken into account in order to determine the total exhaust gas mass within the cylinder at IVC. Therefore, real time estimation of residual gas mass and composition is crucial for designing VVT and EGR management strategies that allow an optimal control of the combustion process.</div> <div class="htmlview paragraph">The new model has been applied to experimental data acquired on a 3.2 liter V6 GDI engine, equipped with intake and exhaust Variable Valve Timing systems. Tests were performed throughout the engine operating range for different combinations of intake and exhaust valve timings, while varying EGR flow. Model results are in good agreement with other measured quantities (such as Spark Advance angle and NO<sub>x</sub> emissions), and the proposed approach therefore represents a powerful tool for on-board optimal combustion control.</div>

<div class="htmlview paragraph">We propose a model of in-cylinder air mass and residual gas fraction of a turbocharged SI engine with Variable Valve Timing (VVT) actuators. VVT devices are used to produce internal exhaust gas recirculation at part load, providing beneficial effects in terms of fuel consumption and pollutant emissions. At full load, VVT actuators permit to push back knock limit by scavenging fresh air to the exhaust pipes. Modeling in-cylinder composition is an essential task for control purpose. Actually, VVT actuators affect in-cylinder fresh air charge. This has an impact on engine torque output (leading to driveability problems), and on Fuel/Air Ratio (leading to pollution peaks). In this paper, we present a model of in-cylinder air mass and residual gas fraction using only commercial-line sensors (engine speed, intake manifold pressure and VVT actuators positions). It is designed for real-time control purpose. The model does not necessitate a lot of calibration time. The proposed method consists in modeling the quantity of fresh air going through the intake valve. The model is composed of three terms. All these terms have their own physical meaning: first term gives in-cylinder total mass, second term gives the gas mass that goes through both valves during the valve overlap (either backflow of burned gas, or scavenging of fresh air), and last term models the residual gas mass staying in the cylinder from one cycle to the next one.</div>

<div class="section abstract"><div class="htmlview paragraph">The acquisition of more authentic cylinder pressure data is the basis of engine combustion analysis. Due to the multiple advantages, quartz piezoelectric pressure transducers are generally applied to the measurement of the cylinder pressure. However, these transducers can only produce dynamic cylinder pressure data which may be significantly different from the actual values. Thus, the cylinder pressure data need to be corrected through a certain method, while different cylinder pressure correction methods will cause result divergences of the combustion analysis. This paper aims to acquire a proper cylinder pressure correction method by carrying out theoretical analysis based on the polytropic process in the compression stroke as well as the experimental research of the cylinder pressure of a turbocharged eight-cylinder diesel engine. The method presented in this paper can not only get a polytropic exponent with higher accuracy by calculation but also revise the cylinder pressure curve at the same time. A further experimental research on this engine shows that the value of the polytropic exponent fluctuates from 1.33 to 1.38 at different working conditions, and is hardly associated with the engine load. However, the value of the polytropic exponent becomes bigger along with the increase of the engine speed.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In recent years, emission regulations have been getting increasingly strict. In the development of engines that comply with these regulations, in-cylinder pressure plays a fundamental role, as it is necessary to analyze combustion characteristics and control combustion-related parameters. The analysis of in-cylinder pressure data enables the modelling of exhaust emissions in which characteristic temperature can be derived from the in-cylinder pressure, and the pressure can be used for other investigations, such as optimizing efficiency and emissions through controlling combustion.</div><div class="htmlview paragraph">Therefore, a piezoelectric pressure sensor to measure in-cylinder pressure is an essential element in the engine research field. However, it is difficult to practice the installation of this pressure sensor on all engines and on-road vehicles owing to cost issues. Therefore, there have been several studies aiming to estimate the in-cylinder pressure using only the data available from the Engine Control Unit (ECU) without an additional pressure sensor.</div><div class="htmlview paragraph">An in-cylinder pressure prediction model for conventional light-duty diesel engines had been established by authors and described in this paper. First, the pressure during the compression stroke was estimated using a variable polytropic index. Next, the Wiebe function was applied to describe pressure during pilot and main combustion. This prediction of the in-cylinder pressure was established for real-time estimation.</div><div class="htmlview paragraph">The complete pressure prediction model consists of subordinate models, where physical phenomena are simplified for the real-time application of the model. The accuracy of the submodels has a direct influence on the error in the parent model the pressure prediction. Therefore, sensitivity analysis was conducted in this study to verify the effect of the submodels, including the polytropic index model, ignition delay model, heat loss model and combustion duration model, on the entire pressure prediction model. This study will contribute to establishing a more accurate pressure prediction through sensitivity analysis and will be useful to many studies that require in-cylinder pressure information.</div></div>

<div class="htmlview paragraph">In this work the influence of various engine load changes with different engine speeds on the soot particle concentrations and properties was investigated because these operating modes are well known for short but high soot emissions. To derive specific information on emission behavior of particle matters tests were carried out with the Two-Color-Method and the so called RAYLIX technique in a four-cylinder CR-Diesel engine.</div> <div class="htmlview paragraph">The Two-Color-Method (2CM) gives crank angle resolved information about soot formation and oxidation processes inside the combustion chamber of a single cylinder.</div> <div class="htmlview paragraph">The RAYLIX technique is a combination of Rayleigh-scattering, <u>L</u>aser-<u>I</u>nduced-<u>I</u>ncandescence (LII) and extinction measurements which enable simultaneous measurements of temporally and spatially resolved soot concentration, mean primary particle radii and number densities in the exhaust gas manifold of the same cylinder investigated by the Two-Color-Method. A laser light sheet was launched into an optical flange mounted between the cylinder head and the exhaust manifold. Both signals were detected by two intensified CCD cameras. Additionally, measurements of the opacity and the Filter Smoke Number were performed in the exhaust gas.</div> <div class="htmlview paragraph">The results of the time resolved measuring techniques 2CM and RAYLIX were correlated with results obtained by the conventional methods in the exhaust gas. During most load changes under investigation temporary higher soot concentrations inside the combustion chamber as well as in the exhaust gas could be found compared to those measured in the stationary engine operation points before and after the load changes. This increase was observed even though the simultaneously measured mean primary particle sizes showed a decreasing behavior. This decrease was overcompensated by a disproportionate increase in the particle number density.</div>