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This paper deals with the influence of a wall soot layer of varying thickness on the unsteady heat transfer between the fluid and the engine cylinder wall during a full cycle of a four-stroke Diesel engine operation. For that purpose a computational investigation has been carried out, using a one-dimensional model of a multi-layer solid wall for simulating the transient response within the confinement of the combustion chamber. The soot layer is thereby of varying thickness over time, depending on the relative rates of deposition and oxidation. Deposition is accounted for due to a thermophoretic mechanism, while oxidation is described by means of an Arrhenius type expression. Results of the computations obtained so far show that the substrate wall temperature has a significant effect on the soot layer dynamics and thus on the wall heat flux to the combustion chamber wall.

This paper presents a phenomenological single-zone combustion model which meets the particular requirements of high speed DI diesel engines with common rail injection. Therefore the model takes into account the freely selectable pilot and main injection and is strongly focusing on result parameters like combustion noise or NO-emission which are affected by this split injection. The premixed combustion, the mixing-controlled combustion and the ignition delay are key parts of the model. The model was developed and tested on more than 200 samples from three different engine types of DaimlerChrysler passenger car engines equipped with common rail injection. A user-friendly parameterization and a short computing time was achieved thanks to the simple structure of the model.

In order to meet future requirements for emission reduction and fuel economy a variety of concepts are available for gasoline engines. In the recent past new pathways have been found using alternative fuels and fuel combinations to establish cost optimized solutions. The presented concept for a SI-engine consists of combined injection of gasoline and hydrogen. A hydrogen enriched gas mixture is being injected additionally to gasoline into the engine manifold. The gas composition represents the output of an onboard gasoline reformer. The simulations and measurements show substantial benefits to improve the combustion process resulting in reduced cold start and warm up emissions and optimized part load operation. The replacement of gasoline by hydrogen-rich gas during engine start leads to zero hydrocarbons in the exhaust gas.

The relative amounts of heat released by premixed and by diffusion controlled combustion is varied in a compression-ignition engine run on the test bench through variation of four operating parameters. Exhaust gas is led to a differential mobility particle sizer and to filters that are loaded for gravimetric analysis. Particle size distributions are acquired in the 16÷630 nm range of electrical mobility diameters. Opacity readings of the exhaust gas are taken, cylinder pressure is indicated, a value for the combustion noise is computed; gaseous emissions are recorded and heat release rates based on cylinder pressure analysis are evaluated. Two full factorial experiments at 2 bar bmep 2000 rpm are run as 24 combinations of four factors: Injection pressure 400 and 1200 bar, with and without pilot injection, 1/3 and 1/4 mass-fraction exhaust gas recirculation, late, middle and early start of injection.

This study presents an application of the conditional moment closure (CMC) combustion model to marine diesel sprays. In particular, the influence of fuel evaporation terms has been investigated for the CMC modeling framework. This is motivated by the fact that substantial overlap between the dense fuel spray and flame area is encountered for sprays in typical large two-stroke marine diesel engines which employ fuel injectors with orifice diameters of the order of one millimeter. Simulation results are first validated by means of experimental data from the Wärtsilä optically accessible marine spray combustion chamber in terms of non-reactive macroscopic spray development. Subsequently, reactive calculations are carried out and validated in terms of ignition delay time, ignition location, flame lift-off length and temporal evolution of the flame region. Finally, the influence of droplet terms on spray combustion is analyzed in detail.

The findings presented in this paper result from a collaboration between two Federal Laboratories in Switzerland. In this research project the characteristics of the particulates from internal combustion engines were investigated in detail. Measurements were carried out on a single-cylinder research engine focusing on exhaust particulate matter emissions. The single-cylinder diesel engine is supercharged and features a common-rail direct injection system. This work analyzes the influence of fuel properties and injection parameters on the particulate number size distribution. For the fuel composition, five different fuels including low sulfur diesel, zero-sulfur and zero-aromatics diesel, two blending portions of oxygenated diesel additive and rapeseedmethylester were used. For the injection parameters the injection pressure, the start of injection and the fuel amount in the pilot- and in the post-injection phases were varied.

We have performed simulations and experiments to characterize the mixture formation in spray-guided direct injected spark ignition (DISI) gasoline engines and to help to understand features of the combustion process, which are characteristic for this engine concept. The 3-D computations are based on the KIVA 3 code, in which basic submodels of spray processes have been systematically modified at ETH during the last years. In this study, the break-up model for the hollow-cone spray typical for DISI engines has been validated through an extended comparison with both shadowgraphs and Mie-scattering results in a high-pressure-high-temperature, constant volume combustion cell at ambient conditions relevant for DISI operation, with and without significant droplet evaporation. Computational results in a single-cylinder research engine have been then obtained at a given engine speed for varying load (fuel mass per stroke), swirl and fuel injection pressure.

The physical behavior of the combustion process in a jet-guided direct injection spark ignition engine has been investigated with three different measurement techniques. These are flame visualization by use of endoscopy, ion-current sensing at 16 different locations in the combustion chamber and the estimation of the flame temperature as well as soot concentration based on multi-wavelength-pyrometry. The results of all these measurement techniques are in good agreement between each other and give a coherent picture of the physical behavior of the combustion process and make it possible to characterize the main influence parameters on combustion. This serves as a basis for validation and improvement of simulation tools for the engine thermodynamics and combustion.

The goal of the Clean Engine Vehicle project (CEV) was the conversion of a gasoline engine to dedicated natural gas operation in order to achieve a significant reduction in CO2 emissions. The targeted reduction was 30% compared with a gasoline vehicle with similar performance. Along with the reduction in emissions, the second major requirement of the project, however, was compliance of the results with Euro-4 and SULEV emission limits. The project entailed modifications to the engine and the pre-existing model-based engine control system, the introduction of an enhanced catalytic converter and downsizing and turbocharging of the engine. As required by the initiators of the project, all components used were commonly available, some of them just being optimized or modified for natural gas operation.

Emission and performance parameters of a medium size, and medium speed D.I. diesel engine equipped with a Miller System, a new developed High Pressure Exhaust Gas Recirculation System (HPEGR), a Common Rail (CR) system and a Turbocharger with Variable Turbine Geometry (VTG) have been measured and compared to the standard engine. While power output, fuel consumption, soot and other emissions are kept constant, nitric oxide emissions could be reduced by 30 to 50% depending on load and for the optimal combination of methods. Heat release rate analysis provides the reasons for the optimised engine behaviour in terms of soot and NOx emissions: The variable Nozzle Turbocharger helps deliver more oxygen to the combustion process (less soot) and lower the peak gas temperature (less NOx).

Ignition systems for large lean burn gas engines are challenged by large energy deposition requirements to ensure stable and reliable inflammation of the premixed charge. In this study, two different ignition systems are investigated experimentally: ignition by means of injecting a small amount of diesel spray and its subsequent autoignition is compared to the ignition with an un-scavenged pre-chamber spark plug over a wide range of engine relevant conditions such as methane equivalence ratios and thermomechanical states. The ignition behavior as well as the combustion phase of the two systems is investigated using an optically accessible Rapid Compression Expansion Machine (RCEM). Filtered OH-chemiluminescence images of the ignition and combustion were taken with a UV intensified high speed camera through the piston window.

Three-dimensional reactive computational fluid dynamics (CFD) plays a crucial role in IC engine development tasks complementing experimental efforts by providing improved understanding of the combustion process. A widely adopted combustion model in the engine community for (partially) premixed combustion is the G-Equation where the flame front is represented by an iso-level of an arbitrary scalar G. A convective-reactive equation for this iso-surface is solved, for which the turbulent flame speed ST must be provided. In this study, the commonly used and well-established Damköhler approach is compared to a novel correlation, derived from an algebraic closure for the scalar dissipation of reaction progress as proposed by Kolla et al. [1].

The combustion of gaseous fuels like methane in internal combustion engines is an interesting alternative to the conventional gasoline and diesel fuels. Reasons are the availability of the resource and the significant advantage in terms of CO2 emissions due to the beneficial C/H ratio. One difficulty of gaseous fuels is the preparation of the gas/air mixtures for all operation points, since the volumetric energy density of the fuel is lower compared to conventional liquid fuels. Low-pressure port-injected systems suffer from substantially reduced volumetric efficiencies. Direct injection systems avoid such losses; in order to deliver enough fuel into the cylinder, high pressures are however needed for the gas injection which forces the fuel to enter the cylinder at supersonic speed followed by a Mach disk. The detailed modeling of these physical effects is very challenging, since the fluid velocities and pressure and velocity gradients at the Mach disc are very high.

Modern Diesel engines have become ever more complex systems with many degrees of freedom. Simultaneously, with increasing computational power, simulations of engines have become more popular, and can be used to find the optimum set up of engine operation parameters which result in the desired point in the emission-efficiency trade off. With increasing number of engine operation parameter combinations, the number of calculations increase exponentially. Therefore, adequate models for combustion and emissions with limited calculation costs are required. For obvious reasons, the accuracy of the ignition timing is a key point for the following combustion and emission model quality. Furthermore, the combination of mixing and chemical processes during the ignition delay is very challenging to model in a fast way for a wide range of operation conditions.

A mean value soot model (MVSM) was developed and validated for the realtime prediction of the raw, engine-out soot emissions from common rail diesel engines. Through the consideration of five representative states during the combustion cycle, the developed MVSM determines the engine out soot emissions based on the soot formation and oxidation processes, using only parameters available from a standard engine control unit. 16 model parameters are used to describe the engine, fuel, and combustion characteristics, and must be determined for each engine and fuel combination. The MVSM was parameterized and validated using the measured soot emissions from two different engines operating with a total of three different fuels. After parameterization, the MVSM was capable of qualitatively and quantitatively reproducing the soot emissions for operating points throughout the entire operating map, including for operating regimes not considered during the parameterization.

Future engine emission legislation regulates soot from Diesel engines strictly and requires improvements in engine calibration, fast response sensor equipment and exhaust gas aftertreatment systems. The in-cylinder phenomena of soot formation and oxidation can be analysed using a pyrometer with optical access to the combustion chamber. The pyrometer collects the radiation of soot particles during diffusion combustion, and allows the calculation of soot temperature and a proportional value for the in-cylinder soot density (KL). A four-cylinder heavy-duty Diesel engine was equipped in all cylinders with prototype pyrometers and state of the art pressure transducers. The cylinder specific data was recorded crank angle-resolved for a set of steady-state and transient operating conditions, as well as exhaust gas recirculation (EGR) addition and over a wide range of soot emissions.

Fuel spray propagation and its morphology are important aspects for the in-cylinder mixture preparation in Diesel engines. Since there is still a lack of suitable measurements with regard to large 2-stroke marine Diesel engines combustion systems, a comprehensive data set of spray characteristics has been investigated using a test facility reflecting the specific features of such combustion systems. The spray penetration, area and cone angle were analysed for a variation of gas density (including the behaviour at evaporation and non-evaporating conditions), injection pressure and nozzle diameter. Moreover, spray and swirl flow interaction as well as fuel quality influences have been studied. To analyse the impacts and effects of each measured parameter, an empirical correlation for the spray penetration has been derived and discussed for all measurements presented.

The behavior of spray auto-ignition and combustion of a diesel spray in a lean premixed methane/air charge was investigated. A rapid compression expansion machine with a free-floating piston was employed to reach engine-relevant conditions at start of injection of the micro diesel pilot. The methane content in the lean ambient gas mixture was varied by injecting different amounts of methane directly into the combustion chamber, the ambient equivalence ratio for the methane content ranged from 0.0 (pure air) to 0.65. Two different nozzle tips with three and six orifices were employed. The amount of pilot fuel injected ranged between 0.8 and 1.8 percent of the total energy in the combustion chamber. Filtered OH chemiluminescence images of the combustion were taken with a UV-intensified high-speed camera through the optical access in the piston.

The current trend in automobiles is towards electrical vehicles, but for the most part these vehicles still require an internal combustion engine to provide additional range and flexibility. These engines are under stringent emissions regulations, in particular, for the reduction of CO2. Gas engines which run lean burn combustion systems provide a viable route to these emission reductions, however designing these engines to provide sustainable and controlled combustion under lean conditions at λ=2.0 is challenging. To address this challenge, it is possible to use a scavenged Pre-Chamber Ignition (PCI) system which can deliver favorable conditions for ignition close to the spark plug. The lean charge in the main combustion chamber is then ignited by flame jets emanating from the pre-chamber nozzles. Accurate prediction of flame kernel development and propagation is essential for the analysis of PCI systems.

Despite significant benefits in terms of the ignition enhancement, the strength and timing of the turbulent flame jets subsequently issuing into the main chamber strongly depend on the pre-chamber combustion process and, thus, are sensitive to the specific engine operating conditions it experienced. This poses considerable difficulties in optimizing engine operating conditions as well as controlling engine performance. This paper investigates the influence of engine operating conditions on the pre-chamber combustion event using both experimental and numerical methods. A miniaturized piezo-electric pressure transducer was designed to be placed inside the engine cylinder head to record the pre-chamber inner volume pressure, in addition to conventional pressure indication inside the main chamber.